Ask The Vet: Equine Ophthalmology

Courtesy of AAEP

Question: Is there any known causes/conditions/predispositions for early cataract development (early teens) in horses?

Answer: The most common cause of cataracts in horses is Equine Recurrent Uveitis (ERU). ERU is an auto-immune disease where the horse’s immune system attacks the delicate tissues inside the eye. One consequence of this immune system attack is cataract. The diagnosis of cataracts secondary to ERU can be made based on the findings of a complete ophthalmic examination, either by your equine veterinarian or a veterinary ophthalmologist.

Other causes of cataracts in adult horses include blunt trauma to the eye, penetrating trauma to the eye and genetic/hereditary cataracts. Cataract secondary to metabolic disease or toxin ingestion is extremely uncommon in horses.

The only treatment available to improve vision in horses with cataracts is surgical removal of the cataracts. Surgery is performed by a veterinary ophthalmologist, although the surgical technique is very similar to what is performed in humans having cataract surgery. A veterinary ophthalmologist can best advise you on whether cataract surgery is a good choice for your horse.

Question: My 14-year-old Thoroughbred gelding will spook at white (other colors don’t bother him) objects on the ground and gets nervous walking over shadows. He does not like to go into dark horse trailers. Is this a depth perception or behavioral issue…or both?

Answer: This is a great question! When you notice a consistent pattern of behavioral abnormalities, such as resistant behavior when moving from light to dark, it is a great idea to have your horse evaluated by a veterinary ophthalmologist. While we are unable to ask horses what they see, there are a variety of ways to assess vision indirectly. I am frequently amazed and the visual deficits that horses can perform with successfully! A veterinary ophthalmologist may be able to rule out a visual abnormality, which then allows you to concentrate on behavior modification without worrying about an underlying medical condition.

To find a veterinary ophthalmologist near you, go to You can search by state and for ophthalmologists that see horses.

Question: I have an 8-year-old Arabian with one blue eye. I do keep a fly mask with UV protection on him during the day from April through September. How concerned should I be about damage to his eye, and what more can I do to protect it?

Answer: Having a blue iris does not necessarily make a horse more likely to get eye disease (including diseases like equine recurrent uveitis or ERU). Unfortunately, many horses with blue irises also have a lack of pigmentation in the skin around their eyes. This means their eyelids and eyelid skin are pink, not black or brown. Horses with a lack of pigment in the skin around their eyes are more likely to get a type of cancer called squamous cell carcinoma. The best thing you can do as a horse owner to decrease the chances of your horse getting squamous cell carcinoma is decrease their UV light exposure. This doesn’t mean your horse has to live in a dark stall for the rest of their life! Management strategies include UV blocking fly masks (such as the Guardian mask) and turnout at night rather than during the day. Decreasing excessive UV light exposure will help decrease the risk of developing squamous cell carcinoma.

Question: My horse had cyrosurgery two months ago. How long can I expect the drainage from his eye to last?

Answer: Cryosurgery is the application of liquid nitrogen directly or via a metal coupling device to tissue. The most common application for cryosurgery in equine ophthalmology is eyelid and third eyelid tumors like squamous cell carcinoma. Unfortunately, without knowing why your horse required cryosurgery, it is difficult for me to answer your question directly. I would recommend that your horse be re-evaluated by the veterinarian who performed the surgery. Best of luck with your horse!