Types of Hearing Loss
Like many body processes, hearing is complex. Many events happen in order but in fractions of seconds: Sound waves enter the outer ear and travel through the ear canal to the eardrum. The eardrum vibrates in response to sound waves. These vibrations travel through the middle ear and inner ear. Specialized cells in the inner ear transform vibrations into an electrical signal. The auditory nerve carries this signal to the brain and the brain interprets it as sound. Hearing loss can occur when there are problems with the structures or functions in any of these steps.
Conductive Hearing Loss
In conductive hearing loss, sound can’t get through the outer and middle ear. Sounds may seem muffled and it can be hard to hear soft sounds. There are several potential causes of conductive hearing loss including:
Earwax impaction and tumors or foreign objects in the ear canal
Fluid in the ear
Malformation of the outer or middle ear
Perforated eardrum, which is a hole or tear in the eardrum
Depending on the cause, surgery or medications can often treat this kind of hearing loss. If treatment can’t fully resolve hearing problems, then hearing aids, cochlear implants, and bone-anchored hearing systems can be helpful.
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is a problem with the inner ear or auditory nerve. It is the most common type of permanent hearing loss. Possible causes include:
Aging, or presbycusis (age-related hearing loss)
Diseases and illnesses including viral infections, autoimmune diseases, and Meniere’s disease
Drugs that damage hearing; these are ototoxic drugs
Exposure to loud noise
Malformation of the inner ear
Some forms of sensorineural hearing loss are treatable with corticosteroids or surgery. Noise-related hearing loss is largely preventable with ear protection. However, age-related hearing loss is not preventable or reversible. Hearing aids can help people with age-related hearing loss hear better. In fact, 90% of people who wear hearing aids have age-related hearing loss.
Mixed Hearing Loss
Like the name sounds, mixed hearing loss is a combination of conductive and sensorineural hearing loss. For example, someone could suffer with age-related hearing loss and have impacted earwax. Together, the two conditions can make hearing worse than having one condition alone. In general, audiologists address any treatable hearing loss first, which usually means treating conductive hearing loss first. Then, they can get a better picture of the remaining hearing loss and how to help it.
Auditory Neuropathy Spectrum Disorder
Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder that may or may not involve hearing loss. It is possible to hear at normal levels with ANSD. However, some people also have significant hearing loss or even deafness.
In ANSD, sound enters the ear normally, but there is a problem transmitting it from the inner ear to the brain. The signal is disorganized and does not arrive in a way the brain can understand. As a result, people with ANSD have extreme difficulty understanding speech or even recognizing spoken words. For some with ANSD, all noise sounds the same, like white noise. They can’t tell the difference between voices and any other sound.
The exact cause of ANSD is unclear. Most people are born with it and doctors find it in the first few months of life, but it can also strike older children and adults. Being born prematurely and having a family history of the disorder increases the risk. Some neurological disorders also increase the risk, such as Charcot-Marie-Tooth syndrome and Friedrich ataxia.
Treatment of ANSD focuses on improving communication skills. For people who already have language skills, lip reading can help. For babies without language yet, experts recommend sign language and other forms of visual communication. Assistive listening devices may also help some people with ANSD. This includes frequency modulation (FM) systems to reduce background noise, hearing aids, and cochlear implants.