From glass shells to plastic
The first contact lenses were made of glass in the 1880s. Glass lenses were heavy and uncomfortable, and most people could wear them only for a short time. The turn to plastic in the 1930s and 1940s changed that. Poly(methyl methacrylate), usually shortened to PMMA and sold under names such as Plexiglas, was a clear, light and easily shaped acrylic that had been developed for uses such as aircraft canopies. Its optical qualities and ease of molding suited it for lenses.
By the late 1930s, makers were using PMMA for scleral lenses, which covered the white of the eye as well as the cornea. A major step came in the late 1940s, when the American optician Kevin Tuohy developed a smaller plastic lens that covered only the cornea. These corneal lenses were lighter and could be worn for longer. They still had problems, because PMMA does not allow oxygen to pass through it, and the cornea gets its oxygen from the air through the tear film. A lens that fitted poorly could cause discomfort and, in some cases, damage to the corneal surface. Many wearers adapted only slowly and gave up.
A chemist with a different idea
The change from rigid to soft lenses owes much to Czechoslovakia, and to industrial chemistry more than to optics. Otto Wichterle was a chemist who had earlier been involved in the development of Silon in the early 1940s, a Czech nylon-type material and one of the synthetic fibers of its day. By the 1950s he was working at the Institute of Macromolecular Chemistry in Prague with his colleague Drahoslav Lím on gels that could hold water and still be clear and strong.
Their material was a hydrogel based on a compound called hydroxyethyl methacrylate, or HEMA. A hydrogel absorbs water and becomes soft and flexible, and because the water in it carries dissolved oxygen, it lets oxygen reach the cornea much more readily than rigid PMMA. The first report of the material appeared around 1960. Wichterle recognized that it might suit contact lenses.
Spin casting
Making a soft lens that held the right curved shape was difficult. According to the widely told story, in 1961 Wichterle built a spin-casting device at home in his own living space from parts of a children’s building set, a bicycle dynamo and other simple things, and used it to make his first lenses. Liquid plastic was placed in a rotating mold and set while spinning, so that centrifugal force shaped the lens. The details of this account are partly legend, but the principle of spin casting became an important method in lens manufacturing.
Political pressure and the Cold War complicated what followed. The patent rights were handled by the Czechoslovak state, which licensed them to a company in the United States, and later to a major lens manufacturer. The inventors themselves did not gain significantly from the commercial success. Wichterle’s role later received international recognition.
Soft lenses reach wearers
In the United States, regulators approved a soft contact lens made of this material in 1971. In the following years, other manufacturers produced their own versions. Compared with rigid lenses, soft lenses were more comfortable from the first day, stayed in place better and were less likely to slip out or trap dust under the edge. This lowered the barrier to adoption, and the number of wearers grew rapidly in the 1970s.
Soft lenses had weaknesses of their own. They could dry out, absorb deposits, and be torn. They did not correct certain visual errors as sharply as rigid lenses, and they needed careful cleaning, since the moist surface could harbor microbes. Eye care professionals, therefore, continued to prescribe different lens types for different needs.
Rigid lenses improve too
Rigid lenses did not disappear. In the 1970s, chemists developed rigid gas-permeable lenses, made of silicone-containing and fluorinated plastics, that allowed oxygen to move through the material. These remain in use for people who need very precise optics, such as some who have an irregular corneal shape. In this period plastics chemistry was progressing fast, in the tradition of earlier materials such as Bakelite plastic, and contact lenses benefited from a growing stock of polymers designed for particular properties.
Disposables and silicone hydrogels
Two further changes shaped how people wear lenses today. First, in the late 1980s the first disposable lenses were introduced, meant to be replaced on a schedule rather than cleaned and reused for a year or more. Regular replacement reduced the build-up of deposits and cut the work of cleaning. The range of schedules later grew to include daily disposables.
Second, in the late 1990s manufacturers released silicone hydrogel lenses, which combine the softness of hydrogels with the high oxygen permeability of silicone. They made longer wear possible for some people. Extended wear, even with these materials, still carries a risk of eye infection, and it is something that eye care professionals advise on individually.
Everyday wear
By the early twenty-first century, many millions of people around the world wore contact lenses, using them for sports, work and appearance, as well as for conditions such as high short-sightedness. Cosmetic and tinted lenses, lenses for astigmatism and lenses with multiple focal zones widened the range. The overall story of soft contact lenses is one of industrial chemistry and design for comfort: gradual improvements in materials, manufacturing and care, more than a single invention.