Contact lenses are small, thin plastic disks that are designed to rest on the cornea. The cornea is a clear tissue on the front surface of the eye and it is surrounded by the white sclera.
It is estimated that there are more than 30 million contact lens wearers in the U.S.
Contact lenses are mostly used to correct blurry vision caused by nearsightedness, farsightedness, and astigmatism. These are conditions in which images are not focused properly on the retina (a clear sheet of nerve tissue located in the inner back wall of the eye which functions much like the film of a camera) and, therefore, cannot be relayed clearly to the brain).
Contact lenses stick to the tear film that covers the front of the eye, so that each time the eyelid blinks, it passes over the lens and causes it to move slightly. This motion allows fresh tears to flow under the lenses providing necessary lubrication and oxygen to the underlying cornea.
Contact lenses are also used to manage many diseases of the cornea, conjunctiva, or lids. Some common disorders treated with contact lenses include keratoconus (an abnormally cone-shaped cornea), a wound leak after eye surgery, and severe blurry vision, caused by high nearsightedness or astigmatism, that is not correctable with conventional glasses.
Types Of Contact Lenses
The first contact lenses developed in the 1950s were hard plastic lenses that fit over the cornea. Because these lenses did not let adequate oxygen into the eye, there were problems with swelling, redness, blurry vision, and general discomfort. Most eye doctors no longer prescribe them because there are now newer, easier-to-wear lenses available.
The two types of contact lenses most often used today are soft lenses and rigid gas permeable (RGP) lenses.
Soft lenses came on the market in 1970, and now about 80 percent of American contact lens wearers use them. Their "softness" comes from the amount of water that the lenses contain, and they feel pliable rather than hard. Because of its soft texture, people usually find them comfortable right away, and its comfort allows one to wear them for longer periods of time than RGP lenses. They are less likely to pop out during strenuous activity, and it is harder for foreign particles to get behind them than behind rigid lenses.
RGP lenses became available in 1979 and are now used by about 15 percent of contact lens wearers. They are stiffer in feel and appearance than soft lenses. RGP lenses allow at least as much oxygen as do soft lenses. They usually give superior vision (especially when someone has astigmatism or very high nearsightedness and farsightedness) and are easier to care for and usually last much longer than soft lenses.
In addition to these basic lenses, new types have been added over the past several years. One of these is extended wear lenses, either soft or RGP, that can be worn continuously for up to six days. Presently over 4 million people wear them. These lenses can be more convenient, but there are concerns about people overwearing them. Continuous use of extended wear contact lenses can increase one’s risk of corneal abrasion or infection. Infection of the cornea can lead to blindness. If contact lenses are not cleaned as instructed, then the risk of infection increases.
Disposable soft lenses arrived on the market several years ago. These lenses can be worn for up to two weeks and then thrown away. Not only are they convenient, but they do not have much chance to get dirty, which makes them clean and comfortable and eliminates many of the worries about infection that come from extended wear. However, it is still recommended that contact lenses be removed during sleep, because the risk of infection increases with overnight use. Not surprisingly, disposable lenses are more expensive, but if one adds up costs of cleaning supplies and replacements for other types of lenses, the expense may be equivalent.
Tinted soft lenses, which actually can change the appearance of the color of your eyes, have become a hot fashion item. There are several types - some that change the color of light-colored eyes, others that color brown eyes. These lenses tend to be more expensive.
Problems Associated With Contact Lenses
Contact lens wearers can encounter problems with their lenses. A small group may be unable to wear contact lenses at all because of hypersensitivity, difficult optical requirements, or personal hygiene habits.
Lenses can irritate the eye because of dryness due to problems with tear production. Tear production may be inadequate, especially in older individuals.
The most dreaded and potentially blinding risk of contact lens wear is corneal ulceration, or infection. Corneal ulcerations occur more commonly in soft contact lens wearers, because the comfort level of soft contact lenses allow one to wear them for extended periods of time, thus increasing the potential for overnight use. Among the contact lens wearers in the U.S., there are an estimated 12,000 corneal ulcers per year. Factors that contribute to infection included prolonged wear time, poor sanitation and cleaning habits (remember to clear your contact lens cases as well), and dry eye syndrome. Some people will often lubricate their contact lenses with their own saliva, on their tongue, if cleaning supplies are not immediately available, and this is certainly not recommended!
Another common problem that can occur with soft lenses is that people develop sensitivity of the eyes and lids, either to the maintenance solutions or to mucus forming on the lens surface itself. Symptoms include decreased lens movement, increased mucus, and redness of the conjunctiva (the clear tissue overlying the white part of the eye). In order to overcome the these symptoms, the person generally must stop wearing contact lenses for several months and then start again with new lenses and a different type of maintenance solution.
With rigid lenses, abrasion of the cornea can occur because of rapid buildup of wearing time during the adaptation period, particularly with a lens that is not fit correctly. Wearing the contact lens too many hours per day can cause the same problem. Symptoms of corneal abrasions are pain and tearing. With patching and/or antibiotics applied to the eye, symptoms usually improve within 24 hours.
Remember that soft lenses present a greater risk of corneal ulceration due to extended wear time. The risk may be as high as 8 times that of daily wear lenses. Disposable lenses do not overcome the risk of corneal ulceration.
The wearing of contact lenses should be stopped if the eyes become red or infected, if vision is blurred, or if the lenses become uncomfortable. If symptoms do not resolve within a few hours, immediate ophthalmologic care should be sought.
Tips On Care Of Contact Lenses
- Wash your hands with soap before touching your lenses; avoid soaps with eye-irritating beeswax or lanolin.
- Mucus, tear proteins and environmental pollutants can build up on your lenses; ask your eye doctor about the best daily cleaner for your type of lenses.
- Many doctors recommend that you disinfect all lens types daily with a heat, chemical, or hydrogen peroxide system.
- Use an enzymatic cleaner weekly to remove residue your daily cleaner missed.
- Always store your lenses clean; rinse your lens case and let it air dry.
- Buy small, instead of large, containers of lens care products; small containers are more quickly emptied and thus less likely to get contaminated.
- Apply eye make-up after putting your lenses in your eyes.
- Use hair sprays, perfumes, and spray deodorants in another room before you insert lenses.
- Check your eyes every morning for redness or unusual mucus at the edges; pain, watery eyes, sensitivity to light or blurry vision are signals to call the doctor.
- Remove lenses at once when your eyes become red or irritated; always carry your glasses with you.