Contact Lenses

Definition

Contact lenses are small, light-weight plastic devices worn on the eye that correct refractive errors in vision. While they appear to be worn in direct contact with the cornea, they actually float on a layer of tears that separates them from the cornea.

Purpose

Contact lenses correct or improve the vision of people with nearsightedness (myopia), farsightedness (hyperopia), presbyopia, and astigmatism. In recent years, some people also wear contact lenses not for medical reasons, but rather to change their eye color.

Precautions

People allergic to certain plastics should not wear contact lenses manufactured from that type of material.

Patients with dry eye or severe seasonal allergies may find contact lenses uncomfortable and may prefer eye glasses. A careful patient history needs to be taken by the physician or contact lens technician to make sure these problems are addressed.

Eye care professionals should ensure that contact lens patients who have disposable or planned replacement lenses keep strictly to their replacement schedules. Contact lenses wear out over time and can damage patients' eyes. Deposits also can build up on the lenses, leading to lid and eye infections.

Patients who have lenses they can sleep in (extended wear lenses) also are advised not to keep their contact lenses in their eyes for longer periods than directed by their physician. Adherence to the schedules recommended by their physicians helps patients avoid infection and long-term damage to the cornea.

People employed in certain occupations may be prohibited from wearing contact lenses, or may be required to wear safety eyewear over the contact lenses. Physicians and employers should be consulted for recommendations.

Description

Ophthalmologists (M.D.s) or optometrists (O.D.s) dispense contact lenses. The prices for lenses vary for the different types. Some physicians offer a "global fee" to their patients that includes the contact lens fitting, lenses, and follow-up visits.

Over 32 million people in the United States wear contact lenses. These lenses provide a field of view unobstructed by eyeglass frames. They do not fog-up or get splattered and are less noticeable than any eyeglass style. On the other hand, they take time to get accustomed to; require more measurements for fitting; require many follow-up visits to the eye doctor; can lead to complications such as infections and corneal damage (but only if not cared for properly or replaced as prescribed); and may not correct astigmatism as well as eye glasses.

Originally, hard contact lenses were made of a material called PMMA. Although still available, it is rarely used because it does not allow oxygen to pass through the lens. The more common types of contact lenses are:

• Rigid gas-permeable (RGP) daily-wear lenses are made of plastic that does not absorb water, but does allow oxygen to permeate from the atmosphere to the cornea. (This is important because the cornea has no blood supply and needs to acquire oxygen from the atmosphere through the film of tears that moves beneath the lens.) They must be removed and cleaned each night.
• Rigid gas-permeable (RGP) extended-wear lenses are made from plastic that also does not absorb water and is more permeable to oxygen than the plastic used for daily-wear lenses. They can be worn for up to a week, then cleaned, and reinserted.
• Daily wear soft lenses are made of plastic that is permeable to oxygen and absorbs water; therefore, they are soft and flexible. These lenses must be removed and cleaned each night, and they do not correct all vision problems. Many patients find it easier to become accustomed to soft lenses, but these lenses are more prone to ripping and do not last as long as rigid lenses.
• Extended-wear soft lenses are highly permeable to oxygen, are flexible by virtue of their ability to absorb water, and can usually be worn for up to one week. They do not correct all vision problems.
• Extended-wear disposable lenses are soft lenses worn continually for up to six days and then discarded, with no need for cleaning.
• One type of disposable soft lenses are worn for one day and then discarded by the patient. Doctors believe these lenses reduce the risk of infection due to poor cleaning habits or over-wearing lenses. They can be price prohibitive for some patients at $1 a day.
• Planned-replacement soft lenses are daily wear lenses that are replaced on a regular schedule, most common- ly every two weeks, monthly, or quarterly. They must also be cleaned.

Soft contact lenses come in a variety of materials. High Dk materials provide high oxygen permeability and allow greater comfort for patients. Advances in toric contact lenses also allow individuals with astigmatism to achieve better visual correction from contact lenses with more comfort.

There are also different kinds of RGP and soft multifocal contact lenses available. There are five basic designs and over one hundred brands that offer variations of these designs. The optics of bifocal contact lenses are improving dramatically, as baby boomers move into presbyopia and more research dollars are devoted to this area. Monovision, where one contact lens corrects for distance vision while the other corrects for near vision, also may be an option for presbyopic patients. However, monovision may affect depth perception and may not be appropriate for everyone. Contact lenses also come in a variety of tints. Soft contact lenses are available that can change eye color. Even though such lenses have no prescription, they must still be fitted and checked to ensure that an eye infection does not occur. People should never wear someone else's contact lenses. This can lead to infection or damage to the eye.

Content licensed from:

Author Info: Mary Bekker, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Nursing and Allied Health, 2002

This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.