deafness(redirected from occupational deafness)
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Sensorineural deafness results from damage to the neural receptors of the inner ear (the hair cells, organ of Corti), the nerve pathways to the brain (notably the auditory nerve), or the area of the brain that receives sound information. Deafness of this type is usually permanent. It can be congenital or accompany other birth-related problems such as erythroblastosis fetalis (Rh incompatibility) or anoxia (lack of oxygen during delivery). Before vaccines were available, German measles (rubella) and common measles (rubeola) were leading causes; maternal cytomegalovirus and genital herpes simplex continue to be threats.
Tumors, injury, stroke, toxic substances (e.g., mercury), and certain over-the-counter and prescription drugs (e.g., streptomycin) are additional factors that can affect auditory pathways and the brain and lead to sensorineural deafness. Continued exposure to loud noise, as in certain industries or from loud music (see noise pollution), can result in damage to the inner ear, causing irreversible hearing loss. Presbycusis, or changes in hearing, especially of high frequencies, in adults has long been accepted as inevitable, but study of cultures where the phenomenon does not exist is bringing this into question. The hearing of patients with sensorineural deafness can sometimes be improved if the patient discontinues harmful medications or avoids exposure to loud noise, e.g., by wearing protective earplugs. In some cases, limited hearing has been restored by cochlear implants, tiny devices implanted into the inner ear that translate sound waves into electrical impulses that are then transmitted to the auditory nerve.
Mechanical and Educational Aids
History of Education for the Deaf
See L. DiCarlo, The Deaf (1964); R. V. Harrison, The Biology of Hearing and Deafness (1988); A. P. Freeland, Deafness (1989).
the complete absence of hearing or a degree of diminution of it so that discrimination of speech sounds becomes impossible. Complete deafness is found rarely; in most deaf persons there are remnants of hearing that permit perception of very loud sounds, including also some speech sounds, and sometimes even a few very familiar words and phrases pronounced loudly near the ear (deafness bordering on hardness of hearing).
The cause of deafness is most often a disease process in the inner ear and the auditory nerve, arising either as a complication of a middle-ear infection or as a consequence of certain infectious diseases (cerebrospinal meningitis, influenza, mumps, measles, and scarlet fever). In some cases a progressive diminution of hearing owing to otosclerosis may lead to deafness. Sometimes deafness arises with prolonged action of loud noise and vibration, and also with intoxication by certain substances such as arsenic, mercury, or lead. In prerevolutionary Russia, as a result of poor organization or the absence of protection for laborers, deafness developed especially frequently among boiler-makers and weavers (noisy industries).
Deafness may also be congenital. It may arise under the influence of genetic (hereditary) factors, as a result of the effect of infection on the developing fetus, or as a result of intoxication of the mother’s body. Congenital deafness, as well as deafness acquired in early childhood, deprives the child of the ability to master speech independently. With deafness that develops at a later age, voice modulation changes and pronunciation defects appear, but the speech as a whole does not suffer.
Speech communication of deaf persons with those around them may be significantly facilitated by means of mastering the skills of visual perception of speech (lip reading) and, when there are substantial remnants of hearing, by the use of sound-amplifying devices. Treatment of deafness in most cases is not very effective. In otosclerosis, and also in deafness associated with the aftereffects of inflammatory processes in the middle ear, improvement of hearing is sometimes achieved by surgical treatment. Prophylaxis of deafness consists in prevention and timely treatment of diseases that lead to persistent disruption of hearing. Principally significant in prevention of congenital deafness is pregnancy hygiene. Marriage between congenitally deaf persons is not recommended.
REFERENCETemkin, Ia. S. Glukhota i tugoukhost’. Moscow, 1957.
L. V. NEIMAN