Article Date: 6/1/2007

Improving Ocular Health and Comfort With Silicone Hydrogel Contact Lenses
CONTINUING EDUCATION

Improving Ocular Health and Comfort With Silicone Hydrogel Contact Lenses

Experts discuss the attributes of various lens materials and the tools used to measure lens wettability in the laboratory and in practice.

PERFECTING LENS CHOICES

Lens Surface Wettability And Comfort — Keys to Lens Wear Success

Put your patient's experience with the new softer, wettable lenses at the top of your priority list.

By Milton M. Hom, OD, FAAO

Health and comfort — the two primary reasons we switch patients to silicone hydrogel contact lenses — are also the top goals of contact lens manufacturers. They enhance these qualities through advances in technology. How can we determine which silicone hydrogel lens will work best for each patient? One technique is to use your slit lamp and assess lens-tear film interaction. As you become familiar with this observation, you will realize that very rapid tear film thinning is associated with drying symptoms.

In this article, I will discuss some of the key features of silicone hydrogel lenses that factor into improved comfort for patients.

MAXIMIZING THE OUTCOME

Silicone hydrogel contact lenses tend to be hydrophobic. Manufacturers deal with this in several ways: Bausch & Lomb has developed a lens with silicate islands to retain wettability; CIBA Vision gave its lenses (O2Optix) a plasma treatment that forms a coating; Vistakon created a lens with polyvinyl pyrrolidone (Acuvue Advance, Acuvue Oasys); and CooperVision designed a lens with comfilcon A (Biofinity), which also has an inherently wettable material. Comfilcon A does not require a surface treatment. Made with a naturally wettable material, the lens has a higher water content and higher Dk (160 Dk), setting it apart from other lenses on the market.

Silicone hydrogels also vary in modulus. An etafilcon A lens (Acuvue) has about 55% water and a low modulus, whereas crofilcon A (CSI) has 38% water and a higher modulus. The original silicone hydrogels have an even higher modulus. Comfilcon A lenses have a significantly higher water content of 48% and a modulus lower than crofilcon but slightly higher than etafilcon. Silicone hydrogels have a higher Dk, in general. But the higher Dk, higher water content and lower modulus of comfilcon A indicate that the lens is a significantly softer material than other silicone hydrogel choices. We're seeing the technology counter-balance the hydrophobic nature of silicone hydrogel lenses, which may maximize our patients' chances of having moist, comfortable eyes.

TESTING NEW MATERIALS

With all the advantages of comfilcon A in terms of its wettability and softness, how does it measure up in surface wetting? The manufacturer used specular reflection to compare the wettability of various prototypes of the lens and arrived at the product we have today. Clinically, we see that patients are more comfortable with this lens and that comfort is associated with a more stable anterior surface tear film.

PINGUECULA IMPROVES

A patient was wearing a higher modulus silicone hydrogel lens that seemed to be inflaming the pinguecula. I refitted her with a comfilcon A (Biofinity) lens. Within days the patient reported she was amazed how the redness resolved and how the whiteness of her eye improved.

Pinqueculas are like volcanos. Sometimes they are dormant and sometimes they erupt. My slit lamp observation of this patient after wearing the lower modulus, more wettable, comfilcon A lens revealed less tissue inflammation, less swelling, and much reduced and nearly eliminated vessel engorgement. We need to be mindful of the health of the conjunctiva as well as the cornea and the limbus when we fit contact lenses as this case reminds us.

THE CLINICAL PICTURE AHEAD

As manufacturers continue to develop healthier, more comfortable lenses, we as clinicians will work on the best ways to measure those characteristics clinically to offer the best lens choices to our patients. CLS

Dr. Hom is in private practice in Southern California. He has published many articles on silicone hydrogel lenses and authored the Manual of Contact Lens Prescribing and Fitting 3e (Butterworth-Heinemann).


Contact Lens Spectrum, Issue: June 2007