Learn more about how hearing works, the different types of hearing loss and how the results are plotted on an audiogram.
Understanding Hearing Loss
How we hear:
- Sound waves enter your outer ear and travel through the ear canal to your eardrum.
- Your eardrum vibrates with the incoming sound and sends the vibrations to three tiny bones in your middle ear.
- The bones in you middle ear amplify the sound vibrations and send them to your inner ear, or cochlea. The sound vibrations activate tiny hair cells in the inner ear, which in turn release neurochemical messengers.
- Your auditory nerve carries this electrical, signal to the brain, which translates it into a sound you can understand.
Types of Hearing Loss
Conductive hearing loss: Caused by any condition or disease that blocks or impedes the transmission of sound through the middle ear resulting in a reduction in the sound level (loudness) that reaches the cochlea. This can be caused by something as simple as earwax build-up! In most cases treatment produces a complete or partial improvement in hearing.
Sensorineural hearing loss: A loss or distortion of sound transmission resulting from damage to the inner ear hair cells or to any of the pathway from the inner ear hair cells or to any of the pathway from the inner ear to the auditory cortex of the brain. This type of hearing loss is usually permanent and irreversible. The treatment for sensorineural hearing loss is amplification through hearing aids.
Mixed hearing loss: This is a combination of conductive and sensorineural hearing loss.
How to read an audiogram
The audiogram is a graphical display of the hearing test. The two main components that are graphed are frequency and intensity. These results are displayed for each ear. When you had your hearing tested, the hearing aid practitioner was determining the softest sound you could hear at each specific frequency.
Frequency (or pitch) is measured in Hertz (Hz). Frequencies range from low-pitch to high-pitch and read from left to right on the audiogram. Each vertical line represents a different frequency. The ones used most often during testing are 250, 500, 1000, 2000, 4000 and 8000 Hz.
Intensity is measured in decibels (dB). The intensity relates to how loud or soft a sound is. Each horizontal line represents a different intensity level. The softest sounds are at the top of the chart and the loudest sounds at the bottom. Each mark on an individual’s hearing test would represent the softest sounds they could hear. The softest intensity tested is typically 0 dB and the loudest is 120 dB.
Right Ear – Left Ear: The right ear is graphed with either a circle or triangle. The left ear is graphed with an X or a square. These responses would all represent the air conduction results of either the right or left ear.
Other symbols seen on the audiogram are obtained during bone conduction testing. The right ear is graphed with < or [. The left ear with > or ]. These responses can help determine whether a hearing loss is sensorineural or conductive.
Speech Testing: Speech discrimination or word recognition ability is scored as a percentage. This score represents how well a list of words could be repeated. The words are presented at a comfortable volume level with no background noise present.
Degrees of Hearing Loss: Hearing loss is classified in degrees of hearing from normal to profound. This classification is determined by the hearing threshold (or the softest a sound was heard at a specific frequency).
Mild hearing loss (21 – 40dB Hearing Threshold) – Soft noises are not heard. Understanding speech is difficult in a loud environment.
Moderate hearing loss (41 – 65dB Hearing Threshold) – Soft and moderately loud noises are not heard. Understanding speech becomes very difficult if background noise is present.
Severe hearing loss (66 – 90dB Hearing Threshold) – Conversations have to be conducted loudly. Group conversations are possible only with a lot of effort.
Profound hearing loss (91+ dB Hearing Threshold) – Some very loud noises are heard. Without a hearing aid, communication is no longer possible even with intense effort.