Hearing loss can be categorized by the part of the auditory system that is damaged. There are four basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, mixed hearing loss and auditory neuropathy/dysynchrony.
Conductive Hearing Loss
Conductive hearing loss occurs when sound does not travel efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear faint sounds. This type of hearing loss can often be medically or surgically corrected.
Conductive hearing loss can be associated with middle ear pathology such as fluid in the middle ear, ear infection, and perforated ear drum. Impacted ear wax (cerumen) and infection in the ear canal can be associated with conductive hearing loss. Additionally, congenital malformation of the outer ear, ear canal or middle ear space may cause a conductive hearing loss.
Sensorineural Hearing Loss
Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (beyond the cochlea) to the brain. Sensorineural hearing loss cannot be medically or surgically corrected. It is a permanent loss.
Sensorineural hearing loss not only involves a reduction in sound level, or the ability to hear faint sounds, but also affects speech understanding, or ability to hear clearly.
Sensorineural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system and genetic syndromes. Sensorineural hearing loss may also occur as a result of noise exposure, viruses, head trauma and aging.
Mixed Hearing Loss
Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.
Auditory neuropathy is a hearing disorder in which sound enters the inner ear normally but the transmission of signals from the inner ear to the brain is impaired. People with auditory neuropathy may have normal hearing, inconsistencies in their hearing, or hearing loss ranging from mild to severe. Even though a person with auditory neuropathy may be able to hear sounds, they may still have trouble understanding speech clearly. It can affect people of all ages, from infancy through adulthood. The exact number of people affected by auditory neuropathy is not known, but the condition is thought to affect a relatively small percentage of people who are deaf or hearing-impaired.
Although auditory neuropathy is not yet fully understood, scientists believe the condition probably has more than one cause. Auditory neuropathy runs in some families, which suggests that genetic factors may be involved in some cases. Although not proven as a direct cause, many cases have been associated with certain health problems such as jaundice, prematurity, low birth weight, neurological disorders, and an inadequate supply of oxygen to the baby at or before birth. There are also some drugs used to treat medical complications in pregnant women or newborns that may damage the inner hair cells in the baby's ears resulting in auditory neuropathy/dysynchrony..
Because each child is unique, there is no one way to treat a child with auditory neuropathy. For some individuals with auditory neuropathy, hearing aids and personal listening devices such as frequency modulation (FM) systems, and/or cochlear implants are helpful. However, no one test is currently available to determine whether an individual with auditory neuropathy might benefit from a hearing aid or cochlear implant.
Language can be acquired through utilization of a visual approach such as sign language, an oral approach that encourages listening and speaking, or a combination of the two such as cued speech or total communication. In order to determine which approach is best for any one child, parents will need to work closely and regularly with a team of professionals including audiologists, qualified speech language pathologists, teachers, and other pertinent medical professionals. The team will consider the individual capabilities of each child as well as his/her family. Changes to the child's communication approach will be made based on his/her progress.