Contact lenses are thin, circular shaped plastic disks that are placed on the cornea. Contact lenses and eyeglasses have the same function that is they both correct several eye conditions. The only difference is that contact lenses are placed inside the eyes. These lenses are use to correct eye conditions such as nearsightedness or myopia, farsightedness or hyperopia and astigmatism. Some lenses have no therapeutic use. They are called cosmetic contact lenses. They are just worn to change the color of the cornea.
There are several types of lenses. The soft ones are made from soft and flexible plastic material combined with water. Water allows oxygen to penetrate the lenses, thus increasing comfort. Because they are flexible, these lenses are easy to place inside the eyes. The following are the forms of soft lenses: daily disposable lenses, extended wear disposable lenses, and toric lenses. Daily disposables carry the least infection risk because they are changed everyday. The extended wear disposables are changed after two to four weeks of use.
Polymethyl methacrylate (PMMA) lenses are hard and rigid, thus very durable. One downside of these lenses is that they do not allow oxygen to pass through, thus they may be uncomfortable to use. A new generation of rigid and hard lens is the gas permeable ones. Gas permeable lenses are made of silicone polymers which permits oxygen to penetrate the cornea.
Bifocal lenses are used for people with presbyopia. Presbyopia is an age-related eye problem. As people grow old, their eyes’ ability to focus properly on near objects will be reduced. Bifocal lenses have both the near prescription and distance prescription in one lens. They may be soft or gas permeable lenses. There are many manufacturers of contact lenses, but the major manufacturers are Acuvue, Bausch & Lomb, Ciba Vision and CooperVision.