CONTACT LENSES

A contact lens (also known simply as contacts for a pair) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye.
Types of contact lenses:
Contact lenses are classified in many different manners:
CORRECTIVE
COSMETIC
THERAPEUTIC

MATERIAL:The first contact lenses were made of glass, which caused eye irritation, and were not wearable for extended periods of time. But when William Feinbloom introduced lenses made from polymethyl methacrylate (PMMA or Perspex/Plexiglass), contact lenses became much more convenient. These PMMA lenses are commonly referred to as "hard" lenses (this term is not used for other types of contact lens). 

In 1998, 'silicone hydrogels' became available. Silicone hydrogels have both the extremely high oxygen permeability of silicone and the comfort and clinical performance of the conventional hydrogels.Silicone also makes the lens surface highly hydrophobic and less "wettable."

Extended Wear Contacts Lenses

Silicone Hydrogel Lenses

Silicone is oxygen permeable. Silicone hydrogel lenses use both their water and polymer content to transmit oxygen to the eye.

The benefits to wearers include comfort and convenience. Silicone hydrogel contact lenses contain less water and deliver more oxygen to the eye than traditional hydrogel lenses. As a result, they aren't as prone to causing dehydration. For some people who wear their lenses for long days, this can mean better end-of-day comfort and allow for overnight wear. Some brands of silicone hydrogel lenses are approved for 30 days of continuous wear.

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Tags: Contact lens