Types of Hearing Loss

When describing hearing loss we generally look at three attributes: type of hearing loss, degree of hearing loss, and the configuration of the hearing loss.

Hearing loss can be categorized by where or what part of the auditory system is damaged. There are three basis types of hearing loss, conductive hearing loss, sensorineural hearing loss and central auditory processing disorders. Terri Bellis' article, "Understanding Auditory Processing Disorders in Children," is available our site

Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer and middle ears, including the ear canal, eardrum, and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear faint sounds. This type of hearing loss can often be corrected through medicine or surgery.

Absence or malformation of the pinna, ear canal, or ossicles can cause a conductive hearing loss. Presence of a foreign body; impacted ear wax (cerumen); fluid in the ear associated with colds, allergies, ear infections (otitis media); or a poorly functioning eustachian tube are all examples of conditions that may cause a conductive hearing loss.

Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the cochlea or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

Sensorineural Hearing Loss

Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear pathway of the acoustic nerve) to the brain.

Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear faint sounds, but also affects speech understanding or ability to hear clearly.

Sensorieneural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system, and genetic syndromes. Sensorineural hearing loss may also occur as a result of noise exposure, viruses, head trauma, aging, and tumors. Sensorineural hearing loss affects some 17 million Americans.

Sensorineural hearing loss cannot be corrected medically or surgically. It is a permanent loss.

Sometimes a sensorineural hearing loss occurs in combination with a conductive hearing loss. In other words there may be damage in the outer or middle ear and the cochlea or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

Central Auditory Processing Disorders

A central auditory processing disorder (CAPD) occurs when auditory centers of the brain are affected by injury, disease, tumor, heredity or unknown causes. CAPD does not necessarily involve (although it may) hearing loss. Central auditory processing involves sound localization and lateralization, auditory discrimination, auditory pattern recognition, the temporal aspects of sounds, and the ability to deal with degraded and competing acoustic signals. Therefore, a deficiency in one or more of the above listed behaviors may constitute a central auditory processing disorder. CAPD is often associated with Attention Deficit disorder (ADD) or Attention Deficit Hyperactivity Disorder (ADHD) .

Degree of Hearing Loss

Degree of hearing loss refers to the severity of the loss. There are seven categories that are typically used. The numerical values are based on the average of the hearing loss at three frequencies 500 Hz, 1000 Hz, and 2000 Hz in the better ear without amplification. Some people may use slightly smaller or slightly larger numbers for each of the categories below:

Normal range or no impairment = -10 dB to 15 dB

Slight Loss/Minimal loss = 16 dB to 25 dB

Mild loss = 26 dB to 30 dB

Moderate loss = 31 dB to 50 dB

Moderate/Severe loss = 51 dB to 70 dB

Severe loss = 71 dB to 90 dB

Profound loss = 91 dB or more)

Configuration of Hearing Loss

The configuration or shape of the hearing loss refers to the extent of hearing loss at each frequency and the overall picture of hearing that is created. For example, a hearing loss that only affects the high frequencies would be described as a high frequency loss. Its configuration would show good hearing in the low frequencies and poor hearing in the high frequencies. On the other hand, if only the low frequencies are affected, the configuration would show poorer hearing for low tones and better hearing for high tones. Some hearing loss configurations are flat, indicating the same amount of hearing loss for low and high tones.

Other descriptors associated with hearing loss are:

Bilateral vs. unilateral. Bilateral hearing loss means both ears are affected. Unilateral hearing loss means only one ear is affected.

Symmetrical vs. aysmmetrical. Symmetrical hearing loss means that the degree and configuration of hearing loss are the same in each ear. An asymmetrical hearing loss is one in which the degree and/or configuration of the loss is different for each ear.

Fluctuating vs. stable hearing loss. Some hearing losses change - sometimes getting better, sometimes getting worse. Such a change commonly occurs in young children who have hearing loss as a result of otitis media, or fluid in the middle ear. Other hearing losses will remain the same year after year and would be regarded as stable.
Progressive vs.sudden hearing loss. Progressive hearing loss is a hearing loss that becomes increasingly worse over time. A sudden hearing loss is one that has an acute or rapid onset and therefore occurs quickly, perhaps as a result of head trauma, or perhaps a tumor in the auditory nerve.

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