Causes of Hearing Loss
Being deaf is a handicap that afflicts millions of people around the world every year. Hearing loss can result from any number of afflictions that can affect the outer, middle, or inner ear. The range of hearing loss can also vary from mild to severe.
The ear is made up of the outer, middle and inner ear. The outer ear consists of the auricle, the external auditory canal and the lobe. The outer ear helps to funnel sound and noise into the middle ear. The middle ear consists of the eardrum and the three middle ear bones, the Mallues, Incus, and the Stapes. The middle ears primary function is to conduct sound. The inner ear is where sound is interpreted through electrical impulses relayed to brain into understandable sounds that we recognize. (Lucente3-8)
The labyrinth of the inner ear contains the nerve endings of the vestibular nerve–the nerve of equilibrium-and the auditory nerve, which are branches of the vestibulocochlear, or eighth cranial, nerve. The vestibular nerve ends supply the semicircular canals and the otolithic membranes in the vestibule. The auditory nerve supplies the cochlea. Diseases of the labyrinth of the inner ear may affect both the vestibular nerve and the auditory nerve, or they may affect only the auditory nerve, with loss of hearing. (Lucente 6)
The most common causes of inner-ear diseases are congenital nerve deafness, viral infections, and ototoxic drugs. Congenital nerve deafness is a defect of the auditory nerve in the cochlea and may be present at birth or acquired during or soon after birth. Usually both inner ears are affected to a similar degree, and there is a severe impairment of hearing, although in some cases of congenital nerve loss the impairment can be moderate. Many cases of congenital nerve deafness have been caused by the rubella (German measles) virus in the mother during the first three months of her pregnancy. This can happen during a rubella epidemic, even when the mother has no symptoms of the infection. In most cases the vestibular nerve is not affected or is affected to a lesser degree, and in most (but not all) cases the outer and middle ear structures are not affected. A vaccine against the rubella virus made available in 1969 has reduced the number of cases of congenital nerve deafness in developed countries. (Lucente 84-87)
Congenital nerve deafness acquired at or soon after birth may result from insufficient oxygen (anoxia) during a difficult and prolonged delivery or from incompatibility between the baby?s blood and that of its mother. In a few cases congenital nerve deafness is an inherited failure of the cochlea to develop properly. When the hearing loss is severe, speech cannot be acquired without special training. Children afflicted with hearing loss must attend special classes or schools for the severely deaf, where they can be taught lip-reading, speech, and sign language. Electrical hearing aids can be helpful, especially during classes, to use the residual hearing.
Another alternative, although controversial within the deaf community, is a cochlear implant, which is sometimes useful in cases of profound hearing loss. In this operation, an electrode is surgically implanted in the ear to directly stimulate the auditory nerve between the brain and the ear. (www.deaf.com)
Viral infections can cause severe degrees of sensorineural hearing loss in one ear, and sometimes in both, at any age. The Mumps virus is one of the most common causes of severe sensorineural hearing loss in one ear. The measles and influenza viruses are less common. There is no effective medical or surgical treatment to restore hearing impaired by a virus. (Lucente 95)
Ototoxic (harmful to the ear) drugs can cause temporary and sometimes permanent impairment of auditory nerve functions. Certain drugs like aspirin in large enough doses may cause ringing in the ears and then a temporary decrease in hearing that ceases when the person stops taking the drug. Quinine can have a similar effect but may cause permanent impairment of auditory nerve functions in some cases. Certain antibiotics, such as streptomycin and neomycin may cause permanent damage to auditory nerve functions. Susceptibility to auditory nerve damage from ototoxic drugs varies greatly among individuals. In most cases, the vestibular nerve is not affected. Streptomycin affects the vestibular nerve more than it affects the auditory nerve. (Lucente 89)
Skull fractures and concussions from a severe blow on or to the head can impair the functioning of the auditory and vestibular nerves in varying degrees. The greatest hearing loss arises when a fracture of the skull passes through the labyrinth of the inner ear, totally destroying its function.
The effect of noise exposure on one’s hearing depends on the intensity and duration of the noise. The effects may be temporary or permanent. A single exposure to an extremely intense sound, such as an explosion, may produce a severe and permanent loss of hearing. Repeated exposures to sounds in excess of 80 to 90 decibels may cause gradual deterioration of hearing by destroying the hair cells of the inner ear, with possible subsequent degeneration of nerve fibers. The level of noise produced by rock music bands usually exceeds 110 decibels. The noise generated by farm tractors, power mowers, and snowmobiles may reach 100 decibels. In the United States, legislation requires that workers exposed to sound levels greater than 90 decibels for an eight-hour day be provided some form of protection, such as earplugs or earmuffs.
Individuals differ in their susceptibility to hearing loss from noise exposure; because hearing loss typically begins at the higher frequencies of 4,000 to 6,000 hertz, the effects of noise exposure may go unnoticed until the hearing loss spreads to the lower frequencies of 1,000 to 2,000 hertz. Inhalation of carbogen, a mixture of 5 percent carbon dioxide and 95 percent oxygen for twenty minutes will accelerate recovery of hearing if administered within a few hours after excessive noise exposure. (Lucente 90)
Labyrinthitis is the inflammation of the labyrinth of the inner ear. This is caused by infections such as meningitis, syphilis, acute otitis media and mastoiditis, or chronic otitis media and cholesteatoma(A complication of chronic otitis media). (Infomedical) Cholesteatoma can create negative pressure in the middle ear such that a mass consisting of keratin and epidermis is drawn into the middle ear through a perforated eardrum. Cholesteatoma typically erodes the mastoid bone and causes damage the ossicles (three small bones of the middle ear). (Infomercial) Loss of both equilibrium and hearing occurs in the affected ear. Prompt antibiotic treatment sometimes arrests the damage and allows for the possibility of partial recovery of the function of the inner ear.(Infomedical)
An acoustic neuroma is a benign tumor that grows on the auditory nerve near the point where it enters the labyrinth of the inner ear. The tumor causes gradual and progressive loss of auditory and vestibular nerve functions on one side. Eventually the tumor grows out into the brain cavity, causing headaches and paralysis. If it is not removed, blindness and death may result. Fortunately, acoustic neuroma usually can be diagnosed early by magnetic resonance imaging (MRI) and removed before it has serious consequences. (Lucente 151)
M?ni?re’s disease, also called endolymphatic hydrops, is a fairly common disorder of the labyrinth of the inner ear that affects both the vestibular nerve, with resultant attacks of vertigo, and the auditory nerve, with impairment of hearing. It was first described in 1861 by a French physician, Prosper M?ni?re. It is now known that the symptoms are caused by an excess of endolymphatic fluid in the inner ear. The diagnosis is made from the recurring attacks of vertigo, often with nausea and vomiting, impairment of hearing with a distortion of sound in the affected ear that fluctuates in degree, and a sense of fullness or pressure in the ear. The cause of the excess of endolymphatic fluid is not always known, although in many cases it results from defective functioning of the endolymphatic duct and sac, the structures that normally reabsorb endolymphatic fluid from the inner ear. Allergic reactions to certain foods may also cause the disease. The treatment of M?ni?re’s disease is directed toward finding the cause of the excess of endolymphatic fluid in order to control it. If medical treatment does not relieve the repeated attacks of vertigo, surgery may be necessary. (Lucente 150-151)
Presbycusis is the gradual decline of hearing function that results from aging. It is similar to other aging processes because it occurs at different ages and at different rates among the population. As a person ages, there is a gradual loss of cochlear hair cells, resulting in gradually reduced and eventually lost hearing. Hearing is reduced at the highest audible frequencies (around 20,000 hertz) and then progressively for sounds of lower frequencies. Usually the slow diminishing of hearing does not begin until after age 60. The affected individual notices increasing difficulty in hearing sounds of high pitch and in understanding conversation. Correction of a nutritional deficiency of zinc, coenzyme Q10, or possibly vitamin A may stabilize the progressive hearing loss. The physician must make certain that the individual does not have a correctable impairment, such as accumulated earwax, secretory otitis media, or stirrup fixation by otosclerosis, as part of the difficulty. An electrical hearing aid is of limited help to some, while others find that a hearing aid makes voices louder but less clear and therefore is of little help.(Lucente 464-465)
The child born deaf or with a severe hearing impairment cannot acquire speech by the normal process but must attend special classes or a school for the deaf to be taught speech and lip-reading. Most of these children have remnants of the sense of hearing that can be utilized in their schooling by the use of aids to amplify sound. The child with a moderate or mild hearing impairment is able to acquire speech independently but a little more slowly than the child with normal hearing, while speech-correction instruction is usually required to improve diction. Cochlear implants can be considered for children and adults with a total absence of hearing or hearing loss so profound that hearing aids are not helpful. Implants make it possible for a deaf child to develop speech and allow a deaf adult to communicate more effectively. (Www.deaf.com)
Advances in hearing-aid technology have served to increase the proportion of hearing-impaired individuals who can benefit substantially from amplification. Selection of an appropriate hearing aid for individuals with sensorineural (or nerve-type) hearing loss may be difficult and time-consuming. Research has demonstrated repeatedly, however, that the ability of listeners with sensorineural hearing loss to understand speech at conversational levels often can be enhanced significantly by use of an appropriate hearing aid. For those individuals whose hearing loss causes severe distortion of speech, use of a hearing aid in combination with lip-reading may increase the amount of speech the individual can understand through lip-reading alone. On the other hand, selection of a hearing aid is often a simpler matter for listeners with hearing loss of the conductive type. Careful selection is necessary to ensure that maximum understanding of speech is obtainable in noisy environments. The hearing-impaired individual should consult with trained professionals such as audiologists, who are trained in evaluating the benefit derived from the use of a hearing aid.
Lip-reading, which actually entails attentive observation of the entire facial expression rather than the movements of the lips alone, is used even by persons with normal hearing who, in the presence of background noise, need these visual clues to supplement hearing. As hearing begins to be impaired, lip-reading, which might better be termed speech reading, becomes increasingly valuable and important.
The hearing-impaired individual who knows a spoken language can learn lip-reading by careful observation of a speaker of that language. Formal instruction in lip-reading by a teacher individually or in classes is necessary for those hearing-impaired persons who have not acquired knowledge of a spoken language. The greater the loss of hearing, the more essential lip-reading becomes, for which good lighting is essential. The hearing-impaired may also be taught a sign language, such as American Sign Language, as a communications tool.
Speech-correction instruction, needed for the young with serious degrees of impaired hearing, also becomes necessary for the adult who suddenly loses all hearing in both ears. Without the monitoring effect of hearing one’s own voice, speech begins to deteriorate and to acquire the flat, toneless quality of the profoundly deaf.
Deafness was once thought of a disease that would leave the individual as a recluse because of their lacking the ability to communicate with society. Medicine has made great amounts of progress in diagnosing and treating hearing disorders, while other have helped to improve the quality of life for the deaf today through deaf culture.
Turkington, Carol. The Encyclopedia of Deafness and Hearing Disorders. New York: Fact on File, 1992.
National Association for the Deaf