Deafness is the inability to hear and can be caused by either conduction or neurologic abnormalities.
Conduction deafness is caused by abnormalities of the pinna (external ear), ear canal, tympanic membrane (eardrum), auditory ossicles or middle ear. Waxy debris occluding the ear canal, tympanic membrane, and severe ear infections are all examples of diseases causing conduction deafness.
Neurologic or sensorineural deafness is caused by abnormalities of the inner ear, auditory nerve or in the brain itself. Inherited deafness, drug toxicity and age-related deafness are diseases causing sensorineural deafness.
Deafness can be unilateral (affecting one ear) or bilateral (affecting both ears). Unilateral deafness is difficult to recognize without specialized equipment. Because of the cost of the equipment, testing is generally limited to veterinary referral hospitals, specialists and university clinics.
There are over 35 breeds of dogs reported to have hereditary sensorineural deafness. Breeding dogs should be tested for deafness. Animals found to have inherited deafness in one or both ears should be removed from breeding programs.
White-haired, blue-eyed cats have a higher incidence of deafness than the general feline population.
What to Watch For
Not responding to spoken commands
Responding only when the pet can see you
Sleeping more than normal
Not waking unless you physically touch them
Turning in the wrong direction when you call them
Shaking the head or pawing at the ears
Diagnostic tests are needed to determine the ability to hear and the presence of an underlying disease or cause of the deafness.
Deafness can be assessed by observing the animal's behavioral response, such as lifting or turning the head, after making a noise out of the animal's view. Dogs suspected of being bilaterally deaf can be challenged with sounds of increasing intensity from different directions. Be careful not to make sounds that can be "felt" through vibrations.
Animals suspected of having hearing deficits should have a thorough otic (ear) and neurologic examination performed. The ear canal and tympanic membrane can be examined with an otoscope for ear wax accumulation, foreign bodies, infections or inflammation.
Other diagnostic tests may be recommended based on the results of the history and physical examination.
Results of the history, physical examination and initial tests will determine the need for further diagnostic tests and will help determine the appropriate treatment for your pet’s deafness.
Conduction deafness can be corrected if the cause, such as wax accumulation or infection, can be eliminated. Cleaning the ears should be done with care to prevent damage to the eardrum. Only well-trained and knowledgeable people should use cotton-tipped applicators such as Q-tips to clean the ears. Caution should be used. Dogs with severely dirty ears may need to be cleaned under
anaesthesia by a veterinarian.
Infection may need to be treated locally (in the ear canal) and systemically with antibiotics.
Sensorineural deafness cannot be reversed with medications, surgery, or hearing aids. Hearing aids have been used in dogs and cats but the majority of the animals do not tolerate the presence of the hearing aid in the ear canal.
Testing can be done at home to assess hearing. Remember that your pet may “feel” sounds such as a door slamming or steps across a hardwood floor.
Treatment prescribed by your veterinarian should be performed as directed. Medications should be given as directed until finished.
Dogs that are born deaf can be trained to respond hand signals. A bell can be attached to a deaf animal’s collar so that if he gets away he can be found.
Deaf animals need to be closely supervised especially around traffic since they cannot hear dangers such as cars.
By Dr. John McDonnell
Acquired Deafness & Hearing Loss
Dogs with acquired deafness are born with the capability of developing and maintaining normal hearing, but hearing is lost as the animal ages. Acquired deafness is not common to any one breed, but rather, is seen in individuals of all breeds. It is usually the result of damage to the ear components such as the eardrum, middle or inner ear structures, and nerves. Diseases such as canine distemper is a common cause of ear damage. Trauma to the ear areas of the head may result in hearing impairment. Various drugs including the Aminoglycoside antibiotics can be toxic to the ear structures and cause deafness. Aminoglycoside antibiotics such as Gentamicin, Neomycin, and Kanamycin should not be used except under strict veterinary supervision. High doses and/or lengthy treatments with these antibiotics should be avoided.
In the authors' experience, the most common cause of acquired deafness in dogs is simply the result of untreated otitis externa and otitis interna. Mild ear infections left untreated always have the potential to cause hearing impairment.
Regardless of cause, most dogs with acquired deafness are not totally deaf, but rather have varying degrees of hearing impairment.
What are the risks?
Dogs with acquired deafness do not all become deaf to the same degree. Some dogs have only a partial hearing loss, in fact, it may not be noticeable to the owner. Others have severe hearing loss. They can be more prone to injuries, since they cannot hear commands or objects coming towards them.
What is the management?
There is no treatment for acquired deafness. Fortunately, most dogs cope very well with a hearing disability. Individuals can be taught hand signals, and the use of lights can be used to signal dogs as well. The book, Deaf Dog: A Book of Advice, Facts and Experiences about Canine Deafness by Susan Cope Becker may provide the owner of a deaf dog with valuable information.
Race Foster, DVM; Marty Smith, DVM
Drs. Foster & Smith, Inc.