Types of hearing impairment

Your hearing is possible when soundwaves are collected, changed to vibrations, and conducted as impulses to the brain.

Each of the ear’s three parts—the external, middle, and inner—is responsible for a part of that process.

Detailed anatomy of the hearing organs

The external ear includes the outer part we can see and the ear canal that leads to the eardrum. It’s responsible for collecting and conducting the soundwaves.

The middle ear is a closed chamber behind the eardrum that includes bones called ossicles that transmit sound vibrations to the inner ear.

The inner ear contains sound receptors in the form of microscopic hair cells that are bathed in a fluid. Movement of the ossicles stimulates the hair cells, which in turn activate the hearing nerve endings that send an electrical impulse to the brain.

Conductive or sensorineural

Hearing impairments are classified by what part of the process is affected. A conductive hearing impairment involves problems with the external or middle ear. Sensorineural hearing loss involves problems with the inner ear and hearing nerve.

Conductive hearing loss

Conductive hearing loss can be caused by blockage of the external canal, perforation of the eardrum, infections and diseases of the middle ear, and disruption or fixation of the small hearing bones.

A person with a conductive hearing loss may hear better in noise than in quiet and generally hears well over the telephone.

Total deafness is rarely the result of conductive hearing impairments, and a properly fitted hearing aid usually provides benefit.

Sometimes a surgical correction can improve the hearing.

Sensorineural hearing impairment

Sensorineural hearing impairment is more common and has many possible causes. Usually the condition results in slow, gradual loss of the sound receptors and nerve endings.

Patients may experience a lack of sensitivity to sound or a lack of interpretation or clarity of sound. Speech understanding is difficult when there is background noise, and hearing sensitivity is usually better for low tones than high-pitched sounds.

Hearing aids provide benefit for many patients with sensorineural impairment by amplifying sounds. However hearing aids typically do not increase the clarity of speech. When speech understanding deteriorates significantly, hearing aids may not provide sufficient benefit. Many of such patients are good candidates for a cochlear implant. These devices are surgically implanted and directly stimulate the hearing nerve to improve the ability to hear sounds and the ability to understand speech.

Causes of sensorineural hearing impairment

Noise
Loud noises frequently result in temporary hearing loss. Long-term exposure to loud noises causes permanent loss of sound receptors and damage to nerve endings.
Aging
Through normal aging, most individuals lose some of their sound receptors or nerve endings. Individuals vary widely in how age-related changes affect their hearing.
Genetics
Genetic factors can play a role in how inner ear structures develop and stay healthy. Inherited factors contribute not only to hearing loss in infants but also greatly influence the development of hearing loss later in life.
Infections
Viral infections can cause hearing loss in infants and adults, usually resulting in a sudden loss.
Autoimmune attacks
Sometimes the body’s own immune system will treat the inner ear as foreign tissue and attack it as an invader, resulting in hearing loss.
Chemicals
Chemical disturbances, through medications or metabolic changes, can affect the makeup of inner ear fluid or change its pressure or volume.

Prevention

  • Protect your ears from loud noises by wearing hearing protection.
  • Avoid high-fat and high-salt diets to reduce your risk of chronic illnesses such as heart disease and diabetes, which have been implicated in accelerating hearing loss.
  • Moderate cardiovascular exercise can help increase blood flow in the inner ear.
  • Quit smoking to decrease the risk of inner ear damage.

Screening

If you suspect hearing loss for yourself or a family member, consider getting a hearing test to determine the level of severity. A thorough test should determine the hearing level in each ear and your ability to discriminate speech.

Hearing levels are measured in decibels (dB). The lower the number (for example 15 dB) the better your hearing. A reading in the 0-20 dB range is considered normal hearing. Results in the 75 dB to 85 dB range indicate severe hearing loss.

Speech discrimination scores in a quiet surrounding are indicated by percentages. A score of 96-100% is considered normal speech discrimination.

Last reviewed: 
April 2018
Alternative Names: 
Deafness
Hard of hearing
Age-related hearing loss

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