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December, 2003 244 DOS Times - Vol.9, No.6 EDITORIAL Dear friends, There have been extraordinary developments in the field of refractive surgery in the past few years. State of the art technology is being developed and used for the treatment of refractive errors. It all started with man’s desire to get rid of his dependence on spectacles which drove ophthalmologist in the early seventies to experiment with procedures that changed the corneal curvature to achieve emetropia, the ultimate goal of any eye surgeon. Radial Keratotomy was considered a revolution of sort when it was first introduced. But as the side affects began to show up newer techniques surfaced. First came PRK and then Lasik. Emergence of excimer laser and its dominance in refractive corneal surgery is one of the most significant advances in recent times. Harnessing the laser to safely perform corneal surgery has been a major technical achievement. Though initially Lasik was recommended for all degrees of myopia it is now clear that this procedure is not recommended in very high myopias (>10D). This is because of limitation in night vision, loss of best spectacle corrected usual acuity, visual aberrations and diminished quality of vision. The surgeon’s goal is not only to provide a satisfactory postoperative visual acuity but also a good quality of vision. We are entering a new age with the introduction of phakic IOLs for correction of high refractive errors where we implant IOL leaving crystalline lens intact. Apart from providing excellent refractive accuracy, it preserves corneal sphericity and allows rapid visual recovery. Compared with techniques that change corneal curvature like Lasik, phakic IOL styles & designs are capable of providing the patient with best visual acuity, better quality of vision and quality of image. Its main advantage over corneal surgery is that it is reversible. However there is some concern about its safety in the long run and also that it demands more surgical skill than the routine cataract surgery. Though not practiced in our country till recently, there are few centers that have started adopting this new technique. R.P.Centre has initiated a project to study the role of Phakic IOL in our Indian setup with special emphasis on its long-term safety. It is a well-observed fact that refractive surgery is often patient driven and sometimes they push the ophthalmologist to provide surgical relief from their dependence on optical devices. Therefore the ophthalmologists has a special responsibility towards the patients, to be sure that the patient has a realistic expectation about surgery and that they are not solely guided by enthusiastic media claims. Patients must understand both the advantages and disadvantages of the surgery and accept that there may be complications from any surgical procedure. These patients must be counseled and must be told of the risk involved even though the percentage of success may be high. Thanks, Dr. Jeewan S. Titiyal Secretary Programme for DOS Monthly Clinical Meeting for December 2003 Venue: Library, Venu Eye Institute & Research Centre, New Delhi Date & Time : 27th December, 2003 (Saturday) at 2.30 P.M. Case Presentation 1. Combined Penetrating Keratoplasty and R.D. Surgery................... Dr. Reny using a Temporary Keratoprosthesis 2. Macular Ischaemia following .............................................................. Dr. Arundhati Intravitreal injection of an aminoglycoside 10 Mins. 10 Mins. Clinical Talk l Dry Eye .................................................................................................... Dr. Ashu Agarwal Mini Symposium: Low Vision 20 Mins. Chairman : Dr. S.C. Gupta, Convenor : Dr. Anil Tara 1. Assessment of a Low Vision Patient .................................................. Dr. Sunita 2. Optical & Non-optical Low Vision Devices ...................................... Dr. Gaurav 3. Indications & Therapeutic Options .................................................... Dr. Ajay Panel Discussions : 15 min. Followed by Tea December, 2003 245 10 Mins. 10 Mins. 10 Mins. DOS Times - Vol.9, No.6 LETTERS TO EDITOR Letters to Editor Low Vision in India Dear Editor, Low Vision corresponds to visual acuity of less than 6/18, but equal to or better than 3/60 in the better eye with best possible correction, according to the International Classification of Diseases (10th edition). In the National Survey on Blindness (2001-02) conducted under the National Programme Control of Blindness, 63337 persons aged 50 years and above were examined in 15 states of the country1. The prevalence of Low Vision was estimated to be 10.3%. Extrapolating this figure to the entire population, the prevalence of Low Vision in the general population approximates 1.3%. In a population-based study in urban Delhi, children aged 5-15 years were examined2. The prevalence of Low Vision was 0.22% in this agegroup. In a similar study in rural Andhra Pradesh, the prevalence of Low Vision was found to be 0.15% in the age-group 7-15 years3. In another population-based study in Andhra Pradesh, persons of all ages were examined 4. In this study, Low Vision was defined as permanent visual impairment that was not correctable with refractive error or surgical intervention. The participants with best-corrected distance visual acuity of <6/18 to perception of light or central visual field <10 degrees because of an untreatable cause in both eyes were considered as having Low Vision. The prevalence of Low Vision was estimated to be 1.05%. The available data thus suggests an estimated prevalence of Low Vision of 1-1.5% in India, in the general population, though there is wide geographic variation, and there is a paucity of data on Low Vision in the young adult population. This is approximately 2.1/2-3 times the prevalence of blindness, when blindness is defined by the W.H.O. criteria. Adequate attention needs to be paid for provision of available and accessible Low Vision Services in our country. References 1. Murthy, GVS, Gupta, S, Tewari, HK, Jose, R, Bachani, D. Eds. National Survey on Blindness & Visual Outcomes after Cataract Surgery 2001-02. Report. National Programme for Control of Blindness, Directorate General of Health Services, Ministry of Health and Family Welfare, Government of India, New Delhi. 2. Murthy, GVS, Gupta, SK et al. Refractive error study in children in an urban population in New Delhi. IOVS, March 2002, Vol. 43, No.3: 623-631. 3. Dandona, R, Dandona, L et al. Refractive error study in children in a rural population in India. IOVS, March 2002, Vol. 43, No.3: 615-622. 4. Dandon, R, Dandona, L et al. Planning Low Vision Services in India: a population based perspective. Ophthalmology 2002 Oct; 109(10): 1871-8. Dr. Sanjeev K. Gupta, Dr. G.V.S. Murthy, Dr. Praveen Vashist Community Ophthalmology Deptt. Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi Pre-Retinal Blood Aspiration-hydraulic Help – A New Surgical Technique Dear Editor, After pars plana vitrectomy a thin layer of blood may often be present on the retinal surface. It is generally easily aspirated with back flush needle or an end opening extrusion needle connected to active aspiration module of the vitrectory machine (Vacuum cleaning). 1,2 If the blood is tenacious because of clotting, forceps removal may be necessitated. We experienced difficulty sometimes in removal of pre-retinal blood with Vacuum cleaning technique. The our surprise when back flush mechanism was actuated, blood of- December, 2003 ten dispersed and could be easily aspirated. This step is repeated in the area where pre-retinal blood could not be aspirated otherwise. We have been using this technique routinely in removing pre-retinal blood whenever vacuum-cleaning technique does not work before resorting to forceps removal. Often times the technique does work obviating forceps blood removal, which can be traumatic to the retina or even cause retinal tears. We believe hydraulic back pressure helps in breaking up tenuous blood clot and hence simplifies its aspiration. 246 We do no recommended that hydraulic technique be used over the optic disc and fovea for fear of inducting traumatic hydraulic damage. References 1. Charles S. Vitreous microsurgery Williams & Wilkins, 1987, 83-84. 2. O’Malley, C. Extrusion Method. Octome fragmatome newsletter, 1987, 3. Dr. Yog Raj Sharma Dr. R.V. Azad, Dr. Deependra V. Singh Dr. R.P. Centre, AIIMS, New Delhi DOS Times - Vol.9, No.6 CURRENT PRACTICE Phakic Intraocular Lenses Namrata Sharma MD, Jeewan S. Titiyal MD, Nishant Taneja MBBS, Rasik B. Vajpayee MS, FRCS (Ed) Phakic intraocular lens (IOL) is any lens located between the cornea and the crystalline lens, which is left undisturbed in the eye. Anterior chamber phakic intraocular lenses have been used since 1950s but the surgical procedure failed due to lack of microsurgery devices and poor understanding of the endothelial function. In 1987, there was a comeback of these lenses and today phakic intraocular lenses are an important area of refractive surgery. Types of Phakic IOLS There are three types of phakic IOLs. These include: 1. Anterior chamberangle fixated IOL e g. ZB M5, NuVita MA20, Phakic 6. 2. Anterior chamber- Iris fixated IOL e g. VerisyseTM Phakic IOL (Artisan lens) 3. Posterior chamber sulcus fixated IOL e g. STAAR Implantable contact lens and phakic refractive lens (PRL) Selection of patients for phakic IOLs 1. Age above 18 years 2. Moderate to high myopes (>-9.00D) & hyperopes (> 4.5 D) 3. Also indicated in lesser degrees of ametropias if LASIK is contraindicated such as Cornea and Refractive Surgery Services, Dr. R.P.Centre for Ophthalmic Sciences, AIIMS, New Delhi. December, 2003 Ø Corneas thinner than 500 microns Ø Steep or flat corneas Ø Topographic change suggestive of keratoconus 4. Endothelial cell density: at least 2250-2500mm3. 5. Pupil smaller than 6 mm in scotopic luminance. 6. Stable refraction for at least 1 year 7. Anterior chamber depth (excluding corneal thickness) at least 2.8mm 8. Angle width at least 30 degrees 9. No eye pathology except refractive 10. No systemic pathology such as diabetes, collagen diseases etc Angle Supported Phakic IOLS First generation angle supported IOLs were developed by Baikoff & Joly in 1997. The first model (ZB DOMILENS) was a modified Kelman type lens with a 4.0mm optic and 2 haptics with a 4-point fixationin the angle. However, this lens had a high vault and was so close to the endothelium that it had to be explanted in 50 % of the eyes due to endothelial damage. In the line of Kelman type angle supported anterior chamber phakic IOL, the only available at present is PHAKIC 6which is made of PMMA, has a 6.0mm optic and 2 haptics with four point fixationin the angle. Two types of foldable intraocular lenses in this group include: 1. Vivarte (Ciba Switzerland) and the Duet (Tekia, USA) in one group and 2. ICARE (Corneal, France) and Acrysof (Alcon, USA) Vivarte and Duet have a foldable optic (acrylic) of 5.5mm and 2 haptics made of PMMA with 3 points for the angle fixation. The difference between these two IOLs is that in the Duet the haptic and optic are implanted separately in the bag and the lens is assembled in the eye whereas in the ICARE and Acrysof the folding occurs outside the eye. Selection of angle supported IOL To select an IOL we need to calculate the power and the size of the implant. As these IOLs are supported by the angle and the size of the anterior chamber varies from patient to patient, the correct size of the anterior chamber must be defined. Most surgeons measure horizontal or vertical white to white with the help of the calipers, Holladay discs or Orbscan. To this white-to-white, a correction factor is added to determine the correct length. For example 1 mm in Phakic 6, 0.5-1.0mm in Vivarte and 1.5mm in Acrysof. To calculate the lens 247 Fig.1: Phakic 6 IOL Fig. 2: Vivarte power we use Van der Heijde nomogram, which takes into account the spherical equivalent, the corneal power and the anterior chamber depth. Surgical Technique To implant an angle supported anterior chamber phakic IOL , the following steps are performed: 1. Pre-operative miosis 2. Incision size of 6.2 mm for Phakic 6 (corneal/ corneoscleral) 3. Incision of 3.2mm (clear corneal self sealing ) 4. Fill anterior chamber with standard viscoelastic 5. Introduce the IOL 6. No iridotomy / iridectomy required 7. Wash out the viscoelastic 8. Suture in case of DOS Times - Vol.9, No.6 CURRENT PRACTICE Fig.4: Nuvita lens Problems of anterior chamber phakic IOLs Fig. 3: Duet IOL 1. Phakic 6 IOL 9. Postoperatively, topical steroids and antibiotics are given for 1 week The problems, which have been encountered with these lenses, are as follows: Iris Supported Anterior Chamber Phakic IOLS Iris fixated IOLs have haptics in the form of lobster claw that fixate the IOL to the mid peripheral iris. The classical type of this phakic IOL is the Artisan (Ophtec, Netherlands & Verisyse AMO). The Artisan lens is a onepiece UV wavelength absorbing PMMA compression molded lens with a diameter of 8.5 mm. The optic is vaulted suitably (0.5mm) to stay clear of the iris cone. It is available in 5.0mm optic (for myopia -3.00 to -23.00 and hyperopia + 3.0 to +12.00) or 6.0mm (available for myopia -3.0 to - 14.50 D). There is also a toric Artisan available in 5.0mm model, which corrects upto astigmatism of 7.00 D. Two models are available: Model A: axis of cylinder in the axis of IOL and Model B: Axis of cylinder 90 degrees of the axis of IOL. December, 2003 Endothelial cell loss ® Intermittent endothelial touch 2. Pupillary ovalisation (4-42%) a) Immediate post operatively ® Iris tuck/ oversized IOL b) Late onset ® Iris root ischemia 3 Iris depigmentation(2.3-4.5%) ® Iris protrusion during surgery 4. Halos & glare® Small optic zones 5. Surgically induced astigmatism® Long incisions Selection of iris fixated IOLs Concerning the power, the rules are same as for anterior chamber fixated phakic IOLs. Concerning the size: ' one size fits all' as these implants are not dependent on the eye dimensions. Surgical Technique The steps of the surgery are as follows: 1. Pre-operative miosis 2. Two side ports are made (2 mm away from each extremity of main incision) 3. Main incision 5.2 or 6.2 mm) corneal or corneoscleral 4. Fill the anterior chamber with standard viscoelastic 5. Introduce the IOL 6. Grasp the iris tissue into the claws 7. Wash out the viscoelastic Problems of Iris fixated phakic IOLs 1. Anterior chamber inflammation: early post-op- 6.4 to 16% of eyes (Fechner et al 1992) 2. Glaucoma 3. Iris atrophy: on fixation sites - 81% cases( Santonja et al) 4. Implant dislocation: lens instability & haptic disincarceration in 9.3% ( Santonja et al.) 5. Decentration : 23.4-56% (Manejo et al.) 6. Endothelial cell loss: mean endothelial cell loss 5.3%, 7.63% &17.9% at 1, 2 &5 years respectively. 7. Cystic wounds and subconjunctival fistulas- rare 248 8. Iridectomy/ Iridotomy recommended 9. Postoperatively, topical steroids and antibiotics are given for 1 week The advantages of these lenses are as follows: 1. Enclavation of the loop tips produce a pillow of iris tissue over the most peripheral part of the haptics 2. The angle of the anterior chamber, the crystalline lens, and the corneal endothelium are not at risk because they are far away 3. The Pupil can be dilated for fundus examination. Iris claw lens does not affect the movements of the iris and the pupil, except at the point where the iris passes through the claw. The crystalline lens is not affected since the implanted lens remains far away from it. These lenses are very easy to explanted of needed new lenses can be important any increased risk. Posterior Chamber Phakic IOLS In the years between 19901998 a new material came into vogue known as the Collamer. This was a hybrid of silicone and collagen and the lens was called as the Implantable contact lens or the ICL. The current version available is the V4, which was introduced in 1998. Fig.5: Artisan lens Phakic IOL (VerisyseTM) DOS Times - Vol.9, No.6 CURRENT PRACTICE Fig.6: Artisan lens Phakic IOL (VerisyseTM) The PRL or the phakic refractive lens is another posterior chamber phakic IOL available with Ciba vision. It is made of new generation ultra thin hydrophobic silicone. It has no anatomical fixation sites and floats on the layer of aqueous humor inside the posterior chamber exerting no traction on the ciliary structures and without coming in contact with the anterior capsule of the crystalline lens. The Sticklens (IOLTECH, France) is available which is made up of hydrophilic acrylic material, which sticks firmly to the anterior surface of the crystalline lens. Surgical Technique 1. To prevent angle closure 2 fully patent sufficiently wide Nd: YAG laser iridotomies must be done 1 to 2 weeks before surgery. 2. Peripheral iridotomies should be placed at 11 and 1 0'clock under the upper lid to avoid the risk of monocular diplopia, ghost images and for aesthetic reasons. 3. Intraoperative surgical iridectomy is a less recommended option. 4. Both ICL and PRL are injected through a less than 2.5 mm incision to provide December, 2003 the patient with the benefits of 'minimally invasive implant surgery'. The current PRL has 2 tiny dots on the haptics in order to avoid inverted implantation. 5. Smooth and gentle retro positioning of the footplates involves maneuvering the haptics through the 1 mm sideports with sand blasted visco cannula or specifically designed 'tuckers'. Bimanual irrigation aspiration is then done to remove the viscoelastic agent. Phakic Iols: Whre Are We Today? Roughly 60,000 phakic IOLs have been implanted (equally divided among angle fixated, iris supported and posterior chamber phakic intraocular lenses. If properly sized and implanted, all these phakic IOLs are likely to produce more or less the acceptable similar results in terms of precision, predictability and stability of the refractive outcome. The anecdotal incidence of catastrophic events like endophthalmitis and retinal detachment is acceptably low if considered in terms of risk/benefit ratio in a population who is also Fig. 7: Staar ICL Collamer Fig. 8: PRL Problems of phakic posterior chamber IOLs Ø Ø Ø Ø Ø Ø Ø Inverted implantation- iatrogenic Endothelial cell damage (2.3-3.0% at 2 yrs) Inflammation Pigment dispersal Elevated IOP Cataractogenesis -0.82 to 4.38% at 5 years Decentration naturally prone to posterior segment disorders. Nighttime symptoms are frequent but disabling only in a few. With latest and future generations wide optic lenses and adequately sized lenses these problems including the problem of cataractogenesis should decrease. Although the short-term results are reassuring, the long-term results are awaited. Sugested Reading 1: Guell JL, Vazquez M, Malecaze F, Manero F, Gris O, Velasco F, Hulin H, Pujol. J. Artisan toric phakic intraocular lens for the correction of high astigmatism. Am J Ophthalmol. 2003 Sep;136(3):442-7. 4: Sanchez-Galeana CA, Smith RJ, Sanders DR, Rodriguez FX, Litwak S, Montes M, Chayet AS. Lens opacities after posterior chamber phakic intraocular lens implantation. Ophthalmology. 2003 Apr; 110(4):781-5. 5: El-Sheikh HF, Tabbara KF. Cataract following posterior chamber phakic intraocular lens. J Refract Surg. 2003 JanFeb;19(1):72-3. 7: Sanders DR, Vukich JA; ICL in Treatment of Myopia (ITM) Study Group. Incidence of lens opacities and clinically significant cataracts with the implantable contact lens: comparison of two lens designs. J Refract Surg. 2002 Nov-Dec; 18(6): 67382. Summary of posterior chamber Phakic IOLs Model ICL ( STAAR) PRL( CIBA Vision) Sticklens(IOLTECH) Optic Single piece Single piece Single piece Geometry Planospherical Planospherical Meniscus Diametrs 5.5/5.25/5.0/4.6 5/4.5 6.5 Material Collamer Hydrophillic Silicone Hydrophillic Acrlic Special features Toric custom No No Power -3 to –21 +3to+17 -3to-20 +3to+15 -7to-25 +4to+7 Power calc. Formula Olson-Feingold Holladay Refractive Van der Hejide Incision size 2.5mm 1.8mm 3.0mm 249 DOS Times - Vol.9, No.6 CURRENT PRACTICE Contrast Sensitivity Measurement and its Practical Implications Parul Sony MD, Vandana Kori BSc Contrast is created by the difference in luminance, and the amount of reflected light, reflected from two adjacent surfaces. It provides critical information about the edges, borders and variation in the brightness of two objects. It can be defined with the following formula: Contrast = Lmax - Lmin Lmax + Lmin Lmax = Luminance on the lighter surface Lmin = Luminance on the darker surface Contrast sensitivity is the reciprocal of the contrast at threshold, i.e., one divided by the lowest contrast at which forms or lines can be recognized. If a person can see details at very low contrast, his or her contrast sensitivity is high and vice versa. Contrast sensitivity measures the ability to see details at low contrast levels. Depending on the structure of the stimulus used in the measurement - either gratings of different size or symbols - contrast sensitivity of a person gets different values. When the darker surface is black and reflects no light, the ratio is 1. Contrast is usually expressed as percent, then the ratio is multiplied by 100. The maximum contrast is thus 100% conDr. R.P.Centre for Ophthalmic Sciences, AIIMS, New Delhi. December, 2003 trast. The symbols of the visual acuity charts are close to the maximum contrast. If the lowest contrast perceived is 5%, contrast sensitivity is 100/5=20. If the lowest contrast perceived by a person is 0.6%, contrast sensitivity is 100/0.6=170. Contrast sensitivity function (CSF) is defined as the visual function that is measured using a range of sinusoidal grating pattern as the visual stimulus. CS assesses the patient’s sensitivity to large, intermediate and small objects (spatial frequency) under the conditions of varying contrast. It is a subjective measurement of a person’s ability to detect a low contrast pattern stimuli and it gives a more accurate representation of the eyes’ visual performance. The CSF usually decreases with age especially for high and intermediate spatial frequencies. A low CSF reduces the amount of detail that can be seen especially in lower levels of lighting or at a distance like, difficulty in reading poor contrasting print materials, difficulty in moving around safely in dim light. The pathological loss of CS is of four types 1. generalized loss at all frequencies 2. high frequency loss 3. mid frequency loss 4. low-mid frequency loss Snellen visual acuity Vs Contrast sensitivity: Snellen’s charts test VA at a very high contrast thus many patients have a good snellens VA but they may be visually handicapped in real life situations. The VA drops in the situations with low contrast and the quality of vision is not good. CS is a useful index of pattern vision. It provides the information that cannot be obtained from visual acuity, and it is often a better predictor of visual performance then VA. There are various causes that may decrease the CS 1. uncorrected refractive errors, 2. keratoconous 3. cataract 4. posterior segment dis- orders: AMD, Diabetic retinopathy, Glaucoma 5. Optic neuritis Methods Testing contrast sensitivity is important as it subjectively assesses the patient’s visual function in day to day life. Various charts and electronic devices are available to measure the contrast sensitivity. The key difference is target type. For example, the Pelli-Robson chart determines the contrast required to read large letters of a fixed size. With the Pelli-Robson chart, the contrast varies while the letter size remains constant. The Regan chart, a low-contrast letter chart having different size letters, reduces the contrast levels of a standard Snellen-type letter acuity chart resulting in several charts. The Functional Acuity Contrast Test uses sine-wave gratings. Most common stimulus used for the clinical evaluation of spatial CS is repetitive patterns of alternating light and dark bars where Contrast sensitivity is the reciprocal of the contrast at threshold, i.e., one divided by the lowest contrast at which forms or lines can be recognized. Fig. 1: Cambridge low contrast charts 250 DOS Times - Vol.9, No.6 CURRENT PRACTICE Plate no Contrast % Demo 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 13 5 2.7 1.6 1 0.72 0.52 0.37 0.27 0.19 0.14 l Bailey Lovie chart Vision contrast test system (VCTS) by Vistech l Cambridge low contrast grating l Regan charts l FACT charts l Cambridge low contrast gratings It is a rapid and simple screening test for contrast sensitivity. Performed at a distance of 6m. It comprises of 12 pair of plates consisting of stripes of varying contrast. First one is for demonstration and rest are for the proper testing and are numbered from 1-10. The plates are changed sequentially starting from plate 1 till the patient fails to respond. Then a new series is begun starting 4 plates prior to where the patient failed to respond. Four such series Fig. 2: Pelli robson contrast sensiare completed and the tivity charts and scoring pad score of each series is noted (numbered as per the luminance of the bars varies sinusoidally along the the number of plate read) single axis (known as sine and added. The final total wave grating). The patient value is converted into consignals when the pattern is trast sensitivity from the first detected. Typically the provided table. spatial frequency varies from 0.5 to 23 cpd. The PELLI ROBSON contrast graphic representation of sensitivity charts This chart utilizes letters the mean and standard deof the same size but with reviation of the threshold of different spatial frequencies ducing contrast to provide a is called the CS curve or CSF. quick means of assessing The CS peaks around 4 cpd patient contrast sensitivity. of spatial frequency. Con- There are two charts and trast sensitivity measures two scoring pads. The two the ability to see details at charts have different letter low contrast levels. The vari- sequence but other wise ous methods available to they are similar. Each chart has 6 letters in each row ormeasure CS include ganized into two triplets of l Pelli Robson test December, 2003 varying contrast. Thus there are two contrast levels in each row. The illumination of the chart is 85 cd/mm2 and glare should be avoided. The test is carried at a distance of 1 meter with patient wearing the best correction and before dilating the pupils. The patient is asked to read the alphabets starting from left hand corner, when he fails to respond several seconds are given to him to retry and guess the alphabet. The score of the test is recorded by the faintest triplet out of which at least 2 letters are correctly identified. The log CS value for this triplet is given by the Contrast sensitivity measures the ability to see details at low contrast levels number on the scoring pad nearest to the triplet, either on the left or the right side. Each eye is tested separately and then the both eyes together. The three measurements should not take longer then 8 minutes. Usually the binocular log CS is higher by 0.15 units then monocular CS. However development of cataract may result in poorer binocular CS when compared to the CS of each eye being tested separately. Functional Acuity Contrast Testing (FACT) FACT charts were developed by Dr. Arthur Ginsburg. FACT comprises of a chart with sine-wave gratings of varying contrast as well as varying spatial fre- 251 quencies. It is an accurate and comprehensive grating chart that tests functional visual acuity. The chart tests five spatial frequencies (sizes) and nine levels of contrast. The Contrast varies in a row, decrease from left to right. And the spatial frequencies increase as one move down the various columns from top to bottom. This test is performed at a distance of 10 feet. The patient determines the last grating seen for each row (A, B, C, D and E) and reports the orientation of the grating: right, up or left. The last correct grating seen for each spatial frequency is plotted on a contrast sensitivity curve. FACT contrast sensitivity scores can also be used to generate images with VSRC’s EyeView™ Functional Analysis Software which demonstrates how the world looks to your patient based on their contrast sensitivity scores. FACT Contrast Sensitivity Charts are available in two sizes: Studies have shown that the contrast sensitivity curve provided by sine-wave grating tests is more sensitive and informative than the results obtained from lowcontrast letter acuity systems. Pelli Robson is more sensitive and most reproducible methods for studying and detecting the mid range loss of CS. Practical application Importance of CSF lies in various practical situations like: l Driving in winter in fog or rain l Radiographic diagnosis l In near vision tasks like DOS Times - Vol.9, No.6 CURRENT PRACTICE Monthly Meetings Calendar For The Year 2003-2004 27th July, 2003 (Sunday) Army Hospital 30th August, 2003 (Saturday) Sir Ganga Ram Hospital 27th September, 2003 (Saturday) Hindu Rao Hospital 19 October, 2003 (Sunday) DOS Midterm Conference Fig. 3: FACT chart 1st November, 2003 (Saturday) R.P. Centre for Ophthalmic Sciences Distance FACT Chart and Near FACT Chart Stimulus type Cambridge low contrast gratings Pelli robson FACT Contrast gratings Alphabets Contrast gratings 1m 85-150cd/ mm 10 feet — 1 chart 1 near, 1 distance Test distance 6m Luminance 100cd/mm2 Number of Plate l l l 12 chart reading and writing, if the information is at low contrast In every day tasks, where there are numerous visual tasks at low contrast, like cutting an onion on a light colored surface, pouring coffee into a dark mug, checking the quality of ironing, etc Development of cataract causes a decrease in the contrast sensitivity. The CS shows improvement after the cataract surgery. Various IOLs have different effect on the postoperative CS. The CS recovery is best with all PMMA IOL>Acrylic IOL> silicone IOL Diffractive multifocal IOL December, 2003 l l 29th November, 2003 (Saturday) Dr. Shroff’s Charity Eye Hospital 27th December, 2003 (Saturday) Venu Eye Hospital & Research Centre 31st January, 2004 (Saturday) Safdarjung Hospital have poorer CS when compared to the monofocal IOL especially for near vision The aspheric IOL (Technis) provides a significant improvement in retinal image contrast. This improvement is significantly better when compared to the performance of conventional spherical silicone and acrylic IOLs. CS decreases after refractive surgery like RK, PRK and LASIK. Lasik has the least effect on CS, though it has been seen that CS improves slightly still it does not return to baseline even by 6 months postoperatively. 252 28th February, 2004 (Saturday) M.A.M.C. (GNEC) 28th March, 2004 (Saturday) Mohan Eye Institute 3-4th April, 2004 (Saturday & Sunday) Annual DOS Conference Attention DOS Members The Hi-tech DOS Library has started functioning on Ground Floor, Dr. R.P. Centre, Delhi Ophthalmic Sciences, AIIMS, New Delhi-110029 from 12.00 Noon to 9.00 P.M. on week days and 10.00 A.M. - 1.00 P.M. on Saturday, Sunday. The Library will remain closed on Gazetted Holidays. Members are requested to utilise the facilities available i.e. Computer, Video Viewing, Latest Books and Journals. We are planning to subscribe two journals. Member can give suggestion in this regard. Dr. Lalit Verma Library Officer, DOS DOS Times - Vol.9, No.6 MANAGEMENT PEARLS Analysis of Problem Situations: Management of IOL Power Calculation Problems After Refractive Surgery Sudipto Pakrasi MD, DNB These days, cataract patients who have previously undergone refractive procedures are taking center stage in many ophthalmic practices. As the popularity of refractive surgeries such as LASIK and PRK grows, surgeons will increasingly be confronted with the problem of calculating the proper IOL power after previous corneal refractive surgery. Surgeons are dancing as fast as they can to try to avoid all-too-common refractive surprises in these patients. Postrefractive surgery patients often bring with them the same high expectations they had for their refractive procedures. They’re going to want the same sort of visual outcomes after cataract surgery that they achieved after refractive surgery. This requires a different approach from that used with the typical cataract patient. The difficulty of IOL power calculation after refractive surgery lies in the ability to accurately calculate corneal powers. The altered corneal shape can result in multiple ranges of corneal power throughout the central corneal surface. The average keratometric Eye Microsurgery Associates Aashlok Hospital, Safdarjung Enclave, New Delhi December, 2003 readings from the standard intraocular lens formulas are inaccurate for these patients. Conventional manual keratometry measures a limited number of points at a 3 to 4 mm annulus, which can vary with steeper or flatter corneal shapes. Another factor introduced by corneal tissue removing surgeries, such as LASIK, has been the change in the standardized refractive index of the cornea due to the change in the corneal power of the front corneal surface. Why a problem? The true corneal power following RK, ALK, PRK and LASIK is difficult to measure by keratometry, or corneal topography. The reasons for this are as follows: Keratometry and topography assume a normal relationship between the anterior and posterior corneal curvatures and measure the anterior corneal radius. Keratorefractive surgery for myopia flattens the anterior corneal radius, but leaves the posterior corneal radius mostly unchanged. This disparity is greater with LASIK and somewhat less with RK. Because the central cornea has been flattened, keratometry may read a falsely large area. Rather than measuring several points within a central 2.5 to 3.5 mm area, the measurement may instead be at 6.0 mm. With the non-incisional forms of keratorefractive surgery, such as LASIK and PRK, the index of refraction of the cornea is probably changed. Automated keratometry and corneal topography analysis therefore use incorrect assumptions in measuring corneal power. The cornea can no longer be compared to a sphere centrally. The back surface is no longer 1.2mm steeper than the front surface. The reading measure the curvature at 3mm. This may not reflect the power in the centre of the cornea. In normal corneas the posterior curvature of the cornea is 1.2 mm less than the anterior surface. Anterior corneal radius of 7.5 mm, using the Standardized Keratometric Index of Refraction of 1.3375, the corneal power would be 45 D. Overestimates total power by 0.56 D. Most IOL calculations today used a net index of refraction of 1.3333 (4/3) and the anterior radius of the cornea to calculate the net power of the cornea. Using this total power of a cornea = 44.44 D. The major source of IOL error in such patients therefore is accu- 253 rately determining the keratometric power. Manual and automated keratometers evaluate the radius of curvature designated by four points in orthogonal meridians separated about 3.2 mm apart with manual keratometers, or about 2.6 mm apart in automated keratometers. Corneal optics in keratometers is assumed to be spherocylindrical. Normal corneas are nearly spherical, or prolate. A patient who, prior to the refractive surgery, is myopic is going to have a relatively flatter cornea in the center and it’s going to get steeper in the periphery. Postrefractive corneas, however, are oblate. Setting The Stage For Trouble For these reasons, keratometry, and corneal topography will typically over-estimate central corneal power following keratorefractive surgery for myopia. For low power myopic corrections by RK (less than -2.00 D), this effect is minimal. But for higher power myopic corrections, and especially those by LASIK, this over-estimation can be quite significant. Failure to keep this important fact in mind will often result in an unexpected and unDOS Times - Vol.9, No.6 MANAGEMENT PEARLS K Value Problems Figures: ractive keratectomy. Direct Change of Central Anterior Corneal Curvature During excimer laser photorefractive keratectomy (PRK), selective removal of tissue across the anterior corneal surface results in a change of the anterior corneal curvature. Although the central anterior surface of the cornea may become flatter (to treat myopia) or steeper (to treat hyperopia), the posterior surface is presumed to remain stable. The same may be true for uncomplicated laser in situ keratomileusis (LASIK) in which direct flattening or steepening of the central anterior corneal surface is achieved by focal keratectomies under a planohinged flap. (A) Normal Cornea (Fig A) Corneal thickness - reduced B) AFTER PRK/LASIK (Fig B) w Anterior curvature changed w Posterior curvature - No change C) AFTER RK (Fig C) w Anterior & posterior - similar changes w No change of corneal thickness pleasant post-operative hyperopic surprise. With the postmyopic refractive laser in-situ keratomileusis patient, this means the practitioner will be measuring the keratometry values from the steeper part of the cornea rather than the centrally flattened portion. The K is going to estimate high, so you’ll estimate your IOL power to be lower than it should be, and you’re going to get a hyperopic surprise. In post-hyperopic LASIK patients, the corneas are December, 2003 steeper in the center and flatter in the periphery. Practitioners are going to be measuring keratometry values from the flatter part of the cornea and estimating low. Therefore, IOL power will be overestimated and practitioners will get a myopic surprise. Potentially adding to the error is the fact that manual and automated keratometers don’t take into account irregular astigmatism, which may occur after radial keratotomy, or central islands and decentrations with LASIK or photoref- Indirect Change of Central Anterior and Posterior Corneal Curvature To correct myopia with radial keratotomy (RK), deep radially oriented incisions are applied in the midperiphery of the cornea to induce midperipheral bulging of the cornea. Indirectly, the central cornea becomes flatter. Since no tissue is removed it is assumed that the anterior and posterior surfaces of the cornea react in an analogous way. Principles In Intraocular Lens Power Calculation Calculation of intraocular lens (IOL) power in cataract surgery is based on measurements of corneal power/radius of curvature, axial length, and estimation of postoperative anterior chamber depth—termed effective lens position (ELP). 254 The term keratometric diopters are used to avoid confusion with optical diopters, since keratometric diopters and optical diopters are not equivalent. There are a number of formulas available for the calculation of IOL power. They can be classified as either empirical regression formulas (most popular are the SandersRetzlaff-Kraff formulas) with (SRK/T) or without (SRK I and II) the inclusion of additional terms accounting for non-linearity or theoretical optical formulas (Holladay, Hoffer, or Haigis). There are five variables in such a formula: 1) Intraocular lens power, which is generally chosen as the dependent variable; 2) Keratometric diopters (average keratometry reading)—the most crucial variable after refractive corneal surgery; 3) Axial length, measured by A-scan ultrasonography or by optical means; 4) Effective lens position; and 5) Target refraction, typically ranges between -2.00 and 0 diopters (D). Calculation of the resulting spectacle correction for a given IOL is typically based on a vertex distance of 12 or 14 mm. The only variable that cannot be measured preoperatively is the effective lens position. Improvements in IOL power calculations over the last 30 years are mainly a result of improving the predictability of effective lens position by additional measurement of horizontal white-to-white DOS Times - Vol.9, No.6 MANAGEMENT PEARLS corneal diameter, preoperative anterior chamber depth, and lens thickness, since the anterior segment dimensions often are not proportional to the axial length Types of Formulae 1. Regression Formulas These are based upon mathematical analysis of a large sampling of post-operative results. Most familiar is SRK formula: works well 22.5 to 25.0 mm in axial length. The formula does not work well for “long” (>25 mm) or “short” (<22.5 mm) eyes. 2. Theoretical Formulas Theoretical formulas are optical formulas based on the optical properties of the eye. They do a better job of predicting post-op outcomes for long and short eyes.3 widely used theoretical formulas, each with their own strengths and weaknesses. These formulas are included in various combinations with many Ascan instruments. They are also available in software products · Holladay between 22 and 26mm · Hoffer Q shorter than 22.5mm · SRK/T for long eyes (>26mm). 3. Recent Developments · Holladay II Tackles severe myopia · Holladay Consultant IOL program – (HIC) uses Holladay 2 formula (uses7 variables) · New Haigis formula optimised for axial length dependency of the type of IOL to be used December, 2003 K = Preoperative Average K - Change in Manifest Reaction Prerefractive and Postrefractive Surgery Ktrue = Kpre + Rpre – Rpost Generally holds true, if the following are known: n Ktrue = the true corneal power after refractive surgery n Kpre = the average corneal power in diopters before refractive surgery, and n Rpre = the spherical equivalent in diopters before refractive surgery, and n Rpost = stable spherical equivalent in diopters after refractive surgery, then To give accurate information, the refractive numbers (Rpre and Rpost) must retain their corresponding plus (hyperopic) and minus (myopic) signs, and be corrected for vertex distance. K = Base Curve + (Difference in Refractive Error without Contact Lens and with Contact Lens) Ktrue = Cbase + Cpower + Rcl - Rbare Generally holds true, if the following are known: l Ktrue = the true corneal power after refractive surgery l Cbase = base curve of the contact lens in diopters, and l Cpower = spherical refractive power of the contact lens in diopters, l Rcl = spherical equivalent refractive error with the contact lens, & l Rbare = spherical equivalent refractive error without the contact lens, then To give accurate information, the refractive numbers ( Rcl and Rbare) must retain their corresponding plus (hyperopic) and minus (myopic) signs, and be corrected for vertex distance. · Gaussian Optics Formula No matter what type of [refractive] procedure the patient has had, the stability of the refraction must be determined. This determination includes daily fluctuations from morning to night, as well as long-term changes. … Each of these factors must be used in determining the desired postop target refraction and to prepare the patient for the visual changes and realistic expectations after the procedure. In these patients, use biomicroscopy, retinoscopy, corneal topography, and endothelial cell counts. The first three help evaluate the amount of irregular astigmatism, which may be contributing to the reduced vision, as well as the cataract. The irregular astigmatism may also limit the patient’s vision after cataract surgery. The endothelial cell count can identify patients with low cell counts from the previous surgery who may be at a higher risk for corneal decompensation or prolonged visual recovery. Secondary tests include the potential acuity meter, super pinhole, and hard contact lens trial. In addition, patients should be informed that only glare from the cata- 255 ract will be eliminated. Any glare from the keratorefractive procedure will remain unchanged. How to Deal with the Problem? 1. Measuring K w A) Manual Keratometry w B) Automated Keratometry w C) Corneal Topography 2. Calculating K w A) Clinical history method w B) Contact Lens method w C) Double K method 3. Other methods w Intraoperative Retinoscopy w Hand held Autorefractometers w Secondary IOL Implant w Piggyback IOL w IOL Exchange 1. Measuring K: Methods to Assess Keratometric Diopters as A Measure of Central Corneal Power Keratometry 1. A) Manual-Manual keratometry is the method that IOL power calculation formulas were originally based upon. Keratometry evaluates only four points separated 3 to 4 mm in two orthogonal meridians on the paracentral cornea, and the corneal optics are assumed to be spherocylindrical. Thus, asphericity or asymmetry of corneal shape cannot be measured with standard keratometry. Manual keratometry probably represents the least accurate method since current instruments, such as the Zeiss, Javal- Schiötz, or Bausch & Lomb keratoDOS Times - Vol.9, No.6 MANAGEMENT PEARLS meters make too many assumptions that do not take into account irregular corneal astigmatism. Nevertheless, the examiner is actually able to see the reflected mires and the amount of irregularity. Seeing the mires does not help get better measurements, but does allow the observer to discount the measurement as unreliable. 1. B) Automated-Automated keratometers may be more accurate than manual keratometers in corneas after RK that have small clear zones (i.e., less than 3 mm) because they sample a smaller central area of the cornea (nominally 2.6 mm). The smaller the clear zone and the greater the number of RK incisions, the greater the probability and magnitude of error. This error occurs because the samples at 2.6 mm are close to the paracentral transition zone (knee) after RK. After PRK or LASIK, automated keratometers accurately measure the front radius of the cornea, because the transition areas are far outside the 2.6- mm zone that is measured. However, derivation of keratometric diopters from the radius of curvature is still wrong. 1. C) Corneal Topography Analysis w Videokeratography derived Simulated Keratometry Readings (Sim-K) using the topography system, the simulated keratometry value (Sim-K) is determined from the power of Placido mires 7, 8, and 9 of the videokeratoscope for 128 equally spaced meridians. Measuring more than 5000 points over the entire cornea December, 2003 256 DOS Times - Vol.9, No.6 MANAGEMENT PEARLS and more than 1000 points within the central 3 mm, videokeratography provides greater accuracy in determining the power of corneas with irregular astigmatism compared to keratometers. However, Sim-K value derivation may vary among different videokeratoscopes, and these values should be compared to the results of conventional keratometry before using them interchangeably. w Average Central Power (ACP) - A new parameter, average central power, from the average of corneal powers inside the region demarcated by the entrance pupil of the TMS-1 videokeratoscope. Because the density of measured points with the videokeratoscope is highest in the central cornea and decreases toward the periphery, areacorrected power was used for compensation. This modified method is supposed to have major advantages over the classic Sim-K after RK with small clear zones, but not after PRK and LASIK. Other similar values are provided by other videokeratoscopes. For example, the EyeSys videokeratoscope has a display called the Holladay Diagnostic Summary in which there is an analogous value calculated called effective refractive power. w Scanning Pancorneal Slit Topography -Using the Orbscan scanning slit-beam videokeratoscope , a threedimensional location of several thousand points of the corneal and anterior chamber surfaces can be deterDecember, 2003 mined. Two scanning slit lamps project 40 calibrated beams onto the eye, angled at 45° to the left and to the right of the video camera axis, covering the whole cornea from limbus to limbus and overlapping in the central 5-mm zone. This system has the potential to provide topographical height and power maps of the anterior and posterior corneal surface as well as a corneal thickness profile, allowing a direct correlation of pachymetry and height data. 2. Calculating K: Combination of the clinical history & contact lens methods are considered the most accurate ways of determining the IOL power after refractive surgery. It should be remembered that these methods will give an estimation of the true central corneal power and may not be exact. At present, these techniques represent the best clinical methods available. Hopefully, in the future we may have a more accurate, and less time-consuming, method for measuring these challenging eyes. 2. A) Clinical history method Requires the following information: Ø Pre-Refractive refraction Ø Pre-Refractive K readings Ø Post-Refractive refraction (preferably current, but before significant cataract formation). Using K reading before and after refractive surgery, refraction derived K is calculated at the corneal plane, and used in the IOL formula. 2B) Contact Lens Method The current refraction = +0.25 D. With a plano hard contact lens BC of 35 D placed on the cornea, the spherical refraction changes to -2 D. Because the patient had a myopic shift with the contact lens, the cornea must be weaker than the base curve of the contact by 2.25 D. Therefore, the cornea must be 32.75 D (35 - 2.25), which is slightly different than the value obtained by the calculation method. SEQ refraction without hard contact lens = +0.25 D Base curve of plano hard contact lens = 35.00 D SEQ refraction with hard contact lens = -2.00 D Change in refraction = -2.00 - (+0.25) = -2.25 D (myopic shift) Mean corneal power = Base curve of plano HCL + change in refraction Mean corneal power = 35.00 + (-2.25) Mean corneal power = 32.75 D 2 B) Contact lens method (Overrefraction) : After refracting the patient, a plano hard CTL with known base curve is placed on the eye and an over-refraction is performed. If the refraction does not change with the lens, then the power of the cornea must be the same as the base curve of the CTL. If there is a myopic shift, the power of the base curve is greater than that of the cornea by the amount of the shift. If there is a hyperopic shift, the power of the base curve of the CTL is less than that of the cornea by the amount of the shift. This works only if visual acuity is better than 6/24. 2 C) Double K method A new method for calculating postrefractive IOL power, developed by Jaime Aramberri, MD, (Spain), uses a modified SRK-T formula. With these standard calculations, in postrefractive surgery patients, a hyperopic refractive error is the rule. 257 Postrefractive K readings are at the center of the problem. However, no matter how flat the cornea gets after refractive surgery, the anterior chamber depth does not change. After corneal refractive surgery, the distance from the cornea to the intraocular lens must remain similar. Therefore, instead of using postrefractive surgery K values alone, which will lead to inaccurate results, they should be paired with the original preoperative Kvalue for the first step of the calculation. Practitioners are advised to use the postrefractive K-value for the remaining calculation — in effect splitting the K values. Each of these methods will assist the cataract surgeons to more accurately select the proper IOL power for patients who have had previous corneal surgery. The most difficult challenge for refractive surgeons is that much of the data necessary are often not present because of the long time interval between a patient’s cataract DOS Times - Vol.9, No.6 MANAGEMENT PEARLS surgery and refractive surgical procedure. A working knowledge of these three basic methods combined with trying to gather as much preoperative patient information as possible, will help surgeons overcome this problem, which will certainly grow in significance as the number of patients receiving refractive surgery increases worldwide. The first two methods, the clinical history method and hard contact lens method, can be used for incisional surgery as well as excimer laser surgery. Care must be taken with the topographic method when analyzing patients who have had previous PRK or LASIK due to a change in effective refractive corneal index of refraction. In the future, our ability to more accurately measure the corneal surfaces including the anterior and posterior curvature, as well as new IOL technologies that may allow for more surgeon customization will help us improve the accuracy of this difficult postrefractive surgical situation. 1. Other Methods Ø 3A) Intraoperative Retinoscopy: Ø 3B) Hand held Autorefractometers: These intraoperative measures may be utilized to reconfirm the IOL power calculated in the preoperative examination. Large refractive surprises can be avoided by intraoperative retinoscopy or handheld autorefractors. Because there are many factors at surgery that may change in the postoperative period, December, 2003 these refractions should not be relied upon, however, for fine-tuning the IOL power. Factors such as the pressure from the lid speculum, axial position of the IOL, intraocular pressure may cause the intraoperative refraction to be different than the final stabilized postoperative refraction. If the intraoperative refraction is within 2 D of the target refraction, no lens exchanges should be considered unless intraoperative keratometry can also be performed. Ø 3C) Secondary IOL Implant: After completing the initial surgery, IOL can be implanted at a secondary stage. Ø 3D) Piggyback IOL: Another IOL can be placed in the sulcus after the primary IOL implantation after 3 – 6 months, when the refraction stabilizes. Ø 3E) IOL Exchange: The most drastic way out can be undertaken, in case the patient is miserable with the initial results. Results after PRK/ LASIK Very few results of cataract surgery following PRK and LASIK are available. Hyperopic shift on the first day and daily fluctuations appear to be much less, similar to the early postoperative period following these procedures. In most cases, the stability of the cornea makes these cases no different than patients who have not had keratorefractive surgery. Postoperative after RK First Postoperative Day – Leads to hyperopic shift, due to the transient corneal edema. Daily fluctuations cause a myopic shift during the day (due to the regression of corneal edema after awakening in the morning). Long-term Results after RK Long-term results of cataract surgery are very good. The long-term hyperopic shifts and against-the-rule astigmatism over time following cataract surgery should be the same as following RK. Glare and starburst patterns are usually minimal - adjusted to these unwanted optical images following the initial RK. If the patient’s primary complaint before cataract surgery is glare and starbursts, it should be made clear to the patient that only the glare due to the cataract will be eliminated by surgery, and the symptoms that are due to the RK will remain unchanged. Post Myopic LASIK Center flatter & periphery steeper, hence, the various methods measure K from steeper part of cornea causing higher K values, giving rise to lower IOL power estimates making the person HYPERMETROPIC. Post Hypermetropic LASIK Center steeper & periphery flatter hence, the various methods measure K from flatter part of cornea causing lower K values, giving rise to higher IOL power estimates making the person MYOPIC. Summary & Practical Recommendations 1. Just like you do before every refractive surgery procedure, make sure that the 258 patient has realistic expectations. 2. Make sure that the refraction is stable (after refractive surgery and before cataract surgery), before you take up the patient for surgery. 3. Discuss the desired target refraction. Aiming for -1.00 D seems to be a good compromise. Do remember that trying to produce monovison in a patient who has never experienced this condition may cause intolerable anisometropia and may require further surgery. 4. Perform corneal topography analysis in all patients, in case you have access to it, to assess the amount of irregular astigmatism and asphericity. 5. If keratometric diopters and refraction before refractive surgery are known, use the clinical history method, considering the change of spherical equivalent refraction at the corneal plane after RK, PRK, or LASIK. If those values are not known, you may want to use the respective calculations at the spectacle plane to be on the safe (ie, myopic) side. Some experts in this field even recommend the use of spherical equivalent refraction change at the spectacle plane routinely and add another 1.00 to 2.00 D to the resulting IOL power, being sure to avoid any potential undercorrection. The clinical history method seems to be the most reliable method after RK, PRK or LASIK. 6. If keratometric diopters but not refraction before refractive surgery is known, use the change in anterior DOS Times - Vol.9, No.6 MANAGEMENT PEARLS surface keratometry readings after PRK or LASIK. 7. If preoperative keratometric diopters and refraction are not known and the visual acuity is 6/24 or better, try the hard contact lens method after RK. 8. If preoperative keratometric diopters and refraction are not known and visual acuity is less than 6/ 24 or plano hard contact lenses are not available, use average central power or the average keratometric diopters at multiple paracentral cursor points of videokeratography after RK, but use refined calculation of keratometric diopters from radius of anterior and posterior corneal surface after PRK or LASIK. 9. Use more than one modern third-generation formula (Hoffer Q, Holladay 2, SRK/T, Haigis). Do not use a regression formula (SRK I or SRK II) to calculate the IOL power and choose the highest value for your implant. 10. During the first days after cataract surgery following RK, patients may experience a significant hyperopic shift similar to the first post- operative days following their RK. This is due to corneal edema. These patients may also exhibit diurnal fluctuations of refraction during the early time period after cataract surgery. No lens exchange should be contemplated until the refraction has stabilized (1 week to 3 months). 11. Following PRK and LASIK, early hyperopic shift or diurnal fluctuations appear to be much less after cataract surgery. In most cases, stability of the cornea makes these cases no different than patients who have had no previous refractive corneal surgery. Future Challenges In many situations today, patients may ask for cataract surgery in centers other than those where the refractive procedure has been performed. Thus, neither the preoperative keratometry reading nor the exact amount of refractive correction may be available. In these eyes, it might be a good option to consider the keratometric diopters of the anterior and posterior cor- neal curvature separately after PRK or LASIK. This can be achieved by means of scanning slit topography, although the accuracy of the Orbscan unit for posterior corneal curvature measurements has not yet been fully validated. However, measuring the accuracy of an instrument on posterior curvature is not possible since the true shape of these surfaces cannot be referenced. However, to be on the safe side, refractive surgeons might consider giving their patients a wallet card indicating their preoperative keratometric reading, preoperative refraction, and postoperative refraction at some stable time point to allow for the application of the clinical history method. An additional approach to adjust keratometry readings after PRK and LASIK may be to apply multiple regression analysis comparing the corrected keratometric diopters to the measured values and to the spherical equivalent refraction change in a large number of cases. Thus, correction of keratometric diopters after PRK or LASIK may be realized by entering the measured value into an empirical quadratic regression formula. Certainly, such a theoretical approach must be refined after clinical data become available from more cataract operations. At this time, no definite statement can be made concerning IOL power calculation in patients with intracorneal rings. However, reversing the refractive corneal effect by timely removal of the ring before assessment of keratometric diopters might be a valid option. This seems even more reasonable in the face of the multiple reports about complete reversibility of the refractive effect after ring removal. The foolproof methodology has not yet been discovered as yet. Since the problem is made more complex by the fact that there are different types of refractive surgeries, the non-availability of most of the pre refractive data, we have to wait for accurate solutions to be developed – till then; the above mentioned suggestions may be followed. Attention DOS Members Applications are invited for DOS Fellowship for partial financial assistance to attend international conference(s). The last date for receiving application is 31st January 2004. For details please see page no. 263. December, 2003 259 DOS Times - Vol.9, No.6 MANAGEMENT PEARLS Management of Common Intra-Operative Complications of Phacoemulsification Sarmi Malik MS, AK Grover MD, FRCS Phaeoemulsification is a technically demanding surgery with often a long learning curve. Complications, especially in the early stages of the learning curve are not uncommon, which gradually reduce to make it an extremely safe procedure. However, one must be aware of all the possible complications, so as to minimize their occurrence and to manage them competently, should they arise. The complications of phacoemulsification may occur at any stage of the procedure. Problems related to the incision 1) Wound burn A wound burn is caused by excess heat energy at the phaco tip. The vibrations of the titanium tip, while causing emulsification of the nucleus, also produce a tremendous amount of heat in the anterior chamber even exceeding 100 degrees centigrade. This heat leads to swelling of the superficial corneal stroma and thus its opacification. Some of the risk factors include hard nucleus, more phaco power, a tight wound and insufficient irrigation (too low flow). Viscoelastic agents Vision the Eye Clinic, 12/27, West Patel Nagar, New Delhi-8 December, 2003 may block the tip and lead to its clogging. Therefore, some amount of viscoelastic must be aspirated before starting the irrigation. Wound burns lead to high astigmatism and inadequate wound closure. Sometimes, they may even necessitate suturing. adjacent conjunctiva balloons up, making the procedure more difficult. If the side port incision is too big, there will be continuous leakage. In such cases, it is advisable to place a suture and continue after making a new side port incision. 2) Wound leak An inadequate corneal valve is responsible for wound leak. As mentioned Descemet’s detachment Descemet’s detachment may occur during phacoemulsification by the follow- Descemets detachment occurs due to the use of blunt instruments in the anterior chamber, accidental injection of viscoelastic under the Descemet’s membrane or attempted insertion of an IOL through an incision that is too small. above, a wound burn may also cause a wound leak. Hydration of the anterior lip of the incision as advocated by Fine, may help to close the incision. In case the wound still leaks despite hydration, it is prudent to place sutures. 3) Induced astigmatism Postoperative astigmatism may be avoided by using either a temporal incision or an incision place in the steeper axis of preexisting astigmatism. Problems with the side port If the side port incision is made too close to the limbus, it impinges on the iris. The ing ways. It may be due to the use of blunt instruments in the anterior chamber, accidental injection of viscoelastic under the Descemet’s membrane or attempted insertion of an IOL through an incision that is too small. The management in such a case would depend on the extent of detachment. If the detachment is small, one can proceed with the phacoemulsification, taking care not to cause further damage. In case of larger detachments, it can be reattached using air or viscoelastic and depending on the situation, the surgery may be postponed or continued as 260 planned. In case of very large detachments transcorneal sutures may be required. Problems with the rhexis In order to achieve the perfect rhexis, there has to be good visibility (good illumination and magnification) and a chamber filled with viscoelastic. The patience of the operating surgeon is of utmost importance during this part of the procedure. A good viscoelastic material such as Sodium hyduranate (Healon) is very helpful. Methyl cellulose, if cooled has a greater viscosity, which helps in capsulorhexis. The most common problem during rhexis is extension into the periphery. This can be managed by using a fine forceps. The advancing edge is grasped and pulled sharply inwards. (Fig. 1 & 2) It can also be managed by making a cut in the intended direction of the rhexis, using a fine scissors. Following this, the rhexis is completed using forceps. Management of a small pupil Performing a phacoemulsification procedure in a patient with a small pupil poses special difficulties during rhexis and greater chances of iris damage. Therefore, the pupil size must be increased using non-surgical or surgical means. Non-surgical DOS Times - Vol.9, No.6 MANAGEMENT PEARLS methods include viscomydriasis (injection of viscoelastics into the anterior chamber), pharmacological treatment and the use of iris hooks. Viscoelastics produce a mechanical mydriasis. Pharmacological mydriasis is produced by instilling intracameral preservativefree adrenaline through a side port incision. It is used in a concentration of I ml of 1: 1000 that is diluted in 10ml of BSS. The most popular iris hooks are De Juan and Mackool hooks. De Juan hooks consist of segments in monofilament nylon threads that are curved at one end. A silicone device is fitted at one end to block the hook at the desired length. Hooks are inserted through a paracentesis site and after retracting the iris, are blocked by the silicone device. Usually four hooks are used to create a square shaped pupil. (Figure 3,4,5) Mackool hooks consist of titanium and are already blocked at a preset distance. Surgical methods of increasing the pupil size include sphincterotomy, pupilloplasty, midperipheral iridectomy, radial iridectomy and keyhole iridectomy. The disadvantages of these surgical maneuvers include bleeding, postoperative inflammation, iris traction and sometimes the need to leave permanent ins sutures in situ. Iris injury Iris injury may be due to performance of the procedure in a patient with a small pupil, shallowing of the anterior chamber or facing the bevel of the phacoprobe December, 2003 downwards. It can be prevented by the following methods. The phaco procedure must only be carried out in the central 5-6mm zone, the rhexis should never be crossed, the phacoprobe should always be parallel to the iris and the bevel of the probe should be pointed upwards. Rupture of the posterior capsule Some principles are to be followed as soon as posterior capsule rupture is detected. a) Stop working as soon as the problem is detected. b) Maintain a closed chamber c) Preserve as much of the posterior capsule as possible. Three possible situations include 1) Rupture without vitreous loss 2) Rupture with vitreous prolapse 3) Rupture with dislocation of nuclear material into the vitreous 1) Rupture without vitreous loss This occurs most commonly during the stage of irrigation and aspiration. Once it is detected, the illumination and magnification of the microscope should be increased. The anterior chamber is filled with an air bubble or viscoelastic and the probe is removed at the same time in order to maintain the anterior chamber. A dry aspiration using a oneway cannula is done. The one-way cannula is attached to a syringe containing BSS. In case the rupture occurs at the stage of early nuclear phaco, viscoelastic is injected beneath the nuclear fragment until the fragment comes into the anterior chamber. Under cover of viscoelastic, phaco may be done in the anterior chamber while using a Lens glide. Alternatively, the incision may be enlarged and the nuclear fragment brought out. 2) Rupture with vitreous loss The remnants of the nucleus are extracted manually with the help of a forceps or gentle phaco after injecting viscoelastic under the fragments and coaxing them into the anterior chamber. Alternatively, the incision may be extended and the fragments removed using a wire vectis and a spatula. A large fragment may be removed using the sandwich method, in which a wire vectis is used below and an iris repository is used above to take out the entire fragment. Depending on the size of the opening and the amount of vitreous loss, a vitrectomy is performed using an anterior or a posterior approach. At the end of irrigation and aspiration, an anterior vitrectomy is done. 3) Rupture with dislocation of nuclear material into the vitreous In such a situation, it is always wise to let an experienced vitreoretinal surgeon take over. The vitrectomy performed may be anteriorly limited if the nuclear material is limited to the anterior portion. A limited 261 vitrectomy may be done depending on the location of the nuclear material. However, if the nuclear material is posteriorly located, a total vitrectomy is done followed by one of the following options: a) Perflorocarbon liquids are used to float up the nucleus and subsequently remove it. It is very important that the PFCL should be completely removed at the end of the procedure. The disadvantages of using PFCL besides the high cost include requirement of a third port and possible toxic effects on the retina. b) A phacofragmenter is used to fragment the nucleus within the vitreous and subsequently remove it. c) The nucleus may be speared and brought up into the anterior chamber with the help of light from an endoilluminator. Suggested reading 1) Textbook of Ophthalmology Volume 3. Eds Sunita Agarwal, Athiya Agarwal, David J Apple, Lucio Buratto, Jorge L Alio, Suresh K Pandey and Amar Agarwal 2) Phacoemulsification- Principles and Technique. Lucio Buratto 3) Phacoemulsification, Laser Cataract Surgery and Foldable IOLS. Eds Sunita Agarwal, Athiya Agarwal, Mahipal Singh Sachdev, Keiki R Mehta, Howard Fine, Amar Agarwal 4) Advances in Ophthalmology 1. Ashok Garg, Suresh K. Pandey, Vidushi Sharma, David J. Apple. DOS Times - Vol.9, No.6 “International Symposium on Uveitis and Intraocular Inflammations” and “3rd Annual Conference of Uveitis Society of India” February 6 – 8, 2004, Venue : PGIMER, Chandigarh FACULTY 1. Dr Narsing A Rao, USA 15. Dr D.N. Shah, Nepal 2. Dr Anita Agarwal, USA 16. Dr J Biswas, Chennai 3. Dr Janet Davis, USA 17. Dr S.R. Rathinam, Madurai 4. Dr Carl P Herbort, Switzerland 18. Dr S.P.Garg, New Delhi 5. Dr Marc de Smet, The Netherlands 19. Dr V.S.Sangwan, Hyderabad 6. Dr Tran Van Tao, Switzerland 20. Dr Alay Banker, Ahmedabad 7. Dr Manfred Zierhut, Germany 21. Dr Vinita Rao, Jalna 8. Dr Ilknur Tugal Tutkun, Turkey 22. Dr M.R.Dogra, Chandigarh 9. Dr Manabu Mochizuki, Japan 10. Dr Khalid F Tabbara, Saudi Arabia 11. Dr James E Puklin, USA 12. Dr Ahmed M Abu EI-Asrar,S Arabia 23. Dr Jagat Ram, Chandigarh 24. Dr Sunil Arora, Chandigarh 25. Dr P.Bambery, Chandigarh 26. Dr Vishali Gupta, Chandigarh 13. Dr Luca Cimino Oculista, Italy 27. Dr Amod Gupta,Chandigarh 14. Dr Peizeng.Yang, China HIGHLIGHTS Plenary Sessions: VKH Syndrome, Serpiginous Choroditis and Ocular Tuberculosis Updates: Comprehensive Coverage of Uveitis and Intraocular Inflammation Current techniques: Diagnosis, Investigations, Pharmacotherapy and surgery · Interactive case presentations by International Faculty · Free paper Narsing A Rao Award Free paper submissions are invited from all 100 words abstract may be e-mailed to the Organising Secretary before 30.12.2003. Registration Fee: Delegates Students Upto 30.11.2003 Rs 800/Rs 600/- After 1.12.2003 Rs 1000/Rs 800/- Spot Rs 1200/Rs 1000/- For more details contact: Dr Vishali Gupta, Organising Secretary, Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh 160 012. Telefax: 0172-2747837, E-mail: [email protected] December, 2003 262 DOS Times - Vol.9, No.6 Delhi Ophthalmological Society Fellowship for Partial Financial Assistance to Attend Conferences Conferences International: Two fellowships per year (two fellowships can be awarded at a time if committee feels that papers are very good) · Maximum of Rs. 25,000/- per fellowship will be sanctioned National: Three fellowships per year (only for AIOS) · Maximum of Rs. 5,000/- per fellowship will be sanctioned Eligibility: · DOS Life Members (Delhi Members only) · 75 or More DCRS Points · Accepted paper for oral presentation, poster, video or instruction course. Time since last DOS Fellowship: Preference will be given to member who has not attended conference in last three years. However if no applicant is found suitable the fellowship money will be passed on to next year. Members who has availed DOS fellowship once will not be eligible for next fellowship for a minimum period of three years. Authorship The fellowship will be given only to presenting author. Presenting author has to obtain certificate from all other co-authors that they are not attending the said conference or not applying for grant for the same conference. (Preference will be given to author where other authors are not attending the same conference). If there is repeatability of same author group in that case preference will be given to new author or new group of authors. Preference will also be given to presenter who is attending the conference for the first time. Quality of Paper The applicant has to submit abstract along with full text to the DOS Fellowship Committee. The committee will review the paper for its scientific and academic standard. The paper should be certified by the head of the department / institution, that the work has been carried out in the institution. In case of individual practitioner he or she should mention the place of study and give undertaking that work is genuine. The fellowship committee while scrutinizing the paper may seek further clarification from the applicant before satisfying itself about the quality and authenticity of the paper. Only Single best paper has to be submitted by the applicant for review (6 copies). Quality of the paper will carry 50% weightage while deciding the final points. Poster and Video The applicant will need to submit poster and video for review. Credit to DOS The presenter will acknowledge DOS partial financial assistance in the abstract book / proceedings. The author will present his or her paper in the immediate next DOS conference and it will be published in DJO/DOS Times. December, 2003 Points Awarded 1) Age of the Applicant Points a) £ 35 years 10 b) 36 to 45 years 07 c) 45 years plus 05 2) Type of Presentation a) Instructor/ Co-instructor of Course 12 b) Free Paper (Oral) / Video 07 c) Poster 05 3) Institutional Affiliation a) Academic Institution 15 b) Private Practitioner 20 4) DCRS Rating in the immediate previous year a) 75-150 05 b) > 150 08 c) < 75 not eligible for fellowship Documents · Proof for age. Date of Birth Certificate · Original / attested copy of letter of acceptance of paper for oral presentation / video / poster or instruction course. · Details of announcement of the conference · Details of both International & National Conferences attended in previous three years. · Copy of letter from other national or international agency / agencies committing to bear partial cost of conference if any. · At least one original document should be provided, that is ticket, boarding pass or registration certificate along with attendance certificate of the conference. · Fellowship Money will be reimbursed only after submission of all the required documents and verified by the committee. · Undertaking from the applicant stating that above given information’s are true. · If found guilty the candidate is liable to be barred for future fellowships. Dr. J C Das (President DOS), Dr. Gurbax Singh (Vice President DOS), Dr. Kamlesh (Editor) Dr. Lalit Verma (Library Officer), Dr. Sudipto Pakrasi (Member) and Dr. Jeewan S. Titiyal (Secretary DOS) will be the members of DOS Fellowship for Partial Financial Assistance to Attend Conferences Committee. Application should reach Secretary’s office addresses to President DOS before 31st July and 31st January for international conference and before 30th September for national conference. The committee will meet thrice in a year in the month of August, October and February with in 2 weeks of last date of receipt of applications. The committee will reply within four week of last date of submission in yes/no to the applicant. No fellowship will be given retrospectively, that means prior sanction of executive will be necessary. Dr. Jeewan S. Titiyal, Secretary Delhi Ophthalmological Society R.No. 476, 4th Floor, Dr. R.P. Centre for Ophthalmic Sciences AIIMS, Ansari Nagar, New Delhi – 110029 263 DOS Times - Vol.9, No.6 REVIEW Ophthalmic Viscosurgical Devices and Anterior Segment Surgery: Surgical Applications and Complications Suresh K. Pandey M.D., Jaya Thakur M.D., Liliana Werner MD Ph.D., David J. Apple M.D. Background Viscoelastic substances are solutions with dual properties; they act as viscous liquids as well as elastic solids or gels. The ideal viscoelastic substance in ophthalmology should be viscous enough to prevent collapse of the anterior chamber at rest, yet liquid enough to be injected precisely through a small cannula. It should be elastic or shock absorbing and should enhance coating yet has minimal surface activity. It should be cohesive enough to be removed easily from the anterior chamber but not so cohesive that it is aspirated during irrigation and aspiration, which would provide no protection to endothelial cells during surgical manipulations. It should be eliminated from the eye in the postoperative period without any effect on intraocular pressure. Viscosurgery was a term coined by Balazs to describe the use of these solutions that had viscous, elastic and pseudo plastic properties during and after surgical procedures. During viscosurgery, viscoelastic substances are used as a fluid or a soft surgical instrument. Moran Eye Center, Department of Ophthalmology and Visual Sciences, Fifth Floor, University of Utah, 50 North Medical Drive Salt Lake City, Utah-84132, USA. December, 2003 The viscoelastic sodium hyaluronate was first used in ophthalmic surgery in 1972, when it was introduced as a replacement for vitreous and aqueous humor. Since then ophthalmic surgical procedures had undergone considerable advancement. The use of viscoelastic materials has become commonplace in anterior and posterior segment surgeries. These agents facilitate delicate and often difficult intraocular manipulations during various ophthalmic gery using phacoemulsification with IOL implantation. Some of these details are shown in the schematic photograph (Figures 1, 2). Capsulorhexis In order to perform an intact and successful capsulorhexis, the contents of the anterior chamber have an important role. Till date balanced salt solution (BSS®), air and OVDs have been used. Out of these three the best is viscoelastic as it is considered the easiest, saf- OVD should be viscous enough to prevent collapse of the anterior chamber at rest, yet liquid enough to be injected precisely through a small cannula. It should be elastic or shock absorbing and should enhance coating yet has minimal surface activity surgical procedures. Surgical Application of the OVDs In recent years the field of viscosurgery has broadened rapidly. It has been used both intraocularly as well as extraocularly, which includes cataract, cornea, glaucoma, viteroretinal, strabismus and oculoplastic surgeries. Use of OVDs in Cataract Surgery OVDs are helpful in each step of modern cataract sur- est, and the most reproducible method in both routine and difficult cases (Figures 2A, 2B). To perform a good capsulorhexis, the viscoelastic to be used should have the four basic features1- High molecular weight and high viscosity at zero shear rate, which maintains the anterior chamber. 2- Excellent visibility provided by high transparency. 3- Make surgical maneuvers easy, due to high elasticity and pseudoplasticity. 264 4- It should give a good capsular flap control, providing the soft and permanent spatula effect. Cleavage of lens structure It is best performed with the use of OVDs. The ideal viscoelastic material keeps the anterior chamber shape unchanged during BSS® injection and also avoids increase in pressure, which can be produced with excessive amount of BSS® known as capsular blockade. Nuclear emulsification During phacoemulsification, the viscoelastic is likely to remain in the anterior chamber instead of leaking out of the eye (Figure 2C). OVDs help in preserving the space and also because of their low cohesiveness, they remain in the anterior chamber despite high irrigation flow. Moreover OVDs adhere to the corneal endothelium, thus protecting the corneal endothelial cells. Healon® and HealonGV® does not trap the air bubble and provide excellent endothelial protection (Figure 2D). This is because of1- Scavenger effect- This effect captures the free radicals released during phaco with consequent inactivation. 2- Binding sites- There are chemical receptors for viscoelastic materials on DOS Times - Vol.9, No.6 REVIEW the corneal endothelium. A molecular bond seems to occur between the viscoelastic solution and the corneal endothelium. 3- High Elasticity- This also smoothes the possible impacts of the lens material against the endothelium. The phaco tip being in a closed system, its vibrations are transmitted to the internal structures of the eye but viscoelastic provides a smothering shield against them. Fig.1A: Injection of the viscoadaptive OVD in the anterior chamber through a 25 G cannula. Irrigation and aspiration The role of viscoelastic during this procedure is the protection of the endothelium. This is possible due to high adhesiveness. It remains where it is placed, without mixing with the cortex because of its low cohesiveness thus helping in easy removal of cortex. Fig.1B: Capsulorhexis is in progress. Capsular bag filling and IOL implantation During IOL implantation, it is necessary to expand the capsular bag with a viscoelastic. It allows the surgeon to keep the bag well opened and formed thus allowing the easy IOL implantation. OVD is also helpful in correct positioning, centering and allowing for possible IOL rotation maneuvers (Figs. 1E, 1F). Beside posterior chamber IOL implantation, OVD has also been used for implantation of other IOL designs (e.g. anterior chamber, iris fixated, artisan lenses, etc.) (Fig. 2). Cataract Surgery in Pediatric Cases Pediatric cataract surgery December, 2003 Fig.1C: Phacoemulsification in progress. like the adult surgery has undergone major changes in recent years with the evolution of techniques including small incision and the development of modern IOLs (Wilson ME, Pandey SK, Werner L, Apple DJ. Pediatric cataract surgery: Past, present and future, Third Prize for “Special Interest”, Annual Video Festival, XX th Congress of the European Society of Cataract and Refractive Surgeons, Nice, France, September 2002). The main principle lies in the control of the very elas- 265 tic nature of ocular tissues. It is difficult to perform a good capsulorhexis in the presence of high capsular elasticity. Moreover there is low scleral rigidity, greater intravitreal pressure that makes the capsulorhexis even more difficult, as the pressure tends to curve the capsulorhexis. But with the use of viscoelastic, e.g. Healon-GV ® the effective push is in the opposite direction and hence completion of capsulorhexis can be done. In pediatric cases, the capsulorhexis must be started in the central portion and not towards the equator, in order to prevent radial extension. The high density viscoelastic agents stabilize the posterior chamber and push back the vitreous face during the posterior capsulorhexis. During IOL implantation, the capsular bag is kept open and the anterior chamber is well formed thus ensuring easy and safe implantation of the IOL in the bag. These agents also help to dilate the pupil thus maintaining a good intraoperative mydriasis. OVDs like Healon-GV® can easily be removed at the end of the surgery including the position which is behind the IOL due to its high cohesiveness thus preventing capsular blockade. Use of the OVDs in Glaucoma Surgery Viscocanalostomy Viscocanalostomy is a new surgical procedure for glaucoma therapy. Viscoelastics play an important role in this procedure. Figure 3 illustrates the surgical DOS Times - Vol.9, No.6 REVIEW Fig.1 D: Viscoadaptive OVD is transparent and easy to see during removal (left). Note the presence of the air bubbles within the anterior chamber after use of dispersive viscoelastic solution (right). Fig.1 E: Implantation of a posterior chamber intraocular lens in the capsular bag. vented and also the related discomfort with it. It minimizes the risk of late infections and is independent from conjuntival and episcleral scarring. Viscocanalostomy allows the aqueous to leave the eye, through Schlemn’s canal and episcleral veins thus restoring the natural outflow pathway. This procedure creates a bypass by which aqueous humor reaches Schlemn’s canal, skipping the trabecular meshwork. A chamber is produced inside the sclera, which is in direct communication with the Schlemn’s canal. There is also a communication through the Descemet’s membrane with the anterior chamber. The OVDs should have high pseudoplasticity to allow injection into Schlemn’s canal through a small needle and should have high viscosity at shear rate of zero to maintain the spaces as long as possible. HealonGV ® and Healon-5 ® are viscoelastics of choice for this procedure. OVDs for Intraocular Delivery of Dyes or Anesthetic Agents Researchers and vision scientists have been using OVDs as a vehicle to deliver capsular dyes for use during cataract surgery. Mixing these substances with the viscoelastic agent was attempted to prolong their effect and to limit the adverse effect on ocular tissues. Ciba Vision Corp. (Duluth, GA, USA), has recently proposed mixing an OVD with lidocaine. This was termed “viscoa- Fig.1 F: Removal of the viscoadaptive OVD using irrigation-aspiration tip. steps of viscocanalosotomy. Viscocanalostomy literally means “opening of the canal by means of viscoelastic substance”. This procedure is a non-penetrating and independent from external filtration. The advantages are December, 2003 decreased risk of infection, and decreased incidence of cataract, hypotony and flat anterior chamber as the anterior chamber is not opened, and moreover, with the absence of external filtration the bleb formation is pre- Fig. 2: Beside posterior chamber IOL fixation in the capsular bag, OVDs can also be used for implantation of the various phakic and aphakic IOL designs in the anterior chamber, ciliary sulcus etc. Use of the OVD facilitated the implantation of the Artisan® IOL as shown in this photograph. (Courtesy: Camil Budo, M.D.). 266 DOS Times - Vol.9, No.6 REVIEW Fig.3. Surgical steps of viscocanalosotomy. (Courtesy: Dr. Med. Tobias Neuhann, M.D., Munich, Germany). Fig.3.A: Deep block construction incision. Fig.3.B: Cutting the deep block in a single plane with a spoon blade. Fig.3.C: Proximal to Schlemm’s canal there is a subtle change in the scleral fibers, from a crossing pattern to a tangential pattern, with an increased opacity. Fig.3.D: Descemet’s window. Fig.3.E: Cannulating Schlemm’s canal with three puffs of viscoelastic directed at the osteum. Fig.3.F: Tight closure suture of the flap. nesthesia” and was intended to prolong the anesthetic effect of intracameral lidocaine, as a complement to topical anesthesia. Also, the steps of intracameral injection of OVDs and of intracameral injection of lidocaine, as a complement to topical anesthesia, would be combined in only one step. Removal of the OVDs Several techniques have been reported in the literature for removal of the OVDs. These include: Rock and roll technique, twocompartment technique and bimanual irrigation/aspiration technique. We would like to emphasize that a careful and thorDecember, 2003 ough removal of the OVDs from the capsular bag and the anterior chamber of the eye is must after the end of the surgery. This is important to avoid complications such as rise in intraocular pressure, crystallization of the IOL surface. Studies have shown that complete removal of viscoelastic material from the capsular bag can be more difficult when some hydrophobic acrylic lenses are used because of the IOL’s tacky surfaces (Apple DJ, Auffarth GU, Pandey SK. Miyake posterior view video analysis of dispersive and cohesive viscoelastics, video presented at the Symposium on Cataract, IOL, and Refrac- tive Surgery, Seattle, WA, April 1999). Complications of OVDs: OVDs have many positive attributes but their drawbacks and complications must be given careful considerations. Some of the important complications are as follows1. Increase in intraocular pressure Increase in intraocular pressure is the most important postoperative complication of OVDs. It was first 267 noted with Healonâ . The increase in pressure can be severe and prolonged, if the material is not thoroughly removed at the end of the surgery. The rise in pressure occurs in the first 6 to 24 hours and resolves spontaneously within 72 hours postoperatively. The rise in pressure is due to the mechanical resistance of the trabecular meshwork to the large molecules of the viscoelastic material, which decreases the outflow facility. Hence to decrease the incidence of this complication, Increase in intraocular pressure is the most important postoperative complication of OVDs. DOS Times - Vol.9, No.6 REVIEW many have advocated removing and aspirating the viscoelastic material from the eyes at the end of the surgery. 2. Capsular block syndrome or capsular bag distension syndrome Capsular block syndrome (CBS), is a newly described complication of cataract-IOL surgery. It is characterized by accumulation of a liquefied substance within a closed chamber inside the capsular bag, formed because the lens nucleus or the posterior chamber IOL optic occluded the anterior capsular opening created by the capsulorhexis. Depending on the time of onset, CBS is classified as intraoperative (CBS seen at the time of lens luxation following hydrodissection), early postoperative (originally described CBS), and late postoperative (CBS with liquefied aftercataract or lacteocrumenasia). Recently use of high-density viscoelastic agents, such as Healon-GV ®, has been found to be associated with complication of late CBS. Main ingredient of the transparent liquid in capsular bags is sodium hyaluronate and that the distention is caused by aqueous humor being drawn into the capsular bag by an osmotic gradient across the capsule when the capsulorhexis diameter is smaller than that of the PC IOL and by viscoelastic material retained and trapped in the bag intraoperatively. Suggested Reading: 1. Arshinoff SA, Opalinski YAV, Ma J. The pharmacology of lens surgery: ophthalmic viscoelastic agents. In: Yanoff M, Ducker JS, eds, Ophthalmology. St Louis, Mosby-Yearbook, 1998; 4:20.1-21.6 2. Pandey SK, Thakur J, Werner L, Sharma V, Izak AM, Apple DJ. Ophthalmic viscosurgical devices: An update. In: Garg A, Pandey SK, Sharma V, Apple DJ, eds., Advances in Ophthalmology. Jaypee Brothers, New Delhi, India 2003, (in press). 3. Liesegang TJ. Viscoelastics. Surv Ophthalmol 1990; 34:268293 4. Pandey SK, Werner L, Apple DJ, et al. Dye-enhanced pediatric cataract surgery. J Pediatr Ophthalmol Strabismus 2003 (in press). 5. Ram J, Pandey SK. Anesthesia for cataract surgery. In: Dutta LC. Modern Ophthalmol- ogy. Jaypee Brothers, New Delhi, India, 2000, PP 325-330. 437-440, 378-384. 6. Saini JS, Pandey SK. Advances in techniques of penetrating keratoplasty. In: Nema HV, Nema N, eds., Recent Advances in Ophthalmology, Volume IV, Jaypee Brothers, New Delhi, India, 1998, pp 37-51 7. Pandey SK, Thakur J, Werner L, Izak AM, Apple DJ. Classification, clinical applications and complications of ophthalmic viscosurgical devices: An update. In: Garg A, Pandey SK, eds., Textbook of Ocular Therapeutics. Jaypee Brothers, New Delhi, India 2002, PP: 392-407 8. Pandey SK, Wilson ME, Apple DJ, Werner L, Ram J. Childhood cataract surgical technique, complications and management. In: Garg A, Pandey SK, eds. Textbook of Ocular Therapeutics. Jaypee Brothers, New Delhi, India 2002, PP 457-486. REQUIRED In Glaucoma Full time Ophthalmologist for a upcoming Eye Hospital in East Delhi Perimetry: Basics, single field and followup. Interpretation, analysis and application in day to day clinical situations . Newer imaging techniques : basics and interpretation : Utility in diagnosis and followup Groups of Ten Each On Sunday : December 14, 2003 February 8, 2004 Contact: Dr. Devindra Sood Glaucoma Imaging Centre P-13, South Extension Part II New Delhi 110049 Tel: (011 ) 26257803 : 26252000 Contact : Dr. Sanjay Bajaj A-1/1, Nathu Colony Chowk, Shahdara, Delhi – 110093 Ph : 9810623636, 9810015012 December, 2003 268 DOS Times - Vol.9, No.6 REVIEW Macular Function Tests Neena Kumar MD, Raj Vardhan Azad FRCS(Ed) Macular function tests are required for diagnosing as well as for following up of macular diseases and for evaluating the potential macular function in eyes with opaque media such as cataract and dense vitreous hemorrhage. The retinal function testing can be divided into psychophysical and physiologic methods. A psychophysical test is subjective. A physical stimulus is presented to the patient and the patient indicates verbally or by other subjective means his detection of the stimulus. Physiologic methods are objective. A stimulus is presented and a response parameter is measured by electrophysiological or other means. Psychophysical tests 1. Visual acuity 2. Pupillary reactions 3. Photostress test 4. Amsler grid 5. Two point discrimination test 6. Entoptic phenomenon 7. Tests dependent on macular pigment 8. Maddox rod test 9. Color vision 10. Foveal flicker sensitivity 11. Grating psychophysics 12. Dark adaptation 13. Perimetry Electrophysiologic tests a. Electroretinography (ERG) Dr. R.P.Centre for Ophthalmic Sciences, AIIMS, New Delhi. December, 2003 b. Electrooculography (EOG) c. Visually evoked response (VER) Psychophysical Tests Visual Acuity Visual acuity measurement is the most common test of foveal function. The best-corrected visual acuity is a measure of actual foveolar function. Visual acuity is measured by the visual resolution of a letter, symbol or a pattern. The smaller the visual angle subtended by the parts of the test letter correctly seen by the observer, the better the resolution of his visual apparatus. Another factor, which affects the letter subtends 5 minutes of visual angle on the retina. Each component of this letter subtends 1 minute at this distance. Other methods of visual acuity testing in cases of clear ocular media are Landolt C chart, grating acuity and Optokinetic Nystagmus (in children). Laser Interferometry and Potential Visual acuity Meter (PAM) are used to measure visual acuity, if media is opaque due to cataract, vitreous hemorrhage etc. Laser Interferometry Laser Interferometry can be used in eyes with immature cataracts.1 The resolving power of the macula is tested by using two coherent beams of light, which create a three dimensional fringe pattern on the retina. The beams produce two point sources be- Laser interferometry over-predicts the visual potential in amblyopic eyes because laser fringe vision is better than the letter acuity. visual acuity, is contrast. Contrast is defined as the difference in the luminance between dark and light parts of the test area divided by the mean luminance. The Snellen chart The Snellen score is expressed as a fraction. The numerator is the test distance and the denominator is determined by the size of the smallest letter correctly identified. The numerical value of the denominator is the distance at which the height of this smallest identified test hind the lens opacity; the light waves emitted from these two points overlap. Where the crest of one wave overlaps the trough of the other, the effect is cancelled and a black band is produced. Where crests or troughs coincide with one another, the enhancement produces bright bands of light. The test is performed as follows: 1. The pupils are widely dilated. 2. The light beam is directed into the center of the pupil in the plane of the iris. 269 3. The pupil is scanned until the fringe pattern is seen. 4. The patient is asked to indicate the orientation of the bands of light. 5. Initially, large gratings are used and then they are gradually diminished until the patient is unable to detect their correct orientation. 6. The potential visual acuity is estimated from the width of the gratings. Laser generated fringes are not dependent on the optical components of the eye for focusing. Therefore, ametropia has little influence on the patterns produced by retina. It also over predicts the visual potential in amblyopic eyes because laser fringe vision is better than the letter acuity. The Potential Visual Acuity Meter (PAM) PAM projects standard Snellen chart through a small clear area of an immature cataract; it is most accurate in eyes with visual acuities of 6/60 or better.2,3 The main components of the PAM are an incandescent light source, a miniature transilluminated Snellen chart and a +12 D lens. In performing the test the pupils should be widely dilated and the patient is asked to read the letters on the chart. Pupillary reactions The pupillary reactions should be normal even in the presence of a mature cataract. The defect usually indicates either a lesion of the optic nerve or extensive retinal disease. DOS Times - Vol.9, No.6 REVIEW Photostress Test Photostress test can differentiate visual loss caused by macular disease from that caused by an optic nerve lesion.4 The test is a gross version of the dark adaptation test in which the visual pigments are bleached by light. This causes a temporary state of retinal insensitivity, which is perceived by the patient as a scotoma. The recovery of vision is dependent on the ability of the photoreceptors to re-synthesize visual pigments. The test is performed as follows: 1. The best-corrected distance visual acuity is determined. 2. The patient fixates the light of a pen torch or an indirect ophthalmoscope held about 3 cm away for about 10 seconds. 3. The photostress recovery time (PSRT) is measured by the time taken to read any three letters of the pre-test acuity line. 4. The test is performed on the other, presumably normal eye and the results are compared. In a patient with macular lesion the PSRT will be longer (50 seconds or longer) as compared with the normal eye whereas in a patient with an optic nerve lesion there will be no difference. The Amsler grid The Amsler grid test evaluates the 10 0 of visual field surrounding fixation. The chart is composed of a grid of lines containing a central black fixation spot. The squares on the grid are 5 mm in size and subtend a visual angle of 10 at 30 cm viewing distance. December, 2003 The chart is to be viewed in modest light monocularly at a distance of 28-30 cm utilizing the correct refraction for this distance. Viewing should be accomplished without previous ophthalmoscopy and without instillation of any drugs affecting papillary size or accommodation. The test is performed as follows: 1. The patient should wear reading spectacles and cover one eye. 2. The patient is asked to look directly at the center dot with the uncovered eye and report any distortion, wavy lines, blurred areas or blank spots anywhere on the grid. Two Point Discrimination Test The ability to distinguish two illuminated points of light suggests good retinal function. Two illuminated points of 2 mm diameter size and 2 inches apart are placed 2 feet away from the patient’s eye. The patient is then asked to indicate whether he can perceive the two points separately. Entoptic Phenomenon Entoptic phenomenon is referred to visual perceptions that are produced or influenced by the native structures of one’s own eye. Illumination of the fundus by parallel light rays allows visualization of small opacities located close to the retina. Since the columns of blood contained within retinal blood vessels are linear opacities situated in front of the retinal photoreceptors, this makes retinal blood vessels visible. If a focal source of light (such as small pen- light) is pressed firmly against the exterior of the eye through closed lids, the arborizing pattern of retinal blood vessels can be made briefly visible. This test is used as test of retinal function. The blue field Entoptic Phenomenon (Flying spots) If one looks at a bright and diffusely illuminated surface with no contrasting features, a series of fast moving, luminous points or spots can be readily seen. The spots tend to move in a generally curved pattern, while trailing short, tapering segments behind them. The spots are best seen if the background is illuminated by blue light in the spectral region of 350 to 450nm. Since this region contains the spectral absorption peak of hemoglobin, it has been suggested that the moving particles represent red blood cells passing through the retinal capillaries.5 In a normal subject 15 or more of moving corpuscles are seen. Abnormal Blue Field Entoptic phenomenon is constituted by the findings of (a) failure to see any corpuscles (b) partial loss of corpuscles in one part of the field (c) visibility of less number of corpuscles (d) slow corpuscular movement Tests dependent on the Macular Pigment Two tests are believed to depend on the arrangement of the yellow pigment in the inner retinal layers of the macula lutea. These are the 270 Haidinger’s brushes and the Maxwell spot. Haidinger’s Brushes This test is commonly used as a screening test for retinal pathology in strabismus patients with amblyopia. If one views a diffusedly illuminated source of planepolarized white or blue light, brushes or sheaves radiating from the point of fixation in the form of Maltese cross can be seen. The brushes have contrasting yellow and blue hues. The darker portions of the Maltese pattern are yellow, whereas the brighter portions are blue. This phenomenon is caused by variations in absorption of planepolarized light by oriented molecules of xanthophyll pigment in the foveal retina. If the yellow pigment arrangement in the fovea is disrupted by pathology in the inner retinal layers, the brushes will not be seen. Maxwell’s Spot A subject with a normal macula will see a 3- degree dark ring surrounding fixation upon looking through a blue filter at a brightly illuminated white surfaced. Usually a smaller dark spot is seen at the fixation point itself. The dark ring and the spot will fade as the eye adapts to the blue light. These can be restored by readapting to a yellow light; i.e. by having the subject look through a yellow filter for a moment. Following this, the blue filter will again elicit the dark ring and spot. Some visual physiologists believe that perception of the Maxwell’s Spot depends on the screening of the photoreDOS Times - Vol.9, No.6 REVIEW ceptors by the macular pigment while others believe that variations in the relative numbers of different types of color receptors in the foveal region explain this phenomenon. The Maddox Rod Test The Maddox rod consists of a series of fused cylindrical red glass rods, which convert the appearance of a white spot of light into a red streak. The optical properties of rods cause the streak of light to be at an angle of 900 with the long axis of the rod; when the glass rods are held horizontally, the streak will be vertical and vice-versa. The rods are placed in front of the right eye. This dissociates the two eyes because the red streak seen by the right eye cannot be fused with the unaltered white spot seen by the left eye. The amount of dissociation is measured by the superimposition of the two images using prisms. The base of the prism is placed in the position opposite to the direction of the deviation. Both vertical and horizontal deviations can be measured in this way. Color Vision The central 30-60 degree of the visual field processes the trichromatic color vision. Hereditary dystrophies of the posterior pole, non-hereditary maculopathies and certain optic nerve conditions often result in acquired color defects. As a rule, congenital trichromatic color deficiencies are not particularly rare, affect males, are symmetric, involve red-green color system, and occur as isolated December, 2003 visual defect. By contrast acquired dyschromatopsias are asymmetric, are accompanied by other visual dysfunctions and most commonly show irregularity in color testing not usually seen in the congenital variety e.g. acquired color defects are the blue-yellow dyschromatopsia of central serous chorioretinopathy and retinitis pigmentosa, or the red-green defect of acquired cone degeneration or optic neuritis. Tests for color vision include color confusion test and in the clinical sphere include the Ishihara test plates, the Farnsworth Penal D-15, the American Optical Hardy-Rand-Rittler pseudoisochromatic plates defective into protan , deutan, tritan (blue blind) axes of confusion. Mild color defectives score normally. 3. AOHRR Plates: The AOHRR plates have colored symbols and a gray background. The hues of the color symbols occur at the neutral points of color defective patients. The saturation of the test symbol colors is progressively increased in successive plates. The colorblind patient has difficulty discerning the test symbols from the gray background. This test is useful for screening and categorization of red-green and blue-yellow defectives in terms of severity of the defect and the axis of confusion. It cannot differ- Nagel Anamoloscope is considered to be the best method for accurate classification of red-green defects. (AOHRR), and the Sloan Achromatopsia Test. Color Confusion Tests 1. Ishihara Plates: This test is based on color confusion in the red-green colorblind patient. The color of the test symbol and the background is of such hue, saturation and the intensity so as to be confused by protans (red blind) and deutans (green blind). 2. Farnsworth Panel D-15: This test is also based on zones of color confusion. The subject is asked to arrange a series of 15 colored caps such that each succeeding cap appears most similar in appearance to the previous cap. The D-15 Panel classifies the moderate and severe color entiate a dichromat (a patient with only two cone pigment) from an anomalous trichromat (one with three cone pigments). 4. Sloan Achromatopsia Test: This test presents to the observer a series of highly saturated colors which he/ she is asked to match to a series of gray shades. The achromat, or totally colorblind patient, makes characteristic matches while a dichromat or trichromat cannot make any match. Hue discrimination test Hue (wavelength) discrimination for the color defective and normal is best at spectral zones of intrinsic desideration and poorest at zones of best saturation 271 (Pitt’s law). The results are diagnostic for the type of dyschromatopsia. The color blind subject exhibits characteristic spectral regions of poor hue discrimination which differ from the normal subject since the intrinsic saturation for the color defective differs from the normal. Farnsworth-Munsell 100 Hue test The subject arranges 85 colored caps (4 separate boxes each containing about 20 caps) such that each succeeding cap is closest in hue to the preceding cap. The FM 100 Hue test is based entirely on hue discrimination and not on color confusion pairs as the caps are balanced for saturation and intensity. The test rates the degree of color discrimination in normal subjects in addition to measuring zones of poor hue discrimination in color defectives. Specific zones of poor hue discrimination identify the nature of the dyschromatopsia. Nagel Anomaloscope This test is based on color matching. It is considered to be the best method for accurate classification of redgreen defects. The subject must match a standard yellow light in color and brightness with a mixture of red and green. Normal subjects give a narrow matching range, the so-called Rayleigh match. Characteristic matching patterns are elicited for the different types of redgreen dyschromatopsias and achromats. DOS Times - Vol.9, No.6 REVIEW Foveal Flicker Sensitivity There is a variation of foveal sensitivity to flicker as a function of temporal frequency. A small flickering test light is superimposed on a constant background luminance (fig.1). The luminance of the flickering test light is sinusoidally modulated; i.e. it increases and decreases in a sinusoidal fashion above and below the mean luminance resulting in maximum and minimum peak luminance. The mean luminance of the test light is equal to that of the surround. The test spot is usually 0.5 – 2.0 degrees in size for foveal flicker sensitivity. For each temporal frequency value (cycles per second or Hz), the threshold is the minimum modulation depth at which detection of flicker occurs. The reciprocal of the threshold is the sensitivity. The falloffs in sensitivity were found at high temporal flicker frequencies in certain retinal disorders, even when visual acuity was normal.6 Grating Psychophysics Traditionally gratings are composed of alternating discrete dark and light bars. These bars have a changing luminance described by a square wave function. In order to explore spatial processing by the visual system, gratings have been introduced with bar luminance constantly changing to follow a sine wave function. Discrete edges are not seen in such gratings. A grating detection test is performed by having the patient fix on the center of a sinusoidal grating, preferably small enough to fall within the macular region. The mean luminance of the grating is held constant at all times. The pattern is alternated at a regular rate with a homogenous screen of the same mean luminance. The patient indicates when he can or cannot see the on – off bar pattern. This test has been applied to visual problems resulting from cerebral and retinal pathology.7 The bar width at the cutoff frequency correlates closely with the component width of the smallest Snellen letter correctly identified. However, in patients with cerebral lesions involving the visual pathways and with the presumed maculopathy of retinitis pigmentosa, the curve is no longer predictable from the visual acuity measurement i.e. different types of contrast sen- sitivity loss can be seen in different patients with the same Snellen acuity score. Dark Adaptation Dark adaptation refers to the ability of visual system both rods and cones to recover sensitivity following exposure to light. Dark adaptation is tested by Goldmann – Weekers adaptometer (fig.2). The eye is exposed to a standard light bleach (preadaptation for 15 minutes). This precedes the plotting of the dark adaptation curve. Fol- lowing the bleach, the patient fixates on a test light located 12-15degrees eccentric to the stimulus light which itself can be varied in diameter. This retinal location is in an area of good cone-rod mix. The intensity of the test light is slowly increased from below threshold until the patient detects it. The minimal intensity for detection is the threshold at this point in time. By taking a threshold reading every minute a curve of the changing threshold versus time of dark adaptation is obtained. Highlights for January Issue of DOS Times Ø Problems in RD Surgery : Dr. C.M. Shroff Ø Ultrasound Biomicroscopy in Glaucoma : Dr. Tanuj Dada Ø Phaconit: Current Prespective : Dr. Amar Agarwal Ø Complication & Management of Contact Lens : Dr. J.S. Saini Ø Focus on AMRD December, 2003 272 DOS Times - Vol.9, No.6 REVIEW a generalized pathologic process and in such cases peripheral field may also show abnormalities. The curve is normally biphasic with a “rod-cone break” at about 10 minutes. The early part of the curve represents cone adaptation and the later part of the curve represents the rod adaptation. With regard to the macular area this test can be modified so that foveal function can be studied. December, 2003 Perimetry Perimetry can also test the retinal function. Central or paracentral scotomas are elicited in posterior pole disease and the plotting of several isopters by variation of test object; color, size and intensity help to better characterize field defects. Macular disease is sometimes part of Electrophysiological Tests 1. E l e c t r o r e t i n o g r a p h y (ERG) The clinical electroretinogram is the recording of the electrical potential waveform generated by the total (preganglionic) retina in response to a diffuse light stimulus (fig.3). The test is performed using a corneal contact lens electrode which records changes in the corneo-retinal potential with each light stimulus. 8 The clinical important components are the initial corneal negative a-wave and the second positive b-wave. The awave is believed to emanate from the inner segments of the photoreceptors and the b-wave from Muller cells in the bipolar region. The peak amplitudes and latencies as well as waveform shape are considered in the interpretation of the ERG. Since the ERG monitors preganglionic retinal activity, a patient due to optic atrophy may have a normal ERG. ERG is a mass retinal response; an isolated lesion of 273 the macula would not be expected to affect this test. 2. E l e c t r o o c u l o g r a p h y (EOG) The EOG measures the changes in the corneoretinal potential of the eye under varying conditions of illumination. To record this , two electrodes are placed on the skin, one at the lateral canthus and the other at the medial canthus. The subject is asked to shift fixation back and forth between two red lights that turn on and off sequentially in an alternating fashion. The angular distance between the lights and consequently the eye movement excursion is generally 30 degrees. Since the corneoretinal potential is positive with regard to the cornea, the EOG recording is positive when the patient’s cornea (gaze) is turned toward the canthus with the recording electrode. The record is negative when the eye turns to the opposite direction (toward the reference electrode). Several measurements are taken every minute for a total of 15 minutes in darkness and then 15 minutes in the light. A plot of the average amplitude DOS Times - Vol.9, No.6 REVIEW value for each minute against time normally shows a minimum trough value during the dark period and a maximum peak value in the light (fig.4). The dark trough of the standing potential is believed to depend on the integrity of the pigment epithelial outer segment region. The light rise depends on the function of the mid-retinal layers in addition to the outer retina-pigment epithelial complex. The absolute value of the corneoretinal potential is variable, the light peak/ dark trough ratio is found to be a reliable parameter of retinal function and the normal lower range is 170% (calculated by taking the ratio of the maximum light adapted to the minimum dark adapted response and multiplying it by 100). This ratio is known as Arden ratio. EOG is a reflection of the generalized retinal responsiveness. Therefore, it is abnormal in most of those conditions in which ERG is ab- normal.9 There are, however several clinical conditions in which this does not hold true which include Best’s Vitelliform macular dystrophy, Butterfly dystrophy, fundus flavimaculatus and generalized drusen. In these conditions ERG is normal but EOG is abnormal. 3. Visually Evoked Response (VER) The visually evoked response is a measure of the electrical potential generated in response to a visual stimulus. It is recorded with scalp electrodes placed over the occipital lobe region, a cortical area with primarily a macular representation.10 There are many different techniques of foveal stimulation in VER testing. In one method diffuse light stimulus flashes intermittently. This method is most useful in the assessment of suspected monocular pathology. In second method retina is stimulated by a patterned stimulus. One such pattern represents alternating dark and light bars in the form of a sinusoidal grating. The light bars become dark and the dark bars become light with the pattern reversing at a constant rate. A third technique employs a checkerboard pattern stimulator with alternation of dark and light checks. The usefulness of the VER in detecting lesions of the macula must be inferred by the fact that the ultimate record reflects neural transmission along the entire visual pathway from retina to occipital lobe. Therefore, abnormality anywhere along the system may result in abnormal VER. References 1. Cohen M.M.: Laser interferometry: evaluation of potential visual acuity in the presence of cataracts. Ann. Ophthalmol 1976; 8: 845-849. 2. Minkowski J.S. and Guyton D.L.: Potential acuity meter using a minute aerial pinhole aperture (poster abstract). Ophthalmology 1981; 88(9S): 95. 3. Guyton D.L.: Instuments for measuring retinal visual acuity behind cataracts. Ophthalmology 1982; 89(8S): 98-103. 4. Severin S., Harper J., Culver J.: Photostress test for the evaluation of macular function. Arch. Ophthalmol. Otolaryngol. 1975; 79: 701. 5. Loebl M. and Riva C.E.: Macular circulation and the flying corpuscles phenomenon. Ophthalmology 1978; 85: 911-917. 6. Tyler C.W.: Flicker frequency response functions in the diagnosis of retinal disorders. Presented at ARVO meeting. Sarasorta Fla. 1976. 7. Bodis-Wollner I., Diamond S.: The measurement of spatial contrast sensitivity in cases of blurred vision associated with cerebral lesion. Brain 1976; 99:695. 8. Lawwill T.: The bar pattern electroretinogram for clinical evaluation of the central retina. Am. J. Ophthalmol. 1974; 78: 121. 9. Francois J., Verriest G., deRouck A.: Electrooculography as a functional test in pathological conditions of the fundus. I. First results. Br. J. Ophthalmol. 1956; 40: 108. 10. Sokol S.: Visually evoked potentials: theory, techniques and clinical applications. Surv. Ophthalmol. 1976; 21; 18. Congratulations! Ø Dr. V.K. Malik, Eye Surgeon, Distt. Hospital, Meerut has got the appreciation award from Govt. of U.P. for doing highest number of I.O.L. Surgeries, year 2002-03. Ø Dr. Pradeep Sharma, Additional Professor, R.P. Centre has been recently awarded the following: w w w Awarded International Membership of American Association of Pediatric Ophthalmology and Strabismus. Awarded Retina Foundation Medal Oration by the Gujarat Ophthalmological Society, 11th October, 2003. Awarded Rustumji Ranji Medal Oration by the Andhra Pradesh State Ophthalmological Society, 18th October, 2003. Ø Dr. Rajiv Mohan, Joint Director & Consultant Mohan Eye Institute, on Being Awarded FRCS (Ophthalmology) and Invited as Examiner at Glasgow by the Royal College of Physicians & Surgeons of Glasgow December, 2003 274 DOS Times - Vol.9, No.6 APPLIANCES Ocular Ultrasonography Atul Kumar MD, Nikhil Pal MD, Sanjeev Nainiwal MD, Raj Vardhan Azad MD, FRCS (Ed) History Developed in the late 1950s and early 1960s, diagnostic ophthalmic ultrasonography remains a critical ancillary test for the clinical evaluation of the opaque media globe and abnormal orbit.Ultrasound was first used in ocular diagnosis in 1956 by Mundt and Hughes, who employed the A-scan technique. Their work was refined in the late 1950s and early 1960s by Oksala and coworkers from Finland, who did extensive work on the detection and differentiation of various ocular disorders, also using the A-scan method. At about the same time, Baum and Greenwood developed the first two-dimensional B-scan for use in ophthalmology, using the immersion technique. Further pioneering work using the immersion B-scan method was performed by Edward Purnel and Jackson Coleman and co-workers. The first commercially available contact B-scanner, in which the handheld probe was applied directly to the closed lid, was introduced by Nathaniel Bronson in 1972. Indications for Echography Indications for ophthalmic ultrasound (i.e., echography) have steadily increased as the capabilities Dr. R.P.Centre for Ophthalmic Sciences, AIIMS, New Delhi. December, 2003 and accuracy of the equipment and methods have improved (see box). Echography is indicated whenever complete or partial opacification of the media prevents an adequate clinical examination of either the anterior or posterior segment. It has also proved to be very useful in clear media for the differentiation and measurement of intraocular tumors and inflammatory lesions. Before beginning any examination, the echographer should be informed of the of diseases, including primary and secondary tumors of the orbit, inflammatory diseases, and changes secondary to thyroid disease. Physics And Instrumentation Ultrasound is an acoustic wave that consists of an oscillation of particles. By definition, ultrasound waves have a frequency greater than 20 kHz (i.e., 20,000 oscillations per second), which renders them inaudible. For diagnostic ophthalmic ultra- Echography is indicated whenever complete or partial opacification of the media prevents an adequate clinical examination of either the anterior or posterior segment. pertinent history and clinical findings. Biometry is another important contribution of ultrasound in ophthalmology. Reliable intraocular lens (IOL) calculations depend on accurate and precise axial length measurements. Measurements of the globe have also become important in evaluating conditions such as congenital glaucoma, microphthalmia and nanophthalmos, persistent hyperplasia of primary vitreous (PHPV), phthisis bulbi, and myopia. Orbital ultrasonography is most useful in evaluation of patients with exophthalmos related to a number sound, frequencies used are generally in the range 8 to 10 MHz (1 MHz = 10G cps). The very high frequencies used in ophthalmology produce short wavelengths, in the range of 0.2 mm. These very short wavelengths allow sufficient resolution of the minute structures in the eye and orbit. In contrast, abdominal and obstetric ultrasound require frequencies in the range 1 to 5 MHz, which provide the longer wavelengths that are necessary for deeper penetration of soft tissue.The speed at which ultrasound travels depends on the medium through which it passes. For example, 275 aqueous and vitreous conduct sound at a velocity of 1532 m/sec, intraocular and orbital soft tissue at a velocity of 1550 m/sec, and the normal lens at 1641 m/sec. As the ultrasound passes through tissues, part of the wave may be reflected back toward the probe; this reflected wave is referred to as an echo. Echoes are produced by acoustic interfaces that are created at the junction of media with different sound velocities.The greater the difference in sound velocity of the media that create the acoustic interface, the stronger the echo. For example, the lens (velocity = 1641 m/sec) produces a stronger echo when adjacent to aqueous (velocity = 1532 m/sec) as opposed to blood (velocity = 1550 m/sec), as in a hyphema. The returning echoes are affected by many factors, including the size and shape of acoustic interfaces, the angle of sound beam incidence, absorption, scattering, and refraction. An understanding of these principles is important for the performance of accurate ultrasound examinations. Clinical echography depends on technology that emits an ultrasound wave and then detects and processes the returning echoes. The basis of the system is the piezo-electric material (e.g., quartz crystal) that is located near the tip of the transducer (i.e., probe). (Fig 1) This transducer emits pulses of ultrasound waves (i.e., the sound beam) and then receives the returning echoes. The detected echoes are processed in the instrument (e.g., filtered and amplified) DOS Times - Vol.9, No.6 APPLIANCES and are then displayed on the screen as echograms. This signal processing differs from one instrument to another and is critical in determining the character of the echogram. The ultrasound instruments used most commonly in ophthalmology are the A-scan and the B-scan. A-scan A-scan is a one-dimensional acoustic display in which echoes are represented as vertical spikes from a baseline. Spacing of the spikes depends on the time it takes for the sound beam to reach a given interface and for its echo to return to the probe. The time between any two echo spikes can then be converted into distance by knowing the sound velocity of the media from which the echoes are received. The height of the displayed spikes indicates the strength (i.e., amplitude) of the echoes (Fig. 2). B-scan B-scan differs from Ascan in that it produces a twodimensional acoustic section (such as a photograph) by using both the vertical and horizontal dimensions of the screen to indicate configuration and location. A section of tissue is examined by an oscillating transducer that emits a sound beam that “slices” through a tissue, much like a slice with a knife. Ophthalmic B-scan instruments require a focused beam that functions at a frequency in the range of 10 MHz. An echo is represented as a dot on the screen rather than as a spike. The strength of the echo is depicted by the brightness of the dot. The December, 2003 OPAQUE OCULAR MEDIA Anterior segment Ø Corneal opacification Ø Anterior chamber hyphema or hypopyon Ø Miosis or pupillary membrane Ø Cataract Posterior segment Ø Vitreous hemorrhage or inflammation CLEAR OCULAR MEDIA Anterior segment Ø Iris lesions Ø Ciliary body lesions Posterior segment Ø Tumors and masses: detection and differentiation Ø Retinal detachment: rhegmatogenous vs. exudative Ø Intraocular foreign bodies: detection and localization Ø Optic disc abnormalities FOLLOW-UP STUDIES BIOMETRY Ø Axial eye length Ø Anterior chamber depth Ø Lens thickness Ø Tumor measurement Indication of orbital USG Ø Orbital pseudo tumour Ø Orbital lymphoma Ø Cavernous hemangioma Ø Orbital lymphangioma Ø Orbital abscess Ø EOM evaluation Ø Thyroid ophthalmopathy Vs Myositis Ø Optic nerve evaluation-Optic disc coloboma coalescence of multiple dots on the screen forms a twodimensional representation of the examined tissue section (Fig. 3). How to get best image l Beam must fall perpendicular to the area of interest l Lesion must be centered to the beam path l Select lowest gain compatible with clear image l Place the probe through open eye lid (preferable) l Avoid scanning through lens Examination technique l Brief clinical history l Set the instrument(Globe1,Orbit-5) l Supine/recline position l Close the eye lid l Apply methyl cellulose l Give fixation target l Probe in desired direction & position l Begin the examination l Start with med – high gain 276 -(70-80db) l Select lowest gain compatible with clear image Types of B-Scan (Globe) q Fundamental (Fig 4a) l Axial(Fig 4b) l Longitudinal(Fig 4c) l Transverse(Fig 4d) q Special l Topographic l Kinetic l Quantitative Special examination technique q Topographic echography q Quantitative echography q Kinetic echography Examination Techniques Specific examination techniques have been carefully designed to allow thorough evaluation of the anterior and posterior segments of the globe. The type of examination performed is determined by the indication for examination. The contact method (i.e., the probe is applied directly to the globe) is used to evaluate the posterior segment. In those cases in which the anterior segment also needs evaluation, an easy immersion technique has been developed that utilizes the same contact instrument Basic screening and special examination techniques for lesion differentiation (topographic, quantitative, and kinetic echography) have been developed for the evaluation of posterior segment disorders. Positioning the patient If separate A-scan and contact B-scan instruments are used, they may be placed on one large or two small carts. The patient is seated in a reclining examining chair of adjustable height. While DOS Times - Vol.9, No.6 APPLIANCES most examinations are performed with the patient reclined, it is occasionally helpful to have the patient in a sitting position. The basic screening examination is performed to detect lesions of the posterior segment. It is best to use both A-scan and B-scan for lesion detection, but it is suggested that the novice begin with Ascan; this is to allow the new echographer to master the Ascan examination techniques in the normal eye, a prerequisite to using the standardized A-scan for the more difficult differentiation of lesions. Furthermore, the small, pencil-like A-scan probe allows thorough screening of the peripheral fundus, including the ciliary body. Special examination techniques Topographic echography— shape, location, and extension As soon as a lesion is detected, topographic echography is performed to determine location, general classification, and specific configuration. B-scan is ideally suited for the initial topographic evaluation since the moving, focused sound beam provides a two-dimensional display. It is also important, however, to appreciate a lesion’s topography with the A-scan in order to carry out subsequent special examination techniques (i.e., quantitative and kinetic). It is essential that scanning techniques be systematically performed with both B-scan and A-scan if reliable results are to be achieved The probe face is always represented by the initial line December, 2003 In the axial scan, the on the left side of the patient fixates in priechogram. The fundus, mary gaze and the located on the side of probe is placed on the the globe opposite the center of the cornea, probe, is represented thus displaying lens on the right side of the and optic nerve in the echogram. The upper center of the echogram. part of the echogram The axial scan does not corresponds to the poryield as much information of the globe where tion and thus is perthe probe marker is di- Fig.1: Parts of ultrasonography machine formed at the end of the rected. The center of topographic examinathe screen corresponds tion. to the central portion of the probe face. Since Transverse scans this provides the best With transverse scans, resolution, a lesion the probe is placed on should always be centhe globe with the longtered within the est diameter of the oval echogram. probe face positioned In practice, the parallel (i.e., tangenechographer applies tial) to the limbus. In methylcellulose to the Fig.2. Normal standardized A-scan this way, the back-andprobe face as a couechograms. I, Initial spike corresponding forth movement of the pling medium. The B- to probe tip (corneal spike hidden by initransducer also occurs scan probe is then tial spike); A, anterior lens; P, posterior parallel to the limbus. placed directly on the lens; M, multiple signal; V, echo-free vitreThe sound beam then globe (i.e., conjunctiva ous cavity; R, retina; S, sclera; O, orbital oscillates back and or cornea). Examina- soft tissue. forth across the oppotion through the lids is site fundus, producing generally avoided bea circumferential slice. cause of sound attenuThis orientation is apation by the lids. In adpropriate for showing dition, with the lids the lateral extent of a leclosed, the sion (e.g., extending echographer can never from 2- to 4-o’clock mebe certain which porridians, from 7- to 9:30tion of the globe is bemeridians, etc.) ing evaluated. The parThe designation of the ticular section of ocutransverse scan is delar tissue displayed on Fig.3: Normal standardized B-scan termined by the meridthe screen depends on echograms ian that lies in the how the probe is posimiddle of the scanning tioned and how the marker is directed. The three cornea. Thus the sound beam section. For example, if the basic probe orientations that bypasses the lens, allowing probe is held horizontally are used to evaluate in- better sound penetration. with its face centered on the traocular lesions are trans- These scans are performed 6-o’clock meridian, the verse, longitudinal, and with the patient’s gaze di- middle of the echogram (on rected away from the probe, the right) will display the 12axial. The transverse and longi- toward the meridian being o’clock meridian of the funtudinal scans are used most examined. This allows a dus; this probe position is commonly because the wide surface of globe on called a transverse scan of the probe is placed on the con- which to place and shift the 12-o’clock meridian. If the probe is placed in a vertical junctiva peripheral to the probe. 277 DOS Times - Vol.9, No.6 APPLIANCES Fig.4a: Schematic diagram of fundamental USG scan (H: Horizontal scan V: Vertical scan O: Oblique scan) Fig.4b: Axial scan Fig.4c: Longitudanal scan Fig.4d: Transverse scan orientation at the 3-o’clock limbus, the sound beam sweeps across the 9-o’clock meridian; this is called a transverse scan of the 9o’clock meridian. By convention, horizontal transverse scans (i.e., transverse scans of the 12- or 6o’clock meridians) are performed with the marker oriented toward the nose. Therefore the upper part of the echogram always represents the nasal portion of the globe. On the other hand, vertical transverse scans (i.e., 3- or 9-o’clock meridians) are performed with the marker directed superiorly, so the top of the echogram represents the upper portion of the globe. Oblique transverse scans (transverse scans of the 1:30, 4:30, 7:30, or 10:30-meridians) are performed with the marker directed toward the upper portion of the globe. parallel) to the limbus. The sound beam sweeps along the meridian opposite the probe rather than across the meridian as does the transverse scan. In this way, the longitudinal scan shows the anteroposterior extent of a lesion rather than the lateral extent Another way to think of this orientation is as a radial section (like the spoke of a wheel) with the sound is being examined. For example, if the probe is placed on the 6-o’clock meridian, the sound beam sweeps along the 12-o’clock meridian; this is designated as a longitudinal scan of the 12o’clock meridian (Fig 4c). The use of the longitudinal probe orientation greatly facilitates three-dimensional thinking and promotes a better understanding of B-scan Axial scans The axial orientation is the third probe position. This is performed with the probe face centered on the cornea; the sound beam is directed through the center of the lens and the optic nerve . As mentioned previously, this scan is the easiest for echographers to understand because it displays the lens and optic nerve in the center of the echogram, thus simplifying orientation of the pathologic condition. Unfortunately, however, sound attenuation and refraction from the lens often hinder resolution of the posterior portion of the globe, thus limiting the usefulness of this scan (Fig. 4b). It is helpful, though, for documenting lesions and membranes in relation to the optic nerve and is also useful for evaluating the macular region. Longitudinal scans Longitudinal scans are also performed with the probe placed peripheral to the limbus. The probe is rotated 90 degrees from the position of the transverse scan so that the longest diameter of the oval probe face is perpendicular (rather than December, 2003 B-scan differs from A-scan in that it produces a two-dimensional acoustic section (such as a photograph) by using both the vertical and horizontal dimensions of the screen to indicate configuration and location. beam sweeping from the optic disc out toward the periphery along a given meridian. In longitudinal scans, the marker is always directed toward the center of the cornea, regardless of which meridian is being examined. This produces an echogram with the optic disc and posterior fundus displayed on the lower portion of the screen, whereas the peripheral globe is displayed superiorly. The designation of the longitudinal scan is simply that meridian which findings. It is often the optimal method of displaying the posterior and peripheral insertion of a membrane, as well as the posterior and anterior borders of tumors. This technique is especially helpful for evaluating those membranes that insert into the optic disc at steep angles or when an anterior structure (e.g., lens or lens implant) produces strong sound attenuation (precluding optimal visualization with an axial scan). 278 Topographic B-scanning If a lesion is detected with either the A- or B-scan basic screening examination, topographic evaluation of the lesion is then performed. The lesion is first assessed with the appropriate transverse approach. For example, if a lesion is detected in the superior temporal quadrant of DOS Times - Vol.9, No.6 APPLIANCES the right eye, a transverse scan of the 10:30 meridian is performed (the probe is placed at 4:30 and the marker is oriented superonasally). The probe is then shifted from limbus to fornix, thus sweeping the sound beam through the lesion from posterior to anterior. This allows display of the lesion’s gross shape and dimensions, as well as lateral extent (i.e., which meridians are affected by the lesion). The longitudinal approach is then applied, with the sound beam oriented radially, perpendicular to the transverse view. For a lesion located at the 10:30 position in the right eye, the probe face is placed on the 4:30 meridian with the marker directed toward the center of the cornea. The lesion’s anteroposterior extent (between the optic disc and ora along the 10:30 meridian) is assessed, and its shape and gross dimensions are reevaluated. apart). These various A-scan maneuvers help to classify the general type of lesion (pointlike, bandlike, membranelike, and masslike) and to evaluate exact location and extent. Topographic A-scanning Once the involved meridians have been generally determined with B-scan, Ascan is also applied. Lesion topography is always evaluated at the tissue sensitivity setting. The probe is first placed at the limbus of the meridian opposite the lesion’s center. It is then shifted between limbus and fornix to assess the lesion anteroposteriorly (i.e., radially). The probe is then shifted from side to side (parallel to the limbus) to evaluate the lesion laterally. Another helpful technique is to examine the lesion from different sound beam directions (i.e., with the probe placed in positions that are 90 degrees Quantitative echography— type II This technique is used solely to differentiate RD from dense vitreous membranes. If a membrane like lesion produces a 100% tall spike at tissue sensitivity during quantitative type I and its other acoustic characteristics are equivocal, quantitative type II may be applied. December, 2003 Quantitative echography— type I Quantitative echography type I is used to estimate the reflectivity (i.e., spike height) of all detected lesions. Once the sound beam is directed perpendicular to a lesion, the amplitude (i.e., height) of its spike is observed in the echogram. This simple technique is of great value in differentiating many types of intraocular lesions, such as dense posterior vitreous detachment (PVD) from retinal detachment (RD), and melanoma from other intraocular tumors. The determination of reflectivity is necessary for evaluation of a mass lesion’s internal structure and sound attenuation. Kinetic echography Kinetic echography is used to dynamically assess the motion of or within a lesion.Two types of motion (i.e., aftermovement and vascularity) can be detected with the appropriate instrumentation. Aftermovement indicates mobility as determined by motion of the lesion echoes following cessation of eye movement. For example, a nonsolid lesion (e.g., PVD or RD) displays aftermovement, whereas a solid lesion (e.g., tumor) does not. Vascularity, spontaneous motion of echoes on the screen, is indicative of blood flow within vessels. Anterior segment evaluation: immersion technique Indications for anterior segment evaluation are limited because this area is optically visible in the vast majority of cases. However, when echographic data are needed, they may be reliably obtained with a simple immersion technique. This is accomplished by inserting a small scleral shell between the lids. The shell is then filled with methylcellulose. Using this standoff technique, the cornea, anterior chamber, iris, lens, and retrolental (or retroiridal) space can be evaluated along the ocular axis with B- and Ascan Immersion axial length measurements can also be obtained with A-scan. More peripherally located, anterior structures (i.e., iris, anterior chamber angle, or ciliary body) can also be assessed by shifting the shell and probe laterally over the area to be displayed. Recently, Pavlin and colleagues have developed a new B-scan method for evaluating the anterior segment. This new technique utilizes frequencies in the range of 50 to 100 MHz and is referred to as Ultrasound Biomicroscopy (UBM). The method provides very high resolution for examining an- 279 terior segment structures and lesions in ciliary body region. UBM provides much higher resolution of 25-50microns than does conventional B-scan ultrasonography (150 microns). The clinical applications of UBM are in glaucoma(open versus closed angle closure glaucoma, plateau iris syndrome), iridocorneal scars, IOL status, post-trauma and can be used to study pars plana sclerotomy ports. Role of Optical Coherence Tomography Optical Coherence Tomography (OCT) is a new imaging modality the principles of which are similar to B-mode ultrasound, that produces high resolution (upto 10 microns) cross sectional images of the retina .However, OCT utilizes the reflection of a superluminescent diode source of light with a wavelength of 830nm rather than sound waves from different structures of the eye and has applications in macular hole, macular edema and ARMD. Suggested Reading 1. Mundt GH, Hughes WF: Ultrasonics in ocular diagnosis. Am J Ophthalmol 41:488, 1956 2. Purnell EW: Intensity modulated (B-scan) ultrasonography. In Goldberg RE, Sarin LK (eds), Ultrasonics in Ophthalmology: Diagnostic and Therapeutic Applications, pp 102123. Philadelphia, Saunders, 1967 3. Dallow RL (ed): Ophthalmic ultrasonography: Comparative techniques. Int Ophthalmol Clin 19:4, 1979 4. Ossoinig KC: Quantitative echography-the basis of tissue differentiation. J Clin Ultrasound 2:33, 1974 5. Coleman DJ: Reliability of ocular and orbital diagnosis with Bscan ultrasound. Am J Ophthalmol 74:708, 1972 DOS Times - Vol.9, No.6 DOS QUIZ NO. 6 DOS QUIZ NO. 6 1. Most common lesion involving anterior segment of eye in AIDS.................................................................. 2. Most common symptomatic metastatic uveal tumors .................................................................................... 3. Dilator pupillae orginates from which embryonal layer ................................................................................ 4. Most common cause of bull’s eye maculopathy .............................................................................................. 5. Cherry red spot disappears after injury by....................................................................................................... 6. Economic blindness is called when snellen acuity falls below .................................................................... 7. Epithelium of canaliculus is lined by ................................................................................................................ 8. Which laser is used in IOL master ..................................................................................................................... 9. Magnification caused by direct ophthalmoscope ............................................................................................ 10. Most common systemic disease associated with necrotizing scleritis ......................................................... Rules: l Please send your entries to the DOS office latest by 25th December, 2003. l Prize Rs. 500/- Courtesy: Syntho Pharmaceuticals l Quiz Trophy will be given to the member who answers maximum number of quizes in a year during the Annual GBM of DOS. Answers for the DOS Quiz No. 4 1. Most common lid tumour in India Sebaceous Cell Carcinoma 2. Epidemic keratoconjuctivitis is caused by Adenovirus 8, 19 3. Stocker line is seen in Pterygium 4. Which Corneal dystrophy is having systemic association Lattice II dystrophy 5. Foldable IOL was invented by Tom Mozzoco 6. Inverse glaucoma is seen in Sphero Phakia 7. "Headlight in the Fog" appearance of fundus is seen in Toxoplasmosis 8. Harada – Ito procedure is indicated in Pure Exclylotropia in Superior oblique palsy 9. Pulfrich Phenomonen is seen in Optic Neuropathy 10. Which acid & alkaji injury is most dangerous NH3OH & HF December, 2003 280 DOS Times - Vol.9, No.6 JOURNAL ABSTRACTS Comparison of scleral buckling with combined scleral buckling and pars plana vitrectomy in the management of rhegmatogenous retinal detachment with unseen retinal breaks Tewari HK, Kedar S, Kumar A, Garg SP, Verma LK. Clin Experiment Ophthalmol. 2003 Oct; 31(5): 403-7. Dr Rajendra Prasad Center for Ophthalmic Sciences, AIIMS, New Delhi, India. Authors compared conventional scleral buckling and combined pars plana vitrectomy and scleral buckling procedures in rhegmatogenous retinal detachments with unseen retinal breaks. Forty-four consecutive eyes with uncomplicated, primary rhegmatogenous retinal detachments with a clear media and unseen retinal breaks were randomized to two groups. The scleral buckling group underwent 360 degrees scleral buckling, cryopexy and external subretinal fluid drainage. In the combined surgery group, 360 degrees scleral buckling, pars plana vitrectomy, air-fluid exchange, endolaser and injection of 14% perfluoropropane gas was done. Results showed at 3 months follow up the primary reattachment rate was 80% (16/ 20 cases) in the combined surgery group, and 70% (14/20 cases) in the scleral buckling group (P = 0.716). The visual acuity improved significantly from a preoperative median of hand movement (HM; range: HM to 6/60; similar in both the groups), to a median of 6/60 (range: perception of light to 6/ 18) in the combined surgery group and a median of 6/36 (range: HM to 6/18) in the scleral buckling group, the difference between the two groups not being statistically significant (P = 0.4). The number of intraoperative and postoperative complications was more in the combined surgery group. (Four cases were lost to follow up and were doing well when last examined.) They conclude the conventional scleral buckling was found to be a safe and effective technique in the primary management of uncomplicated, rhegmatogenous retinal detachments with unseen retinal breaks when the media is clear. Pars plana vitrectomy, intraocular gas, and radial neurotomy in ischaemic central retinal vein occlusion TH Williamson, W Poon, L Whitefield, N Strothoudis and P Jaycock British Journal of Ophthalmology 2003;87:1126-1129 Department of Ophthalmology, St Thomas’s Hospital, London SE1 7EH, and Department of Ophthalmology, Queen Mary’s Hospital, Sidcup, Kent, UK In this study pars plana vitrectomy (PPV), mild panretinal photocoagulation, and intraocular gas injection were employed to prevent NVG. The potential role of incision of the lamina cribrosa (radial neurotomy) for visual recovery was examined. Eight eyes of seven patients with ischaemic CRVO had PPV, mild panretinal photocoagulation, and intraocular December, 2003 perfluoropropane gas injection. Four eyes had radial neurotomies performed. The patients were examined by fundus photography, fundus fluorescein angiography, optical coherence tomography, and Goldmann visual field analysis. No patients suffered from neovascular glaucoma. Visual recovery was seen in patients with and without neurotomy but some patients had cataract extraction to allow visualisation for PPV. Fundus photography demonstrated reduced engorgement of retinal veins in two of the patients with neurotomy and one with PPV alone. Optical coherence tomography demonstrated macular oedema in three patients with neurotomy and all patients with PPV alone. Segmental visual field loss was seen in one patient with neurotomy suggesting damage to the optic nerve head. PPV is safe in ischaemic CRVO. Combined with mild PRP and intraocular gas injection the risk of neovascular glaucoma is low. Neurotomy can be added to try to improve the chances of recovery of central vision but may cause additional peripheral visual field loss. Therapeutic contact lenses: the role of high-Dk lenses. Foulks GN, Harvey T, Raj CV. Ophthalmol Clin North Am. 2003 Sep;16(3):455-61. Department of Ophthalmology, University of Pittsburgh School of Medicine Currently, the armamentarium of contact lenses that can be used for therapeutic effect provides a wider selection of lenses than ever before. If the therapeutic goal is protection and healing of the corneal epithelium, epithelial or stromal edema is best avoided, and the selection of a high-Dk silicone hydrogel (balafilcon A, lotrafilcon A) lens or a very thin membrane-type lens (crofilcon) is the best choice. If the goal is surface protection as well as stimulation of stromal wound vascularization, selection of a low-water content, thick, hydrophilic lens is the better option. If the patient is prone to lens loss or requires frequent replacement of the therapeutic lens, a prudent economic decision is to select a daily disposable moderate-water content lens. Specific circumstances may mandate the selection of a specific therapeutic lens. Patients with a prior history of active giant papillary conjunctivitis may be better served by the use of a crofilcon glyceryl methacrylate lens, which has a lower incidence of this complication. Patients who have dry eye may benefit from a higher-water content lens if adequate unpreserved tear supplementation is provided with or without punctal occlusion. The options when selecting a therapeutic contact lens are wider than ever before. Although the new generation of high-Dk lenses promises fewer limiting problems of vascularization and infection, one can use the older traditional therapeutic lenses when induced vascularization of the cornea is needed or when an economic necessity exists. Not all of the available lenses are FDA approved for therapeutic use, and such wear is an off-label use. The patient should be informed of the goal of therapy as well as the benefits and risks of therapeutic contact lenses. 281 DOS Times - Vol.9, No.6 EVENTS Forthcoming Events – NATIONAL ——————————————————————————————————————————————————— Event Conference Date Venue Contact Person and Address ——————————————————————————————————————————————————— 7th Annual Conference of Punjab Opthalmological Society 13th-14th Dec. 2003 Akal Eye Hospital & LASIK Contact Person: Dr. Balbir Singh Bhaura (M.S.) Laser Centre, Akal Eye Hospital & Lasik Laser Centre, Jalandhar Model Town, Jalandhar - 144 003 Telefax: 0181-2273606, 2271606, 2461606, 5073604 E-mail: [email protected] Conference E-mail: [email protected] 62nd All India Ophthalmological Conference 8-11 Jan. 2004 Banaras Hindu University, Varanasi Conference Secretariat: Prof. V. Thakur Nataraj Eye & Laser Centre, 156B, Ravindrapuri, Varanasi - 221 005, India Phone: 0542-2276505, 09415201167 Fax: 0542-2276707 Email: [email protected] XI International Congress of Ocular Oncology 23-27th Jan. 2004 L.V. Prasad Eye Institute, Hyderabad Contact Person: Dr. Santosh G. Honavar, ICOO Secretariat, LV Prasad Eye Institute, LV Prasad Marg, Banjara Hills, Hyderabad Tel.:+91-40-23548267, e-mail: [email protected] 12th Annual Meeting Vitreo Retinal Society of India 20-22nd Feb. 2004 Corbett Claridges Hideaway, Ramnagar Uttaranchal Contact Person: Mr. Shobhit Chawla, Organising Secretary, Prakash Netra Kendra, NH 2, Vipul Khand-4, Gomtinagar, Lucknow (U.P.) Annual DOS Conference 3rd-4th April 2004 India Habitat Centre Lodhi Road, New Delhi Contact Person: Dr. Jeewan S. Titiyal, Secretariat (DOS) R.No. 476, 4th Floor, Dr. R.P. Centre for Opthalmic Sciences, New Delhi - 110 029 Ph.: 26589549, Fax : 26588919, E-mail: [email protected] Website: http://www.dosonline.org INTERNATIONAL Event Conference Date Venue Contact Person and Address ——————————————————————————————————————————————————— Euro Asian Opthalmology Congress 11-15 Dec. 2003 Shanghai, China 8th ESCRS Winter Refractive Surgery Meeting 23-25 Jan. 2004 Barcelona International Symposium on Ocular Pharmacology and 11-14 Mar. 2004 MONTE CARLO ASCRS Annual Symposium 1-5 May 2004 18-22 Sept. 2004 SAN DIEGO, CA USA XXII Congress of the ESCRS December, 2003 PARIS, FRANCE 282 Contact: Euro Asian Congress Secretariat Tel.: 86-2163-031-757, Fax: 86-2163-029-643 E-mail: [email protected] Contact: ESCRS Temple House, Temple Road, Blackrock, Co Dublin, Ireland. Tel.: 3531-209-1100 Fax: 3531-209-1112 E-mail: [email protected] Contact: Iliana Eliar, Assistant Project Manager, Kenes International Global Congress Organizers & Association Management Services E-mail: <[email protected]> Contact: ASCRS Tel.: 1703-591-2220 Fax: 1703 591 0614, Web: www.ascrs.org Temple House, Temple Road, Blackrock, Co Dublin, Ireland Tel.: 3531-209-1100 Fax: 3531-209-1112 E-mail: [email protected] DOS Times - Vol.9, No.6 DELHI OPHTHALMOLOGICAL SOCIETY Stamp Size 2 Colour Photograph (LIFE MEMBERSHIP FORM) Name (In Block Letters) _________________________________________________________________________ S/D/W/o _____________________________________________________________ Date of Birth _____________ Qualifications _________________________________________________________ Registration No. __________ Sub Speciality (if any) ___________________________________________________________________________ ADDRESS Clinic/Hospital/Practice ______________________________________________________________________ _______________________________________________________________ Phone _________________ Residence ________________________________________________________________________________ _______________________________________________________________ Phone _________________ Correspondence ___________________________________________________________________________ _______________________________________________________________ Phone _________________ Email ___________________________________________________________ Fax No. ________________ Proposed by Dr. _______________________________ Member Ship No. ______________ Signature _________________ Seconded by Dr. ________________________________ Membership No. ______________ Signature _________________ [Must submit a photocopy of the MBBS/MD/DO Certificate for our records.] I agree to become a life member of the Delhi Ophthalmological Society and shall abide by the Rules and Regulations of the Society. (Please Note : Life membership fee Rs. 3100/- payable by DD for outstation members. Local Cheques acceptable, payable to Delhi Ophthalmological Society) Please find enclosed Rs.____________in words ______________________________________________________ by Cheque/DD No.______________________ Dated____________ Drawn on_____________________________________ Three specimen signatures for I.D. Card. Signature of Applicant with Date FOR OFFICIAL USE ONLY Dr._______________________________________________________________has been admitted as Life Member of the Delhi Ophthalmological Society by the General Body in their meeting held on________________________________ His/her membership No. is _______________. Fee received by Cheque/DD No._______________ dated__________ drawn on __________________________________________________________________. (Secretary DOS) December, 2003 283 DOS Times - Vol.9, No.6 INSTRUCTIONS 1. The Society reserves all rights to accepts or reject the application. 2. No reasons shall be given for any application rejected by the Society. 3. No application for membership will be accepted unless it is complete in all respects and accompanied by a Demand Draft of Rs. 3100/- in favour of “Delhi Ophthalmological Society” payable at New Delhi. 4. Every new member is entitled to received Society’s Bulletin (DOS Times) and Annual proceedings of the Society free. 5. Every new member will initially be admitted provisionally and shall be deemed to have become a full member only after formal ratification by the General Body and issue of Ratification order by the Society. Only then he or she will be eligible to vote, or apply for any Fellowship propose or contest for any election of the Society. 6. Application for the membership along with the Bank Draft for the membership fee should be addressed to Dr. Jeewan S. Titiyal, Secretary, Delhi Ophthalmological Society, R.No. 476, 4th Floor, Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, Ansari Nagar, New Delhi – 110029. 7. Licence Size Coloured Photograph is to be pasted on the form in the space provided and two Stamp/ Licences Size Coloured photographs are required to be sent along with this form for issue of Laminated Photo Identity Card (to be issued only after the Membership ratification). DOS Credit Rating System Report Card DCRS July 2003 Army Hospital (R&R) Total No. of Delegates ....................................................................................................................................................................... 121 Delegates from Out side (N) ............................................................................................................................................................. 114 Delegates from Army Hospital (n) ........................................................................................................................................................7 Overall assessment by outside delegates (M) ............................................................................................................................ 888.5 Assessment of case presentation-I (Dr. Lt. Col.A. Banarji) by outside delegates .................................................................... 803.5 Assessment of case presentation-II (Dr. Lt. Col. (Mrs.) Madhu Bhaduria) by outside delegates ............................................ 814.5 Assessment of clinical talk (Dr. D.P. Vats) by outside delegates ................................................................................................ 862.5 DCRS 30th August, 2003 Sir Ganga Ram Hospital Total No. of Delegates ................................................................................................................................................................. 82 Delegates from Out side (N) ....................................................................................................................................................... 66 Delegates from Sir Ganga Ram Hospital (n) ............................................................................................................................... 16 Overall assessment by outside delegates (M) ...................................................................................................................... 468.5 Assessment of case presentation-I (Dr. Jasmita Popli) by outside delegates ..................................................................... 440.5 Assessment of case presentation-II (Dr. Anita Sethi) by outside delegates ........................................................................ 476.5 Assessment of Clinical Talk (Dr. S.N. Jha) by outside delegates .................................................................................... …..450.0 DCRS 27th September, 2003 Hindu Rao Hospital Total No. of Delegates ................................................................................................................................................................. 70 Delegates from Out side (N) ....................................................................................................................................................... 59 Delegates from Hindu Rao Hospital (n) ...................................................................................................................................... 11 Overall assessment by outside delegates (M) ......................................................................................................................... 432 Assessment of Case Presentation-I (Dr. Ruchi Goel) by outside delegates ............................................................................ 414 Assessment of Case Presentation-II (Dr. A.K. Nagpaul) by outside delegates ................................................................... 401.5 Assessment of Clinical Talk (Dr. Ruchi Goel) by outside delegates .................................................................................... ..433.5 DCRS 1st November, 2003 – Dr. R.P. Centre for Ophthalmic Sciences Total No. of Delegates ................................................................................................................................................................. 86 Delegates from Out side (N) ....................................................................................................................................................... 62 Delegates from Dr. R.P. Centre for Ophthalmic Sciences (n) ..................................................................................................... 24 Overall assessment by outside delegates (M) ......................................................................................................................... 473 Assessment of Case Presentation-I (Dr. Sachin Kedar) by outside delegates ....................................................................... 447 Assessment of Case Presentation-II (Dr. Murlidhar R.) by outside delegates ..................................................................... 455.5 Assessment of Clinical Talk (Prof. S. Ghose) by outside delegates .................................................................................... ..460.5 December, 2003 284 DOS Times - Vol.9, No.6 TEAR SHEET NO. 6 Newer Diagnostic Modalities in Ophthalmology Cornea Confocal microscope: scanning slit corneal confocal microscope Frame size: 300X200microns with 5 microns thickness. Uses: For detailed assessment of 1. Endothelium – ¡ high quality specular microscope ¡ endothelial count ¡ guttate, endothelial polymegathism and pleomorphism 2. Stroma ¡ anterior stroma keratocytes morphology ¡ nerve fibres especially after LASIK ¡ Flap interface morphology after LASIK. 3. Epithelium and bowman’s membrane Lens: IOL masters ¡ Non-contact optical device based on partial coherence interferometer ¡ Measures the AL from the corneal vertex to the retinal pigment epithelium ¡ Accurate to within ±0.02 mm or better. ¡ Five times higher accuracy in measuring AL as compared to USG. ¡ Measures: AL, Km, Anterior chamber depth, white-to-white corneal diameter. ¡ Based on Haigis formula ¡ Provides IOL power according to desired IOL type, desired post-operative refraction Draw back: cannot be used in dense cataract and opaque media. Anterior Segment Ultrasound biomicroscopy (UBM) l High resolution ultrasound (50MHz ) l Resolution 25-50 microns. l Used to evaluate the structural details of the anterior segment structure, iris angle ciliary body, lens zonules. l Useful in assessing angle, iris and trabecular meshwork relationships in eyes with corneal edema and corneal opacity l Measurement of angle in ACG, OAG, checking patency of PI Glaucoma SWAP [Short wave automated perimetry (blue on yellow perimetry)] l Evaluates the blue cones that are lost early in glaucoma l Uses yellow background and blue stimulus to selectively stimulate the blue cones l Advantage: detects the glaucomatous VFD earlier than standard white on white perimetry. l Uses: early diagnosis of glaucoma, early detection of progression, predict the risk of conversion of OHT to glaucoma l Drawback: nuclear sclerosis and cataract may mimic early progression on SWAP Frequency doubling perimetry (FDP) Detects early loss of the Nonlinear M-cells (a subset of magnocellular cells) l Based on frequency doubling illusion(high temporal and low spatial frequency) l December, 2003 l l l Advantages: very quick test (45 sec to 6 min), portable instrumentation, no spectacle correction required upto 7D of refractive error. Use: for screening Drawbacks: lack of any longitudinal data, early progression and focal defects may be missed Heidelberg retinal tomography (HRT) Confocal Laser Scanning ophthalmoscope (CSLO). l Gives three-dimensional images retina and optic nerve head. l Uses a diode laser (670 nm), resolution 30 µ, field of view 10° × 10°, 15° × 15°, or 20° × 20°. Pupil dilation is not necessary. l A three-dimensional image is acquired as 32 consecutive and equidistant optical section images, consisting of 256 × 256 picture elements. l Uses Moorefield regression analysis to classify various disc sectors as normal borderline or abnormal. l Use for early diagnosis, detection of early progression and follow-up of glaucoma. l GDx VCC (Retinal nerve fibre layer analyzer with variable corneal compensation) l NFA-GDx works on the principle of scanning laser polarimetry. l Measures retardation of polarized light by RNFL l GDx-VCC has a variable corneal compensator that compensates for corneal birefringence, giving more accurate thickness of RNFL. RETINA & Posterior Segment HRA (Heidelberg Retinal Angiograph) ¡ Scanning laser tomography ¡ Uses argon (488 nm) laser for the fluorescein angiogram and a diode (788 nm) laser for the ICG angiography. ¡ Simultaneous, side-by-side delivery of both fluorescein and ICG angiographies ¡ Single images can be captured at up to 20 frames per second with 512 x 512 resolutions. ¡ Acquires upto 12 frames-per-second with a resolution of 256 x 256 pixels. providing real time high speed angiography Optical Coherence tomography (OCT) Non contact, non invasive tool l Uses low coherence near infrared light 830nm l Resolution 10-15µm, field of view 300, requires pupillary dilatation and clear media l Based on Michaelson interferometer. l Uses: macular thickness assessment in v Diabetes, v ARMD, v Cystoid macular edema, v Macular hole, v CSR l In glaucoma v Optic disc tomography v Retinal nerve fibre layer thickness measurement l Parul Sony, MD Dr. R.P. Centre, AIIMS, New Delhi - 110029 285 DOS Times - Vol.9, No.6