ANNIVERSARY SECTION - 20th
20 Years and Beyond: A Brief History of Modern Lenses
BY MICHAEL A. WARD, MMSC, FAAO
Bausch & Lomb introduced the first daily wear soft contact lenses in the United States in 1971. In the late '70s and early '80s we investigated aphakic hydrogel extended wear (EW). EW lenses seemed like a miracle, especially for aphakic patients, but we didn't know for how long the eye could tolerate leaving a lens in place three months, six months, one year, two years? We didn't appreciate the oxygen requirements of the cornea, nor the inflammatory response associated with lens deposits (GPC).
EW soft lenses offered great advantages over cataract spectacles. The contact lens industry blossomed. Polymer chemists were creating new soft lens materials with better oxygenation and deposit resistance.
The need for aphakic EW contact lenses diminished as the 1980s progressed and intraocular lenses became mainstream. However, cosmetic EW lenses hit the scene in 1981 and represented a much larger potential market. Unfortunately, a rising incidence of microbial keratitis was recognized as a complication of extended lens wear.
History of Lens Care
Originally heat was the only approved method of contact lens disinfection. It was complicated: Patients first used a separate cleaner to clean the lens, which they then rinsed off with homemade saline (more on that later) before placing the lens and saline into a heating unit (plugged into the wall) for disinfection. Additional weekly cleaning with proteolytic enzyme tablets was necessary for these long-life lenses.
Lens wearers made the homemade saline with salt tablets and distilled water which resulted in increased incidence of bacterial and other infections.
Modern lens care uses all-in-one-bottle technologies: Multipurpose solution products contain surfactant cleaning agents, disinfectants, protein removers and lubricants all in the same bottle for convenience.
The Acuvue (Vistakon) contact lens revolutionized the soft lens market in 1987 by offering an inexpensive, one-week EW disposable lens. This development redefined contact lens life from durable to disposable. Recommended lens replacement schedules now range from daily up to one year, with hopes of decreasing the infectious keratitis rate by replacing lenses more frequently.
In the 1990s lens manufacturing economics allowed the single-use daily disposable lens to hit the market, presenting the safest lens wear modality available.
GP Lens Innovations
Let's not forget the advances in GP materials. PMMA was the only hard lens material we had until the late '60s. Following brief use of CAB material, the silicone acrylate Polycon (Syntex) arrived in the late '70s. Its ease of fitting and thin, gas permeable characteristics revolutionized the GP lens market.
The Polycon lens material had a Dk value of about 12. Today's GP materials range up to 168 Dk, and some have six- and 30-day continuous wear capability. Current laboratory lathes can make virtually any design imaginable.
The most recent development is silicone hydrogel soft lens technologies. These materials offer exceptional gas exchange for both daily and continuous wear. (Did you notice that 'extended' wear became 'continuous' wear? This helps dissociate silicone hydrogel technologies from previous EW problems.) Silicone hydrogel surface chemistries are different from HEMA, offering both new opportunities and new challenges.
The future is bright.
Mr. Ward is an instructor in ophthalmology at Emory University School of Medicine and Director, Emory Contact Lens Service.