Encyclopedia - Contact Lenses

When were contact lenses developed?
What types of lenses are available?

Contact lenses are thin, finely crafted plastic discs designed to fit over the cornea (See Anatomy of the Eye) of the eye, usually to correct vision problems caused by refractive error. They are held in place by a natural layer of tears on the surface of the eye. In addition to their obvious cosmetic advantages over eyeglasses, contact lenses provide better peripheral vision and virtually eliminate the image distortion sometimes caused by eyeglasses. Contact lenses are now available for the correction of most vision problems caused by refractive defects of the eye including nearsightedness, farsightedness, astigmatism, and presbyopia.

When were contact lenses developed?

Contact lenses were first described and sketched by Leonardo da Vinci in the early 1500s, and the first workable model - a 1/4-inch-long glass tube filled with water and containing a microscopic lens - was developed and used by Thomas Young in 1801. In 1887, a German glassblower produced the first see-through eye covering, and in 1888 two European researchers simultaneously reported using contact lenses to correct optical defects.

In 1929, Hungarian physician Dr. Joseph Dallos perfected a method of making molds from living eyes. This enabled the manufacture of lenses that, for the first time, conformed to the actual shape of the eye. William Feinbloom, a New York optometrist, made the first American contact lens and also introduced the use of plastic to the manufacturing process. Contact lenses were made an official part of the practice of optometry in 1945 when the American Optometric Association formally recognized contact lens fitting as an integral part of their profession.

The first soft contact lenses were developed in 1960, but weren't generally available to the public until 1971. Toric lenses for astigmatism were approved in 1978 and the first rigid gas permeable (RGP) lenses became available in 1979. The next decade saw many advances including the introduction of tinted lenses, bifocal lenses, daily wear soft lenses, disposable lenses, and extended wear RGP lenses. The 1990s saw more advances including disposable tinted lenses, daily disposable lenses and the first disposable lenses that included protection against ultraviolet sunrays.

What types of lenses are available?

Contact lenses are generally categorized as "hard" lenses or "soft" lenses. As the name implies, hard contact lenses are manufactured from a rigid material, polymethylmethacrylate (PMMA). PMMA is a tough, clear material that was the original plastic used in the development of contact lenses. In modern hard lenses, PMMA is often combined with other plastics to increase the oxygen permeability. These are called rigid gas permeable (RGP) lenses. Soft contact lenses are made from a plastic hydrogel polymer, hydroxyethylmethacrylate (HEMA) and have a high water content.

In addition to being categorized as either "hard" or "soft," contact lenses may also be identified by their "wearing" characteristics (extended wear, daily wear, disposable, etc.) and according to the type of prescription (toric, aspheric, bifocal, etc.). The following descriptions are those generally used by the ophthalmic community in describing the various types of contacts lenses.

Daily wear soft lenses
These lenses are made of flexible, soft plastics that allow oxygen to pass through to the eye. They are easy to get used to and comfortable to wear. Because they fit close to the eye and are more difficult to dislodge, they are often recommended for sports. They won't work to correct all vision problems and may not provide the sharp vision required by some wearers. They also require daily removal and cleaning.

Disposable soft lenses
Disposable soft lenses are normally worn for one or two weeks and then discarded. They are easy to get used to and comfortable to wear. Because they fit close to the eye and are more difficult to dislodge, they are often recommended for sports. They won't work to correct all vision problems and may not provide the sharp vision required by some wearers. They also require daily removal and cleaning, but they require less cleaning than daily wear soft lenses.

Daily wear disposable soft lenses
This type of lens is designed to be worn for a single day, discarded at night, and replaced by a new pair in the morning. The big advantages are that no lens care is needed and a fresh pair of lenses is worn every day.

Planned replacement soft lenses
These contact lenses are replaced on a planned schedule, usually every two weeks, monthly, or quarterly. They are available for most prescriptions and require minimal care because they are frequently replaced.

Extended-wear lenses
Either soft or RGP lenses, these can usually be worn for up to 7 days without removal. Because of the continuous wear, more frequent visits to the eye doctor for follow-up care may be required.

Daily wear rigid gas permeable (RGP) lenses
RGP lenses are manufactured from slightly flexible plastics that allow oxygen to pass through. These lenses may provide sharper vision than soft lenses and can be used to correct most vision problems. They are also more durable and easier to care for, but often require a longer adaptation period.

Spherical contact lenses
Soft or hard contact lens that contain a single prescription power.

Aspheric contact lenses
Premium contact lenses for borderline astigmatic patients and for those who are just beginning to develop presbyopia.

Toric contact lenses
Soft or hard contact lenses that contain both a spherical and cylinder component to correct prescriptions that have astigmatism. These lenses may be thicker in one area than another in order to maintain correct orientation on the eye.

Bifocal contact lenses
Like bifocal eyeglasses, bifocal contact lenses are designed to provide sharp vision up close and at a distance. Several different designs are available depending on the specific needs and adaptability of the patient.

Monovision contact lenses
A term sometimes used in a special contact lens fitting technique that is an alternative to bifocal contacts. Using this technique, the eye doctor fits a near vision contact for reading in one eye and a distance vision contact in the other. The technique is very effective for some patients, but does require some adaptation and sometimes results in compromised depth perception.