Urban Sky Trust

Types of Hearing Loss

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Quantification of hearing loss
 
An audiologist conducting an audiometric hearing test in a sound-proof testing boothThe severity of a hearing impairment is ranked according to the loudness (measured in decibels (dB)) a sound must be before being detected by an individual. Hearing impairment may be ranked as mild, moderate, severe or profound as defined below:

Mild: for adults: between 25 and 40 dB and for children: between 20 and 40 dB
Moderate: between 41 and 55 dB
Moderately severe: between 56 and 70 dB
Severe: between 71 and 90 dB
Profound: 90 dB or greater

Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram. (http://en.wikipedia.org/wiki/Hearing_impairment)

Conductive Hearing Loss

Conductive hearing loss is due to any condition that interferes with the transmission of sound through the outer and middle ear to the inner ear. This type of hearing loss can be successfully treated in most cases.In cases of conductive hearing loss, sound waves are not transmitted effectively to the inner ear because of some interference in:

The external ear canal

The mobility of the eardrum (problems with the mobility of the eardrum are often caused by accumulation of fluid in the eustachian tube, the tube that connects the middle ear to the back of the throat)

The three tiny bones inside the middle ear

The middle-ear cavity

The openings into the inner ear

The eustachian tube

Modern techniques make it possible to cure or at least improve the vast majority of cases involving problems with the outer or middle ear. Even if people with conductive hearing loss are not improved medically or surgically, they stand to benefit greatly from a hearing aid, because what they need most is amplification.

Sensorineural Hearing Loss

In sensorineural hearing loss, the damage lies in the inner ear, the acoustic nerve, or both. Most physicians call this condition "nerve deafness."

The cochlea has approximately 30,000 hearing nerve endings (hair cells). The hair cells in the large end of the cochlea respond to very high-pitched sounds, and those in the small end (and throughout much of the rest of the cochlea) respond to low-pitched sounds. These hair cells, and the nerve that connects them to the brain, are susceptible to damage from a variety of causes.

The term "sensory" hearing loss is applied when the damage is in the inner ear. Common synonyms are "cochlear" or "inner-ear" hearing loss.

"Neural" hearing loss is the correct term to use when the damage is in the acoustic nerve, anywhere between its fibers at the base of the hair cells and the relay stations in the brain (the auditory nuclei). Other common names for this type of loss are "nerve deafness" and "retrocochlear" hearing loss.

Central Hearing Loss

In central hearing loss, the problem lies in the central nervous system, at some point within the brain. Interpreting speech is a complex task. Some people can hear perfectly well but have trouble interpreting or understanding what is being said. Although information about central hearing loss is accumulating, it remains somewhat a mystery in otology (the medical specialty of ear medicine and surgery).

A condition called central auditory processing disorder frequently leads people to think they have hearing loss when their hearing is actually normal. Despite the fact that this problem is extremely common and present in many highly successful people, it is actually classified as a learning disability.

Basically, the problem involves a person's inability to filter out competing auditory signals. People with central auditory processing disorders have difficulties that include:

Problems "hearing" when there are several conversations going on

Inability to read or study with the radio or television on

Problems reading if someone turns on a vacuum cleaner or air conditioner near them

Generally missing the first sentence from people talking to them if they are involved in an auditory attention task (such as watching television)

Although such people (and their families and friends) frequently suspect that they have a hearing loss, the function of the ears is usually normal, and routine hearing tests are normal. Naturally, people with this condition may also develop hearing loss from other causes, and this can make it even more difficult for them to function under everyday circumstances.

There is no good treatment for central auditory processing disorders other than educating the person, family, and friends, and trying to control the environment. This is especially important for children, whose grades may go from F to A if they are provided with a silent place in which to do their homework.

Functional Hearing Loss

Functional hearing loss involves a psychological or emotional problem, rather than physical damage to the hearing pathway. Individuals with this type of hearing loss do not seem to hear or respond; yet, in reality, they have normal hearing.

The most important challenge for physicians is to classify this condition properly. It may be difficult to determine the specific emotional cause, but if the classification is made accurately, the proper therapy can begin.

Too often, a functional hearing loss is not recognized, and individuals receive useless treatments for prolonged periods. In turn, this process may aggravate the emotional element and cause the condition to become more resistant to treatment.

Mixed Hearing Loss

Frequently, a person experiences two or more types of hearing impairment, and this is called mixed hearing loss. This term is used only when both conductive and sensorineural hearing losses are present in the same ear. However, the emphasis is on the conductive hearing loss, because available therapy is so much more effective for this disorder. (http://www.ehealthmd.com/library/hearingloss/HL_types.html)