Cataracts in Horses

Cataracts are deep inside the eye, so it is hard to see the milky white opaqueness and some people believe when the outer eye is white and cloudy that it is a cataract. However, that type of situation is the cornea and may become milky or white for several reasons not related to cataracts. In some cases of genetic cataracts, the damage may be very small and not even cause any symptoms. These are usually found during a routine veterinary visit. Cataracts in an older horse are usually more serious and affect both eyes so the horse will need cataract surgery to regain vision.

Cataracts of the eye are a common cause of blindness in horses. In this condition, an opaque white coating covers the eyes, causing cloudy and blurry vision. In young horses, cataracts are a common genetic defect most often seen in Thoroughbred, Morgan, Rocky Mountain and Belgian horses. However, in older horses, cataracts usually affect both eyes and are caused by the swelling from repeated bouts of eye inflammation and irritation. This may be from eye infections or injuries of the eye. When horses are over 20 years old, the cataracts are considered to be senile cataracts. The cause of the senile type of cataracts are thought to be from the lack of antioxidants as the horse gets older caused by repeated eye inflammation.

The signs that your horse may have cataracts include: 

• Cloudiness or white opacity of the pupil
• Walking into things
• Shying back for no reason
• Jumpiness
• Inability to walk straight

 Types

Cataracts are separated into three categories, which are:

• Incipient (or early) cataracts only affect a small part of the lens and usually does not cause a reduction in sight
• Immature cataracts are more serious and create a deterioration in sight that progresses with age
• Mature cataracts involve the whole lens and cause blindness if not treated

• Congenital cataracts are genetic and affect mostly Thoroughbred, Morgan, and Belgian horses
• Senile cataracts are thought to be caused by repeated bouts of eye inflammation and affects older horses
• Nutritional deficiency and being exposed to certain toxins can cause cataracts in some cases
• Trauma or injury to the eye can cause cataracts

Your equine veterinarian is the best equipped to diagnose cataracts in your horse. The veterinarian will do a comprehensive physical examination including height, weight, temperature, lameness check, body condition score, blood pressure, and breath sounds. Also, the veterinarian will check your horse’s vision and ability to maneuver while walking. Some vision tests such as blink reflex and pupillary light reflex will be done to be sure the retina is not detached. 

Laboratory tests needed to rule out other eye diseases include a blood chemical analysis, complete blood count (CBC), blood gases, blood urea nitrogen (BUN), packed cell volume (PCV), and a glucose test. In addition, your veterinarian will need to get cranial x-rays and an ultrasound to look for abnormalities that may be causing the vision trouble. If necessary, a CT scan or MRI will be performed for a more detailed view.

The only treatment for cataracts in horses is surgical removal of the cataracts. You will most likely be referred to a veterinary ophthalmologist for this procedure because this is their specialty. Cataract removal is a common surgery in horses and only takes a short time.

Examination

The ophthalmologist will need to do a vision examination to make sure your horse is a good candidate for this surgery because it is not usually successful in horses with inflammation, infection, or other problems.

Medication

If your horse has a condition, the veterinarian will prescribe medication to treat the problem before surgery can be done. For inflammation, the veterinarian will give corticosteroids and antibiotics for an infection.

Surgery

The surgery to remove cataracts is called phacoemulsification. This is a relatively modern procedure that is done by using a small probe that creates high frequency waves. These ultrasonic waves actually shatter the cataract and turn it into a liquid so it can be vacuumed from the eye. The eye is then stitched up with small absorbable sutures that will be absorbed in the next 6 to 8 weeks.

Observation

The veterinary ophthalmologist will keep your horse in the hospital for about 7 to 10 days for observation and to monitor your pet’s intraocular pressure.

You will have to spend a lot of time taking care of your horse after the surgery. The veterinarian will give you prescriptions for pain medication, corticosteroids, and antibiotics which you will have to administer 4 to 5 times a day. The medication will have to be continued for about three months. During the recuperation period, your horse must be kept in a darkened stall with little activity. Be sure to return for the follow up appointments and call the veterinarian if you have any questions or concerns.