Properties of Polymer Contact Lenses

Polymer is a general word used to describe the molecules that make up plastics. There are many kinds of polymers which were created to have different characteristics and allow them to perform specific jobs. Polymers that were good enough to be used as contact lenses did not exist until 1930. The first polymer contacts were made in 1950, but the versions we know today were not widely available until the 1960s and 1970s.

Required Qualities

• In order to be effective as a contact lens, the polymer must possess certain characteristics: It needs to be flexible in order to mold properly to the eye and to stay in place during eye movement. It must be light, but tough enough to withstand handling. It has to be easy to care for and easy to manufacture from common materials. It has to be hydrophilic, or water-loving, and let oxygen pass through it to the eye, as well as nonreactive to chemicals. It also has to be transparent and able to refract light properly. No polymer available for contacts can do all of these things perfectly, but they can do all of these things to some degree. Manufacturers are constantly creating new polymers in the quest for the perfect lens.

Moldability and Flexibility

• The ability to mold properly to the eye is essential for comfort, vision correction and placement. Flexibility is what allows the lens to adjust to the shape of the eye and its movement so that it can stay in place on the eye. Soft contacts were a dramatic improvement to hard contacts in this regard. They are also much more comfortable and are easier to adapt to.

Weight and Strength

• Early forms of polymer contacts could only be worn for short periods at a time, eight hours at most, because the weight of the lens would pull at the eye. Vision would get distorted and the lens would become very uncomfortable. However, because these lenses were thicker and heavier, they were very tough. They would not rip or tear like soft contacts during rough handling.

Practicality

• In order to be practical, a lens has to be easy to care for. People generally do not have the patience to go through a long routine in order to maintain their contacts, as evidenced by the popularity of disposable contacts. In order to be of consistent quality and to be affordable, the polymer and the lens have to be easy to manufacture, preferably with existing technology. The use of common materials is important because it allows for the lowest cost and the greatest availability.

Compatibility with the Eye

• The eye needs moisture and a steady supply of oxygen in order to stay healthy. Hard lenses were effective on many levels, but one of their biggest drawbacks was that they did not allow a great deal of oxygen through to the eye, which cut down considerably on the amount of time they could be worn safely. Contacts also need to be able to slough off the proteins, acids and other chemicals produced by the eye in order to ensure consistent clear vision. Chemical buildup would make the lenses cloudy.