There are four types of hearing loss:
1. Sensorineural hearing loss: When the problem is in the inner ear, a sensorineural hearing loss is the result. This commonly occurs from damage to the small hair cells, or nerve fibers, in the organ of hearing. Sensorineural hearing loss is the most common type of hearing loss and accounts for more than 90 percent of hearing loss in all hearing aid wearers. The most common causes of this hearing loss are age-related changes and noise exposure. Loss may also result from disturbance of inner ear circulation, increased inner ear fluid pressure, or from disturbances of nerve transmission. There are many excellent options for the patient with sensorineural hearing loss.
2. Conductive hearing loss: When there is a problem in the external or middle ear, a conductive hearing impairment occurs. Conductive hearing loss occurs when sound is not conducted efficiently through the ear canal, eardrum, or tiny bones of the middle ear, resulting in a reduction of the loudness of sound that is heard. Conductive losses may result from earwax blocking the ear canal, fluid in the middle ear, middle ear infection, obstruction of the ear canal, perforation (hole) in the eardrum membrane, or disease of any of the three middle ear bones. All conductive hearing losses should be evaluated by a physician to explore medical and surgical options.
3. Mixed hearing loss – When there are problems in the middle and inner ear, a mixed hearing impairment is the result (i.e. conductive and a sensorineural impairment).
4. Auditory neuropathy spectrum disorder (ANSD): The least common hearing impairment is ANSD. This type of loss requires more in-depth diagnostic testing, including a hearing evaluation with pure tones, otoacoustic emissions (OAEs) and auditory brainstem response (ABR) testing. In this type of hearing loss, the nerve fibers in the organ of hearing typically appear to be functioning well, but a breakdown of the information occurs along the pathway to the brain. A person may still have normal hearing, but the sound is not encoded properly in the brain. This type of hearing disorder is diagnosed more often in children, due in part to newborn hearing screenings that use automated ABR equipment and routine speech screenings by pediatricians and school systems, but can be present in adults as well.