Contact lens is a device used to correct vision. Contact lenses are most commonly used to correct myopia (nearsightedness) and hyperopia (farsightedness). The lenses can be made of hard or soft plastic. They float on a thin layer of tears on the surface of the cornea (clear front surface of the eyeball). Contact lenses are curved to focus light rays on the retina. When the light rays are properly focused, a person sees clear images of normal size. Contact lenses provide more natural vision than glasses because they also allow normal side vision.
Most people who wear contact lenses instead of glasses do so to look better and to feel more confident. Athletes and other active people like contact lenses because the lenses are less obstructive than glasses.
Hard contact lenses
came into use in the early 1950’s. They are made of rigid plastic and are relatively easy to clean and sterilize. Hard contact lenses that allow oxygen to pass through to the eye are called gas permeable contact lenses. These lenses are produced from special plastic. For many wearers, gas permeable contact lenses are more comfortable than normal hard contact lenses. Hard contact lenses are useful in correcting such eye disorders as keratoconus and astigmatism. These are conditions caused by a misshapen cornea.
Soft contact lenses
originated in the early 1970’s. They are softer and larger than hard contact lenses. Soft contact lenses absorb moisture and contain water. This composition enables the lenses to bend easily and makes them more comfortable than hard contact lenses. Originally it was necessary to remove soft contact lenses from the eye once a day. Now a type of soft contact lenses called extended-wear contact lenses can be worn on the eye without removal for up to seven days.
Soft contact lenses are more likely to cause infection than other types of contact lenses because impurities or bacteria may get into the water in the lenses. To avoid infection, wearers of soft contact lenses must regularly and thoroughly clean them in a special solution and sterilize them. Contact lenses called disposable contact lenses can be worn for a day or a week and then discarded and replaced with new ones. Other types can be worn for 30 days. These lenses do not require cleaning or sterilizing.
Special types of contact lenses
have been developed for unique needs. People with normal vision who want to change the color of their eyes may buy contact lenses that come in different colors and that do not alter vision. Some soft contact lenses are used to treat diseases. They contain medicine that is gradually released to the eye.
Both hard and soft contact lenses have been developed for use as bifocal contact lenses. These lenses are designed to help people who have trouble seeing both at a distance and close up. They are made to replace bifocal glasses. Wearers look through one part of the lenses to see in the distance and through another part to see close up. The success rate of bifocal contact lenses remains limited for various reasons.
Monovision contact lenses offer another way to correct a problem with near and distant vision. A wearer uses a lens in one eye for close vision and one in the other eye for distant vision. Monovision lenses allow only one eye to be used at a time, and wearers sacrifice some depth perception.
