The causes of feline blindness can be categorised under three headings:
- an obstruction to light getting into the eye
- inflammation of the “deep structures” of the eye and
- a reduction in the sensitivity of the retina of the eye (light-sensitive tissue lining the inner surface of the eye).
This covers diseases of the cornea and of the lens. The former is called keratitis, the latter cataracts.
Keratitis is a condition where the eye’s cornea, the front part of the eye, becomes inflamed.
Cataracts refers to “any opacity on the lens that interferes with the transmission of light to the retina”1. They are rare in cats. They are mostly caused by injury and infections. They can be inherited.
A blue haze on the lens might not be cataracts but nuclear sclerosis, a condition to which older cats are prone and which does not block vision and so does not require treatment.
In a cat cataracts are dealt with if they are severe enough to impair vision in both eyes. The lens is removed, removing the cataracts but leaving images that are not focused.
The human test for glaucoma in the UK is to squirt a jet of air at the eye ball to test intraocular pressure – awful. Glaucoma produces a hard eyeball due to an increase of the pressure of the fluid in the eye. This pressure can stop the blood getting to the retina, damaging it, which in turn can lead to feline blindness. The timescale for this to happen can be a few weeks.
Glaucoma is usually caused by inflammation and infection in the eye. It can also be caused by:
The signs are to be distinguished from conjunctivitis and uveitis (see below) are:
- large eye
- slight redness to the white part of the eye
Soft eye (Uveitis) is an inflammation of the “inner pigmented structures of the eye”1. The inflammation can be caused one of the many infectious diseases that can affect the eye such as:
- feline leukemia
- feline infectious peritonitis
- feline immunodeficiency syndrome
- fungus infections
- roundworm larvae
- eye injury
- bacterial infections in the blood
Soft eye can lead to feline blindness.
Reduction in Sensitivity
This concerns the retina, the light sensitive layer at the rear of the eye that receives the focused light from the exterior via the lens.
When the retina is diseased it cannot interpret the light cast upon it leading to feline blindness. The degree of blindness varies. Loss of night vision can be the beginning of retinal disease. The cat may decide not to go out or stops jumping on furniture in a dark room.
A genetically inherited disease causes retinal disease: Progressive Retinal Atrophy (PRA). Bengal cats are susceptible as are Abyssinian cats – to name two breeds. See: Genetic Diseases in Purebred Cats for a full list.
An inflammation of the retina which is caused by:
- feline toxoplasmosis
- feline infectious peritonitis
- systemic fungal infections
is called retinitis and leads to the destruction of the light receptors in the retina.
A lack of taurine an essential amino acid can cause a degeneration of the central part of the retina.
This is not comprehensive. Please see a good vet if concerned.
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