When hearing aids no longer work well enough or are too inconvenient, it may be time to consider auditory implants. There are four main types of auditory implants: cochlear implants, bone-anchored hearing aids, middle ear implants and auditory brainstem implants.

To understand how each type works and how they differ, it’s important to understand how the ear works. When we hear, the sound takes two different pathways. With aerial conduction, sound enters through the outer ear and into the auditory canal, vibrating the eardrum and the ossicles. Next, the sound travels through the inner ear by making the liquid and cilia in the cochlea vibrate, then reaches the brain through the auditory nerve. With bone conduction, sound vibrates the skull and stimulates the cochlea directly, without going through the eardrum and the ossicles.

Cochlear implants are a solution for people whose deafness originates in the inner ear, particularly the cochlea. This alternative is generally chosen for people who have significant hearing loss in both ears and do not benefit from hearing aids.

During a surgery, an electrode array is implanted directly into the inner ear. Because this array is placed in the cochlea, most—if not all—residual hearing is destroyed. Another part of the device, the receiver/stimulator, is placed under the skin behind the ear. Finally, the processor is hooked on the outside of the ear. It captures sound and transmits it to the antenna, which in turn sends signals to the receiver/stimulator. From there, the sound is transformed into electrical impulses and retransmitted to the electrode array. This stimulates the cochlea electronically.

For people whose hearing loss is the result of damage to the auditory nerve, an auditory brainstem implant is more useful. However, this type of implant is not very common.

Bone-anchored hearing aids, commonly known as BAHAs, are primarily designed for people whose deafness is caused by a problem in the middle ear. These people generally cannot wear hearing aids because they have a malformation of the outer ear or are susceptible to repeated infections. Candidates for BAHAs must have inner ears that work mostly or fully.

They may be offered for people who are fully deaf in one ear, but other options must be considered first for that type of hearing loss.  

A titanium screw is surgically placed in the skull behind the ear. Following a healing period to allow for osseointegration (process where the screw melds with the bone), a processor is placed over the screw. This device works a bit like a push-button. It captures the sound and transmits it to the cochlea by vibrating the bones of the skull.

Middle ear implants are designed for people with sensorineural (caused by problems in the inner ear) or mixed (caused by problems in both the middle and inner ear) hearing loss that cannot wear external hearing aids because of repeated otitis or other issues like psoriasis or chronic eczema.

A transducer is surgically placed on the ossicles or the round window of the middle ear. Residual hearing is therefore preserved. During the same surgery, an antenna is placed under the skin behind the ear, as with a cochlear implant. The sound is captured by the processor, transmitted to the antenna and sent to the transducer. The transducer reproduces the vibrations of the structures of the inner ear, allowing the information to be sent to the cochlea.

Note that no auditory implants are fully implantable. Currently, all types of implant have an external portion.

To receive an auditory implant, you will have to meet certain audiological, medical and psychological criteria. All types of auditory implants require a healing and rehabilitation period. For more information, talk to an audiologist practicing in the nearest Lobe clinic.