Types Of Contact Lenses：By Function
May 25, 2008 – 6:48 pmContact lenses are classified in many different manners.
By function
(This article is from wikipedia.com)
Corrective contact lenses
A corrective contact lens is a lens designed to improve vision. In many people, there is a mismatch between the refractive power of the eye and the length of the eye, leading to a refraction error. A contact lens neutralizes this mismatch and allows for correct focusing of light onto the retina. Conditions correctable with contact lenses include near (or short) sightedness (myopia), far (or long) sightedness (hypermetropia), astigmatism and presbyopia. Contact wearers must usually take their contacts out every night or every few days, depending on the brand and style of the contact. Recently there has been renewed interest in orthokeratology, the correction of myopia by deliberate overnight flattening of the cornea, leaving the eye without contact lens or eyeglasses correction during the day.
For those with certain color deficiencies, a red-tinted “X-Chrom” contact lens may be used. Although the lens does not restore normal color vision, it allows some colorblind individuals to distinguish colors better
ChromaGen lenses have been used and these have been shown to have some limitations with vision at night although otherwise producing significant improvements in colour vision.An earlier study showed very significant improvements in colour vision and patient satisfaction
Later work that used these ChromaGen lenses with dyslexics in a randomised, double-blind, placebo controlled trial showed highly significant improvements in reading ability over reading without the lenses This system has been granted FDA approval in the United States, which is reassuring to patients.
Cosmetic contact lenses
A cosmetic contact lens is designed to change the appearance of the eye. These lenses may also correct the vision, but some blurring or obstruction of vision may occur as a result of the color or design. In the United States, the FDA frequently calls non-corrective cosmetic contact lenses decorative contact lenses.
Theatrical contact lenses are a type of cosmetic contact lens that are used primarily in the entertainment industry to make the eye appear pleasing, unusual or unnatural in appearance, most often in horror and zombie movies, where lenses can make one’s eyes appear demonic, cloudy and lifeless, or even to make the pupils of the wearer appear dilated to simulate the natural appearance of the pupils under the influence of various illicit drugs.
Scleral lenses cover the white part of the eye (i.e. sclera) and are used in many theatrical lenses..Due to their size, these lenses are difficult to insert and do not move very well within the eye. They may also hamper the vision as the lens has a small area for the user to see through. As a result they generally cannot be worn for more than 3 hours as they can cause temporary vision disturbances.
Similar lenses have more direct medical applications. For example, some lenses can give the iris an enlarged appearance, or mask defects such as absence (aniridia) or damage (dyscoria) to the iris.
Although many brands of contact lenses are lightly tinted to make them easier to handle, cosmetic lenses worn to change the color of the eye are far less common, accounting for only 3% of contact lens fits in 2004.
Therapeutic contact lenses
Soft lenses are often used in the treatment and management of non-refractive disorders of the eye. A bandage contact lens protects an injured or diseased cornea from the constant rubbing of blinking eyelids thereby allowing it to heal.They are used in the treatment of conditions including bullous keratopathy, dry eyes, corneal ulcers and erosion, keratitis, corneal edema, descemetocele, corneal ectasis, Mooren’s ulcer, anterior corneal dystrophy, and neurotrophic keratoconjunctivitis. Contact lenses that deliver drugs to the eye have also been developed.
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