25th Anniversary Perspective
The Last 25 Years of Soft Lenses
By Brien Holden, PhD, DSc, OAM, FAAO & Desmond Fonn, MOptom, FAAO
It's fair to say that soft contact lenses have provided the lifeblood for Contact Lens Spectrum's (CLS) 25 years of existence, and 25 years of CLS is a significant milestone—let's toast that!
Early Soft Lens Development
However, 2010 marked the 50th anniversary of the invention of hydrophilic materials by Otto Wichterle. Next year will be the 50th anniversary of the first soft contact lens made in Otto Wichterle's garage in Prague, Czechoslovakia.
But it wasn't until 40 years ago (1970) that the first soft contact lenses came to market. It took Otto many years to convince people that something that soft could correct vision. But once people experienced the comfort of soft lenses compared to hard, the industry came alive.
Fast tracking through the first 25 years, a real boon to the industry was the excitement of so many more people being able to wear soft contact lenses. Like rigid lenses, these had to be disinfected and cleaned with what we would consider primitive systems, although hydrogen peroxide has stood the test of time.
It didn't take long for astute observers and then researchers to document the shortcomings of hydrogel lenses. They were expensive and thus had to last a long time. “Disturbing” was one way to describe the appearance of old, deposited, discolored lenses and their effects on the ocular surfaces then, and corneal hypoxia became commonplace. In the '80s, scientists and the industry started looking for ways to solve the problems of complications.
A Look at the Last 25 Years
Now for the highlights and low-lights of soft contact lenses over the last 25 years.
Oxygen Transmission In the '70s, everyone thought that these water-bearing lenses supplied all the oxygen the eye needed. But Bailey and Carney (1973) through pachymetry, Sarver and Polse (1975) and others through slit lamp observation, and Weissman et al (1984) through infections cast doubt on this assumption.
Early '80s measurement techniques were adapted to characterize the oxygen performance of hydrogel contact lenses. A critical oxygen transmission of 24 barrers for daily wear and 87 barrers for extended wear to eliminate corneal edema set the goals for the next generation of lenses.
Around the same time that hydrogel lenses were developed, pure silicone soft lenses were manufactured. These lenses demonstrated how limited hydrogel lens oxygen transmission was despite maximized water content or reduced thickness of low-water hydrogel lenses. If sufficiently high oxygen permeability was available, we could eliminate the chronic hypoxic problems that were endemic with soft lens wear.
Extended Wear The United Kingdom led the way in extended wear in the '70s, claiming impressive results with high-water soft lenses. The modality became fairly popular in the United States as a result of the FDA approval of extended wear in the early '80s. Reports of complications and particularly microbial keratitis influenced the FDA to change this from 30-night approval to six-night approval in the late '80s.
However, the FDA decided to approve silicone hydrogel (SiHy) lenses for 30 nights of continuous wear in 2001.
Disposable Lenses A strong association between soiled lenses and ocular complications in early soft lenses became well established. Rigorous cleaning materials and procedures to prevent deposition didn't work because patients were not compliant.
The technology of mass production drastically reduced the cost of lenses and led to frequent replacement and disposable lenses. The introduction of frequent replacement lenses in the mid-1980s offered hope that these would reduce the rate of corneal infections with extended wear, but they didn't.
In the last five years, daily disposable lenses have become very popular in many markets with an unquestionable reduction in ocular surface complications that were commonplace with conventional (non-disposable) lenses.
Lenses that were thin, low-modulus, easy-to-fit, forgiving, initially very comfortable, and mass produced at substantially reduced cost changed the perception for some people of what a contact lens is, specifically moving away from the medical device and toward a commodity. This has been fuelled to a great degree by lens availability through such sources as the Internet. A convenience and cost-saving perception for some, a concern for others.
Silicone Hydrogels The development of an innovative cycle of chemistry and physics based on physiological requirements in the 1990s led to the development of the first highly oxygen permeable SiHy lens, which was arguably the most significant contact lens development in the last 25 years. With hypoxia-free wear for almost everybody, even during extended wear, a major milestone was reached. When SiHy lenses became available in 2000, they created a revolution.
SiHy lenses have continued to evolve from the initial stiffer, less comfortable lenses of immense oxygen transmissibility to more hydrophilic and flexible newer versions. This product category has taken the lion's share of the market in the developed world.
Soft Torics and Multifocals Excellent designs, engineering sophistication, and manufacturing precision have undoubtedly improved the success of toric soft lens wear to near appropriate levels commensurate with the percentage of astigmats seeking contact lenses. Also, this year the annual survey of contact lens prescribing reported that multifocals account for 75 percent of the lenses prescribed for presbyopic wearers, compared to monovision at 25 percent.
Contact Lens Care
Remember salt tablets dissolved in distilled water and heat disinfection? Then there were chemically preserved disinfection solutions with chlorhexidine and thimerosal that sometimes caused nasty ocular reactions.
Although clumsy, hydrogen peroxide became the method of choice and has had a resurgence in the last five years because the system is effective at cleaning and disinfection. Multipurpose solutions, however, have “ruled the roost” because of “one step” simplicity and convenience for patients. But—SiHy contact lenses in the last 10 years have made us rethink multipurpose solutions because their interaction with these lenses may lead to ocular side effects.
Dreaded Dropouts and Adverse Events
The industry has been plagued by two major issues. One is end-of-day discomfort. Surveys in the last 10 years suggest that the annual dropout rate is globally around 15 percent, with discomfort the predominant reason. This is an alarming statistic: 125 million wearers and 125 million dropouts. It is hard to think of another healthcare product with such a record. Although there have been attempts to improve contact lens comfort and reduce dryness, the industry has been reluctant to spend the funds to really understand the nature of the discomfort.
The second problem has been adverse effects and infections. Even today, a 1-in-10,000 microbial keratitis rate means more than 12,000 infections per year worldwide. These two problems—end-of-day discomfort and adverse events/infections—must be solved as we move forward into the 2020 era. And they can only be solved by a concerted effort of greater understanding of the fundamental mechanisms.
Myopia is an epidemic. It is estimated that 42 percent of the U.S. adult population is myopic and that by 2020 there will be 2.5 billion myopes on the planet if no preventive treatment is instituted. If, as the early results of myopia-control soft lenses based on Dr. Earl Smith's hypothesis (2006) indicate, we can reduce myopia progression after one year in children who have myopic parents by 50 percent, these new lens designs will revolutionize the field. We will change from practitioners who correct vision to practitioners who control vision.
If this does occur, then contact lenses will need to step up and be extremely safe and effective. The potential of a five- to 10-fold increase in the number of lens wearers is not unreasonable if myopia-control, comfortable, relatively risk-free contact lenses are developed. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #184.
Brien Holden is professor of the University of New South Wales, CEO of the Brien Holden Vision Institute (formerly the Institute for Eye Research), and CEO of the Vision Cooperative Research Centre. He is also CEO and president, Adventus Technology Inc. He has received research funding from Ciba, Allergan, and Alcon and has proprietary interest in a product from Ciba. Desmond Fonn is professor emeritus and the founding director of the Centre for Contact Lens Research at the School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. He is a Diplomate in the Cornea and Contact Lenses Section of the American Academy of Optometry and currently serves as editor-in-chief of Eye and Contact Lens.