There are various forms of hearing impairment. Some are caused by physical damage or abnormalities in the person's auditory system, while others are caused by problems in the central nervous system. The different forms of hearing impairment are grouped into the following categories: sensorineural hearing loss (SNHL), conductive hearing loss, central hearing loss, functional hearing loss, and mixed hearing loss. A specialist must decide which type of hearing loss is present so that the proper treatment may be administered.
SNHL occurs when the inner ear or cochlea is damaged. Some causes of SNHL are aging, illness, head trauma, exposure to loud noise, and hereditary factors. This is the most common form of hearing impairment, and the vast majority of people who wear hearing aids have it. A person with SNHL may be able to hear, but the sounds are muffled and difficult to understand. There is no cure, although a cochlear implant is sometimes recommended for people whose hearing doesn’t improve with hearing aids.
Conductive hearing loss can be caused by a wide variety of conditions. A perforated ear drum, excessive ear wax, middle and outer ear infections, fluid in the ear caused by colds, or a foreign body in the ear can cause conductive hearing loss. Other possible causes are a poorly functioning eustachian tube, tumors, and allergies. People with conductive hearing loss will experience a reduced level of sound, and may lose the ability to hear faint noises. This type of hearing impairment is often temporary. Some with permanent conductive hearing loss can be helped by surgery or other forms of medical intervention.
In some cases, a person will have both SNHL and conductive hearing loss. When both of these hearing impairments occur inside the same ear, the condition is known as mixed hearing loss. Treatment usually focuses on the conductive hearing loss because that type of therapy is more effective.
Central hearing loss is caused by a problem in the central nervous system. A person with central hearing loss may actually be able to hear quite well, but experiences troubles processing and interpreting the sound. This condition is known as central auditory processing disorder. It is fairly common and is classified as a disability, even though many successful people function very well with this form of hearing impairment.
Functional hearing loss occurs when there is a psychological or emotional problem, and is not due to any physical factors. Individuals with functional hearing impairment are able to hear normally, but seem unable to hear or respond. This is the most difficult type of hearing impairment to identify and is often misdiagnosed. With proper diagnosis, treatment is possible.