Sudden onset blindness in cats can be a very worrying and confusing disease.
For the affected cat they can become extremely disorientated and may behave in a strange and unusual way. They may wander apparently aimlessly, may bump into things, and may become distressed. One of the difficulties is that it may not necessarily be obvious to an owner that the cat has become blind and it may only be when your cat is examined by a vet that you will know why they have started to behave strangely.
One of the signs that may be noticed though is that the pupils (the dark central part of the eye) usually become very dilated if a cat becomes blind.
Causes of blindness in cats
There are many potential causes of blindness in the cat - some will cause a gradual slow deterioration in vision, and in these cases cats often learn to adapt to their reduced sight remarkably well showing few, if any, signs that they have any difficulty. However, if the blindness develops very rapidly then there is no chance for the cat to adapt and he or she will be very disorientated and confused. Some of the causes of sudden onset blindness include:
This is a condition where the optic nerves (the nerves that carries the visual information to the brain) become inflamed and as a result no longer function, causing blindness. This is a rare disease in cats.
Hypertension (high blood pressure)
Hypertension is an important disease in cats and one of the most common causes of acute onset blindness. With high blood pressure, damage can occur to small blood vessels in the back of the eye that can lead to bleeding, or fluid leaking out of the vessels. This may in turn cause the retina (the layer of light-sensitive cells that line the back of they eye and enable us to see) to become detached. If the retina is detached it can no longer function and blindness will occur. In some cats, high blood pressure may also cause some bleeding towards the front of the eye which can be easily seen.
Diseases of the brain
Because the visual signals pass through the optic nerves to the brain and are processed within the brain, if there are diseases affecting the brain (such as infections, inflammatory conditions or tumours) this can potentially lead to blindness.
Just as with humans, cats can suffer with degeneration of the layer of light sensitive cells at the back of the eye (the retina) which is responsible for vision. When this occurs it is often a slow process, which allows cats time to adjust to their reduced vision. However, on rare occasions this can be sudden in onset.
Your vet will first want to confirm or establish that blindness is the cause of your cats clinical signs. This is usually very straightforward and involves some simple examination techniques.
Once blindness is confirmed, because there are a number of potential underlying causes, careful further evaluation will be required. Investigations will include:
- Careful examination of the eye - many causes of blindness may be evident through careful examination of the eye with an ophthalmoscope (the instrument a vet or doctor uses to examine structures within the eye).
- Measurement of blood pressure - as hypertension is one of the common causes of blindness, your vet will want to measure your cat's blood pressure. This is easier than it sounds, and as in humans is usually done by wrapping an cuff around a leg which is inflated and deflated while blood flow is detected through a vessel below the cuff.
- Routine blood and urine tests - these will usually be done to help detect underlying diseases. For example, chronic kidney disease (kidney failure) is a common cause of high blood pressure in cats.
- Brain scans - in some cases, especially if disease of the brain is suspected, your vet may suggest a brain scan is done (an MRI or CT scan). It is possible that your vet will refer you to a special clinic for this.
Treatment and prognosis
The treatment for acute onset blindness will vary according to the underlying cause, but may often involve use of medications (eg, tablets to reduce blood pressure or relieve inflammation). In some cases the underlying cause of the blindness will be reversible and normal vision may return. However, in other cases, even if the underlying cause is resolved, the damage to the sight may be permanent and there may be no change or improvement in the cat's vision.
Adjusting to loss of sight
Even if vision does not return, cats are actually very good at adjusting to loss of sight. They compensate remarkably well by using their senses of hearing, smell and touch (using their whiskers to prevent bumping into objects). However, sudden loss of sight is obviously initially very distressing for a cat. They may bump into objects in the house or garden or become withdrawn and only go where they feel very safe.
Caring for a blind cat has challenges. Affected cats will adjust well but certain changes will make their lives a lot happier. Furniture should be kept in the same position and resources (food, water, litter trays) made easily accessible. Care should be taken to avoid noisy approaches and any children should be told to move slowly, quietly and be careful not to frighten the cat who cannot see them coming.
Blind cats may be able to go outside, but only into an enclosed garden as they may otherwise lose their way or be vulnerable to attack by other cats or dogs. Over time, and with a constant environment that does not change, most blind cats will adapt extremely well and live a very happy life.