Types of Hearing Loss

Hearing loss can be categorized by where or what part of the auditory system is damaged or compromised. There are two basic types of hearing loss, and a third which is a mixture of the other two:

• conductive hearing loss,
• sensorineural hearing loss and
• mixed hearing loss.

 

Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the 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. Often this type of hearing loss can be medically or surgically corrected.

Examples of conditions that may cause a conductive hearing loss include:

• Conditions associated with middle ear pathology such as fluid in the middle ear from colds, allergies (serous otitis media), poor Eustachian tube function, ear infection (otitis media), perforated eardrum, benign tumors
• Impacted earwax (cerumen)
• Infection in the ear canal (external otitis)
• Presence of a foreign body
• Absence or malformation of the outer ear, ear canal, or middle ear

 

Sensori-neural Hearing Loss

Sensori-neural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear) to the brain. Sensori-neural hearing loss cannot be medically or surgically corrected. It is a permanent loss.

Sensori-neural 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.

Sensori-neural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system, and genetic syndromes. Sensori-neural hearing loss may also occur as a result of noise exposure, viruses, head trauma, aging, and tumours.

 

Mixed 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 inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

 

Degree of Hearing Loss

Degree of hearing loss refers to the severity of the loss. The numbers are representative of the patient's thresholds, or the softest intensity at which sound is perceived. The following is one of the more commonly used classification systems:

Degree of hearing loss	Hearing loss range (dB HL)
Normal	-10 to 15
Slight	16 to 25
Mild	26 to 40
Moderate	41 to 55
Moderately severe	56 to 70
Severe	71 to 90
Profound	91+

Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493-500. 

 

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.