The ability to detect sound may not be essential for life, but it is a major factor in one's quality of life. Hearing allows a person to fully enjoy a multitude of life experiences and to communicate with others. In fact, hearing is necessary for young children to acquire verbal language skills.
Several million people, both children and adults, may have some degree of hearing loss, ranging from slight hearing impairment to complete deafness. There are many causes of hearing loss, either temporary or permanent. A physician evaluating a patient with hearing loss must explore all of the possibilities.
Causes of Hearing Loss
The human ear is divided into an outer ear with an auditory canal and eardrum (tympanic membrane), a middle ear with three small bones (malleus or hammer, incus or anvil, and stapes or stirrup), and an inner with the seashell-like cochlea connected to the central nervous system. Based on these anatomical sections, hearing loss may result from problems in the outer to middle ear (conductive hearing loss) or within the inner ear and central nervous system (sensorineural hearing loss).
Conductive hearing loss is often caused by trauma or excessive exposure to loud noise, especially for individuals with inherently noisy occupations. Another etiology for acquired conductive hearing loss is middle ear infection (otitis media), one that is frequently noticed in children. Other causes include, but are not limited to, abnormal growth of bone in the middle ear (otosclerosis), certain genetic disorders, and various factors harming a fetus before birth.
Sensorineural hearing loss is frequently caused by aging, also known as presbycusis, in which the cochlea slowly degenerates. Other causes of this type of hearing loss include, but are not limited to, inner ear damage secondary to certain medications (ototoxicity), a tumor along the eighth cranial nerve (acoustic neuroma), and exposure to excess noise.
Assessment of Hearing Loss
The initial evaluation of hearing loss begins with a patient history. A physician asks about the nature of the problem and explores all of the possible causes and risk factors. In addition, the physician examines the ear for any abnormal signs that could further pinpoint the cause.
Further examination may entail the use of a tuning fork to perform two tests. One is the Weber test in which the vibrating fork is placed on top of the patient's head to see if the patient perceives a unilateral difference in sound. The other is the Rinne test, which involves assessing sound conduction through bone and air. The results of the Weber and Rinne test determine what type of hearing loss is present and which ear is involved.
Another means of evaluating hearing loss is audiometry. Performed by an audiologist, this test presents multiple sounds at different frequencies through air and bone for each ear. Hearing loss is detected when the minimum frequency required to hear noise (auditory threshold) is significantly higher than normal.
Treatment of Hearing Loss
In some cases, hearing loss can be fully or partially corrected by addressing the underlying cause, such as cessation of ototoxic medications and surgery for acoustic neuroma. Otherwise, patients would cope with the hearing impairment in various ways, including nonauditory means of communication, environmental modification to ease certain situations, hearing aids, and cochlear implants. For every individual, regardless of hearing ability, prevention by minimizing loud noise is very important.
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