Hearing loss is a major social burden. According to the World Health Organization (WHO) 5,3% of people worldwide suffer from disabling hearing impairment. In South Africa 7,5% of schoolchildren have some form of hearing impairment.
The outer ear consists of the pinna (external ear lobe) and the external acoustic meatus (ear canal). It picks up and relays sound to the Tympanic membrane(eardrum). The eardrum, tympanic space (middle ear space) and 3 ossicles (bones for hearing) constitute the middle ear. The eardrum vibrates and transmits the sound waves via the bones of hearing (malleus, incus and stapes) to the inner ear. The vibration of the loose stapes in the oval window of the cochlea of the inner ear transmits the sound waves to the fluid in the cochlea. In the cochlea the sound waves are converted to electrical impulses that travel with the cochlear nerve (part of the cochleovestibular or eight cranial nerve) to the brain for sound awareness and interpretation.
There are three types of hearing loss:
Conductive hearing loss. Impairment of sound conduction in the outer and/or middle ear.
Sensorineural hearing loss. Impairment of the conversion of mechanical sound waves into electrical nerve impulses in the cochlea of the inner ear (sensory) and/or the impairment of the of the electrical impulses via the cochlear nerve to the brain (neural). These two types are usually coined together as sensorineural hearing loss.
Mixed hearing loss. A combination of conductive and sensorineural hearing loss
An auditory processing disorder is a condition where sound reaches the brain in a normal way but due to neural dysfunction of the brain the sound cannot be interpreted or properly understood. People with normal hearing can present with an auditory processing disorder.
Hearing and auditory processing disorders can be tested by an audiologist.
When present in a baby and small child the development of speech will be impaired. In many cases the hearing can be improved with a surgical operation. The defective conduction mechanism in the outer and middle ear can be surgically corrected with a grommet, tympanoplasty, ossiculopalsty or stapedotomy. The inner ear function can be restored with a cochlear implantation if a hearing aid is not effective. Bone anchored hearing aids are implants that deliver sound directly to the inner ear. Dr Hofmeyr has more than 10 years experience in implantable hearing aids. An auditory brainstem implant (ABI) is an implant that delivers sound directly to the brainstem.