Types of Hearing Loss
Hearing loss can be categorised based on where or what part of the auditory system is damaged. There are four types of hearing loss: conductive hearing loss, sensorineural hearing loss, mixed hearing loss and central hearing impairment.
Conductive Hearing Loss
Conductive hearing loss occurs when sound is not conducted efficiently through the outer and middle ears, including the ear canal, eardrum, and the small bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear soft sounds. This type of hearing loss can often be corrected through medicine or surgery.
Presence of fluid in the ear associated with colds, allergies, ear infections (otitis media); or a poorly functioning Eustachian tube are common causes of conductive hearing loss. Other common causes of this hearing loss include a build-up of wax in the ear canal, perforated eardrum, or damaged or defective ossicles.
Sensorineural Hearing Loss
Sensorineural hearing loss is the most common type of hearing loss. More than 90 percent of all hearing aid wearers have sensorineural hearing loss. This can occur in one of two ways. The first is when the delicate hearing cells (hair cells) in the inner ear are damaged, and they become unable to convert sound vibrations into the electrical signals needed by the auditory nerve. Secondly, when nerve pathways in the auditory nerve itself become damaged, preventing the signals from reaching the brain.
Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear soft sounds, but also affects the ability to hear and understand speech clearly.
Although this damage can be caused by exposure to loud noise – through working in a noisy environment for too long – the primary cause of sensorineural hearing loss in adults is ageing. Sensorineural hearing loss is a permanent loss and cannot be corrected medically or surgically.
Mixed Hearing Loss
Sometimes a sensorineural hearing loss may occur in combination with a conductive hearing loss. In other words there may be damage in the outer or middle ear and the inner ear or auditory nerve. If this happens, the hearing loss is referred to as a mixed hearing loss.
Central Hearing Impairment
Central hearing impairment occurs when auditory centers of the brain are affected by injury, tumor, disease, heredity or unknown causes. Central hearing impairment does not necessarily involve (although it may) hearing loss. Central hearing impairment involves auditory discrimination, sound localisation, auditory pattern recognition, the temporal aspects of sounds, and the ability to deal with degraded and competing acoustic signals.