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. Its primary function is 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. Its primary function is to conduct sound. The inner ear is where sound is interpreted through electrical impulses relayed to the brain, making it understandable sounds that we recognize.
The labyrinth of the inner ear contains the nerve endings of the vestibular nerve, which is the nerve of equilibrium, and the auditory nerve. These are branches of the vestibulocochlear or eighth cranial nerve. The vestibular nerve ends supply the semicircular canals and the otolithic membranes in the vestibule, while 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 only affect the auditory nerve, resulting in hearing loss. 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, resulting in severe hearing impairment. However, 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 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.
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. www.deaf.com
There is no effective medical or surgical treatment to restore hearing impaired by a virus (Lucente 95). Ototoxic 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 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 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.
