Optimizing Success With Irregular Cornea Patients, Part 1
BY EDWARD S. BENNETT, OD, MSED, SHAWNA HILL, OD, & ROBERT M. GROHE, OD
The Global Keratoconus Congress in Las Vegas included information on new options for managing irregular corneas. These options, including large-diameter GP, hybrid and soft lens designs, can increase the likelihood of a successful fit while in many cases preventing a surgical outcome.
For GP lenses, newer, higher quality specialty lathes can produce back-surface geometries that are more likely to achieve an alignment or near-alignment lens-to-cornea fitting relationship in patients for whom this was not possible a few years ago. Some designs allow the inferior quadrant of the lens to have a steeper curvature and essentially tuck in toward the cornea, and others feature quadrant-specific curvatures to allow better alignment of each lens quadrant to the variable curvature of an irregular cornea.
We'll discuss inferior quadrant designs in this column and quadrant-specific designs in Part 2.
Choosing the Right Candidates
Designs with a steeper inferior curvature are most successful for keratoconus and pellucid marginal degeneration cases. Post-corneal transplant and refractive surgery cases that result in problematic inferior edge clearance or edge stand-off can benefit as well. The aspheric or variable eccentricity zones collapse the vast zone of inferior edge lift clearance and permit a more uniform annular peripheral curve appearance.
Reducing excessive inferior edge lift may also prove helpful in cases of high with-the-rule astigmatism by minimizing excess movement while improving overall GP comfort.
Figures 1a (left) and 1b show how the ACT system can improve the fitting relationship for a keratoconus patient who has Intacs.
Several inferior quadrant designs are currently available, with more forthcoming. The Rose K (Blanchard Contact Lens) series of designs features the Asymmetric Corneal Technology (ACT) system that allows you to customize peripheral clearance. Use Grade 1 (0.7mm) for mild inferior edge clearance, Grade 2 (1.0mm) for moderate edge clearance and Grade 3 (1.3mm) for maximum edge clearance suppression.
A more diffuse but equally effective design is the Lens Dynamics Dyna Intra-Limbal Steep/Flat option, which employs a 1.25 prism ballast at 6 o'clock combined with a two-step steeper peripheral curve zone.
Patients who have Intacs (Addition Technology, Inc.) present a challenge. In addition to the steep cone, Intacs introduces another area of steepening in the midperiphery where the segment is placed. A GP lens must be steep enough midperipherally to not bear on the segment, yet this causes insufficient edge lift. Figure 1a shows a keratoconic eye with Intacs fit with a Rose K lens. We used the ACT system to lessen the standoff and improve the fit (Figure 1b).
These designs not only improve the lens fit, but also comfort and patient satisfaction. CLS
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.
Dr. Hill specializes in contact lenses, refractive surgery comanagement and ocular disease at the Wang Eye Institute and Laser MedSpa in Nashville, TN.
Dr. Grohe specializes in contact lenses and anterior segment in his suburban Chicago practice and is also associated with the Northwestern University School of Medicine.