Cataracts are opacities of the lens, which is a transparent 'smartie-shaped' organ, which sits behind the iris. The role of the lens is to help in focusing.

There are two broad types of cataracts, congenital and acquired:

Congenital: This means 'present at birth'. Cataracts are the commonest congenital eye problem in foalsThere are several causes of congenital cataracts

• Inherited: This has been reported in Belgian, Thoroughbred and organ horses.
• Traumatic: Damage to the foal during late pregnancy or during foaling.
• Second to illness: Certain infections or metabolic imbalances in the mother whilst pregnant can result in congenital cataracts.

Acquired: These cataracts appear later on in life. They are not present at birth.Again there are several causes:

• Secondary to Equine Recurrent Uveitis ('moon blindness') or trauma: This is the commonest cause of acquired cataracts
• Senile cataracts: These are rarely seen in horse less than 20 years old
• Inherited developmental cataracts: This is an uncommon cause of cataracts, they can appear at any age but tend to be seen in juvenile horses. The method of inheritance is complicated and we still have much to learn about how this works.

My horse has a cataract- will he go blind?

Cataracts can be further classified as progressive or stationary. Progressive cataracts enlarge at different rates, in the worst cases resulting in a completely opaque lens, which renders the horse effectively blind. Stationary cataracts remain the same size- in many cases these are small cataracts which have no effect on the horses vision.In order to determine that a cataract will progress, repeat examinations are required ideally by a Veterinary Ophthalmologist who has special equipment for examining cataracts. This is further complicated by the unpredictability of some cataracts progression. Some cataracts will show an initial increase in size and then become stationary, whilst, more rarely, some cataracts which have remained unchanged for many years can start to enlarge at a later date.By examining the position cataracts we can get an idea of their likely behaviour. Cataracts in specific locations we know tend to behave in similar ways. Thus for example, cataracts, which are at the very edge of the lens (capsulo-lenticular cataracts), tend to be non-progressive and never cause any visual impairment.

Can cataracts be removed, as they are in people?Cataract surgery is possible in horses. In young foals surgery can be very successful. In adult horses the surgery becomes much more difficult as the size of the eye is so large. Cataract surgery is not done routinely in the UK although there are several specialist centres in Europe who have a good success rate.