Compared with conventional soft lenses, the extended-wear lenses offer almost all the same liabilities , as well as a few more. They are the most expensive contact lenses (about six hundred dollars), in part because of the cost of the special lenses but mainly because of the extensive professional follow-up examinations required.
The visual acuity provided by the extended-wear lenses is similar to that of conventional daily-wear soft lenses. So far these lenses are available only for those who are nearsighted and for those who have undergone cataract extraction. They cannot correct significant amounts of astigmatism. However, research is going on in this field. Read the rest of this entry »
Gas-permeable contact lenses are also known as oxygen permeable, semisoft, semihard, semirigid, or flexible lenses. As their names suggest, they are more flexible than conventional hard lenses, but less pliable than soft ones; and they are made from materials that allow oxygen and the waste gas carbon dioxide to pass through them. When the cornea can “breathe,” it experiences no edema (swelling), which causes discomfort, and there is very little distortion of the vision after the lenses are removed (spectacle blur). The eye remains healthier, even when the lenses are worn for long periods of time. Contrast this with conventional hard (PMMA) lenses, which allow virtually no oxygen to pass through them, and with soft lenses, which allow some oxygen to pass through via the tears they absorb (but less oxygen than passes through gas-permeable material via the atmosphere). Read the rest of this entry »
Contact Lenses Care .
