Odd eyed cat

Odd-Eyed Cats (Heterochromia)

About   Types of heterochromia   Breeds with odd-eye colours

Odd eyed cat

About odd eyes

Also known as dichroic eyes, heterochromia iridis (hetero = different, chromia = colours, iridis = iris), is a condition in which cats have odd-coloured eyes. One will be blue, the other may be green, copper or brown. The condition may be inherited, congenital or acquired.

  • Inherited heterochromia, it is mostly found in epistatic white cats (which means the cat is genetically another colour, but it is hidden by the white masking gene)  or in bi-colour cats,  due to the white spotting gene.
  • Congenital heterochromia may be due to mosaicism in which two distinct populations of cells arise from one fertilised egg, or chimerism in which two zygotes merge early on in the development stage. This possibly explains heterochromia in solid coloured cats who don’t carry the white spotting gene.
  • Acquired heterochromia may be caused by uveitis, certain medications, iris tumours and trauma.
Back to epistatic white cats for a moment. People commonly associate white animals with albinism, and in many cases this is true, but with cats, true albinism is quite rare and when it does occur, the eyes will be very pale blue or pink. It should be noted that a form of albinism occurs in cats which is responsible for the pointed pattern most
commonly associated with Siamese cats, but is also found in other breeds such as the Tonkinese, Burmese and Himalayan cats, it  can also occur in mixed-breed (domestics). Most white cats with odd or coloured eyes are white due to the white masking gene (W)  a dominant gene, which is why it is represented with an uppercase W. Recessive are shown in lower case w, which symbolises non-white. This gene masks the effect of all other colour genes. It is this gene which is also responsible for deafness in some white cats with blue eyes. Remember that cats have two sets of genes, one from their mother and one from their father. Three combinations can occur:

  • WW – White cat
  • Ww – White cat (the dominant white W overrides the
    recessive w)
  • ww – Coloured cat

It is also possible for a cat to be white due to the white spotting gene, which presents in varying grades from 1-10. The higher the grade, the more white, and in some cases only a tiny patch containing only a few coloured hairs may be present.

Melanin is a complex polymer found in the hair, skin and eyes, it is responsible for determining your cat’s coat and eye colour.  Its role is to protect the skin and eyes from UV radiation. The amount of melanin in the iris determines the colour of the eye.  Cats with blue irises have the least amount of melanin and brown eyed cats have the most. All kittens are born with blue eyes, but for those whose eyes change colour, melanocytes begin to
produce melanin in the eye from 6-7 weeks of age when light hitting the eyes triggers this event. As melanin concentration builds up, the eyes begin to change colour, however, with epistatic white or cats with the white
spotting gene,  melanin is prevented from forming in the iris. Epistatic white cats with one blue eye may also be deaf on that side too as this particular gene can cause degeneration of the inner ear.

Forms of heterochromia:

Heterochromia comes in three forms. Complete, partial and central

Complete heterochromia: One eye is blue, the other eye another colour.

Complete heterochromia

Central heterochromia: Two colours are present in one eye, usually there is a ring or halo surrounding the pupil with another colour on the outer portion of the iris. This type of heterochromia is rarely seen in cats.

Central heterochromia

Sectoral heterochromia: Two colours are present in one eye, with one portion being blue, and the other a darker colour.

Sectoral heterochromia

Interestingly, David Bowie was known for his odd coloured eyes, and many believe he had heterochromia, however, his different eyes are due to a condition known as anisocoria, in which one of his pupils remained permanently dilated (large) as a result of a fight he had with a friend as a teenager. The fixed pupil gave him the appearance of one blue eye and one darker coloured eye.

Anisocoria

Image courtesy Martin Cathrae, Flickr

Odd eyed cat

Image courtesy Chris Yarzab, Flickr

Breeds of cat who can have odd eyes:

Footnote:

Before I finish this article, I would like to mention dark spots which can sometimes appear in your cat’s eyes, which are known as iris freckles, iris hyperpigmentation or iris melanosis and similar to moles that people get. Brown
spots should always be checked out by a veterinarian as in some cases they can become cancerous over time or more commonly, lead to glaucoma. If you notice any changes to your cat’s eye, seek medical advice.

Brown spots in cat

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