Fighting Surface Plaque on Contact Lenses

BY ROBERT CAMPBELL, M.D. & PATRICK CAROLINE, C.O.T., F.A.A.O.
DEC. 1996

Biologic buildup on in-vitro prosthetic plastics has been a topic of great interest to contact lens researchers and clinicians. The actual composition and morphology of most hydrogel and RGP lens deposits have been studied and reported. However, one form of lens deposition, clinically referred to as surface plaque, remains somewhat a mystery. Commonly found in dentistry, surface plaque is defined as a gelatinous accumulation of bacteria and salivary mucin that forms on the teeth.

Fowler et al. first described contact lens plaque in a scanning electron microscopy study on worn RGPs. They classified RGP lens deposits as surface plaques as well as granular, trabecular and cellular deposits.

PLAQUE & LENS INTOLERANCE

This month's case history (Figs. 1-4) describes two patients who presented with similar histories of long-term RGP success, but with recent symptoms of decreasing lens tolerance. Slit lamp evaluations revealed elevated, semi-opaque, anterior surface plaques with discrete boundaries. All of the lenses had been worn more than one year. When viewed under scanning electron microscopy, the deposits revealed a thick, amorphous structure with multiple fractures or cracks in the anterior layers of the plaque.

FIG. 1: SLIT LAMP APPEARANCE OF ANTERIOR SURFACE PLAQUE.	FIG. 2: SCANNING ELECTRON MICROSCOPIC VIEW (500X) OF SURFACE PLAQUE.
FIG. 3: RGP SURFACE PLAQUE.	FIG. 4: SCANNING ELECTRON MICROSCOPIC VIEW (250X) OF SURFACE PLAQUE.

Surface plaques on silicone acrylate or fluorosilicone acrylate lenses can be localized on the anterior or posterior surface, on the anterior bevel or on the peripheral curve zones. The deposits appear to be independent of the lens type or brand and occur in conjunction with all RGP lens care products.

PLAQUE BUSTERS

To date, there is little data on the exact composition of RGP surface plaque. The most striking clinical feature of this deposit is its tenacious attachment to the lens surface. Because of this glue-like adhesion, removal of an established plaque can be extremely difficult. Commercially available abrasive surfactants are rarely effective in removing plaque. In our experience, aggressive surface polishing is the only means of removing it. However, the required digital pressure and polishing time may change lens parameters or compromise lens surfaces. Therefore, for thick, multilayered plaques, we suggest replacing the lens and we advocate more aggressive daily surfactant cleaning by the patient. We've also had success with Polish Brite, a laboratory cleaner by Contex, Inc. This product is not approved for patient use, but when used once a week, it effectively eradicates anterior and posterior surface plaques. CLS

Dr. Campbell is medical director of the Park Nicollet Contact Lens Clinic & Research Center, Minnetonka, Minn. Patrick Caroline is an assistant professor of optometry at Pacific University, Forest Grove, Ore., and director of contact lens research at Oregon Health Sciences University in Portland.