| The Columbia Encyclopedia, Sixth Edition. 2001-07. |
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| farsightedness |
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| or hyperopia, condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the retina of the eye rather than upon it, either because the eyeball is too short or because the refractive power of the lens is too weak. Presbyopia, a similarly faulty vision, is attributable to physiological changes in the lens brought on by age. Corrective eyeglasses with convex lenses compensate for the refractive errors. |
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| | | The Columbia Encyclopedia, Sixth Edition. Copyright © 2007 Columbia University Press. |
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