There are some cases of hearing loss in which surgical repair or hearing aids may be ineffective.

 

 

The main function of the ear is to convert sound signals, which are pressure waves, into electrical signals that can be transmitted by the hearing (cochlear) nerve to the brain. The external ear, including the ear canal, collects the sound energy and directs it to the ear drum (tympanic membrane). At this point, the air pressure waves of sound then become mechanical (vibrational) energy. The signal then goes through the three middle ear bones (malleus, incus, and stapes) and enters the inner ear (cochlea) as fluid energy waves. The cochlea contains hair cells that turn the fluid vibrational signals into electrochemical signals that communicate with the hearing (auditory) nerve.

  

Figure 1  Normal hearing mechanism

 

 

The BAHA allows patients with a conductive hearing loss (problem with area 2 in Figure 1) to hear. It can also help patients with a severe to profound sensorineural hearing loss (problem with area 1 in Figure 1) on one side if the hearing on the other side is still functional. 

 

The cochlear implant is for patients with hearing loss on both sides that is so severe that reconstructive surgery or hearing aids are not effective.