RGPs for Borderline
BY EDWARD S. BENNETT, O.D., M.S. ED.
Who are the borderline dry eye patients? Certainly anyone with symptoms or signs of ocular dryness would qualify. Partial blinkers and patients who have long interblink intervals also fall into this category, as do those with a tear break-up time of five to nine seconds or a phenol red thread test value of 10mm to 20mm in 15 seconds. We also associate contact lens surface deposits, conjunctival injection and coalesced 3 and 9 o'clock staining with dry eye.
Often you can minimize borderline dry eye problems prior to prescribing contact lenses. Teach partial blinkers to concentrate on a more complete blink process, and establish good lid hygiene to resolve conditions such as Meibomian gland dysfunction or blepharitis.
CHOOSE THE RIGHT MATERIAL
Always consider RGP lenses first for borderline dry eye patients. A deficient or unstable tear film requires high oxygen permeability, low surface reactivity, and a lens that moves adequately to minimize the risk of complications such as giant papillary conjunctivitis and ulcerative keratitis.
Clinical studies have shown that fluorosilicone acrylate lens materials maintain the tear film mucin longer than silicone acrylate lens materials. This is important because, if the tear film dries out quickly after the blink, there is a potential for a thick mucus-like film to develop on the lens surface, and 3 and 9 o'clock staining from the drying of the peripheral cornea. I've always preferred the low Dk F-S/A (i.e., 25-50) materials although more stable, high Dk materials with better wettability are forthcoming.
DESIGN, FITTING RELATIONSHIP, WETTABILITY
Studies have shown that an optimum fit facilitates better wetting and smooth movement of the contact lens across the ocular surface, resulting in adequate wetting of the corneal periphery. A lens that exhibits excessive vertical movement can compromise the quality of the blink response and result in increased staining. Good centration via the appropriate use of lenticulars complemented by a thin lens design will assist in this process.
Fluorescein evaluation is imperative to ensure an alignment or near-alignment fitting relationship and adequate peripheral clearance. A bitoric lens on a cornea with greater than or equal to 2.50D of corneal astigmatism will minimize the excessive vertical peripheral clearance which could otherwise impede a normal blink. Likewise, a smooth, rounded edge is important for a normal blink response in a borderline dry eye patient. La Hood has shown that the anterior section of the edge is particularly important. Finally, the application of well-blended peripheral curves facilitates tear exchange and debris removal.
Maintaining good surface wettability is also desirable in borderline dry eye. Some lens materials are more prone to poor initial wettability. Clean these lenses with a laboratory cleaner or solvent followed by a pre-soak in the recommended wetting/soaking solution before dispensing. Instruct patients to clean their lenses thoroughly in the palm of the hand every night and then soak them overnight. Likewise, weekly enzymatic cleaning is mandatory for these patients.
Tear supplements or rewetting drops, if used liberally, may be helpful although they're usually more useful with soft lenses.
A TIME FOR HYDROGELS
Should every borderline dry eye patient wear RGPs? Obviously not. For patients who desire occasional wear or eye color change, or who are very motivated to wear soft lenses and have no history of ocular compromise, soft lenses are a viable option. Some borderline dry eye patients may be unable to adapt to RGPs due to dryness or lens awareness and might benefit from the ability to rehydrate soft lenses with rewetting drops or a midday 10-minute saline soak. However, these patients, especially hyperopes, should be limited to daily wear, and should be monitored carefully. Disposable lenses can be very advantageous in these cases.
When prescribing contact lenses for the borderline dry eye patient, make RGPs your first option. The larger diameter, more comfortable designs complemented by more uniform peripheral designs will enhance surface wettability and subjective patient response. Likewise, advances in manufacturing technology will result in improved lens edge and surface quality of RGP contact lenses. CLS
Dr. Bennett is an associate professor of optometry at the University of
Missouri-St. Louis; he is executive director of the RGP Lens Institute.