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Ask A Vet: Why Are Kittens Born With Blue Eyes?

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Don’t you adore kittens? They are so darling and soft. They invite you to snuggle them with their cute faces and blue eyes. But why do kittens always have blue eyes?

Actually, it is not the final pigment that creates the blue-eyed kitten look. Kittens are just like any baby mammal, it takes time for them to mature. When they are born, their eyes are not even open, so it is not until they are around 10 days old that we can even see their eyes. When we do, the eyes look bluish and are not the eventual color that the cat’s eyes will be when they reach adulthood.

It is only weeks later that the eyes start to show their true color as the pigments start to appear. Cats’ eye colors can range from yellow, green, brown, or blue and many shades in between.  A single cat can even have different color eyes, called heterochromia, and these traits are determined by the cat’s genetics. In fact, eye color is so genetically defined that some breeds of cat have specific colors allowed by the breed registry.

With that said, some cats are destined to have blue eyes permanently. The lack of pigment that appears blue is defined by their DNA as well. White cats sometimes have blue eyes that is associated with congenital deafness. In fact, up to 85% of white cats with blue eyes will also suffer from congenital deafness 1. Sometimes the deafness will only affect one ear, so these cats may seem to behave normally. It seems that the gene for blue eyes is also associated with hearing.

Studies have suggested that some cats with permanently blue eyes (in this case, Siamese) have changes in their brains because of the difference that the lack of pigment makes in the way the eye handles light.² Who your cat is, the way he hears, sees, and even looks are expressions of his genetic map.

Adult eye color is genetically defined, but baby kitten blue eyes are not the same. This blue that you can see is almost like an optical illusion. Because the eyes are still developing, the pigment responsible for the permanent eye color has not deposited or been affected by the light yet, so they appear to be blue. If you love your kitten’s baby blues, don’t despair. If he is meant to be a Frank Sinatra among cats, like the Siamese  (in eyes and voice), it is already written on his genes and all you have to do is wait and see.

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  1. http://www.vet.cornell.edu/fhc/Health_Information/deaf.cfm
  2. Kaas JH. Serendipity and the Siamese cat: the discovery that genes for coat and eye pigment affect the brain. ILAR J. 2005;46(4):357-63. Review. PubMed PMID: 16179744.

 

Written by Dr. Kathryn Primm

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