Monday 11 June 2007

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!

11 comments:

Orbiter said...

No, but perhaps blondness is linked to cerebral atrophy (shrunken brains).

Pink Elle said...

Luckily pinkness isn't related to anything!

It's me, T.J. said...

Great post with a lot of details.

Sorry I haven't been by in a while.

I've just been really busy.

later...

Anonymous said...

This is a great article on deafness in white cats. I have a white cat with a grey striped cap and saddle who is also deaf. The backs of his eyes are pink instead of red-Does that mean anything?

Anonymous said...

I have a cap and saddle cat, white with grey tiger marks that is deaf. He eyes also glow pink instead of red in the light. What does that mean?

Orbiter said...

Thanks for visiting Cheryl!

Sorry for the late reply. I was in Istanbul recently, and just happened to read your comment and interesting query now.

Firstly, may I make doubly sure that your cat's eyes are not orange but mistaken for pink?

Otherwise, well...it starts to get a little bit complicated, but I will do all I can to keep it simple.

The deafness associated to the eye-and-coat colour combination you described is pretty unusual. It is quite rare, but there is such a thing called partial albinism. A small percentage of albino cats are also deaf. Then, even more uncommon but still possible, is that your cat is dominant white but incompletely masked. Last but not least, the deafness of your cat could also be congenital, caused by a variety of hereditary factors. Due to random mutation or the wide gene pool, cats of any colour can be born deaf, but again this is extremely rare.

I suspect your cat is one of these, but can come to no solid conclusion.

akthaw4u said...

{sory for bad English plz forgive me}
Hi sir My Find.. has Cat it has Give birth onely one to white cat with blue eyes iam Planing to adopt it..
is ther any KEY thinks to keep in mind...
HI Sir my Friend has white color Cat & it has give birth to Onely one kitten & it is white cat with blue eyes :-) & iam Planing to adopt it..& is ther any KEY thinks to keep in mind.befor
adopt it.(without consorning doctor)Plz Mail me on My E-mail about this .
akthaw
akthaw4u@gmail.com

Orbiter said...

Hi Mr. Thaw,

As long as your kitten is healthy and vaccinated, there is no real reason for concern!

As long as you provide food, shelter and love, it will do just fine!

All the very best!

Unknown said...

I have a white blue eyed cat. My cat has her hearing, which is luckey for her. Diamond is very beautiful, and has had a couple litters of kittens all of which have had there hearing. the only thing abouy Diamond is her attidude, she is not a very loving cat. She will not let you hold her or pet her unless she wants to be peted.

Nobody's home said...

I have a question for you, if I may and if you check this blog?

This post explained a lot about my odd eyed (one is blue), deaf white cat. She has trouble seeing at night (I have nightlights for her). Thank you much for explaining why!

My question: would her blue eye be affected by this other than in darkness? Her blue eye reacts to light but the pupil looks slightly more dilated than her yellow eye. During the day she also seems to have problems with depth perception.

Could her blue eye be affected when it is light out? Could yer yellow eye be affected in general?

She is fine but I am just curious.

Orbiter said...

Hi Arisztid,

Thanks for your query and sorry I have not had the time to post any new blogs recently.

The deafness I described that usually occurs in blue-eyed whites is not at all linked to blindness.

I suggest you get her eyes examined by a veterinary ophthalmologist who can determine if her sight in each eye is indeed compromised.