Types of Hearing Loss
Hearing loss is categorized as sensorineural hearing loss, conductive hearing loss or mixed hearing loss (a combination of both sensorineural and conductive).
The difference between sensorineural and conductive hearing loss is where along the auditory chain the hearing loss occurs. The auditory system takes vibrations in the air, channels them into the middle ear and then turns vibrations of the ear drum into movement of fluid within the middle ear. The fluid movement then is captured by sensations within the inner ear and transferred to the brain through the acoustic nerve.
If the hearing loss is a result of the conduction of the sound from the outside air into the inner ear, then the hearing loss is considered conductive hearing loss. When the loss of hearing is due to the inability of the hearing system to interpret the fluid movements within the inner ear as sound signals to the brain, then the hearing loss is considered sensorineural hearing loss.
Conductive Hearing Loss
Conductive hearing loss occurs when there is damage or blockage to the outer ear or damage to the ear drum. Conductive hearing loss typically causes a patient to be unable to hear faint sounds or causes the sound level to be reduced, but it rarely results in total hearing loss. Many times, conductive hearing loss can be corrected or improved through medical or surgical treatment. Some of the factors that can affect conductive hearing loss include:
- fluid build-up in the middle ear due to the flu, allergies, or infection, which prevents the ossicles from properly transmitting ear drum vibrations to the inner ear
- any type of obstruction in the ear canal, such as wax build up or a foreign object;
- any infection of the ear canal that causes the canal to swell and partially or fully close
- poor eustachian tube functioning so that pressure cannot equalize between the middle ear and outside air
- congenital birth defects such as poor formation of the middle or outer ear.
Sensorineural Hearing Loss
Sensorineural hearing loss can be caused by damage to the inner ear (he auditory nerve that carries sound signals to the brain) or damage to the auditory cortex within the brain. Damage anywhere along this pathway can result in the auditory system being unable to carry the sound signals from the inner ear to the brain.
Sensorineural hearing loss may not only reduce a person’s ability to hear faint sounds, but may also reduce a person’s ability to hear clearly or understand speech.
Sensorineural hearing loss is often permanent and cannot be medically or surgically treated. Common factors that can cause sensorineural hearing loss include:
- drugs that poison the auditory nervous system or auditory area of the brain
- excessive and prolonged exposure to loud sounds
- congenital birth defects where the inner ear, auditory nerve, or auditory area of the brain are malformed
- direct damage caused by head trauma or tumors.
Combined or Mixed Hearing Loss
When both the ability to conduct sound and relay the sounds to the brain are impaired, this is called mixer or combination hearing loss.
Degree of Hearing Loss
The level or degree of hearing loss can be defined in five categories. The degree of hearing loss is determined by how loud the sound must be in order for a person to hear it. Sounds are measured in dB or decibels. (For a range of loudness levels in dB for typical sounds click here: dB Loudness Levels.)
Patient Cannot Hear Sounds Below Degree of Hearing Loss This Level
80 dB Profound Loss
60 to 80 dB Severe Loss
40 to 60 dB Moderate Loss
20 to 40 dB Mild Loss
20dB or lower Normal*
*For young children, lower than 15 dB is considered normal, while for older adults, lower than 25 dB is considered normal.