Hearing loss can be comprised of various factors, which generally include: type of hearing loss, degree of hearing loss, and the configuration of the hearing loss. Hearing care professionals perform a specialized hearing evaluation to determine each patient’s type, degree and configuration of hearing loss.
TYPES OF HEARING LOSS
There are four basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, mixed hearing loss and central auditory processing disorders.
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 and can often be corrected through medicine or surgery.
Although absence or malformation of certain parts of the ear 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.
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 to the brain. People with Sensorineural hearing loss experience a reduction in sound level, speech understanding and hearing clarity.
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 over 17 million Americans and cannot be corrected medically or surgically. It is a permanent loss, but hearing clarity can be improved by the use of hearing aids and assistive listening devices.
Mixed Hearing 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.
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. A deficiency in one or more of the above listed behaviors may constitute a central auditory processing disorder, although CAPD does not necessarily involve hearing loss. . 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 to describe degrees of hearing loss.
| Hearing Threshold (in decibels, dB) | Degree of Hearing loss | Ability to Hear Speech |
| 0–25 dB | none | no significant difficulty |
| 26–40 dB | mild | difficulty with faint or distant speech |
| 41–55 dB | moderate | difficulty with conversational speech |
| 56–70 dB | moderate to severe | speech must be loud; difficulty with group conversation |
| 71–90 dB | severe | difficulty with loud speech; understands only shouted or amplified speech |
| 91+ dB | profound | may not understand amplified speech |
Numerical values measured in sound decibels (dB) 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. Slightly smaller or slightly larger numbers may be used by some hearing care professionals for each of the categories listed above.
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, a “low frequency loss”. Some hearing loss configurations are “flat”, indicating the same amount of hearing loss for low and high tones.
The following represent a selection of other descriptions associated with configuration of hearing loss:
- Bilateral vs. Unilateral. Bilateral hearing loss means both ears are affected. Unilateral hearing loss means only one ear is affected.
- Symmetrical vs. Asymmetrical. 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. 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. 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.