Maximizing Comfort With RGPs

BY THOMAS G. QUINN, O.D., M.S.
MAR. 1997

Rigid gas permeable lenses are often well suited for visual correction of the astigmatic patient. However, their ultimate success often lies in your ability to fit a lens that meets the patient's comfort requirements. Here are some strategies I've found helpful in maximizing patient comfort with RGPs.

PSYCHOLOGY

How you and your staff present RGPs can have a significant impact on how patients perceive them. In our office, we refer to RGPs as "gas permeable" lenses, omitting the possible negative association with the word "rigid." Provide realistic expectations, such as in telling the patient, "you will notice some awareness of the lens initially, which will subside," and stress the optical, physiological and durability benefits.

FITTING

Fit big and slightly flat. If the upper lid covers the upper aspect of the cornea, a lid attachment approach will be most comfortable. This minimizes the need for the upper lid to blink over the apex of the lens, which is what promotes lens awareness in the unadapted patient. If the upper lid lies above the upper limbus, fit the lens interpalpebrally.

EDGE DESIGN

Proper edge design is critical for comfort. An edge thickness of approximately 0.09mm and an apex that is centered or slightly posterior is ideal. A tricurve lens design uses a tertiary curve to manipulate edge thickness. Some studies suggest that a three-to-one, secondary-to-tertiary curve width ratio is best.

Strive for an axial edge lift of 0.08mm. Edge lift less than this may promote lens binding or peripheral chafing, possibly leading to vascularized limbal keratitis. Excessive lift may promote poor lens positioning or 3 and 9 o'clock staining.

Use a CN bevel or lenticulation to achieve proper edge thickness. A CN bevel is created when a 90-degree diamond tool is used to remove excessive edge thickness from the anterior lens surface. While often effective, this modification may form an abrupt anterior surface junction, creating lens awareness during the blink (Fig. 1).

FIG. 1: CN BEVEL.

Lenticulation involves using a lathe to cut a known curvature on the peripheral anterior lens surface. This allows for a smooth, regular change in peripheral geometry. Some labs charge an additional fee for lenticulation, but the enhanced comfort that a regular or plus carrier lenticular design provides for myopic lenses of -4.00D and above is well worth the cost. For hyperopic designs of +1.00D and up, a regular or minus carrier lenticular design can reduce center thickness and minimize excessive lens dropping. Smooth blending of the posterior surface curves can enhance comfort.

MATERIAL SELECTION

I begin with a fluorosilicone acrylate material, which tends to be more wettable than silicone acrylate. A lens material in the permeability range of 30 is a generally a good daily wear workhorse lens because it's usually stable and wettable. If a high power or prismatic design is needed, increase the Dk to minimize the likelihood of corneal hypoxia.

PREDISPENSING PREPARATION

Following inspection and prior to dispensing, clean all RGPs with lab cleaner and soak them for a minimum of four hours. Any lab residue on the lens surface can affect wetting, which may reduce comfort or blur vision (Fig. 2). Soaking the lens provides a more hydrophilic surface when placed on the eye. CLS

FIG. 2: POOR SURFACE WETTING.

References are available upon written request to the editors at Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #22.

Dr. Quinn has served as a faculty member and research associate at The Ohio State University College of Optometry. He is in group practice in Athens, Ohio.