Enhancing RGP Surface Wetting
BY THOMAS G. QUINN, OD, MS
An RGP lens that wets well is more comfortable and provides a smooth optical surface for optimal visual performance -- two very important factors in having a happy patient. Therefore, it's imperative to educate your patients on how they can aid in this process. As a general rule, fluorosilicone acrylate (FSA) materials wet better than silicone acrylate (SA) materials. Because the fluorine found in FSA materials can contribute to oxygen transmissibility, the silicone content can be reduced, further aiding surface wetting. Reducing silicone content also diminishes protein deposition during wear (Fig. 1), which further assists wetting. Although the vast majority of patients perform best with FSA materials, there is a small percentage of patients who may prefer SA materials. These are patients who tend to coat FSA lenses with an oily, lipid-based surface film (Fig. 2). Keep in mind, however, that a lens' wetting characteristics are dictated not only by its material chemistry, but also by what agents are brought into contact with the lens surface during handling and from treatment during lens fabrication.
FIG. 1: A protein coated RGP lens.
FIG. 2: A lipid coated RGP lens.
An oily film can result from contact with contaminants such as lanolin-based lotions. Educate your patients about this before ordering a lens in a new material. Lotions should be applied before bedtime or after lens application in the morning. Some soaps can also contribute to filming problems by leaving a residue on the fingers. Encourage your patients to use soaps that don't contain perfumes or lotions.
A lens surface may also wet poorly if too much heat is generated during fabrication or polishing. This can "burn" the surface, subsequently leading to a hydrophobic surface. This can usually be recognized after polishing or when a lost or broken lens is replaced utilizing the identical material and no change in patient care has been instituted.
All lenses received from the lab should be cleaned with a laboratory cleaner and soaked in conditioning solution for at least four hours or preferably overnight before dispensing, to clean off any residual pitch remaining on the surface (Fig. 3).
FIG. 3: A poorly wetting RGP lens.
Once lenses are dispensed, instruct patients to clean and soak them overnight. Cleaning lenses immediately prior to application risks getting residual cleaner in the eye and reverses the wettability gained from the overnight soak. A similar compromise results from rinsing the lens prior to application. Instruct patients to remove their lenses from the case with a straight-up motion to minimize scratching and to apply them directly to the eye. The pay-off will be enhanced comfort and clear vision!
Dr. Quinn is in group practice in Athens, Ohio, and has served as a faculty member at The Ohio State University College of Optometry.