Description

Cataracts occur in many species of animals and horses are no exception. A cataract is any opacity of the lens or its capsule. Many people think that any area of the horse's eye that is white or cloudy is a cataract. For example, the outward part of the eye is the cornea and it can turn white or milky-looking due to many different conditions; however, this is not a cataract.

The lens where cataracts develop is deep within the eye. To determine whether or not a horse has a cataract, a veterinarian needs to dilate the eye and perform an examination. Some cataracts are very small and have little effect on vision. Others are progressive and, in time, can lead to blindness.

Some foals are born with cataracts, but most horses develop them as they age. Injuries to the eye, infections inside the eye, and inflammatory diseases of the eye can lead to the development of cataracts.

For cataracts that have caused the horse to go blind, cataract surgery is the only treatment that may help the horse regain sight. In a mature horse, this procedure is rather difficult due to the large size of the horse's eyeball.

Symptoms

• Cloudiness or milkiness in the lens of the eye
• Behavior that shows horse has a difficult time seeing, i.e. shying suddenly, jumping poorly

Causes

• Congenital cataracts caused by genetic factors
• Trauma resulting from damage to the foal during late pregnancy or during foaling
• Infection or metabolic imbalances in the mare while pregnant
• A result of Equine Recurrent Uveitis ('moon blindness') or trauma
• Senile cataracts in older horses
• Inherited developmental cataracts

Prevention

A horse's eyes are critical to the animal's usefulness. Blind horses are usually not safe to ride and are unable to maneuver well. In addition, they may shy suddenly and may develop phobias that make them untrustworthy around people.

Any time a horse has an observable eye problem, a veterinarian should make a diagnosis. Many eye problems have similar symptoms, and a treatment that works well for one eye problem may cause further damage if attempted in the presence of other eye disorders.

Any time a horse gets a foreign object in the eye it needs to be removed and treated promptly. Trauma, bacterial or viral eye infections, occular parasites, or systemic infections can lead to equine recurrent uveitis and the development of cataracts and blindness. The best prevention of cataracts is to work with a veterinarian any time infection, tearing, squinting, or refusal to open an eye occurs.

Treatment

The treatment of equine cataracts depends on the type of cataract present. In the case of small non-progressive cataracts, little or no treatment is needed beyond periodic checks to make sure the cataract hasn't started increasing in size.

Congenital cataracts in foals may require surgical removal of the lens if they cause blindness. When an animal is less than a year old, it is possible to remove the entire lens under general anesthesia by breaking up the lens with a needle and aspirating it from the eye. Usually this procedure has a 60-80% success rate.

Cataracts in an adult horse may be removed if the eye does not have other inflammatory diseases and if the deeper structures of the eye are functional. This surgery is rather complicated because of the size of the eyeball in a mature horse. Lens removal in the adult horse has approximately a 50% chance of success.

Surgical removal of the lens is followed by intensive treatment with medications for several weeks or months. Veterinarians may incorporate a lavage system into the treatment to deliver medication to the horse's eye easily and efficiently. Medication is introduced into a flexible tube that is passed through the upper eyelid into the conjuctival fornix. Upon reaching the end of the tube, the medication runs over the eye and flows into the system.

During treatment, the horse should be kept in a darkened stall with limited exercise. Hay should be fed from the ground.

While many horses are able to return to normal activities and exercise after successful cataract removal, any horse that has had surgical lens removal is not considered "sound" because vision is somewhat altered from that of a normal eye. .