CONTACT LENSES

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

Contact lenses usually serve the same corrective purpose as conventional glasses, but are lightweight and virtually invisible — many commercial lenses are tinted a faint blue to make them more visible when immersed in cleaning and storage solutions. Cosmetic lenses are deliberately coloured for altering the appearance of the eye.

Types of contact lenses

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.

Cosmetic contact lenses - A cosmetic contact lens is designed to change the appearance of the eye. Non-corrective cosmetic contact lenses are also referred to as decorative contact lenses.

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 to deliver drugs to the eye have also been developed.

Complications

Complications due to contact lens wear affect roughly 5% of contact lens wearers each year. Excessive wear of contact lenses, particularly overnight wear, is associated with the most serious safety concerns.

Problems associated with contact lens wear may affect the eyelid, the conjunctiva, the various layers of the cornea, and even the tear film that covers the outer surface of the eye.

Eyelid:
* Ptosis

Conjunctiva:
* Contact dermatitis
* Giant papillary conjunctivitis
* Superior limbic keratoconjunctivitis

Cornea:
* Corneal abrasion
* Corneal erosion
* Corneal ulcer
* Infection and keratitis
* Keratoconus

Source: wikipedia GFDL