The most common cause of sudden blindness in cats is high blood pressure. Some cats with high blood pressure, also known as hypertension, may appear to have headaches. They keep to themselves, are a bit crabby or stare into space.
Older cats, especially if they have kidney disease or hyperthyroidism, may develop high blood pressure.
If hypertension is not controlled the blood vessels at the back of the eye may burst causing instant blindness. More insidiously any existing heart or kidney disease worsens, and vascular dementia develops.
We routinely check the blood pressure of cats older than 10 years of age with a machine that amplifies the sound of their pulse, but is otherwise very similar to the device used on humans. Most cats are like the old chum above, happy and reasonably relaxed – as long as their person is close by.
Treatment is relatively simple and effective. Many cats even regain their sight.