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Download Glaucoma Workup Review: From A to OCT By: Nathan Rains, OD
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Glaucoma Workup Review: from A to OCT Dr. Nathan Rains Eye Center of Northern Colorado What is Glaucoma? 3 million Americans have glaucoma One of the leading causes of adult blindness No symptoms until extensive peripheral vision loss (for most types of glaucoma) “sneak thief of sight” Chronic condition, no cure, just control Control is lower eye pressures by Eye drops, laser surgeries, or medical surgeries What is Glaucoma? Prevalence http://www.nei.nih.gov/eyedata/glaucoma.asp#1 What is Glaucoma? Definition ... optic neuropathy with associated visual function loss, with intraocular pressure (IOP) being one of the primary risk factors... American Academy of Ophthalmology Optic Neuropathy? Pic 1: http://www.hopkinsmedicine.org/wilmer/glaucoma_center_excellence/bo ok/chapter_what_is_glaucoma.html Optic Neuropathy? http://www.cehjournal.org/article/the-optic-nerve-head-in-glaucoma/ Goals of Glaucoma Testing The ultimate goal of glaucoma testing is three fold: To Diagnose Glaucoma (probably the hardest step) Is the test RELIABLE Is the test REPEATABLE To Determine its Severity Suspect, mild, moderate, severe Initiate treatment, set appropriate target pressures, etc. To Monitor Progression Glaucoma Testing Tonometry Pachymetry Gonioscopy Tomography Perimetry *Biomicroscopy *Photography *Corneal Hysteresis *Ganglion Cell Complex What is Tonometry? The measurement of intraocular pressure (IOP) recorded in mmHg Normal IOP – 10-20 mmHg (avg ~ 16mmHg) Diurnal fluctuations – 4-6 mmHg >4-6 is suspicious Only treatable measure of glaucoma Pressure is highest at night, in the supine position (3 am) Difference between eyes – 2-3 mmHg Ocular hypertension - >20-22mmHg All medicine and surgery is geared to this one task, lower IOP Tested at every examination and followup care Diurnal Variation http://www.eyecalcs.com/DWAN/pages/v3/v3c046.html How is Tonometry Measured Digital Palpation Tonometry Instruments Indentation – iCare & Tonopen http://www.icaretonometer.com/rebound-technology/ Good 38 sec video Tonometry Instruments Non-Contact Tonometry Advantages No anesthesia *No contact Ease of use Quick Disadvantages Patients 'love' to hate this test Accuracy? Tonometry Instruments Goldmann Applanation Tonometry Gold standard Accurate Inexpensive easy to use Disadvantages Anesthesia still dependent on corneal properties Tonometry Instruments Take homes Digital Indentation portable, cheap, supine Non-contact tonometry basic, only detects extremely high pressures expensive machine, touchless, quick, patient discomfort Applanation gold standard, inexpensive, easy to use, less variability Pachymetry What is Pachymetry? The measurement of corneal thickness, in microns (um) Average CENTRAL corneal thickness ~ 555 um In glaucoma, used as a risk factor in the development of glaucoma Ocular Hypertensive Treatment Study (OHTS) CCT <555, high risk CCT 555-585 no increased risk CCT >585 low risk Pachymetry and IOP correction table? Theory The thicker the cornea, the artificially high reading The thinner the cornea, the artificially low reading IOP correction table? 1975 study Every 100um adjust by 7mmHg 17 other studies, all different IOP per 100um adjustment… no consensus Reason Thickness of cornea is only one part of it: Corneal properties (steep/flat, hysteresis (stiffness), etc.) Pachymetry Pearls Center of cornea Compare symmetry (>30, repeat) LASIK/PRK? Diseased Corneas? Fuchs, keratoconus? Used as a RISK factor No universal agreement on IOP correction table to use So, we do NOT adjust IOP measurement Goals of Glaucoma Testing The ultimate goal of glaucoma testing is three fold: To Diagnose Glaucoma (probably the hardest step) Is the test RELIABLE Is the test REPEATABLE To Determine its Severity Suspect, mild, moderate, severe Initiate treatment, set appropriate target pressures, etc. To Monitor Progression What is Glaucoma? By Type Primary Open Angle Glaucoma Acute Angle Closure Glaucoma Pseudoexfoliative Glaucoma Pigmentary Glaucoma Normal/Low Tension Glaucoma Neovascular Glaucoma Congenital Glaucoma Traumatic Glaucoma Secondary Glaucoma And more… over 60 types... Gonioscopy Obtain a view of the drainage angle formed between the eye’s cornea and iris Aids in diagnosis and monitoring of glaucoma Performed under slit lamp, with a gonio lens Used in laser treatment of the angle (SLT – selective laser trabeculoplasty) Gonioscopy Gonioscopy.org Video Clip Can’t See That Stupid Line Normal angle Pigmented Angle http://www.academy.org.uk/tutorials/gongrade.jpg Anterior Segment OCT http://www.iovs.org/content/52/5/2095/F1.expansion.html Gonioscopy Take home Helps diagnose and determine type of glaucoma Check out gonioscopy.org Glaucoma Testing Tonometry Pachymetry Gonioscopy Tomography Perimetry *Biomicroscopy *Photography *Corneal Hysteresis *Ganglion Cell Complex Optic Neuropathy? http://www.cehjournal.org/article/the-optic-nerve-head-in-glaucoma/ Optical Coherence Tomography Non-invasive, high resolution, imaging technology Time Domain vs Spectral Domain TD – 400 scans per sec, 10um SD – 20,000-40,000 per sec, 3um 3-D reconstructions AWESOME! Scan types Retinal (macular) Optic Disc http://www.docvadis.fr/aobeffroi/page/l_oeil_et_les_examens/les_machines_utilisees_par_l_ ophtalmologiste/oct_ou_tomographie_en_coherence_optique.html OCT Optic Disc Scans the optic disc using a 6mm cube Obtains Retinal Nerve Fiber Layer Thickness Color codes a thickness map ‘hour glass’ appearance Red (350um), to blue (0um) Normative table RNFL thickness Symmetry C/D ratio Etc. RNFL TSNIT Map Quadrant and Clock Hour RNFL thickness chart Normal OCT OCT Optic Disc Diagnosing Glaucoma Average RNFL Symmetry Quadrant RNFL layout Inferior and Superior are the greatest indicators Clock Hour RNFL layout >20um difference is statistically significant Inferior temp and/or superior temp thin Lastly – does it correlate with the visual field ***structural loss precedes VF loss*** OCT optic disc Example OCT Optic Disc Monitoring Glaucoma Average NFL Symmetry Progression Analysis http://www.healio.com/ophthalmology/journals/osli/2011-7-42-4supplemental/%7Bde06c09a-2d95-42f4-b403-2fc1fa6a3550%7D/clinical-use-of-octin-assessing-glaucoma-progression Retinal Nerve Fiber Layer Anatomy Fibers Make an arc Do NOT cross horizontal axis Temporal raphe Defects on nerve are opposite on fields Carl Zeiss Webinar Photo – Effective Perimetry Perimetry Automated Visual Field Automated Perimetry for Glaucoma Types of tests used 30-2, 24-2, and 10-2 Strategies used SITA Standard, SITA Fast Visual Field Types: 30-2, 24-2, 10-2 1st number refers to the degrees AROUND fixation 2nd Ex: 10-2 – 10 degrees around the fovea (20 degrees total) number refers to the protocol Protocol 1 – points directly on the horiz and vert axis Protocol 2 – points directly above and below axis Points Easier to interpret and used exclusively now tested 30-2 – 6 degrees apart, total points 76, ~8 min per eye 24-2 – 6 degrees apart, total points 54, ~5 min per eye 10-2 – 2 degrees apart, total points 54 30-2 vs 24-2? 24-2 advantages Faster time (~5 min per eye) Less variable Similar results 30-2 advantages More May degrees of field tested help detect/monitor neurological defects, ie. Idiopathic intracranial hypertension SITA Standard vs SITA Fast SITA Standard Best threshold test Better for early detection in glaucoma More reliable, more sensitive SITA Fast Fast(er) Can be used for screening purposes More Variable, less sensitive (underestimates) scotomas When to use 10-2 in Glaucoma? Previously, used exclusively in severe peripheral field loss 24-2 not providing enough information to monitor progression, so 10-2 replaces 24-2 Recently, published in the JAMA Ophthalmology, January 2014, 10-2 VF testing was found to detect early glaucomatous defects missed on 24-2 Of 22 eyes tested as normal on 24-2 testing, 22.7% were abnormal in 10-2 testing May use 10-2 in addition to 24-2 Automated Perimetry Glaucoma VF Types Types Nasal Step Arcuate Paracentral Severity Mild to Very Severe http://www.medrounds.org/glaucoma-guide/2006/02/section-1-cunderstanding-vision-loss.html Visual Field Diagnosing Glaucoma Reliability Fixation losses, false positive, false negatives, etc. Repeatability When there’s a defect, is it repeatable? Three consecutive fields to reliably confirm glaucoma* Global Indices GHT – glaucoma hemifield test MD – Mean Deviation PSD – Pattern Standard Deviation VFI – Visual Field Index (percentage) *Keltner et al. for the Ocular Hypertenstion Treatment Study Group, Arch Ophthalmol 123:1201 (2005) Normal Visual Field Visual Field - Glaucoma Visual Field - Monitoring Progression Visual Field/OCT Integration Visual Field/OCT Integration Glaucoma Workup Review The End! Questions?
