The “eyes” have it: recognizing ocular emergencies in horses

By Emily Fray, DMV, Pilchuck Veterinary Hospital

HorsesWith one of the largest eyes of any land animal, your horse is equipped with a fine sense of vision, as any rider knows. How many times has your horse shied away from dappling sunlight on the ground or started at the motion of a windblown branch? Vision is of immense importance to your horse, as it is one of the primary ways that your animal detects dangers and maneuvers through a world of obstacles. Which is why it’s vital that you recognize equine eye emergencies.
Such emergencies come in many shapes and sizes. The equine specialists at Pilchuck Veterinary Hospital are trained to diagnose and treat common eye emergencies in horses. In complex cases, we work with a veterinary ophthalmologist.

Any change in your horse's eyes should be evaluated sooner rather than later, as the health of the eye can change rapidly. Signs that your horse is experiencing ocular pain include squinting, tearing, and redness or cloudiness of the eye. The following are the most common eye emergencies we see at Pilchuck Veterinary Hospital.

Corneal ulcers are caused by a disruption of the corneal barrier, usually as the result of trauma, such as getting scratched by a low hanging branch. Along with symptoms of eye pain, signs of corneal ulcers include opaque spots and roughened or irregular areas on the corneal surface. Simple ulcers will heal with minimal treatment, but complex, infected ulcers require aggressive, round-the-clock care. Certain ointments can exacerbate corneal ulcers, so check with your veterinarian before applying anything to your horse's eye.

Conjunctivitis can be caused by environmental allergens, trauma, parasites, or fungal, bacterial, and viral infections. Conjunctivitis causes swelling of the conjunctiva and other soft tissue structures that surround the eye, often resulting in an eye that is swollen shut with pink conjunctival tissue protruding between the eyelids. One or both eyes can be affected. Most cases resolve quickly with appropriate care, but conjunctivitis can lead to more serious infections if left untreated.

Cataracts cause an opacity of the eye’s lens, signs of which include a white lens or whitish discoloration over the pupil. This common condition affects horses of all ages and can be congenital or inherited, or can result from another disease process or an environmental trigger. Small cataracts cause only minor visual disturbances, but larger ones can encompass the entire lens and eventually lead to blindness.

Uveitis is inflammation of the tissue at the back of the eye and can have many causes. One of the most common types is equine recurrent uveitis (ERU), which occurs when an immune reaction triggers repeated episodes of inflammation. A very painful condition, ERU is characterized by redness, tearing, and squinting, along with a cloudy cornea, a small pupil, and changes in the color of the eye’s iris. The frequent inflammation can lead to permanent changes in the eye, making ERU the leading cause of blindness in horses.

Glaucoma is an increase in ocular pressure caused by a buildup of fluid in the eye. It is characterized by a cloudy cornea, dilated pupils, an enlarged eyeball, and inflammation of the iris. Glaucoma is a common complication of uveitis, as the chronic inflammation inhibits the ability of the eye to drain fluid normally. The increased pressure on the optic nerve and other sensitive structures can result in blindness.

Tumors of several types can affect the equine eye. The most common is squamous cell carcinoma, which usually presents as a rough, raised, red mass that forms on the third eyelid, conjunctiva, cornea, or eyelids. This type of tumor occurs most commonly in older horses who have white around the eyes. Other ocular tumors include melanomas and sarcoids, as well as secondary tumors caused by lymphoma.

Any changes in your horse’s eyes should be considered an emergency and should be evaluated as soon as possible to come up with an appropriate treatment. Swift intervention will help prevent complications that can lead to blindness, rupture of the eyeball, or eventual removal of the eye.