By Erika Gagnon, Au.D., CCC-A
Types of Hearing Loss:
The image above displays the outer, middle and inner ear. Sound comes in the ear canal and vibrates the eardrum. This vibration then moves the hearing bones or ossicles which stimulates the cochlea, a fluid filled organ. Vibrations move the fluid to stimulate hair cells sending the signal up the hearing/auditory nerve to the brain. The cochlea is snail shaped and different parts of the cochlea are responsible for stimulating high to low pitch sounds. There are three kinds of hearing loss, defined by the region of the auditory pathway where the hearing loss occurs.
Conductive hearing loss is when sound cannot be transmitted or sent properly to the cochlea. This can be caused by a variety of reasons such as excessive wax blocking the ear canal, middle ear fluid such as an ear infection, or an issue with the middle ear ossicles. While some conductive hearing losses can be permanent, they are often resolved with medical intervention.
Sensorineural hearing loss is hearing loss of the inner ear, or damage to the cochlea or auditory nerve. This kind of hearing loss is most often permanent and does not improve. Often the hair cells or other regions of the cochlea are damaged causing this hearing loss.
Mixed hearing loss is when there is both a combination of conductive and sensorineural hearing loss. For example, someone with sensorineural hearing loss has an ear infection or significant wax making their hearing loss temporarily worse.
How to Read an Audiogram:
The audiogram is a graph of hearing responses. The vertical lines indicate the frequency or pitch that was tested. From left to right the audiogram goes from low to high frequency, similar to keys on a piano. The horizontal lines indicate volume in decibels. A threshold is the softest place someone can consistently hear a sound at each frequency. Once a threshold is determined it will be marked on the graph, an “X” is for the left ear and “O” is the right. The lower the number or the higher up on the graph the better the hearing. This graph displays where some familiar environmental sounds occur as reference. The blue “banana” shape shows the speech banana or where important speech sounds occur. When a threshold is determined it will be marked on the graph, an “X” is for the left ear and “O” is the right.
|Normal Hearing||0-20 dB HL|
|Mild Hearing Loss||21-40 dB HL|
|Moderate Hearing Loss||41-55 dB HL|
|Moderately-Severe Hearing Loss||56-70 dB HL|
|Severe Hearing Loss||71-90 dB HL|
|Profound Hearing Loss||>90 dB HL|
Hearing loss is not defined in a percentage but instead as a degree of hearing loss. The range of hearing loss for each degree is above. The degree of hearing loss is not the sole indication of how someone with hearing loss functions. Speech discrimination or word understanding is another vital test that is performed by the audiologist. Two people can have the same speech understanding scores with very different degrees of hearing loss. This is why some people are more successful users of hearing aids than others. When speech perception scores are poor despite properly fit hearing aids, a cochlear implant can be another intervention option.
Gelfand, S. (2009). Essentials of Audiology. 333 Seventh Ave. New York, NY 10001: Thieme Medical Publishers.