continuous wear colloquy
Make Silicone Hydrogel Your Soft Lens Material of Choice
BY N. REX GHORMLEY, OD, FAAO

Silicone hydrogels are the fastest growing contact lens category in the United States, but they still account for only five percent of total fits and 13 percent of new fits. Why do so many clinicians still use a low-Dk (25-30) lens as their soft lens of choice?

Healthier Lenses Make Sense

Table 1 shows the currently available silicone hydrogel lenses. Why use a soft lens with low oxygen permeability when you can prescribe a silicone hydrogel lens that provides three to six times more oxygen to the cornea?

The eyecare world is undergoing a transition similar to that of 20 years ago when GP lenses were replacing PMMA lenses. Many practitioners just didn't see the ocular health benefits of the new GP technology -- but once they did, PMMA disappeared from the market.

More O₂ is the Way to Go

Mertz and Holden (1984) found that contact lenses need a Dk/t of 87 to reduce corneal edema to four percent in overnight wear. LaHood (1988) calculated that to reduce corneal edema to 3.2 percent in overnight wear, a contact lens needed a Dk/t of 125. And yet a CIBA Vision study found that 20 percent of our daily wear patients routinely sleep in their lenses! Because of this fact, you should consider fitting more of your patients with hyper-Dk (Dk/t >80) contact lenses for maximum corneal protection.

Silicone hydrogel lenses also reduce corneal health complications. Soloman (1994) found that increased hypoxia causes higher rates of corneal ulcers. Latkovic and Nilsson (1994) stated that hypoxia might decrease the corneal defense mechanism. Ren et al (1999) found decreased Pseudomonas aeruginosa binding with hyper-Dk lenses, and Dwight Cavanagh, MD, PhD, has said, "Hyper-oxygen lens materials should replace all existing contact lenses for daily and continuous wear."

Why is the Jury Still Out?

Clinicians have recommended silicone hydrogel contact lenses for many patients who might otherwise have problems with contact lens wear. Why, then, don't we make them the lens of choice for the majority of our patients?

I predict that HEMA (low Dk) soft contact lenses will become extinct by the end of this decade, following the same path as PMMA contact lenses. All new lens research and development in the soft contact lens industry focuses on silicone hydrogel-based materials.

In the future, we can expect many new silicone hydrogel contact lens polymers, expanded parameters and multifocal contact lenses. In 2006, CooperVision/
Ocular Sciences, Inc. plans to introduce a new silicone hydrogel contact lens. Vistakon is working on another high-Dk silicone hydrogel lens. In addition, I expect CIBA Vision and Bausch & Lomb to bring toric silicone hydrogel contact lenses to the United States next year.

Make the Switch

I suggest that we all "get on the train" now by endorsing this new technology and by prescribing a better contact lens for our patients. You don't want to be left at the station!

Dr. Ghormley is in private practice in St. Louis, MO. He is a past president of the American Academy of Optometry and is a Diplomate of its Cornea & Contact Lens Section.