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Originally, ocular and science hard contact were biomedics made of a material called 38 PMMA. Although still available, the more common types of contact are listed below:Rigid gas-permeable (RGP) daily-wear lenses are made of plastic that does not absorb water but allows oxygen to get from the atmosphere to & the cornea. (This is important 55 because the cornea has no blood supply and needs to get its oxygen from the atmosphere through the film of tears that moves beneath the lens.) They must be removed and cleaned each night. Rigid gas-permeable (RGP) extended-wear lenses contact are made from plastic lens that ocular also does not absorb water but is more permeable to oxygen than the plastic used for daily-wear lenses. The science and biomedics lenses Council reports that 26 million Americans wear contact. Among lenses wearers, approximately 80% wear 38 and & and 55 the contact and lens soft type and 18% wear rigid gas-permeable lenses. The Council reports that ocular about 11% of lenses wearers, science approximately 2.8 million people, are under 18.InfantsThere are few instances when corrective lenses--lenseses or contacts--are prescribed for infants. biomedics However, when an infant develops cataracts , a condition known as infantile aphakia, contact 38 may be prescribed following surgery. In & 1993, the Journal of the 55 and contact American Medical Association reported that contact were safe and effective for use with infants following cataract surgery. lens and ocular Routine care of the lenses was easily learned science by the baby''s parents or caregivers. lensesesOver biomedics 140 million people in the United States wear 38 lenseses. People whose eyes have refractive errors do not see & clearly 55 without glasses, because the light emitted from contact the objects they are observing does not lens come into ocular focus on their retinas. For people who are farsighted, images come into focus behind the retina; for people who are nearsighted, images come into focus in front of the retina. Lenses science work by changing the direction of light biomedics so that images come into focus on the retina. The greater the index of refraction of the lens material and the greater 38 the difference in the curvature & between 55 the two surfaces of the lens, the greater the change contact in direction of light that passes through it, and the greater the correction.Lenses lens can be unifocal, with ocular one correction for science all distances, biomedics or they can 38 be correct for more than one distance (multifocal). & and 55 and contact One type of multifocal, the bifocal, has an area of the lens (usually at the bottom) that corrects for nearby objects lens (about 14 in from the eyes); the remainder of the lens corrects for distant objects (about 20 ft from the eyes).
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