HEARING LOSS

There are two main causes of hearing loss. Conductive hearing loss occurs when sound is not transmitted through the middle ear. Sensory-neural loss is due to faulty nerve cells in the cochlea (inner ear) or in the nerves that transmit cochlear signals to the auditory centers in the brain The two types of hearing loss may occur separately or together in one (unilateral) or both ears (bilateral). All degrees of hearing loss, from slight to total, may occur. Conductive hearing loss can usually be surgically corrected. Sensory-neural hearing loss is likely to be irreversible.

Causes of Hearing Impairment?
Deafness caused during pregnancy or at birth is called congenital deafness. Defects as the foetus develops sometimes produce congenital conductive deafness. Most cases of deafness at birth are sensory-neural and are due to German measles (rubella) affecting the mother in early pregnancy. Rubella may also cause other defects in the baby apart from deafness. Less frequently, other infections or complications of pregnancy and birth may cause deafness. Acquired deafness in children is most often due to fluid forming in the middle ear. This condition can be successfully treated and is due to poor function of the Eustachian tube, a channel that connects the middle ear to the back of the nose to equalize air pressure at the eardrum. The commonest cause of deafness in adults is called presbyacusis. It is due to degeneration of the cochlea (inner ear) as part of the aging process. There are many other causes of acquired deafness and these include wax, injury, infections, rare tumors, some drugs, Meniere’s disease and high noise levels.

Why does Deafness occur?
Rubella deafness occurs either because the mother has not been immunized or has not previously had German measles. If the mother develops rubella in early pregnancy, there is a high risk of deafness occurring in the baby. Aging may contribute to the high frequency tone loss of presbyacusis. Very loud noise in industry or from hobbies, such as pop music or shooting, may also cause a high tone loss (acoustic trauma). The ears should be protected by earplugs or earmuffs when there is exposure to very loud noise over prolonged periods. The trauma of head injury, often from accidents, can cause both types of deafness.

Treatment for Hearing Loss
A doctor will start by removing any wax in the ears. If there is no improvement a referral to a specialist may be considered. The specialist will take a history and carry out an examination. A hearing test (audiogram) and other tests, including blood tests and x-rays or MRI (magnetic resonance imaging) may be done. It may be necessary to have repeated hearing tests. Depending on the results and the type of deafness diagnosed, different treatments may be suggested. For most patients with sensory-neural deafness the main treatment is the provision of a hearing aid. Hearing levels are measured in decibels. If the hearing level is say, 30 decibels (30 dB), then 30% of hearing may have been lost. At this level quiet conversation will be missed. If the hearing loss is 30 decibels or greater, the use of a hearing aid is usually appropriate. Modern hearing aids are much smaller and better than those of years ago. They can be inserted in the ear canal and are hardly visible. The latest digital hearing aids can be programmed (just like a computer) to have virtually any frequency response, and can selectively exclude loud or interfering noise.

Anatomy of the ear