Why do some people need eyeglasses or contact lenses?
Ametropia, also called refractive error, is blurry vision from having nearsightedness, farsightedness, astigmatism, or presbyopia. Ideally, when light rays enter the eye, they intersect on the retinal nerve tissue in the back of the eye. The retina then sends the visual information to the brain for processing into vision. Often, the structures of the eye are imperfect, and the light rays intersect in front of or in back of the retina, causing blurry vision. Eye structures that commonly cause this problem are the curvature of the cornea (the clear dome of the eye), the length of the eye, and the shape of the lens.