Blue-Eyed White

A client once brought in a white coated cat with blue eyes, complaining that she couldn't get her new pet to come to her when she called, even after frequently making various noises in attempts to attract its attention. Staring perceptively at the textbook blue-eyed white combination on the playful, lively creature on the examination table, I asked her a few more questions, and managed to establish that her cat didn't come to the door to meet her when she came home like most cats do, but continued to sleep on contentedly.

Because I had no means to perform the Brainstem Auditory Evoked Response (BAER) hearing test, I resorted to conducting my own, self-designed "vacuum cleaner" test. I cautioned the surprised owner as I plugged in a vacuum cleaner and switched it on to 'low', all ready in case the cat should fly off in fright at the sudden noise the machine created...but instead, as I anticipated, it looked curiously at the hoover and started to play with the intake nozzle!

Yes, blue-eyed cats with white fur are commonly deaf! Dominant white, denoted by the gene symbol 'W', is the colour associated with deafness in cats. Dominant white masks all other colours and cats may have blue, orange or odd eyes. Those with blue eyes have a high chance of deafness. Odd-eyed cats with only one blue eye have a high chance of unilateral deafness on the blue-eyed side. Those with orange eyes are far less likely to be deaf. Some dominant white kittens are born with smudges of coloured fur on top of their heads where the colour is incompletely masked by the gene. This smudge of colour usually disappears by adulthood, but kittens with colour smudges are more likely to have normal hearing.

The tapetum lucidum, which literally means 'bright carpet' in Latin, is a layer between the retina and choroid of the cat's eye that reflects light back to the retina, causing the eyes to glow at night when struck by light. It is made up of several layers of flattened cells covered by a zone of doubly refractive crystals. It serves to increase the quantity of light caught by the retina, granting excellent night vision to nocturnal animals such as cats. The tapetum is generated from the same stem cells as melanocytes. The blue eyes in a piebald or epistatic white cat indicates a lack of tapetum. Deafness is caused by the absence of a cell layer in the inner ear that originates from the same stem cells as the tapetum.

However, it is important to note that not all blue-eyed whites are deaf, as there are several different genes causing the same physical attributes, so it all depends on the cat's genotype and not its phenotype. Blue-eyedness and whiteness can both be caused by different genes. In odd-eyed white cats, the ear on the blue-eyed side may be deaf, but the one on the orange-eyed side usually has normal hearing.

In some animals, the blue-eyed white trait is sex-linked, which means it is carried on the X chromosome. It is also found in males more often than in females. However, in cats, the gene for white is carried on an autosome, which is a chromosome other than the X or Y sex chromosomes. The trait occurs equally in both male and female cats. Blue-eyed white is not sex-linked in cats.

"What should I do?!" asked the anxious owner, now obviously upset. "Nothing!" I replied, "A cat deals with its deafness very well and compensates for the lack of hearing with its other senses. So well, in fact, that it is almost impossible to distinguish a deaf cat from cats with normal hearing. Naturally you can't command your deaf cat by yelling, but do even hearing cats obey all the time?"

I however advised her not to breed her cat, as this trait could potentially be passed down to her kittens. Deafness can cause problems when a mother cat cannot hear her kittens crying and may neglect them. Deaf kittens cannot hear their mother calling to them and may get lost. Deafness may also affect free-roaming cats because they cannot hear danger approaching. Apart from these disadvantages, I see nothing much that is glaringly lacking in a deaf cat.



Deaf cats are more people-loving cats than those who can hear. However, these cats may have louder voices, presumably because they can't hear how loudly they meow!