Describe the defects that affect the mammalian eye and how they could be corrected.
Short-sightedness (myopia); -A condition where light rays from a distant object are focused in front of the retina; while those from a near object are clearly focused on the retina; -It is caused by an abnormally elongated eyeball; or too much refractive power of the eye lens; it is corrected by wearing concave/diverging lenses; which diverge light rays; or reduce the refractive power of the eye before they reach the eye lens; Long-sightedness (Hypermetropia); -light rays from a near object are not focused by the time they reach the retina; or may be focused behind the retina; while the rays from a distant object are sharply focused; -The defect is caused by an eyeball that is too short; or an elongated/weak lens system (distance between lens and the retina is short/low refractive power); -Corrected by wearing a converging/convex lens; which refracts light