Cataracts may affect all species. The predominantly affected species in veterinary medicine is the dog. Cats, rabbits and horses are presented less frequently.

A cataract is an opacity of the lens and, or, the capsule which surrounds it and which separates the lens from the remainder of the eye.

Cataracts may be described by their shape, extent, maturity, position within the lens and the cause. These factors may determine whether or not a cataract may be simply ignored or whether treatment may be required.

The minor cataracts of little consequence may be simply monitored for potential growth and development. The more significant cataracts that affect the quality of sight may require treatment. The treatment for cataracts is almost always surgical removal.

Medical treatment of cataracts has been attempted but to this date there has been no medical treatment that has proved to provide any significant improvement in the resolution of cataracts or the quality of sight.

Surgical treatment involves the removal of the lens material and in the majority of cases, replacement of the natural lens with an acrylic prosthetic intraocular implant. There is routinely a four days pre-operative course of medication that experience has proved will control the dog’s very sensitive ocular immune response and lead to greater success from the surgery. This is less important in the cat in which the surgical trauma appears to have less impact.

The cause of the cataract, if identified, may determine its urgency. Cataracts that result from diabetes mellitus are always regarded as an emergency until a detailed assessment has been made. They should be referred as early after diagnosis as possible. This is because swelling of the lens due to the high sugar content allows the absorption of water and thus swelling (lens intumescence) and possible rupture of the lens capsule. For this reason, many diabetic cataracts may bypass the usual pre-operative course of medication for surgery the following day.

What happens if surgery is not performed on a cataract? The outcome will depend on the cause and type of cataract to some extent but the proteins of the cataractous lens will leach through the lens capsule into the eye where a severe inflammatory response may develop. The success of surgery by this stage will be reduced and although medication with anti-inflammatory drugs may delay progression of the inflammation, many of these eyes will be surgically removed as they become very painful.

What is success? Success is the ability to achieve the aim. The aim will vary but In most dogs this would be to restore the quality of sight to allow confident walking to avoid obstacles. In some patients which have deteriorating sight due to retinal degeneration with secondary cataracts, the removal of the cataract will remove an obstruction to the deteriorating retina that will allow the dog to remain visual for longer, albeit with a continuing deterioration of sight. It will also prevent the painful uveitis that may result were the lens left in situ.

Genetics. Some breeds, particularly in dogs, may be affected by genetic form of cataract. Affected individuals should be removed from the breeding pool. Selection is currently made by ophthalmoscopic examination for clinical signs of the disease, though in future, genetic tests may become available. A dog or bitch may have a cataract of which they may be hardly be aware, and that will be most unlikely to progress to a stage where the sight will be noticeably affected but should they be used for breeding with a similarly affected mate then offspring which will develop a blinding cataract may result. The Labrador retriever is the most frequently presented breed in which this applies.