Contact lens

A contact lens (also known as a "contact") is a corrective, cosmetic, or sometimes protective lens placed on the cornea of the eye.

Corrective contact lenses

Contact lenses typically correct vision by refracting or bending light to focus on the eye's retina. The specific dioptre that is required to treat the patient's condition can be found with the help of an optometrist and provided by an oculist. The thickness and shape of the contact lens will also vary with the increase in dioptres, and according to the condition that is being treated: Near (or short) sightedness (myopia), far (or long) sightedness (hypermetropia), or astigmatism.

Related Topics:
Dioptre - Optometrist - Oculist - Myopia - Hypermetropia - Astigmatism

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Some contact lenses correct nearsightedness by flattening the cornea. (See main article: Orthokeratology.)

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Extended wear lenses

Extended wear lenses are designed to be worn continuously for 6 or more consecutive nights. Newer materials, such as silicone hydrogels, allow for even longer wear periods up to 30 consecutive nights; these longer-wear lenses are often referred to as continuous wear (CW). Generally, EW lenses are discarded after the specified length of time. These are increasing in popularity owing to their obvious convenience. Such contact lenses are able to be worn for this extended period because of their high oxygen permeability (typically 5-6 times greater than conventional soft lenses), which allows the eye to remain remarkably healthy.

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Extended lens wearers generally have an increased risk for corneal infections and corneal ulcers primarily due to tear film instability and bacterial stagnation.

Related Topics:
Risk - Corneal ulcer

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Toric lenses

People with astigmatism, both myopic (nearsighted) and hypermetropic (farsighted), who have been told they are not suitable for regular contact lenses may be able to use Toric lenses. Toric lenses are made from the same materials as regular contact lenses but have a couple of extra characteristics:

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• They have two powers in them, one for spherical correction and the other for the 'cylinder'.
• They are designed to keep the lens in a stable position regardless of eye movement. Typically, the lens is weighted more at the bottom and is marked by tiny striations so the wearer can insert them in the correct position, or they are designed in such a way that blinking will reset the lens to the correct orientation.