VISUAL DEFECTS

Common visual defects so often affect behavior and adjustment that they are usually included in the field of psychology. Most of them are due to a faulty optical mechanism, although some difficulties may be purely functional and emotionally produced.In myopia, or nearsightedness, the eyeball is too long and the image focuses in front of the retina. Objects at ordinary distances appear fuzzy and paper work must be held close to the eye to improve focus. In hyperopia, or farsightedness, the image falls behind the retina since the eyeball is too short for close vision. In this case distant objects are seen distinctly but nearer ones are blurred. Contrary to common opinion, farsighted people do not see any better or farther than others; they see as well as normals at a distance, but less well when objects are close.Myopia and hyperopia can both be corrected by glasses. Slight cases, however, often go uncorrected and can have subtle effects on interests and activities. Since vision is such an important information sense, a child’s comprehension of the world may be seriously hampered by these conditions. He may have trouble learning to read, and will not get enough practice because the task is so difficult, unpleasant and frustrating. He may also have difficulty with sports, may fail to develop self-confidence, and may later choose a vocation that is far below his intelligence level. Because of the importance of good vision, periodic eye examinations are recommended at all ages.Presbyopia, or oldsightedness, can develop from either far- or nearsightedness. With advancing age, the lens becomes hardened, loses elasticity and grows flat and weak. It becomes increasingly difficult to focus on close objects, and the blur point—the point at which print becomes illegible—is more and more distant. The normal blur point distances for type of about the size of the print on this page is 3 inches at age 10, 4 at 20, 5.5 at 30, 8.5 at 40, 15.25 at 50, and 39 or more at 60. Presbyopia is correctible with glasses.Astigmatism is a defect caused by irregularities in the cornea or lens. As a result, vision is clear in one dimension and unfocused in another. Slight astigmatism often goes unnoticed, but may cause visual fatigue after an extensive period of reading. It can be corrected by glasses.Diplopia, or double vision, is most often due to an inherent weakness of the eye muscles. The eye does not receive light from an object on corresponding parts of the two retinas, and two different images are transmitted to the brain. The effect is somewhat like watching a 3-D movie without special glasses. Strabismus, or squint, is a form of diplopia, and is also due to a defect in the eye muscles. If not corrected before age five or six severe emotional difficulties may result. Perception is so blurred and unpleasant that the child may keep one eye continually closed until the condition known as amblyopia develops (dimness or loss of vision not due to discoverable lesions in the eye or optic nerve). Children suffering from strabismus are often taunted by names like “squinty” or “cross-eyes,” and the ridicule affects their social adjustment. Surgical correction can remove this social stigma even when it is too late to restore normal functioning to the unused eye.Double vision may also be caused by disease, various poisons or temporarily by alcohol. Emotional conflict is believed to be responsible in some cases. The excessive use of alcohol or tobacco or overexposure to light may produce amblyopia or a temporary or permanent blind spot, a scotoma. Scotomas are also found in cases of tumor and migraine headache, and may be caused by retinal injury or disease, optic nerve damage, or brain defect