Overview

Who is affected by hearing loss?

Hearing loss is one of the most common physical disorders in the United States with about 28 million people having some level of hearing impairment that interferes with their ability to understand normal speech and participate in conversations. Another 2 million cannot hear at all.

Age is the most common factor in developing hearing loss. About 30 percent of people between 65 and 74 experience some difficulty in hearing. That percentage and the severity of the loss increase with age.

Younger people can develop hearing loss as well. Fourteen percent of people between the ages of 45 and 65, and another 8 million people between 18 and 44, suffer from some form of hearing impairment. About 3 out of every 1000 children are born deaf or hard-of-hearing and 9 out of 10 children who are born deaf have parents who can hear.

What are the major types of hearing loss?

There are two major types of hearing loss:

• Conductive is related to how the ear gathers sound.
• Sensorineural is related to how the nervous system transmits that sound to the brain.

Conductive

Your outer ear gathers sound waves from the environment and funnels them into the ear canal. At the end of the canal, the waves strike the eardrum, causing it to vibrate. Three tiny bones in the middle ear conduct the vibrations from the eardrum to the cochlea (a spiral-shaped chamber that looks somewhat like a snail) in the inner ear. If anything interferes with the transfer of sound waves up to this point (for example: earwax, ear infection, fluid from a cold or allergies or a foreign object in the ear), the resulting type of hearing loss is called conductive. Conductive hearing loss may be temporary or permanent.

Sensorineural

Problems beyond this point (for example: damage to the inner ear or nerves to the brain) lead to sensorineural hearing loss, also known as nerve deafness. Normally, the vibrations from the middle ear create waves in the fluid inside the cochlea. The waves in turn stimulate thousands of delicate hair cells that line the cochlea. Their movement generates nerve impulses in the auditory nerve, which lies just beyond the cochlea and carries the impulses to the brain.

Ultimately, the brain interprets and makes sense of sound, distinguishing and giving meaning to words, music and everything else you hear. Anything that damages the hair cells or blocks the transmission of the nerve impulses can lead to sensorineural hearing loss.

Sensorineural hearing loss, which is almost always permanent and far more common than conductive, is most often caused by presbycusis, a form of age-related hearing loss that destroys hair cells. It may also be caused by diseases, birth injury or head trauma.

Prognosis

Surgical procedures and medications can frequently treat conductive hearing loss, but only rarely can they help people with sensorineural hearing loss. Even so, most people with hearing loss can be helped by hearing aids, assisted listening devices or cochlear implants.

Hearing aids work by amplifying sounds so the damaged ear can detect them. Assisted listening devices (ALDs) can be used along with hearing aids to enhance hearing. Some examples of ALDs are personal frequency modulation (FM) systems, infrared systems and one-on-one communicators. These are all devices that allow the users to hear each other more clearly in large settings, such as a theater or conference hall. There are also amplifying devices for telephones, answering machines and alarms, just to name a few.

A cochlear implant sends sounds directly to the auditory nerve which sends the sounds to the brain. This implant is surgically placed under the skin with an external portion that sits behind the ear. A cochlear implant does not restore normal hearing, but provides a deaf person with a representation of sounds that can help them understand speech. It takes time to learn or relearn hearing sounds with this type of implant.

More on Hearing Loss

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This article was reviewed and updated June 2007.