Contact Lenses

Abstract

Contact lenses are small, hemispherical‐shaped optical devices placed in contact with the transparent tissue at the front of the eye called the cornea. The capillary attraction of the liquid tear layer between the contact lens and the cornea and the partial coverage of the lens by the eyelids prevent contact lenses from being dislodged. All contact lenses can be divided according to the wearing modality. There are two types of general categories of contact lenses soft and rigid gas permeable. There are extended wear lenses available for overnight or for up to 30 days. Disposable lenses are to be used once and then discarded. Contact lenses also are divided into the type of vision problem for which they provide optical correction, ie, myopia, hyperopia, presbyopia, sand astigmatism. Contact lenses are manufactured by molding or spin casting. Poly(methyl methacrylate) was the first plastic to be used as a hard lens. Most of today's lenses are made of silicone hydrogels. Tinted lenses are used for cosmetic purposes. Colorants used have to be FDA approved. Contact lens wearers must be aware of the possibility of infection from microbes. Strict cleaning schedules must be followed. Contact lenses are now being investigated for other purposes than vision correction. Disease monitoring, drug delivery, and filtering of light are newer uses.