Leaving with a deaf cat
A healthy cat has very acute vision, smell and hearing. Losing one of these senses still leaves her with two powerful tools; which is why cats which are either blind or deaf can still enjoy very active and happy lives. Cats adjust very well to physical impairment, to the extent that it often comes as a shock for the owner to discover that his cat is disabled.
Many white cats are born deaf. This so-called congenital deafness is hereditary and is associated with the same gene (W) that makes the cat's fur white. This gene is most common in white cats with blue eyes, and blue eyes are more common in long-haired white cats than short-haired cats. As a result these are the cats most likely to be born deaf. The problem is caused by the degeneration of the cochlear blood supply at the age of 3 to 4 weeks - the parts required for hearing do not get a sufficient blood supply to develop. Interestingly, white cats carrying the underlying Siamese dilution pigment gene (cs) can have blue eyes without being predisposed to deafness.
It is because many purebred white cats have this dilution pigment gene (cs) that they are less likely to become deaf than mixed-breed white cats.
Loss of hearing may also be the result of illness, accident or old age. As with blindness, deafness varies in degree - probably the majority of cats with an impediment retain some limited sight or hearing. In many older cats, hearing loss is gradual and not apparent until the later stages. It's not easy for an owner to test a cat's hearing, since as every owner knows cats respond only when they wish to hear, and practice "selective deafness" from kittenhood. However, there are a number of things that one can watch out for. For example, deaf cats sleep more soundly. Usually someone whose approach is heard but not seen will cause the cat to turn its head for a visual inspection. And cats usually hear people coming; so if your cat does not, this may be cause for concern. A cat with one deaf ear will probably frequently turn its head to increase the chance of picking up sounds with the working ear. Cats which are born deaf, or which gradually loose their hearing, adapt much better to deafness than cats that lose their hearing suddenly. The latter may show behavioral changes, for example, appearing confused, irritable, over-attached to the owner or insecure. Some deaf cats become more vocal and vocalization is louder because they can not regulate the volume. Other deaf cats may become completely mute.
a working radar set
Remember that deaf cats are missing one of their early-warning systems, and can be easily startled. And startled cats may respond in self defense by biting or scratching. So if your cat has a hearing problem approach from where it can see you. You can also teach your cat to recognize hand gestures, for example clapping. It is recommended that deaf cats are raised as indoor cats. Because a deaf cat cannot hear a car bearing down on her she is more likely to be involved in a road accident. She may be slower to realize the presence of other dangers (for example, the growl of a dangerous dog) until it is too late to run away. However, if the cat is used to being outdoors, locking her in will be yet more stressful for a newly deaf cat. (Who will certainly manage to share that stress with her owner.) Therefore it is worth exploring the possibilities of creating a fenced-off part of the garden or teaching the cat to use a lead. While outside, it is recommended that the cat wears a collar with the information that she is deaf. Attaching a loud bell to the collar will also help you find the cat if she gets lost. (Remember, she will not hear you calling.)
In June 2003, Dr Hans-Rainer Kurza, an acoustic expert, developed a hearing aid for cats. The hearing aid can be implanted into the cat's outer ear. Although it will not fully restore cat's hearing, the aid ensures that the cat is able to take the usual acoustic signals and re-work them into sounds in the brain. Quiet sounds that hearing-impaired cats cannot pick out become distinguishable. Your veterinary surgeon will be able to advise of details if you chose to take this route. Hearing aids are not cheap (expect to pay several hundred pounds) and not all cats tolerate the hearing aid implant. However, the vet will be able to do tests to determine the suitability of a hearing aid for your cat.
As a final thought - a cat is able to hear frequencies many times higher than the human ear can manage. For the average domestic cat, life is always spent in the company of partially deaf humans.