Yes, Siamese cats have eye problems relating to vision. They are quite well known because of the Siamese cat’s squint. However, the extent of the eye problems are probably not fully appreciated by most cat owners.
Line breeding – aka inbreeding – of Siamese cats has perpetuated the genes that are a disadvantage to the cat and which would have been selected out if these genes had been carried by free-roaming stray cats. Genes which cause problems get in the way of survival and therefore they are selected out over time.
Siamese cats have poor stereoscopic vision2. This is because of a lack of nerves in their brains designed to compare the signals coming from the left and right eyes. Stereoscopic vision provides 3-D vision giving depth to the image.
This results in Siamese cats seeing double. Or Dr Bradshaw says, ‘one eye may shut down completely, sometimes causing a squint to develop’.
There is another Siamese cat eye problem. A malformation in the retina1 which may cause a temporary impairment in their vision by blurring when they move their attention from one object to another.
A condition called nystagmus is also quite common in Siamese cats. The eyes jerk back and forth. This condition is not confined to Siamese cats. This is may be caused by vestibular disease (disease of the inner ear where a cat’s balance is regulated).
Note 1: the retinas of cats contain two types of ganglion cells, Y-type and X-type. Y-type responds to movements and inhibit the output of X-type cells when the eyes are moving. Siamese cats have about 14% of Y-cells compared to 35-45% in cross-breed non-orientals.
Note 2: Normally around 35% of the cat’s nerve fibres stay on the same side of the brain. This allows comparisons to be made between the images from each eye. However, in Siamese cats ‘few binocular driven calls can be detected….’. Behavioral evidence suggests that they do not have stereoscopic vision.
Source: Cat Sense by Dr John Bradshaw and The Behavior of the Domestic Cat by the same author and Rachel Casey and Sarah Brown.
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