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THE HUMAN LENS can change its shape, becoming more spherical as the ciliary muscle contracts to focus the image of close objects on the retina. Each year about 1 million Americans have cataract surgery, 90% of them having their lens replaced by an intraocular prosthesis. Most artificial lenses now in use focus the image of distant objects.
However, a lens that focuses near objects as well is being developed, according to Richard Keates, MD, professor of ophthalmology, The Ohio State University, Columbus. The lens has concentric optics, with the central one focusing near objects, and the circumferential one focusing far objects.
Consequently, two images are projected onto the retina. If the optics have a difference of at least 3 diopters, the images are dissimilar enough for the brain to interpret them separately. The sharper image is selected and the more blurred image is suppressed.
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Olson CM. Artificial Lenses Under Development to Focus on Near, as Well as More Distant, Objects. JAMA. 1989;261(5):678. doi:10.1001/jama.1989.03420050020006
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