Since dogs cannot tell us what they hear, or whether they hear at all, the best criterion for confirming deafness is careful assessment of the dog’s conscious response to sound. A dog’s reaction to sound must be differentiated from its reaction to smells, sight and touch. There are some classic signs that a veterinarian will look for if an owner suspects that his dog might be losing its hearing. The veterinarian will assess the dog’s reaction, if any, to increasingly loud noises coming from areas outside of the dog’s field of vision. Often, pets with intact hearing will display an involuntary flicking or twitching of the ears (called "Pryor's reflex) in response to sound. The veterinarian will also try to determine whether only one or both ears are affected. Typically a complete neurological and aural (ear) examination will be conducted.
The veterinarian will take a thorough history of the dog’s behavior, in addition to conducting a thorough physical and behavioral examination. Dogs experiencing hearing loss are usually very sound sleepers. Soft or even very loud noises might not wake them. If a dog only rouses from sleep when touched, that is a red flag for developing deafness. If a dog does not come when called, he may not simply be testing his owner’s patience. He could be experiencing hearing loss. The veterinarian will ask the owner about these and other behavioral signs of hearing impairment. Some veterinary teaching hospitals have had some degree of success with objective evaluations of canine hearing using electrodiagnostic procedures. Laboratory tests and radiographic imaging can identify infections of the ear canal, including the inner, middle and outer ear (otitis interna, media or externa), which could be contributing to hearing impairment.
While in many cases diagnosis can be made by observation alone, the only way to definitively diagnose deafness or hearing loss – especially unilateral deafness - is through use of the brainstem auditory evoked response (BAER) test, sometimes referred to as the brainstem auditory evoked potential (BAEP) test or the auditory brainstem response (ABR) test. The procedure is virtually painless and takes only a short time to administer. It evaluates and records the brainstem’s electrical response to some auditory stimulus, which usually is a clicking sound given rapidly (up to 1000 to 1500 times) to each ear through headphones or foam insert microphones. Sedation may be required in some cases, depending on the patience and comfort of the particular dog. The patient must lie quietly for about 15 minutes for the test to be completed. Subdermal electrodes are placed in and around the ears and neck, in particular areas. These are essentially specialized discs with tiny sensitive “prongs” that are pressed onto and into the skin. This can cause very mild discomfort, but most dogs do not react to the sensation. Specialized computers then measure the electrical activity of the dog’s brain in response to the sounds administered separately into each ear.
The BAER test is most commonly used to detect congenital deafness in puppies at or over 6 weeks of age. It also can detect varying levels of hearing function or loss. The test is fairly expensive and is only offered at veterinary teaching hospitals and select specialty practices. As a result, many owners rely on an observational behavioral diagnosis of deafness, based on subjective assessment of a dog’s reaction to loud noises. However, there are no accurate alternatives for diagnosing either unilateral or bilateral deafness in dogs other than the BAER test. It is available for owners who would like to be certain about their dog’s capacity to hear.
The Institute for Genetic Disease Control in Animals (GDC) maintains an open registry for dogs and cats with hereditary deafness that is determined by a BAER examination protocol at a minimum age of 35 days. Most of this deafness registry information has been transferred to the Orthopedic Foundation for Animals (OFA). It can be helpful to breeders and others trying to determine how deafness is inherited, as well as in the selection of appropriate animals for use in a breeding program.
Most dogs diagnosed with hearing loss live happy lives. Deaf dogs can easily be taught to respond to hand signals, facial expressions or even flashlights. Owners will need to change some of the ways in which they deal with their dogs, but there are many success stories about the adventures of living with and being loved by a deaf dog.