Cornell Feline Health Center
Cornell University College of Veterinary Medicine
Ithaca, New York 14853
Among the many attributes of a normal and properly cared-for cat is an impressively acute sense of hearing. Owners should be aware, however, that a variety of conditions—either heritable or acquired—can compromise a cat’s hearing and possibly render the animal partially or totally deaf.
A cat’s ears, like those of other mammals, are made up of three structural areas: the outer ear, middle ear, and inner ear. The outer ear consists of the external earflap (pinna), and the ear canal—a narrow tubular passage through which sound vibrations enter the ear from the outside environment. The middle ear contains the eardrum, a taut membrane that vibrates correspondingly to the incoming sound waves, and the auditory ossicles, small bones that transmit the eardrum vibrations to the inner ear. And the inner ear, located deeper within the skull, contains the cochlea, a snail-shaped structure containing nerve endings that receive the vibrations and pass nervous system signals along to the brain, thereby enabling a cat’s hearing.
Some cats are born deaf, and the disability cannot be corrected. Due to an anomaly in their genetic makeup, for example, white cats with blue eyes are at greatest risk for congenital deafness. Indeed, says James Flanders, DVM, associate professor of surgery at Cornell University’s College of Veterinary Medicine, “About 80 percent of white cats with two blue eyes will start to show signs of deafness when they are about four days old as the result of cochlear degeneration.” Another primarily heritable abnormality that may cause deafness, says Dr. Flanders, is atresia—a defect in the development of the ear canal that may result in partial or total obstruction of the channel.
The great majority of feline ear disorders that may cause deafness, however, are acquired. These disorders include: tumors, polyps, and cancerous growths in the ear canal; hypothyroidism; certain antibiotic and diuretic medications; and a wide variety of household chemicals that may be either ingested or seep into the depths of the ear through a perforated ear drum. Among all acquired feline ear conditions, Dr. Flanders notes, the most common by far is otitis externa, an infection of the outer ear canal that, if untreated, can progress into the middle and inner ear. This disorder usually results from infestation of the ear canal with infectious agents, such as yeast, bacteria, or ear mites, and leads to inflammation. Owners should also keep in mind that a cat’s eardrum thickens with age. Thus, hearing difficulties and potential deafness are often found in geriatric cats.
Most acquired feline ear disorders, including otitis externa, can be treated with medicine, says Dr. Flanders, although surgery may sometimes be the only option. Unfortunately, deafness in one or both ears is most often a permanent condition.
A few simple measures, he points out, will substantially reduce the chances that a cat will experience a serious ear disorder that might lead to deafness. He advises the following: maintain a clean environment that will discourage the proliferation of ear mites and other infectious agents; and routinely examine your cat’s ears for such signs of infection as swelling, discharge, and the collection of dirt and debris.
If you observe any of these signs or notice that your cat is persistently scratching at its ears, advises Dr. Flanders, do not probe into the ears in search of the cause. Instead, consult your veterinarian as soon as possible. Although congenital deafness cannot be reversed, a variety of medicines and surgical measures can be effective in countering the progression of an acquired condition that, if untreated, can lead to a total loss of hearing.
To accommodate the needs of a deaf cat, Dr. Flanders advises, the first thing you’ll want to do is confine the animal strictly to the indoors, out of harm’s way when it comes to outdoor sounds that it can no longer perceive and respond to—the roar of an oncoming car, for instance.
Indoors, he points out, you must always be aware of your cat’s hearing loss and adjust your behavior accordingly. He suggests the following: “Avoid startling the animal. Never approach it from behind without signaling your presence. Clap your hands sharply or stomp on the floor. The vibrations will let the cat know that you’re nearby. If the cat has been trained to respond to verbal cues, you’ll have to replace those cues with visual commands—hand signals, for example, or flicking a light switch on and off.”
By Tom Ewing
January 30, 2011