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The Scleral Lens Education Society: Case Report 1 Management of Pellucid Marginal Corneal Degeneration with the Use of a Gas Permeable Scleral Contact Lens Brett Larson, O.D. 2560 Associated Rd #12 Fullerton, CA 92835 (714) 393-9890 [email protected] Abstract Pellucid Marginal Corneal Degeneration (PMCD) is a progressive, non-inflammatory, idiopathic disease affecting the cornea. Currently, very little is known about the cause of this condition and there is no cure, however, much can be done to manage patients with this condition and improve their quality of life. Treatment of PMCD depends greatly on the severity of the condition or the patient’s stage of progression. Of all treatment modalities, gas permeable (GP) contact lenses provide the clearest vision for the patient. Although fitting patients with PMCD with gas permeable lenses is a challenge due to high amounts of corneal irregularity and the high probability of corneal complications, scleral lenses can provide the patient with clear vision, improved comfort, and reduced risk of future corneal complications. Key words: Pellucid marginal corneal degeneration (PMCD), irregular astigmatism, ectasia, scleral lens. Introduction Pellucid marginal corneal degeneration (PMCD) is a relatively rare, bilateral, progressive, ectatic corneal disorder characterized by a noninflammatory thinning of the inferior peripheral cornea1. One of the more specific characteristics of PMCD is an area of corneal protrusion that occurs above the area of thinning rather than within this area as is seen in keratoconus. Typically, a 1 to 2 millimeter area of non-ectatic normal cornea separates the area of the corneal thinning from the limbus itself1,6,13. Topography can aid in the diagnosis of PMCD. A topographical map of the cornea will show inferior corneal steepening with a claw like pattern and against-the-rule astigmatism. Although PMCD commonly has an inferior presentation, superior PMCD has also been reported in the literature6. Patients typically present in their third to fifth decade of life with decreased visual acuity secondary to high amounts of irregular corneal astigmatism1,13. Reported complications of PMCD are hydrops and spontaneous perforation7,14. Successful management of PMCD relies heavily on the severity of the condition. In its early stages, PMCD can be managed with the use of spectacles. Patients with high amounts of regular or irregular astigmatism cannot be managed with glasses and need to utilize gas permeable contact lenses in order to achieve acceptable visual outcomes3,8. Surgical options for the correction of PMCD include intrastromal corneal rings, and several different types of deep lamellar and penetrating keratoplasty2,13,14. All of these surgical procedures, however, have a high probability of still requiring the patient to wear gas permeable contact lenses even after surgery is completed. A scleral contact lens is defined as a lens 18 millimeters or larger in diameter that completely vaults over the corneal surface and rests on the sclera. These lenses are a viable option in the management of PMCD because of their high probability to center over the cornea as opposed to small diameter corneal lenses11,16. Mechanical irritation of the ectatic portion of the cornea is also less likely because of the corneal vault that occurs with these lenses. Studies have shown that scleral lenses provide similar and often improved visual outcomes when compared with corneal contact lens designs11,15. Case Report Patient #1, a 51-year-old Hispanic male, presented to the clinic on 17 July 2008. He had been referred by an outside optometrist for the fitting of a gas permeable contact lens OD. The fitting of this lens was for the treatment of what he reported as “unilateral keratoconus OD only”. The patient reported reduced vision OD with “blurry, distorted, and double vision” occurring constantly. He had been diagnosed with keratoconus three years prior but suspected that he had suffered from the condition since his early 20’s. The patient reported that he was “not eager” to be fit with gas permeable lenses having attempted to wear them in the past without success due to discomfort. The patient showed no other significant ocular history and his medical history was negative. He denied taking medications in any form or having any allergies. He had a family history of diabetes, high blood pressure, and glaucoma. His blood pressure was 118/76. The patient was pleasant and oriented to time, place and person. The patient’s last eye examination had been completed in June 2008. The referring doctor reported that the patient was “intolerant to gas permeable contact lenses” and “should consider surgery to successfully wear disposable soft lenses”. His record showed other wise healthy eyes with an unremarkable fundus evaluation. Subjective refraction was reported as +1.25-6.75 x 060 OD and -1.00-0.50 x 100 OS with visual acuities of 20/50- and 20/20 respectively. The patient presented wearing soft toric disposable contact lenses with powers of -2.252.75 x 070OD and -0.75-0.75 x 100 with resulting acuities of 20/400 and 20/20 respectively. The habitual lenses centered well, had good rotational stability and moved well on blink. He reported wearing +1.75 OTC readers over his contact lenses when reading with adequate vision. The patient’s uncorrected distance visual acuity was counting fingers at distance and near OD and 20/40 at distance, 20/25 at near OS. Best corrected visual acuity showed 20/50 OD and 20/20 OS with a manifest refraction of +1.25-6.75 x 060 OD and -1.00-0.50 x 100 OS. Pinhole acuity was not documented. Pupils were equally round and reactive to light with no afferent pupillary defect OU. Confrontation visual fields were full to finger count OD/OS. Extraocular muscles were unrestricted in all gazes. Binocularity measures were not performed at this visit secondary to decreased visual acuity OD. Intraocular pressures were 16mmHg OD and OS at 10:20 a.m. with Goldman applantation tonometry. Slit lamp examination revealed the bulbar and palpebral conjuntiva to be white and quiet OU, clean eyelid margins and lashes OU, brown irises OU, clear lenses OU, and open anterior chambers that were deep and quiet OU. Evaluation of corneal health with the slit lamp showed inferior corneal thinning and associated Fuch’s Striae OD, and clear corneal tissue OS. An undilated examination of the poster pole with a 90 diopter fundus lens revealed cup-to-disc ratios of 0.3 round OU. Retinal arteries and veins had a normal appearance with a ratio of 2/3 respectively. Macular areas were flat and avascular with a positive foveal reflex OU. The fundus background was homogenous with no significant retinal findings. Corneal topography was taken OD/OS. OD topography showed an irregular corneal surface with a corneal toricity of approximately 14 diopters. Simulated keratometry showed values of 37.17 x 51.53 diopters with corneal steepness increasing in the inferior 1/3rd of the cornea. The topographical pattern OD was indicative of pellucid corneal degeneration. OS simulated keratometry values were recorded as 41.00 x 41.26 diopters. The topographical pattern showed a nearly spherical corneal surface with no signs of an irregular surface. The patient was therefore diagnosed with unilateral pellucid marginal corneal degeneration (PMCD) OD. The differential diagnoses in this case include: 1. Pellucid Marginal Corneal Degeneration (PMCD) On topography, PMCD has a “claw-like” appearance with the inferior portion of the cornea steepening drastically as compared to the superior cornea. This type of patient will typically show a large amount of against-rule-corneal toricity and against-the-rule astigmatism on refraction. 2. Keratoconus On topography, keratoconus has the appearance of localized steepening which is commonly inferior and temporal (although the localized area can be located anywhere on the cornea). Ocular signs will include Fleischer’s ring, Fuch’s striae, and Munson’s sign in advanced cases. 3. High Amount of Regular Corneal Astigmatism On topography, regular astigmatism will show a somewhat symmetrical bowtie-pattern rather than a localized area of steepening (as in keratoconus) or a claw like appearance (as in PMCD). Patients with high amounts of regular corneal astigmatism will not show signs of corneal thinning such as Fuch’s striae for example. Regular astigmatism theoretically should be correctable to 20/20 visual acuity with glasses if there are no other confounding factors present (such as amblyopia). Several small diameter trial lenses designed for fitting corneas with keratoconus were placed on the right eye in order to determine the most appropriate contact lens. The goal of the fitting process was to determine the particular base curve, diameter, and peripheral curve system that would provide adequate lens centration and movement while still maintaining acceptable ocular health by lightly touching, or completely vaulting the area of corneal ectasia. After several trial contact lenses were placed on the eye, the following order was placed OD: Material: Fluroperm 60 Base Curve: 52.75(6.39) Power: -13.75 DS Diameter: 8.8 Optic zone: 6.3 Secondary curve: 8.8 Tertiary curve: 12.50 Although this particular lens tended to decenter inferiorly, it was determined that this lens was a good “starting point” to begin the fitting process. The patient was counseled on the risks of PMD and was scheduled to return in 1 week for a dispensing of the ordered gas permeable lens. Follow up #1 The patient returned on 23 July 2009 to have his gas permeable contact lens dispensed. He reported no changes to his vision or ocular symptoms. His visual acuities through his habitual soft toric disposable lenses were consistent with the previous examination (20/400 OD and 20/20 OS). The previously ordered lens with the following parameters was placed on the right eye and fit and vision were assessed. Material: Fluroperm 60 Base Curve: 52.75(6.39) Power: -13.75 DS Diameter: 8.8 Optic zone: 6.3 Secondary curve: 8.8 Tertiary curve: 12.50 With the gas permeable lens in place, the patient’s vision improved to 20/20- OD. Fit assessment showed that the lens was decentered inferiorly, had minimal movement on blink, showed moderate apical touch inferiorly over the ectatic portion of the cornea, had small bubbles superiorly within the optic zone, and displayed minimal peripheral clearance. The patient reported poor comfort with the lens in place. It was determined that the lens would not be dispensed at this visit, and instead would be re-ordered with a steeper base curve to reduce the amount of corneal touch, a smaller optic zone to eliminate the bubbles within optic zone, and a steeper tertiary curve to reduce the amount of edge lift. The re-ordered lens would have the following parameters. Material: Fluroperm 60 Base Curve: 53.50(6.31) Power: -14.00DS Diameter: 8.8 Optic zone: 6.0 Secondary curve: 8.7 Tertiary curve: 12.0 The patient was rescheduled to return in 1 week to dispense the new gas permeable lens. Follow up #2 The patient returned on 4 August 2008 for the dispense of his new gas permeable lens OD. He, again, reported no changes to his vision or ocular symptoms. His visual acuities through his habitual soft toric disposable lenses were consistent with previous visits (20/400 OD and 20/20 OS). The previously ordered lens with the following parameters was placed on the right eye and the fit and vision were assessed. Material: Fluroperm 60 Base Curve: 53.50(6.31) Power: -14.00DS Diameter: 8.8 Optic zone: 6.0 Secondary curve: 8.7 Tertiary curve: 12.0 With the gas permeable lens in place, the patient’s vision improved to 20/20- OD. Fit assessment showed that he lens was decentered inferiorly, had minimal movement on blink, showed a feather three point apical touch inferiorly over the ectatic portion of the cornea, had no bubbles within the optic zone, and had average peripheral clearance. The patient reported poor comfort with the lens in place. The lens was dispensed to the patient and he was scheduled for a contact lens progress evaluation two weeks later. The patient was educated on the importance of full and complete blinking throughout the day in order to adequately wet the lens and achieve sufficient lens movement. He was informed that lens wear should be slowly increased over the next two weeks in order to adequately become accustomed to the lens. Follow up #3 The patient returned on 18 August 2008 for a two week follow up on the previously dispensed lens OD. He had been wearing the lens for two hours that day and had achieved an average wear time of 8 hours per day. The patient reported inadequate comfort throughout the day. “Systane” artificial tears had been utilized as needed in an attempt to improve comfort with no relief. The patient also reported “flare and glare” in the evening, and “ghosting” of images that occurred constantly with lens use. The patient’s visual acuities through the GP lens OD and habitual soft toric disposable lens OS were consistent with the previous visit (20/20 OD, 20/20 OS). Fit assessment of the GP lens OD showed that the lens was riding inferiorly on the cornea. A feather three point touch, no movement on blink, and minimum peripheral clearance with lens seal off were also noted. When the lens was removed, the cornea displayed a mild compression ring where the lens had been sitting with a ring of grade 2 SPK at the lens border. Mild staining was also reported in the area of the cone apex. The patient was advised to continue to wear the current GP for as many hours per day as possible to continue building up his wear time. The lens would be re-ordered with a larger overall diameter for better centration, a larger optic zone in order to reduce the symptoms of flare and glare, and a flatter peripheral system in order to reduce the risk of lens seal off and impression rings on the corneal surface. The re-ordered OD lens would have the following parameters. Design: Dyna Z Intra-limbal Material: Boston XO Base Curve: 47.50(7.11) Power: -8.75DS Diameter: 10.8 Optic zone: 8.5 Peripheral Curve: 1.5 steeps flatter than base curve. The patient was scheduled to return in 1 week to dispense the new GP contact lens OD. Follow up #4-19 Over the following 10 months the patient’s contact lens parameters were repeatedly changed in an attempt to improve lens centration, eliminate symptoms of flare and ghosting, and improve movement on blink. Each of these lenses was a large diameter “Dyna Z Intra-limbal” lens design. The trial lenses were routinely dispensed to the patient at each visit for a week long trial. At the end of each trial period, it was determined that the lens provided inadequate corneal health and comfort. Each lens consistently provided the patient with 20/20 vision OD. On 1 July 2009, the optometrist providing care to the patient was replaced by a new provider (Dr. Brett Larson). Under this new provider, it was determined that a scleral lens would need to be fit OD in order to achieve the desired outcome. The patient was scheduled for a fitting on 3 August 2009. Follow up #20 The patient returned on 3 August 2009 to be fit with a gas permeable scleral lens OD. The patient had been wearing a previously dispensed gas permeable lens with the following parameters for 2 weeks. Design: Dyna Z Intra-limbal Material: Boston XO Base Curve: 50.50(6.68) Power: -10.00DS Diameter: 11.2 Optic zone: 8.8 Peripheral Curve: 10 steeps flatter than base curve. The patient reported reduced flare, glare and ghosting of images. Improved comfort and clarity of vision were also observed. He had been using Systane artificial tears as needed for improved comfort OD with the lens in place. The lens had been worn an average of 11 hours per day with no complications reported. The patient did not admit to sleeping in his lens. Fit assessment of the lens showed inferior centration, inadequate movement on blink, minimal peripheral clearance and lens seal off. When the lens was removed, the patient had an impression ring inferiorly where the lens had been sitting and grade 2 SPK at the lens border and at the apex of the ectatic area. The patient was advised to wear this lens as little as possible and for a maximum of five hours per day. He was also advised to use artificial tears four times per day until a scleral lens fit could be finalized. A Jupiter scleral gas permeable contact lens was placed on the patient’s eye OD and a fit assessment was completed. Because the clinic only had a fitting set with a diameter of 18.2, this diameter was used in the fitting process. A contact lens with a base curve one diopter steeper than steepest keratometry reading OD was selected as the initial trial lens. Design: Jupiter Scleral Lens Base Curve: 52.00(6.49) Diameter: 18.2 Power: -12.75 Peripheral Curve: Series B Fit assessment of the lens showed good centration, full corneal clearance with a tear lens approximately 400 microns in width, inadequate limbal clearance on the nasal and temporal edges of the cornea, and minimal blanching of the conjunctival vessels. The over refraction for this trial lens was plano DS with a resulting acuity of 20/20 OD. A scleral lens was designed and ordered with the following parameters: Design: Jupiter Scleral Lens Base Curve: 52.00(6.49) Power: -12.75 DS Diameter: 18.8mm Optic Zone: 8.2 Peripheral Curve 1/Width: 6.89mm/2.6mm Peripheral Curve 2/Width: 8.35mm/0.7mm Peripheral Curve 3/Width: 12.75mm/1.5mm Peripheral Curve 4/Width: 14.75mm/0.5mm The above lens was ordered with a diameter of 18.8mm rather than 18.2mm in order to achieve adequate limbal clearance while maintaining lens centration and corneal clearance. Peripheral curves three and four were also flattened slightly from the standard trial lens parameters in order to more evenly distribute the weight of the lens over the conjunctiva and eliminate blanching of conjunctival vessels. The patient was informed that he would be notified when the lens was received, and could then be scheduled for a follow-up examination where the lens would be dispensed. He was instructed to wear the smaller diameter habitual lens for a maximum of five hours per day until the dispensing appointment for the scleral lens. Follow up #21 The patient returned to the clinic on 16 September 2009 for dispense of his new scleral lens OD. The patient had no changes to his visual or ocular health complaints. He reported mild irritation when wearing his habitual GP lens for longer than five hours. He reported adequate vision OD/OS when wearing his habitual contact lenses. He achieved 20/20 vision OD/OS with his habitual contact lenses. When a slit lamp evaluation was performed with no lenses in place, grade 2 SPK was seen at the highest point of the cornea, an impression ring where the lens edge typically sat was also present with associated grade 2 SPK at the edge of the corneal impression OD. The following trial lens was place on the eye OD and fit and vision were assessed. Design: Jupiter Scleral Lens, OD only. Base Curve: 52.00(6.49) Power: -12.75 DS Diameter: 18.8mm Optic Zone: 8.2 Peripheral Curve 1/Width: 6.89mm/2.6mm Peripheral Curve 2/Width: 8.35mm/0.7mm Peripheral Curve 3/Width: 12.75mm/1.5mm Peripheral Curve 4/Width: 14.75mm/0.5mm Fit assessment showed adequate centration, full corneal clearance with a tear lens approximately 400 microns in width, adequate limbal clearance on the nasal and temporal edges of the cornea, and average blanching of the conjunctival vessels. There was not movement on blink. The over refraction for this trial lens was plano DS with a resulting acuity of 20/20 OD. Because of the blanching of the conjunctival vessels, it was decided that this lens would not be dispensed. Instead, the lens was reordered with the following parameters. Design: Jupiter Scleral Lens, OD only. Base Curve: 54.00(6.25) Power: -14.75 DS Diameter: 18.8mm Optic Zone: 8.2 Peripheral Curve 1/Width: 6.89mm/2.6mm Peripheral Curve 2/Width: 8.35mm/0.7mm Peripheral Curve 3/Width: 13.25mm/1.5mm Peripheral Curve 4/Width: 15.25mm/0.5mm In the above lens order, peripheral curves three and four were flattened slightly in order to allow increased blood flow of the conjunctiva and decrease signs of blanching. The base curve was steepened by two diopters in order to compensate for the loss in overall sagittal height that occurs by flattening the peripheral curves. The patient was, again, informed that he would be notified when the lens was received, and could then be scheduled for a follow-up examination where the lens would be dispensed. He was instructed to wear the smaller diameter habitual lens for a maximum of five hours per day until the dispensing appointment for the scleral lens. He was offered soft disposable lenses to be used as piggyback lenses, but declined the offer reporting that he’d “prefer to wait for the next dispensing visit”. Follow up #22 The patient returned on 23 September 2009 for dispense of his new scleral lens OD. As reported previously, the patient had no changes to his visual or ocular health complaints. He reported mild irritation when wearing his habitual GP lens OD for any period of time. He reported adequate vision OD/OS when wearing his habitual contact lenses. He had 20/20 vision OD/OS with his habitual contact lenses. When a slit lamp evaluation was performed with no lenses in place, grade 2 SPK was seen at the highest point of the cornea, an impression ring where the lens edge typically sat was also present with associated grade 2 SPK at the edge of the corneal impression OD. The following trial lens was place on the eye OD and fit and vision were assessed. Design: Jupiter Scleral Lens (OD only) Base Curve: 54.00(6.25) Power: -14.75 DS Diameter: 18.8mm Optic Zone: 8.2 Peripheral Curve 1/Width: 6.89mm/2.6mm Peripheral Curve 2/Width: 8.35mm/0.7mm Peripheral Curve 3/Width: 13.25mm/1.5mm Peripheral Curve 4/Width: 15.25mm/0.5mm Fit assessment of the lens showed good centration, full corneal clearance with a tear lens approximately 300 microns in width, adequate limbal clearance in all locations, and no blanching of the conjunctival vessels. There was no movement on blink. The over refraction for this trial lens was plano DS with a resulting acuity of 20/20 OD. The patient reported good comfort and vision. The lens was left on the patient’s eye for 40 minutes in order to assess the fit after the lens was allowed to settle. After 40 minutes of wear, the fit remained the same in every regard accepting the fact that the tear lens was decreased from approximately 300 microns to approximately 250 microns in width. The patient received instruction on application and removal of the lens and the lens was dispensed. He was told to slowly build up wear time over the next week and return for a final follow up appointment. The final appointment was scheduled for the evening in order to be able to assess the fit after a full day of wear. Follow up #23 The patient returned to the clinic on 30 September 2009 for a final follow up on the scleral lens dispensed one week previously OD. He had been wearing the lens for 10 hours previous to the appointment and reported wearing the lens for an average of 15 hours per day with good vision and comfort. The patient reported that the irritation felt with the previous lens was no longer present. Presenting visual acuities were 20/20 OD/OS. Fit assessment of the lens showed good centration, adequate corneal clearance with a tear lens width of approximately 250 microns, adequate limbal clearance, no movement on blink, and no blanching of the conjunctival vasculature. Slit lamp examination after lens removal was performed to assess ocular health after lens wear. The cornea showed no staining and no lens impression marks from the previous smaller diameter lens. The conjunctival and limbal areas also displayed no staining. The lens was finalized and the patient was instructed to wear the lens full time. He was scheduled for a 6 month progress evaluation to assess corneal health and lens wear. Six Month Progress Evaluation The patient reported to the clinic on 23 March 2010 for a progress evaluation to assess ocular health and lens wear with the scleral lens OD. The patient had been wearing the lens for 11 hours that day and reported average wear time of 15 hours per day with good vision and comfort. Presenting visual acuities were 20/20 OD/OS. Fit assessment showed good centration, adequate corneal clearance with a tear lens width of approximately 250 microns, adequate limbal clearance, no movement on blink, and no blanching of the conjunctival vasculature. As was found in the previous visit, assessment of the ocular surface showed no corneal staining or compression rings. The conjunctival and limbal areas also were healthy with no signs of staining. The patient was instructed to continue full time wear of the scleral lens OD and soft disposable lens OS. He was scheduled for a comprehensive examination in six months for a yearly evaluation. Discussion PMCD is defined as a progressive noninflammatory ectatic corneal disorder involving the inferior cornea in a crescent like shape1. The corneal ectasia typically extends from the 4-o’clock position to the 9-o’clock position, 1-2mm from the limbus. One of the differentiating factors of PMCD from other ectactic corneal disorders, such as keratoconus, is that the ectatic portion of the cornea is found above the area of thinning, rather than being located at the area of thinning1,6,13. Although rare, superior PMCD has also been reported. Differentiating PMCD from other ectactic corneal disorders based on topography has been the source of much debate. Commonly, PMCD appears as an area of rapid steepening inferiorly. The steep portion of the cornea has the appearance of “crab claws” or “kissing birds” coming together typically near the visual axis4. It has also been noted that the central portion of the eye appears to be flattening in the vertical meridian producing an against-rule-astigmatic appearance. Although corneal ectasia associated with keratoconus is frequently located in the inferior portion of the cornea, it has a more localized presentation and will not have the “crab claw” appearance4. Some reports have mentioned the presence of PMCD and keratoconus within the same patient4,6. This is another source of controversy among researchers. Patients with PMCD typically present in their fourth to fifth decades of life with reduced visual acuity due to high amounts of irregular astigmatism. The disorder is more prevalent in the male population than in females1. There seems to be no connection between ethnicity and disease prevalence13. PMCD is usually a bilateral condition, although there have been a few isolated case reports of unilateral presentation as was the case with this patient. Data regarding the genetic component of PMCD is lacking in current literature. Some articles assume that PMCD has a similar inheritance pattern to keratoconus, but, this has yet to be proven or substantiated4. As with keratoconus, studies have shown that the progression of PMCD decreases dramatically with age and tends to stabilize in the fifth and sixth decade. Two commonly reported complications that occur with PMCD are corneal hydrops and corneal perforation1,7. Both of these conditions are reported to occur at or near the area of corneal thinning. The mode of management for PMCD depends completely on disease severity. Early in the disease process, patients can be managed with spectacles or toric soft contact lenses with moderately successful results8. In more moderate to severe cases, the patient will need to be fit with GP lenses in order to obtain acceptable visual acuity5. Several surgical procedures have been attempted in the literature with variable results. Even in the presence of surgery, however, the majority of reported cases have still necessitated the use of GP lenses in order to obtain adequate vision5. Gas permeable contact lenses have been documented as a successful and consistent way to provide clear vision for patients with irregular corneal surfaces9,11. Although GP lenses are commonly used for management of PMCD, they can be one of the most challenging treatment methods to achieve successfully. The difficulty with PMCD is the challenge of successfully designing a contact lens that will provide clear vision, adequate comfort, and maintain the health of the corneal surface11. The collaborative longitudinal evaluation of keratoconus (CLEK) studies reported that contact lenses fit excessively too flat will cause the lens to come in contact with the area of corneal ectasia10. Excessive contact with these areas results in corneal scarring. Therefore, when fitting patients with corneal irregularities, it is important the lens be fit steep enough to avoid unnecessary contact with the ectatic area. Small diameter lenses tend to center themselves over the steepest portion of the eye causing the lens to drop down in cases with inferior steepness such as PMCD. Inferiorly decentered lenses result in less than adequate vision for the patient and may result in harmful contact with the ectactic area. Larger diameter lenses (Greater than 10mm and less than 12.9mm) have the ability to vault over the area of ectasia successfully and center over the visual axis8. In extreme cases, however, these lenses will attract bubbles under the optic zone resulting in blurry and distorted vision. A scleral lens is defined as a lens with a diameter of 18mm or greater11. These lenses vault over the corneal and limbal area completely and rest on the sclera. Though there are few published cases regarding the use of these lenses in the treatment of irregular corneas, they have many features that may be of great benefit to the patient. Scleral lenses aid in lens centration secondary to the fact that they do not rely on corneal curvature to determine lens position. This makes it possible for any patient, regardless of corneal irregularity to successfully wear contact lenses (provided they do not have other confounding factors). Because these lenses have no contact with the cornea, studies have shown that the risk of corneal scarring is much lower than with a smaller diameter lens11. Other studies have also shown that scleral lenses provide improved comfort for the patient due their large diameter and decreased interaction with the lid margins15. In many cases, this provides a valuable option for those patients who were otherwise considered to be “contact lens intolerant”. These lenses are also designed to hold a reservoir of liquid throughout the day that slowly exchanges with the patient’s tears on blink12. These lenses have been researched predominantly for their use in dry eye therapy and other severe ocular surface diseases9. This ability to maintain a “liquid bandage” over the cornea for extended periods of time provides relief and healing for many of these conditions. Conclusion This case demonstrates the many characteristics of PMCD and the role of scleral lenses in the management of this and other severe corneal irregularities. In all cases, PMCD can be most accurately diagnosed through the use of corneal topography and careful evaluation with a slit lamp. Although it may be difficult to differentiate PMCD from keratoconus, it is important to know their differences in order to provide patients with the most appropriate care possible. Management of PMCD is determined by the severity of the condition. The most common, and successful, non-surgical option in the management of PMCD is the use of GP lenses. GP scleral lenses provide numerous benefits to PMCD patients by way of improved vision, comfort, fit, and corneal health. Bibliography 1. Ambrosio R, Klyce S, Smolek M, Wilson S. Pellucid marginal corneal degeneration. Journal of Refractive Surgery 2002; 18:86-87. 2. Busin M, Kerdraon Y, Scorcia V. Combined wedge resection and beveled penetrating relaxing incisions for the treatment of pellucid marginal corneal degeneration. Cornea 2008; 27(5): 595-600. 3. Dominguez C, Shah A, Weissman B. Bitoric gas-permeable contact lens application in pellucid marginal corneal degeneration. Eye and Contact Lens 2005; 31(5): 241-243. 4. Ertan A. Differentiating keratoconus and pellucid marginal degeneration. Journal of refractive surgery 2007; 23:221-222. 5. Gruenauer-Kloevekorn C, Fischer U, Duncker G. Pellucid marginal corneal degeneration: evaluation of corneal surface and contact lens fitting. British Journal of Opthalmology 2006; 90:318-323. 6. Lee B, Jurkunas U, Harissi-Dagher M, Poothullil A. Ectatic disorders associated with a claw-shaped pattern on corneal topography. American Journal of Ophthalmology 2007; 144(1): 154-157. 7. Lee W, O’Halloran H, Grossniklaus H. Pellucid marginal degeneration and bilateral corneal perforation: case report and review of literature. Eye and Contact Lens 2008; 34(4): 229-233. 8. Ozbek Z, Cohen E. Use of intralimbal rigid gas-permeable lenses for pellucid marginal degeneration, keratoconus, and after penetrating keratoplasty. Eye and Contact Lens 2006; 32(1): 33-36. 9. Pullum K, Buckley R. Therapeutic and ocular surface indications or scleral contact lenses. The Ocular Surface 2007; 5(1):40-48. 10. Szczotka L, Barr J, Zadnik K. A summary of the findings from the collaborative longitudinal evaluation of keratoconus study. Optometry 2001; 72(9): 574-584 11. Segal O, Barkana Y, Hourovitz D. Scleral contact lenses may help where other modalities fail. Cornea 2003; 22(4): 308-310 12. Smith G, Mireskandari K, Pullum K. Corneal swelling with overinight wear of scleral contact lenses. Cornea 2004; 23(1); 29-33 13. Sridhar M, Mahesh S, Bansal A, Nutheti R. Pellucid marginal corneal degeneration. Opthalmology 2004; 111(6): 1102-1107 14. Tzelikis P, Cohen E, Rapuano C. Management of pellucid marginal corneal degeneration. Cornea 2005; 24(5): 555-560. 15. Visser E, Visser R, Lier H. Advantages of toric scleral lenes. Optometry and Vision Science 2006; 83(4); 233-236. 16. Ye P, Sun A, Weissman B. Role of mini-scleral gas permeable lenses in the treatment of corneal disorders. Eye and Contact Lens 2007; 33(2): 111-113.