Deafness is often difficult to assess accurately, mainly because pets are not able to tell us when they have trouble hearing. Usually, it is their failure to obey our commands or respond to familiar noises that first alerts us to a deafness problem.
Compared to humans, dogs and cats have a much different range of hearing. Humans can hear sounds in the 20 Hz (low sounds) to 20 kHz (high sounds) range. By comparison, a cat has a range of about 48 Hz to 85 kHz and a dog has a range of about 67 Hz to 45 KHz. Deafness in dogs and cats can be of two kinds: conductive or sensorineural. If sounds cannot travel properly in the external or middle ear (i.e. sound does not conduct properly), the problem is said to be conductive. This can occur when there is an ear infection, a ruptured eardrum, blocked ear canals or fluid in the ear. Usually in these patients, hearing loss is only partial and treatment involves medical or surgical correction. If this is the case with your dog, a veterinarian may be able to resolve your pet's deafness. If the deafness is sensorineural, the inner ear is involved and deafness is usually total. Sensorineural deafness is often due to nerve abnormalities or problems with the hydrodynamics or physics of the inner ear. As pets get older, deafness is a common occurrence and sensorineural deafness may be the cause.
Deafness can be hereditary in many breeds. Breeds most commonly affected include Dalmatians, border collies, English setters, Boston terriers, Collies, and Rottweilers. It can also be associated with a genetic predisposition. Dogs with the merle coat color gene and cats with white coat color and blue iris genes are predisposed to deafness. Deafness is difficult to evaluate in both dogs and cats, especially if only one ear is involved or if there is only partial deafness. Since pets cannot tell us what they hear, the best criterion for confirming whether a pet can hear or not is by its response to sound (i.e. the pet must consciously perceive the sound).
You can determine your pet's ability to hear by making various noises (from quiet to increasingly louder noises) and seeing if your pet reacts. Often, pets will display an involuntary flicking or twitching of the ears (called "Pryor's reflex@) in response to a sound. Some veterinary schools have also had some degree of success with objective evaluations of hearing, using electro diagnostic procedures.
If you suspect that your pet has a hearing problem, consult your veterinarian so that he or she can determine what kind of deafness is involved and what can be done about it.