GP Lens Case Grand Rounds Troubleshooting Guide – 40

Pellucid Marginal Degeneration: Phyllis Rakow, COT

Background

J.D., a 42-year-old white male, presented with a history of “keratoconus” OU that was diagnosed at a commercial optical chain. He stated that both of his GP lenses pop out of his eyes, more often his right than his left.

Test Procedures, Fitting/Refitting, Design & Ordering

Biomicroscopy: Inferior corneal thinning; negative for Vogt’s striae; Fleischer’s ring OU.

Visual Acuity:

OD: 20/40 J1 @ 14″
OS: 20/25 J1 @ 14″

Current Contact Lens Parameters:

ODOS

Material: Boston ES Boston ES
Base Curve Radii: 8.18/7.41mm 8.10mm
Power(s): +0.75/-3.00D +0.75D
Overall Diameter: 9.40mm 9.40mm

Corneal Topography. An inferior butterfly-shaped region of corneal steepening was present.

Patient Consultation and Education

On the basis of the corneal topography, pellucid marginal degeneration, rather than keratoconus was diagnosed. Pellucid marginal degeneration usually appears between the ages of 20 and 40 and results in the development of high degrees of astigmatism as it progresses. The area of greatest thinning in keratoconus is usually central or paracentral; in pellucid it is generally about 1.0 mm above the inferior limbus.

The typical topography pattern of pellucid has been described as “two birds kissing,” “a handlebar moustache,” “crab claws,” or “butterfly wings.” Although the condition is usually bilateral, like keratoconus, it tends to be asymmetric, with the corneal irregularity and thinning more advanced in one eye than in the other.

J.D.’s Orbscan maps showed more advanced pellucid marginal degeneration in his right eye, with the greatest thinning (lower right map) inferiorly. Due to the extreme inferior ectasias, J.D.’s lenses exhibited inferior edge standoff, right lens greater than left lens, and the lenses popped out occasionally, due to the interaction of the lower edge of the lenses with his lower lids as he blinked.

Large diameter lenses are usually needed to achieve adequate centration and pupillary coverage in pellucid marginal degeneration, although inferior edge standoff in the ectatic region of the cornea may be difficult to overcome.

We discussed this with J.D., explained the colors and patterns of the topography, and proceeded with a GP lens fitting, using Dyna Intra-Limbal 11.2 mm lenses from Lens Dynamics, of Golden, Colorado. Unfortunately, we were not able to eliminate the inferior edge standoff with the standard Dyna Intra-Limbal lens design.

For corneal irregularities that vary significantly in curvature from one quadrant to another, Lens Dynamics has developed “Flat/Steep” designs. The inferior portion of these lenses can be steepened and prism ballasted to align with the flat and steep zones of the cornea and minimize or eliminate edge standoff. We were able to optimize the fit on J.D. with:

Current Contact Lens Parameters:

ODOS

Material: Optimum Extra (100Dk) Optimum Extra
Base Curve Radii: 7.18mm 7.67mm
Power(s): -1.37D -4.37D
Overall Diameter: 11.20mm 11.20mm
Optical Zone Diameter: 9.80mm 9.40mm
Peripheral Curve Radii: Standard @ 090; 3 steps steep @ 270˚ Standard @ 090; 1 step steep @ @ 270˚
Prism: 1 1/4∆ Base Down 1 1/4∆ Base Down

The care system prescribed was the Boston Advance Daily Cleaner and the Boston Conditioning Solution (Original Formula).

Visual Acuity:

OD: 20/40 J1 @ 14″
OS: 20/25 J1 @ 14″

Follow-Up Care/Final Outcome

J.D. has been able to wear the Dyna Intra-Limbal lenses comfortably and has not experienced any lens displacement or loss since being refit. He is using the Boston Conditioning Solution Original Formula because of a sensitivity to the polyaminopropyl biguanide (PAPB) in the Boston Advance Conditioning Solution, which resulted in a very fine limbus-to-limbus superficial punctate keratitis.

Discussion/Alternative Management Options

Although J.D. was initially resistant to the ordering of large diameter lenses, we explained that we would not be able to achieve good centration and eliminate lens displacement and expulsion from the eye with smaller lenses (even though they can also be made in a “flat/steep” design) due to the inferior location of the steepest areas of his corneas.

J.D. had inquired about a possible corneal transplant in his right eye, but was told by our corneal surgeon that it was not an option, since the area of greatest thinning is where the graft/host junction would be. He also inquired about soft lenses, as he had worn soft torics at one time in the past. By emphasizing the extent of his corneal irregularities with corneal topography, he was able to grasp the reason why soft lenses were no longer an option. Therefore, he accepted our recommendations and adjusted nicely to the large GP lenses.

Intra-Limbal lenses have many other applications besides pellucid marginal degeneration. They are problem-solvers for achieving better centration and corneal alignment in keratoconus patients with low, sagging cones or globus cones. In post-graft patients, where it is essential to avoid impingement on the graft/host junction, the Intra-Limbal is often the “problem-solver.” It provides better centration, avoids impingement on the graft/host junction, and can be ordered in “flat/steep” designs for post-keratoplasty patients with tilted or highly astigmatic grafts.

Intra-Limbal lenses are also available in reverse geometry designs for post-refractive surgery patients. These patients, especially those who underwent radial keratometry procedures many years ago, tend to have very flat, irregular corneas, and are unable to achieve an acceptable fit with smaller lenses. Lastly, they make exceptional “sports” lenses, since they are much less likely to displace during contact sports than standard GPs and are much more likely to provide crisper vision for the athlete than a soft lens.

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