(1) Emmetropia—normal. Light focuses on the retina.
(2) Hypertropia—farsighted. Light focuses behind the retina and is corrected with a convex lens.
(3) Myopia—nearsighted. Light focuses in front of the retina and is corrected with a biconcave lens.
(4) Astigmatism. Curvature of the lens is not uniform and is corrected with a cylindric lens.
(5) Presbyopia is a result of loss of the accommodation power of the lens that occurs with aging. The near point (closest point on which one can focus by accommodation of the lens) moves farther from the eye and is corrected with a convex lens.
2. Layers of the retina (Figure 2-3)
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