I have a deaf cat, Molly.  We rescued her when she was eight or nine years
old and now she's 16-17 years.  We don't know how long she's been deaf--it
came on very gradually--she may have been deaf when we got her but it never
has seemed to bother her.  She's extremely mellow and I keep her (and all my
cats) strictly indoors.  I'm sure it's harder for a cat who suddenly goes
deaf but Molly doesn't seem to be bothered by much of anything.

Bonnie

My parent's late cat, Berries, went deaf in her last year or two of
life. (I later learned it's a symptom of Feline Cognitive Disorder, aka
kitty alzheimers). I started using hand gestures to get her attention.
Another tip I once read was that if you come up to a deaf kitty who is
resting, to gently tap your fingers next to them. They will feel the
vibrations of your fingers and not be so startled (vs just touching
them). That seemed to work quite well.

The only odd thing she did (which I can't say I blame her) was she
started meowing quite loudly, because she obviously could not hear
herself.

My parents had a blue eyed white cat who was deaf. It never seemed to bother
her, but I don't remember her ever meowing.

I've wondered if Espy is deaf. He doesn't seem to hear vey well but
maybe he is very sensitive to vibrations because he will react to my
clapping hands together. Most of the time anyway. If I talk fairly
quietly behind him or call his name, he usually does not react.

He is certainly a very heavy sleeper for a cat if he isn't deaf. I
think he's hard of hearing because there are just signs that he's deaf
and signs that he isn't. Weird. He does talk pretty loudly when he
thinks it's time to be fed or treated.