Vision is the learned ability to see for information and performance; it allows us to understand things that we cannot touch, taste, smell or hear. 20/20 vision does not mean perfect eyesight. 20/20 vision simply means that at a 20 ft. distance a person is able to see a certain letter than an average eye should be able to see at that distance. You can have 20/20 vision and lack the abilities to use your two eyes together as a team, to judge distances, to identify colors and to coordinate your eyes with hand and body movements. About four in ten people have "perfect" vision. There are also various eye disorders associated with eyesight such as astigmatism, farsightedness, and nearsightedness. Astigmatism is a condition in which vision at all distances may be blurred or distorted. An irregularly shaped cornea, causing light images to focus on two separate points in the eye, characterizes this condition. When the front of the eye is more oval than round, light does not focus properly on the back of the eye, also known as the retina. Astigmatism is not a disease, but is actually a vision condition that is quite common--only moderate to highly astigmatic eyes need corrective lenses. The signs and symptoms of severe astigmatism are blurred or distorted vision. For mild astigmatism the symptoms are headaches, eyestrain, fatigue, and blurred vision at certain angles. The causes of astigmatism are unclear. It may be genetically inherited or may result from various environmental factors such as poor lighting, incorrect posture, or an increased use of the eyes for close work.
Another eye disorder is farsightedness, also known as hyperopia. With this disorder, objects are seen clearly far away but are blurry close up. The eyeball is too short for the lens to focus a clear image on the retina. More than half of all people who wear glasses are farsighted. The signs and symptoms of farsightedness are aching or burning eyes, suffering from eyestrain,...
Please join StudyMode to read the full document