Types & Causes of Hearing Loss
The ear is a very complex organ comprising three parts: the outer ear, the middle ear and the inner ear. Hearing loss can result from an obstruction or damage to any of these three parts. In order to gain a better understanding of hearing loss, it is important to know how the ear functions:
Sound transmission process:
- Pinna catches sound waves and directs them into the ear canal. Ear canal carries the sound waves to the eardrum (tympanic membrane).
- Sound waves cause the eardrum (tympanic membrane) to vibrate. The bones in the middle ear (malleus, incus and stapes) pick up these vibrations.
- Vibrations pass through the oval window to the cochlea, setting the fluid inside in motion. This causes special nerve cells to turn the sound waves into electrical impulses. The auditory nerve sends these electrical impulses to the brain where they are heard as sound.
The severity of a hearing impairment is categorized according to how much louder a sound must be made over the usual levels before the listener can detect it. Normal hearing people can hear sounds as soft as 25 dB HL. Hearing level exceeds this normal range is considered as hearing loss. The degree of hearing loss is universally classified into 5 categories: mild, moderate, moderately severe, severe and profound.
Hearing impairment comes from different biologic causes. Type of hearing loss could be classified into 3 types according to the causes: Conductive hearing loss, sensorineural hearing loss and mixed hearing loss.
Conductive Hearing loss
Conductive hearing loss results from an abnormality of the outer or middle ear, which results in a loss of loudness. Some common causes include infection in the middle ear, perforated ear drum, excessive ear wax blockage and otoscelerosis, etc.
Sensorineural Hearing Loss
Sensorineural hearing loss is caused by damage to the inner ear or hearing nerve, which results in a loss of loudness and clarity of speech perceived. A sensorineural loss can result from virus infection, disease, aging, certain drugs and excessive noise, etc.
Mixed hearing loss
Mixed hearing loss is caused by damage to the outer/middle ear and the inner ear. Typically, sound waves are not conducted efficiently through the middle ear, and once they reach the inner ear the vibrations cannot be picked up or sent to the brain. Therefore, a mixed hearing loss is the combination of a conductive and sensorineural hearing loss.
Early detection and treatment of hearing loss is crucial. See a Hearing Health Consultant immediately for a complete hearing evaluation if you suspect any type of hearing loss.