This condition was first identified in Abyssinian cats more than thirty years ago. Then in 2009 a study of many different breeds showed the gene mutation responsible was far more widespread than originally believed.

A cat with one copy of the faulty gene (heterozygous or carrier) is not affected but a cat with two copies (homozygous or affected) will go blind gradually over time. Some cats will be blind by the time they are three and some will be spared until relatively old age. The oldest we know of was thirteen but generally the age at which loss of sight is complete will be between these two extremes.

The bad news

From the genetic testing so far carried out, it seems this gene is worryingly common in the Siamese and Oriental breeds in this country.

The good news

If all breeders test their breeding cats and always mate affected and carrier cats to negative mates, no more cats will be born destined for the dark.

If you belong to a breed club that has a 20% discount on DNA testing at Langford ( see our MEMBERSHIP page on this site ) the cost of ensuring you are breeding responsibly is not all that great.

Facts worth noting

Vets in general practice are unable to diagnose the condition since the Pupillary Light Reflex (PLR) remains even when sight is gone.

 (Although the first two pictures look normal these two cats are blind)


There have been four stages identified in the progression of the disease. The older the cat when it reaches stage one, the slower the destruction of the retinas.

The change in the appearance of the eye is far less marked in Siamese even in poor light. It will be more noticeable in dilute Orientals’ eyes than in the dense colours.


 For further information about the condition, help in managing breeding or just to discuss ways of coping with the problem,

please see our WELFARE page for details of how to contact our Welfare Officer