Contact Lenses
Modern contact lenses are thin corrective pieces of eyewear made of plastic. Because they float on a thin film of tears and cover the cornea--the transparent tissue covering the pupil and the iris--they offer the benefits of near invisibility, unimpaired side vision, and ease of wear.
The first contact lenses were made by Adolf Fick in 1887 for the purpose of correcting irregular astigmatism. Like eyeglasses, they were comprised of glass. In 1912, Carl Zeiss (1816-1888) also designed glass lenses. Then, in 1938, Obrig and Muller developed the first hard plastic lenses ( scleral, or haptic, lenses that virtually covered the front of the eyeball). Although optically inferior to glass, plastic proved considerably lighter and more comfortable to wear. Such contact lenses were prevalent until the 1950s; they required an impression of the eyeball to mold the lenses.
In 1948, Kevin Touhy designed plasticcorneallenses, which were decidedly smaller than scleral lenses and allowed for increased circulation of tears and oxygen. The development of the keratometer, which takes measurements of the cornea reflected from a light source, eliminated the need for eyeball impressions.
Bifocal contact lenses were first produced in 1958. In 1971, soft or hydrophilic lenses --made from a water-absorbent plastic gel--were developed. Although more comfortable to wear than hard-plastic lenses (though gas\-permeable hard lenses have been offered as a compromise), soft lenses are subject to easy damage and must be sterilized before each insertion to avoid any bacterial infection.
Despite their widespread use for cosmetic reasons, contact lenses do offer some medical advantages over eyeglasses. For example, contacts are more effective for restoring sight in people who have had cataracts surgically removed. Contacts are also effective when the refracting ability of each eye is different and are used successfully on people with keratoconus, a condition that causes the cornea to bulge at its center and cannot be corrected by ordinary glasses. However, contact lenses cannot be used by everyone and often are not recommended for patients with chronic glaucoma, diabetes, allergies, or eye inflammations.
Contacts can be made in different colors and can be shaded as sunglasses. In addition, they can incorporate magnifying lenses to help people read small print. Because of their popularity, advances continue to be made in developing new types of contact lenses. Recent advances included extended-wear lenses, which may be worn for several days before cleaning, and disposable lenses, which can be safely worn for up to one week without removing.
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