Cats can become deaf as they age, or may be deaf from birth (called neonatal or hereditary deafness). A cat with hereditary deafness can be born with normal ears, but within a few days, the inner structures of the ear degenerate.
The gene for deafness is in close proximity to the gene for white hair color in cats and the gene for blue eyes. Often, if one gene is passed on, the other genes close to it are passed on also. So, if a cat gets the gene for white hair coat, it is more likely to get the gene for deafness, too. Evidently, it requires more than just the gene for deafness to be present for a cat to have hereditary deafness. So, we understand that most white kittens are not deaf, but most deaf kittens are white.
White cats may have yellow or blue eyes, and occasionally, one eye of each color. While cats with any of these three eye color combinations may be deaf, most commonly, those with at least one blue eye are affected.
Some cats with hereditary deafness may not be completely deaf. Occasionally, only one ear is affected while the other remains normal. A cat with one yellow eye and one blue eye may have normal hearing on the side with the yellow eye, but be deaf in the ear on the side with the blue eye.
Cats with hereditary deafness should not be bred. Breeding deaf white cats greatly increases the odds of the kittens being deaf.
In summary, most white cats, even those with blue eyes are not deaf. Many have normal hearing, or at least normal hearing in one ear. Simply put, white cats with blue eyes have a greater than normal chance of deafness when compared to other colored cats, but most white cats with blue eyes have normal hearing.