lensesesOver 140 million people in the United States wear lenseses. People whose eyes have refractive errors do not see clearly without glasses, because the light emitted from the objects they are observing does not come into 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 work by changing the direction of light sfxtheatricalgreysparklecontactlenses so that images come into focus on the retina. The greater the index of refraction of the lens material and the greater the difference in the curvature between the two surfaces of the lens, the greater the change in direction of light that passes through it, and the greater the correction.Lenses can be unifocal, with one correction for all distances, or they can be correct for more than one distance (multifocal). One type of multifocal, the bifocal, has an area of the lens (usually at the bottom) that corrects for nearby objects (about 14 in from the eyes); the remainder of the lens corrects for distant objects (about 20 ft from the eyes).

lensesesOver 140 million people in the United States wear lenseses. People whose eyes have refractive errors do not see clearly without glasses, because the light emitted from the objects they are observing does not come into 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 work by changing the direction of light sfxtheatricalgreysparklecontactlenses so that images come into focus on the retina. The greater the index of refraction of the lens material and the greater the difference in the curvature between the two surfaces of the lens, the greater the change in direction of light that passes through it, and the greater the correction.Lenses can be unifocal, with one correction for all distances, or they can be correct for more than one distance (multifocal). One type of multifocal, the bifocal, has an area of the lens (usually at the bottom) that corrects for nearby objects (about 14 in from the eyes); the remainder of the lens corrects for distant objects (about 20 ft from the eyes).

Simultaneous lenses bring distant and near objects into focus at the same time. The center of the lens corrects distance vision; the outer part corrects near vision. * Segmented lenses correct distance vision in the top half and near vision in the bottom half.Monovision An alternative to bifocal contacts, monovision lenses correct distance vision in one eye and near vision in the other. sfxtheatricalgreysparklecontactlenses Modified monovision allows wearers to put a bifocal lens in one eye and a single-vision lens in the other.Implants Designed for mild nearsightedness, KeraVision Intacs are placed in the periphery of the cornea by an ophthalmic surgeon. Made of polymer, a type of hard plastic, they require no maintenance and can be surgically removed. The outpatient procedure has a 97-percent success rate of 20/40 vision or better.