The question is frequently asked whether hearing aids are available for deaf animals. In recent years hearing aids have become increasingly sophisticated, but at the bottom line all aids are merely sound amplifiers. They boost sound so that any residual hearing can better detect the sound. Since most congenital deafness in animals is pigment-associated, and the ear is totally deaf, no amount of amplification makes the sound available to the animal. Thus in these cases an aid would never be of benefit.
Several investigators have developed hearing aids for use in dogs where residual auditory function remains most notably Dr. A.E. Marshall at Auburn University in Alabama. He placed used human aids in a collar-mounted container, and led a plastic tube from the aid that terminated in a foam plug placed in the ear canal since the aids would not remain in the dog's canal. He reported that smaller breeds tolerated the presence of a foam plug in the ear better than large breed dogs, but not all small dogs were tolerant. Due to the high cost of the units and the uncertainty of acceptance, my personal recommendation has never been in favor of attempting use in dogs with partial hearing loss. [Note: Dr. Marshall no longer has units available, but will advise veterinarians making their own.] Although an owner may empathize with a pet's deafness, the reality is that most deaf dogs and cats give no evidence of being bothered by their deafness, and adapt quite well, relying on their other senses. It is incumbent on the owner, however, to protect a deaf pet from undetected dangers, such as motor vehicles, and to protect people (especially small children) from reflexive dog bites after being startled.
Questions have also been raised about the feasibility of cochlear prostheses or cochlear implants in dogs. These devices are implanted in deaf humans, with a bundle of stimulating electrodes inserted surgically into one of the coils of the cochlea. Because the nerves from the cochlea into the brain usually remain after loss of the hair cells of the cochlea, they may still be capable of responding to stimulation. Deaf Dalmatians were used in the development of these devices, but no one is presently implanting them in client cases. The devices cost $20K - $25K before the costs of the surgery itself, and considerable post-implant training is required. As a result these devices are not practical in deaf dogs or cats.
January 28, 2004
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