The two reasons for the inability to hear or deafness in cats is conduction and neurological problems.
Conduction anomalies are associated with the structures of the ear. The outer ear is known as the Pinna, then there is the Tympanic membrane which is the eardrum, the ear canal, and the middle ear which is also called the auditory ossicles.
Neurological problems can occur in the brain, inner ear, or the auditory nerve.
There is unilateral deafness implying that one ear is involved or bilateral deafness involving both ears.
Congenital deafness is a neurological condition and is prevalent in white cats particularly those with blue eyes. Somehow the melanocytes which are the cells responsible producing color pigmentation do not generate sufficiently and that disrupts the blood supply to the cochlea, the portion of the inner ear which is responsible for hearing. It is not known at present why or how this condition is passed down to the white cat with blue eyes.
A secondary condition results from hair cell loss within the cochlea. The cochlea separates into several parts: the scala vestibuli, and the scala media (or cochlear duct). The scala vestibuli is joined to another section called the scala tympani. This section of the cochlea is responsible for the production of fluid essential in hearing. If the vascular bed of this portion of the ear is damaged it affects the sensory hairs that conduct sound causing them to die. It is not certain what exactly causes them to die. Perhaps these hairs die from loss of melanocytes, or their death could be due to abnormal high K+ (potassium levels). Either way, the cat becomes deaf.
Brown waxy buildup in the ear.
Kittens that are born deaf will use their other senses to understand their world. They will still get cues from their mother; gentle nudging, etc, to make sense of their world. Even though their ear canal is shut they will still hear very loud noises.
As the cat grows, if it has unilateral deafness (deafness in one ear) it will be very hard to detect, the only symptom seems to be the inability to sense the direction in which the sound is coming from. Even then, kittens will adapt and will take cues from the rest of the litter and their environment, whether one ear or both ears are affected.
Kittens who do not wake up during a loud noise are suffering from bilateral deafness.
Taking the history of the cat
Examining the inner ear with an otoscope
Electro diagnosis testing, several are used to analyze the auditory response system in the brain stem. The brain stem auditory evoked response (BAER) is a test which measures auditory electrical charges in the cochlea and related auditory passageways.
For conduction deafness the veterinarian will clean the ear canal with a cotton swap, prescribe antibiotics and other medication. Surgery may be required if the ear way is deep within the ear canal.
Unfortunately neurological deafness cannot be cured.
Conduction deafness is easy to cure; simply rid the cat of the waxy buildup in the ear. But there is no cure for neurological deafness. If you have a white cat with blue eyes, it is important to have your pet assessed to determine if it is deaf or not. Your veterinarian will show you ways to help your cat explore and be comfortable in its world. Your pet may not hear sounds but it can feel them. It is also important that it wear a collar with a bell so that if it gets away from you, runs outside for example, you will be able to find it. Having said that, be careful not to let the cat out alone. It will not hear the sound of traffic and it will be defenseless against any kind of danger.