Pentacam CSP Software to Improve Efficiency and Efficacy of Complex Custom Scleral Lens Design

Pellucid marginal degeneration (PMD) is a condition that is classified as part of, but differentiated from, other corneal ectatic diseases. PMD is a clear, bilateral, noninflammatory, progressive, corneal thinning condition that occurs between one and two millimeters from the inferior limbus, typically in the 4 o’clock and 8 o’clock positions, and results in irregular astigmatism, optical distortions, and decreasing visual acuity.

Rare cases of ocular pain, hydrops, and spontaneous perforation have been reported. Since PMD is noninflammatory it is also separated from inflammatory conditions causing peripheral corneal thinning such as Mooren’s Ulcer and Terrien’s Marginal Degeneration. Often PMD has been grouped with keratoconus by the literature and by clinicians, however there are distinct features that differentiate PMD from keratoconus. Keratoconus and PMD share the diagnostic description of bilateral noninflammatory, progressive, corneal thinning disorders. However, the location of the thinning is markedly different and can be observed at the biomicroscope. The corneal protrusion in keratoconus is typically just below the center of the cornea at the apex of the cone, but the corneal protrusion in PMD is very close to the inferior limbus. PMD is considered rare, but the prevalence of PMD is likely higher than is currently recognized due to its confusion in diagnosis with keratoconus. Corneal topography can be helpful in identifying conditions such as keratoconus and PMD; the “crab claw” appearance on anterior corneal surface topography that is typically used by clinicians to differentiate PMD from keratoconus has been shown to be an ineffective diagnostic tool.

Case Presentation

A 61-year-old woman reported for a comprehensive eye examination and contact lens care. Her chief complaint was that her vision was poor with her contact lenses and her spectacles. Additional complaints included dry, irritated, and red eyes, and great difficulty with night driving. Her maximum wear time of her contact lenses was limited to 8 hours due to the dryness. She reported no history of eye rubbing. She was employed part-time at a local hospital and her duties were primarily clerical and included computer work for 2 to 3 hours a day.

The patient reported a prior diagnosis of keratoconus, dry, red, and irritated eyes, the use of soft toric contact lenses worn daily and disposed of on a 3-month basis, and the use of over-the-counter artificial tears multiple times per day. The soft toric contact lenses were worn between 4 and 8 hours per day depending on how long she was able to tolerate them. She had a history of approximately 40 years of contact lenses. Her contact lens history included hard contact lenses (PMMA), corneal gas permeable lenses, scleral gas permeable lenses, hybrid lenses, and most recently quarterly replacement soft toric contact lenses. She reported that she had reasonably good success with the hard lenses and the gas permeable lenses over the course of approximately thirty years. The main difficulty with those lenses was continued loss due to the lenses unintentionally dislodging themselves very easily. She was then refit into soft lenses but the difficulty with those were poor vision, red watery eyes, and discomfort leading to very limited wear. Scleral gas permeable lenses were attempted but failed due to discomfort while they were worn as well as great logistical problems for her to apply and remove the lenses. Hybrid lenses of various designs were then tried and she reported that the vision was much better than with the soft lenses, but she was unable to wear the lenses for more than 3 to 4 hours per day due to her eyes getting very red and watery, which degraded the vision quality, as well as the lenses became increasingly uncomfortable to wear.

The combination of multiple preservative-free artificial tears, Lipiflow (Johnson & Johnson Vision) treatments, Lid Scrubs (Ocusoft), and cyclosporine ophthalmic emulsion 0.05% (Restasis, Allergan) all failed to resolve the red, watery uncomfortable eyes and improve her ability to wear contact lenses. Although the disposable soft toric lenses were far from ideal and provided rather poor vision, they were the only contact lens option that she was able to tolerate for as much as 8 hours per day.

Examination

Entering acuity with the current soft lenses was OD 20/200, OS 20/100. The soft lenses were well centered with good coverage. There was notable vascularization of 1.0 mm of both corneas inferiorly from the 8 o’clock to 4 o’clock position. Her current spectacles were OD -2.00-8.25 x 091 and OS -4.50-7.50 x 088. Retinoscopy showed OD -4.50-9.00 x 090 20/70+ and OS -4.50-12.00 x 090 20/60+. She was unable to respond to subjective refraction. Corneal topography and corneal tomography (Figures 1 and 2) are seen below.

In Figures 1 and 2, it can also be seen that the central cornea on both the right eye and the left eye show the pachymetry apex at 627 µ and 555 µ, respectively. The pachymetry readings that show significant thinning are in an arc near the inferior limbus, with values in the 300 µ range, and a greater area affected on the right eye.

The overall distortion to this pair of corneas, displacement of the corneal apex, and the area of greatest thinning can be visualized much better on the actual photographic Scheimpflug images in Figure 3. The remainder of the examination clinical data are noncontributory.

The patient was desperately in need of being refit more appropriately into better performing lenses both visually and physiologically. Given that the thinned apex of the cornea was displaced so inferiorly and close to the limbus, a pair of custom scleral lenses was recommended. She was very apprehensive about pursuing scleral lenses as an option because her previous experience with this modality was both very negative and totally fruitless. She also cited her extreme difficulty in dealing with the logistics of application and removal. Because a custom design would be created for her, the discussion of keeping the lenses as small as possible helped to allay her fears moving into gas permeable scleral lenses.

Given her age, it was likely that she was presbyopic. Once the scleral lenses were fit and corrected the optical distortions, the distance vision would have been clear, but the near vision would still have been blurred. Since much of the patient’s daily activities required near vision, it was discussed that a pair of reading spectacles would be necessary over the scleral contact lenses for all of the near tasks. If, however, all proceeded well with the scleral fitting and optical correction, it might have been possible to incorporate a multifocal into the custom scleral lens design.

The traditional approach to fitting a scleral lens would involve either diagnostic trial lens fitting or empirical fitting based on collected data. Empirically ordering a lens that is designed for the patient will mean that the first lens applied will be a very positive experience for the patient since the fit and vision should be fairly close to what is needed, and they may even be able to leave with the lenses.

In this case, the Oculus Pentacam CSP software data were exported into the Wave software. The CSP report for the right and left eye can be seen in Figure 4.

The Oculus Pentacam CSP software captures the corneal and scleral sagittal values by taking cross-sectional meridional scans while rotating. This creates a matrix of sagittal data (100K+ data points) from the center of the cornea to a diameter of approximately 16.5 mm. It is important to have the patient eyelids out of the way so the camera can capture the superior and inferior sclera and the ability to get the lids out of the way will determine how large an area can be scanned. It can be seen how holding the inferior lid out of the way while the Oculus Pentacam CSP software is capturing the inferior sclera in Figure 5 aids in obtaining this sagittal data (lower left image).

Treatment and Outcome

Wave imports all of the scanned sagittal data to create a virtual model of the cornea and sclera to be used as a reference surface to design a unique lens. Utilizing the Wave design software, the first pair of scleral gas permeable lenses was designed for the patient and can be seen in Figure 6.

By way of demonstrating just how asymmetric this first empirically designed lens actually is, the sagittal depths at the edge of the right lens are nasally, superiorly, temporally, inferiorly, 3866 µ, 3777 µ, 4150 µ, 4911 µ, respectively. The inferior edge has over 1.1 mm greater sagittal depth than the superior edge of the lens (Table).

The lenses were applied and upon the lenses settling for 15 minutes, acuity was measured, and a spherocylindrical over-refraction was done. OD 20/30+ with an over-refraction of -0.50-0.25 x 045 20/25- and OS 20/30- with an over-refraction of -0.50-0.75 x 120 20/25-.

The biomicroscope assessment of the lenses showed lenses very well centered both vertically and horizontally. The right lens showed the flange as slightly tight superiorly and nasally. The remainder of the flange was well aligned showing no compression or blanching of the conjunctival vessels. The left lens showed the flange as slightly tight superiorly. The remainder of the flange was well aligned showing no compression or blanching of the conjunctival vessels. There was approximately 100 µ of central clearance of the right lens and approximately 50 µ of central clearance of the left lens. The limbus of each eye showed minimal clearance of the lenses 360º.

The patient was very comfortable with the new lenses and despite that there was a small over-refraction present resulting in better acuity, she was already very happy with the improved acuity as compared with her previous lenses. There was a concern that the left lens had insufficient central vault and the lens was perhaps slightly tight, specifically superiorly. It was mutually decided that the patient would leave with this pair of lenses with the stipulation that she would need to be capable of applying and removing the lenses as well as she might need to limit wear time. The patient was instructed on the application and removal of the lenses and undeterred by her history of failures, she did well handling these lenses. She returned for a 1-week follow-up.

The patient reported that she had worn the lenses every day and that the application and removal had been steadily improving. Also reported was that the vision and comfort were good, but there was some night starbursting noticed. The overall sense of dryness as well as the generally red and watery appearance that was present with the previous soft lenses had improved immensely. Wear time had been somewhat limited to less than the full day due to fogging that occurred at approximately nine hours of wear. The lenses were on prior to evaluation at this follow-up for 4 hours. Acuity with the lenses was OD 20/20- over-refraction Plano, OS 20/25- with -0.25-0.75 x 135 20/20-. The biomicroscope assessment of the lenses showed the lenses to be well centered with no conjunctival compression or vascular blanching at the lens flange for both eyes.

After reviewing solution care, application and removal techniques, and making some minor adjustments to the lens design for each eye to improve the central vault and add multifocal optics, a new pair of lenses were ordered. With the new pair of lenses, the patient is now OD 20/20, OS 20/25 with J1 at near. She comfortably wears the lenses 14 to 16 hours a day with no more late-day fogging and her eyes are no longer red, watery, or irritated.

CONCLUSION

PMD can be challenging to fit with rigid contact lenses because the apex of the cornea is significantly decentered and the highest elevation of the cornea is so close to the limbus. A corneal lens is often too unstable on corneas distorted from PMD and a scleral lens normally needs to be very large to have sufficient vault over the very high inferior elevation. Both of these options had been previously tried and failed. By collecting the specific detailed corneal and scleral elevation data with the Oculus Pentacam CSP software, an empirically designed asymmetric Wave small scleral lens was possible to design. This allowed the first pair of lenses that were placed on this patient’s eyes to be an overwhelmingly positive experience. This would not have been possible without having the initially captured sagittal data from her corneas and scleras. In addition to such an excellent outcome, this also allowed this case to be efficiently handled, minimizing both patient visits, and chair time.

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