Avoid Aberration With RGPs
BY LORETTA B. SZCZOTKA, OD, MS, FAAO
At the recent American Academy of Optometry meeting in Orlando, the visual aberrations and limits of refractive surgery were highlighted during this year's excellent Annual Research Symposium. Speakers discussed ophthalmic wavefront sensing as a method to permit creation of diffraction-limited rather
Symposium. Speakers discussed ophthalmic wavefront sensing as a method to permit creation of diffraction-limited rather than aberration-limited optical corrections that may someday enable normal patients to achieve 20/10 to 20/8 acuity. However, not all speakers agreed that an aberration-free surface is possible with current methods of LASIK or PRK, which convert a myopic cornea to a more oblate shape rather than the pre-operative prolate shape. This post-operative shape is responsible for increased refractive aberrations and presents significant difficulties during contact lens fitting.
Fortunately, many unsuccessful refractive surgery patients have the option of pursuing contact lens fitting for visual improvement. At the AAO meeting, 13 case reports on eight posters described the successful use of contact lenses after RK, PRK or LASIK. Over half of the case reports required RGP lenses to achieve a successful visual outcome (Table 1).
Although soft lenses were reported to work well on some post-LASIK patients, in my practice over 75 percent of all post-refractive surgery patients require RGP lenses, which far outweigh soft lenses in the visual improvement of unhappy RK, PRK or LASIK patients. The shift toward fitting soft lenses occurs due to patient (or practitioner) preconceived resistance towards RGP lenses or the patient's inability to adapt to rigid lenses.
Best RGP Designs
I have found that most successful post-refractive surgery patients are those fit in specialty RGP designs such as reverse geometry, ultra large diameter and hyper Dk RGP polymers. The most important feature in RGP lens fitting is to limit the harsh bearing areas most often found beneath the mid to far periphery of a spherical lens. Usually, a reverse geometry lens can alleviate the excessive impingement in this area to provide for a smooth post-lens tear layer. Ultra large diameter (10.0mm to 11.5mm) RGP corneal lenses have worked well for some patients in alleviating edge awareness by achieving lid attachment and vaulting over the LASIK or PRK ablation zone.
Semi-scleral RGP lenses are being introduced as problem solvers for irregular corneas and RGP-intolerant patients. Two such lenses are now available in the United States: Macrolens (C&H Contact Lenses) and Epicon (Specialty UltraVision). At the AAO meeting, the Epicon was reported successful in fitting two LASIK eyes, although it is currently approved for use only in keratoconus. I look forward to adding these lenses to my armamentarium for fitting post-refractive surgery eyes. I encourage all to continually seek innovative ways to correct refractive surgery visual limitations with RGP lenses until the aberration barrier can be broken.
TABLE 1: Post-refractive Surgery Contact Lens Types
NUMBER OF EYES FIT INTO EACH LENS TYPE
|PROCEDURE||RGP/SOFTPERM/SPECIALTY RGP||SPHERICAL OR TORIC SOFT LENS|
|LASIK (10 EYES)||5||5|
|PRK (2 EYES)||2||NA|
|RK (1 EYE)||1||NA|
Dr. Szczotka is an assistant professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens Service at University Hospitals of Cleveland.