While hearing aids amplify sounds that are eventually processed by the cochlea (the main organ of hearing), a cochlear implant does not amplify sounds, but instead changes sounds into electrical energy that stimulates the auditory nerve directly, bypassing the damaged parts of the cochlea.
Although both types of devices work best for people with sensorineural (permanent) hearing loss, cochlear implants are traditionally recommended for people with severe to profound hearing loss, while hearing aids are recommended for people with mild to severe hearing loss.
A cochlear implant has two parts: the internal receiver that is surgically implanted directly into the cochlea, while the external microphone and magnetic transmitting processor fit behind the ear and on the side of the head. The electrical energy that is sent to the electrodes in the cochlea, eventually travel to the brain for processing.
A hearing aid has three basic parts: a microphone that picks up the sound; an amplifier that makes sound louder; and a speaker that delivers the amplified sound to the ear canal. Once the sound reaches the ear canal, it travels to the eardrum, then the middle ear (bones), and ends up in the cochlea, where it will be sent to the brain for processing.
Although there are advantages and disadvantages for each device, an evaluation by an audiologist and ear, nose and throat physician can help to decide which works best for you.