The eyes are the window to your soul, and that applies to cats who have a stunning variety of eye colours. All kittens are born with blue eyes, some will keep the blue eye colour for life, but others will change colour from 6-8 weeks. The reason eye colour is blue at birth is that kittens aren’t born with all of the melanin, which is a naturally occurring pigment produced by star-shaped cells called melanocytes (pronounced melano-site) that they will eventually have.
Melanocytes contain spheres known as melanosomes, which produce melanin; this pigment affects hair, skin and eye colour. While the number of melanocytes is similar in all cats, the amount of melanin in each melanosome, as well as the number of melanosomes, differs. The more melanin, the darker the eye colour.
There are three possible ways a cat can have blue eyes:
- Dominant white (epistatic white cats) – The gene responsible is symbolised with the letter W (for white). The uppercase means it is dominant, and only one copy is needed for the trait to be expressed. The W gene has pleiotropic effects, which means it influences two or more characteristics. In this case, the W gene suppresses the expression of coat colour, with incomplete penetrance for the blue eye colour and hearing. So, genetically the cat may be black or red, but the W overrides this, some cats will have blue eyes, but not all, and some will be deaf due to degeneration of the organ of Corti. Deafness usually, on the same side, the blue eye colour is.
- White spotting gene (piebald) – White-spotted cats are widespread; the amount of white can range from almost complete to just a few hairs of white (known as lockets). If the white spotting occurs around the eyes, they will be blue. The white spotting gene does not affect hearing.
- Albinism – Five alleles for albinism exist in cats. Full colour (C), Burmese (cb), Siamese (cs), blue-eyed albino (ca), pink-eyed albino (c). Siamese cats (cs) and blue-eyed albino cats (ca) are the only two from the albino group who have blue eyes. The gene responsible for the Siamese cat and other colourpoint breeds (cs) is recessive, which means the offspring must inherit a copy from each of the parents. The gene causes partial albinism in Siamese and pointed cats (Himalayan albinism). This gene causes the coat colour to be heat sensitive, so the cooler extremities such as the nose, ears and tail show colouration and the rest of the body are cream to white.
How many eye colours do cats have?
There are three primary eye colours; brown, green and blue. Each of these colours will vary in hue, so brown can range from chestnut brown through to copper, gold and yellow. Green can be a deep violet down to a gooseberry green, and blue can vary from deep blue to almost translucent blue.
Cat eye colours
The darkest of all cat eye colours, brown has the highest number of melanocytes.
Heterochromia, odd-eyed cats