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What Is Hearing Loss?

What Is Hearing Loss?
April 7, 2010 DrPerry

hearing lossHearing loss or hearing impairment is the diminished ability to hear sounds. Degree of impairment can vary widely. Hearing loss can occur suddenly or gradually over time. The Journal of the American Medical Association states that hearing loss is the third most prevalent chronic condition in older Americans. JAMA also reports that the diminished ability to hear and to communicate can cause frustration, depression and functional decline.

To understand hearing loss or impairment we must know how the ear functions. The ear is made up of three sections: the outer, middle and inner ear. The outer ear, or pinna, picks up sounds and then they travel through the outer ear canal. The sound waves hit the eardrum in the middle ear and this causes vibrations. These vibrations move the tiny bones in your middle ear called the hammer (or malleus), anvil (or incus), and stirrup (or stapes). The sound then moves to the inner ear to the cochlea which is filled with liquid and lined with cells that have thousands of tiny hairs on their surfaces. The sound vibrations make the tiny hairs move. The outer hair cells take the sound information, amplify it (make it louder), and tune it. The inner hair cells send the sound information to your hearing nerve, which then sends it to your brain, allowing you to hear sounds.

Sound can be measured by units known as decibels (dB). A drop of more than 10 dB in the level of sound a person can hear is significant. Degrees or severity of hearing loss are known by mild, moderate, severe and profound classifications. Patients’ thresholds are measured by the softest intensity at which sound is perceived. ASHA (American Speech -Language-Hearing Association) guidelines are:

Normal / -10 to 15 dB
Slight / 16 to 25 dB
Mild / 26 to 40 dB
Moderate / 41 to 55 dB
Moderately Severe / 56 to 70 dB
Severe / 71 to 90 dB
Profound / 91+

There are three basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.

Conductive hearing loss involves abnormalities of the middle and external ear and generally have a mechanical cause such as: perforated eardrum, fluid in the middle ear, cerumen accumulation, infection in the ear canal, or benign tumors. Treatment is often surgical.

Sensorineural hearing loss (nerve deafness) accounts for 90% of hearing loss caused by permanent damage to the hair cells of the cochlea. It is related to aging or presbycusis. Other causes are diseases, birth injury, drugs that are toxic to the auditory system, genetic syndromes, noise exposure, viruses, head trauma and tumors. Sensorineural hearing loss is typically gradual, bilateral (both ears) and characterized by high-frequency hearing loss. Patients with this loss have difficulty filtering background noise. Treatment is hearing aids, or cochlear implants for profound loss.

Mixed hearing loss occurs when there is a combination of conductive and sensorineural hearing loss. For instance, there may be damage in the outer or middle ear and in the inner ear or auditory nerve.

The configuration or shape of the hearing loss refers to the extent of loss at each frequency and the overall picture of hearing that is created. Hearing loss can be in the high frequency range, the low tones or flat (meaning same amount of loss in both high and low tones). Other descriptors associated with hearing loss are:

Unilateral hearing loss means that hearing is normal in one ear, but there is hearing loss in the other ear.
Bilateral hearing loss means that both ears are affected by hearing loss.
Symmetrical hearing loss means that the degree and configuration of loss are the same in both ears.
Asymmetrical hearing loss is one in which the degree and/or configuration of loss is different for each ear.
Progressive hearing loss is a loss that becomes increasingly worse over time.
Sudden hearing loss is one that has an acute or rapid onset which requires immediate medical attention to determine the cause and treatment.
Fluctuating hearing loss is typically a symptom of conductive hearing loss caused by ear infection and fluid, but also can be present with Miniere’s disease.

Screenings by your primary care physician for symptoms or treatable causes of hearing loss are important. If loss is suspected then a comprehensive evaluation by an licensed audiologist is recommended.