SPECIAL
ANNIVERSARY SECTION - 20th
anniversary perspective
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.
Disposable Lenses
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.
Silicone Hydrogels
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.
Contact Lens Spectrum, Issue: June 2006