contact lens case reports

Inadvertent Patient Modification of RGP Lenses

BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRE, FCLSA
JANUARY 1999

Patients occasionally complain of a progressive decrease in visual acuity while wearing rigid gas permeable contact lenses. These symptoms are usually related to surface deposits, filming, warp, blink-in

blink-induced lens flexure or simple changes in refractive error. Patient F.S., 33 years old, had a 12-year history of successful RGP lens wear. Lens comfort was excellent, with a habitual wearing time of 12 to 14 hours a day. The specifications of F.S.'s lenses at dispensing three years prior were: OD 7.60mm, -2.75D, 9.0mm, 0.12mm CT; OS 7.65mm, -2.50D, 9.0mm, 0.12mm CT.

Visual acuity was 20/25 OU, and slit lamp examination showed both lenses to be moving and positioning well. At this visit, the lenses were neutralized at: OD 7.60mm, -4.75D, 9.0mm, 0.04mm CT; OS 7.70mm, -4.25D, 9.0mm, 0.04mm CT.

The patient's nightly lens care protocol consisted of removing the lenses and aggressively cleaning each in the palm of his hand for 60 seconds with the original Boston Cleaner. The abrasives in the cleaner, combined with excessive digital pressure during lens cleaning, resulted in anterior surface polishing of approximately 2.00D of additional minus power. The years of excessive cleaning also resulted in a reduction in central thickness from 0.12mm to 0.04mm (Fig. 1).

FIG. 1: F.S.'s right lens, with a center thickness of 0.04mm.

An Abrasive Personality

The original Boston lens care regimen has been a dominant product in the RGP solution market since its introduction in 1982. One of the major reasons for its success has been the incorporation of two silica-based (sand) abrasives (Fig. 2). When suspended in the surfactant gel, the abrasives do an excellent job of removing the tenaciously-bound surface debris.

FIG. 2: Electron microscopy view of the original Boston Cleaner.

When used improperly, however, the cleaner has a tendency to alter lens power and thickness, especially when patients vigorously clean their lenses for a time period that's longer than necessary. This cleaning action is similar to the addition of minus lens power through in-office lens modification.

The original cleaner's ability to alter contact lens power and thickness was recognized and corrected with the formulation of the new Boston Advanced Cleaner. To date, we have not seen any lens parameter changes with the new formulation.

It is important to periodically neutralize the lenses of patients using the original Boston Cleaner to rule out subtle or severe changes in lens power or thickness caused by the cleaner and the patient's lens care practices. Our experience has shown that the problem can easily be remedied by switching susceptible patients to the Boston Advanced Cleaner or one of the many abrasive-free RGP lens care regimens with additional enzyme cleaner.

Patrick Caroline is an assistant professor of ophthalmology at the Oregon Health Sciences University and an assistant professor of optometry at Pacific University.
Mark Andr� is director of contact lens services at the Oregon Health Sciences University.