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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