Equine Eye Vets Veterinary Eye Care for Horses in Texas
A cataract is any opacity in the lens of the eye. If the opaque area is large enough it will affect the horse’s vision. Cataracts appear as gray or white areas in the lens.
In older animals the lens normally develop a grayish appearance (nuclear sclerosis) due to changes in lens proteins in the center (nucleus) of the lens. This is different from a cataract and will transmit light with minimal affect on vision.
Cataracts may develop in animals at any age, although tend to be more common in older animals. The causes of cataracts include:
Although inherited cataracts affect both eyes they may be asymmetrical in their development and progression – affecting the eyes at different times and with differing severity. Inherited cataracts have been poorly dexcribed in horses unlike some other species (dogs). They have been reported in
Cataracts can be associated with other problems in the eye, some of which can be themselves be painful and blinding. These include:
Some cataracts in younger animals may resorb (the lens material leaks out of the lens capsule) - however there is never any certainty this will happen in all eyes. Resorbing cataracts tend to increase the risk of other problems developing (inflammation, glaucoma, and retinal detachment).
Currently the only treatment for cataract is surgical removal (see Cataract Surgery). There are no medical treatments (eye drops or oral medications) which will remove or break up a cataract. Periodically eye drops are marketed which allegedly will cure or reduce cataracts. So far none of these have been shown to have any value in either animals or people.
Cataracts are removed in animals in the same way as in people. After a small incision is made into the eye at the edge of the cornea the lens capsule is opened and the cataract broken up using ultrasound (phakoemulsification) and then aspirated from the eye. Historically various instruments (phako-emulsifiers) have been used to remove equine cataracts - all based on the principle of ultrasonic disruption and aspiration of the cataractous lens fibers.
Horses present a unique problem however in that the eye size is much larger than that of humans, dogs and cats - the species in which cataract surgery is most often perfomed. Because most phakoemulsifiers are designed for people most commercially available ultrasonic probes which is inserted into the eye to disrupt the lens are not of adequate length to reach into the deeper areas of the horses lens for adequate cataract removal. In the past human cataract phakoemulsifiers have been used to remove horse cataracts but the limited probe size may prevent removal of all of the cataract or require a larget (and more traumatic) corneal incision to access the deeper areas of the lens.
At Equine Eye Vets we use a phakoemulsifier developed in Germany which is the first to incorporate probes specially designed for the larger equine eye.
In the past in horses, after the cataract has been removed, the eye has been left without a lens. Horses in this state are rather far sighted but can still have useful vision. In the early 1990's Drs. Millichamp and Dziezyc were the first to implant intraocular lenses in horses after cataract removal (introperative photograph shown here). We now have available foldable lenses which require a small corneal incision for implantation and aims is to be able to maintain optimal vision as can be achieved in people, dogs and cats
For more information on surgery see our Cataract Surgery page.