Horse Red Eye: Causes, Corneal Ulcer Risks & When to Call the Vet

Redness can come from several different eye problems, and some are much more urgent than they look. Mild conjunctivitis can cause redness, swelling, and discharge, often from irritation, dust, flies, allergies, or infection. Merck notes that conjunctivitis in horses commonly causes redness, swelling around the cornea, discharge, and mild discomfort. That said, a horse with a very painful red eye may have something deeper than conjunctivitis alone.

One of the biggest concerns is a corneal ulcer. Horses are especially prone to corneal trauma because their eyes are large and prominent. Cornell explains that even a superficial scratch can become infected quickly with bacteria or fungi, leading to severe inflammation and vision-threatening damage. A red eye with squinting, tearing, cloudiness, or a visible spot on the cornea should make your vet think about an ulcer right away.

Another major cause is uveitis, which is inflammation inside the eye. Merck describes anterior uveitis as causing redness, repeated blinking, light sensitivity, a constricted pupil, and pain. In horses, recurrent uveitis is also a leading cause of blindness. Trauma, immune-mediated disease, and infections such as leptospirosis can all play a role.

Foreign bodies under the eyelid, eyelid injuries, corneal lacerations, and deeper infections can also make the eye look red. Because several serious conditions can look similar at first glance, a horse red eye is usually treated as an eye emergency until your vet proves otherwise.

See your vet immediately if your horse is squinting, holding the eye shut, acting painful, avoiding light, rubbing the face, or has a cloudy blue-white cornea. Those signs raise concern for a corneal ulcer, deeper corneal infection, uveitis, or trauma. Merck lists deep ulcers, descemetoceles, and globe rupture among true ophthalmic emergencies, and Cornell notes that severe corneal infections can lead to loss of vision or even removal of the eye.

You should also call urgently if there is yellow or green discharge, eyelid swelling, blood in or around the eye, a visible wound, unequal pupils, sudden vision change, or if the eye looks sunken or bulging. If the horse had recent turnout, trailering, hay exposure, or a known facial injury, tell your vet. Those details can help narrow down whether trauma or a foreign body is likely.

There are only a few situations where brief monitoring may be reasonable, such as very mild redness without squinting, cloudiness, swelling, discharge, or behavior change, and only if your vet agrees. Even then, horses can hide eye pain well, and eye disease can progress fast. If the redness is still present the same day, or anything worsens, your vet should examine the eye.

Do not use leftover eye medication unless your vet told you to. This is especially important with steroid-containing eye drops or ointments, because steroids can worsen corneal ulcers and delay healing. A medication that helped one eye problem before may be the wrong choice for this one.

Your vet will start with a careful eye exam and pain assessment. That usually includes checking the eyelids, conjunctiva, cornea, pupil size, and whether the horse is visual. Fluorescein stain is a key first test because it highlights areas where the corneal surface is missing. Cornell notes that fluorescein sticks to the deeper corneal layers when the top layer has been lost, helping confirm a corneal ulcer.

Your vet may also look under the eyelids for plant material or debris, check tear production and eye pressure when appropriate, and assess for signs of uveitis such as a painful constricted pupil. If the ulcer looks infected or unusually deep, your vet may recommend corneal cytology, culture, or referral to an equine ophthalmologist. Merck notes that horses with complicated ulcers often need frequent medication, and some require antifungal treatment because fungal keratitis is a common risk in this species.

Treatment depends on the cause. Options may include topical antibiotic medication for uncomplicated ulcers or bacterial conjunctivitis, atropine for pain and reflex uveitis when indicated, anti-inflammatory medication, antifungal medication for suspected fungal disease, and a fly mask plus stall rest in a dim environment. If very frequent eye medication is needed, your vet may discuss a subpalpebral lavage system, which allows repeated treatment through a small eyelid tube.

If the eye is deeply ulcerated, melting, perforated, or not responding to treatment, referral care may include advanced imaging, corneal debridement, conjunctival grafting, hospitalization, or surgery. Early treatment gives the best chance of preserving comfort and vision.

While you are waiting for your vet, move your horse to a clean, dim stall or shaded area if possible. Bright light can make painful eyes much worse, especially with uveitis or a corneal ulcer. A fly mask can help reduce light, insects, and rubbing, as long as it does not press on the eye and your horse tolerates it calmly.

Try to prevent rubbing on legs, walls, or feeders. Rubbing can turn a small corneal injury into a much larger one. Do not patch the eye unless your vet specifically recommends it. Avoid over-the-counter human eye drops, leftover ointments, herbal rinses, or steroid products. In horses, the wrong eye medication can worsen infection or delay healing.

If your vet has already examined the eye and prescribed medication, give it exactly as directed and keep recheck appointments. Eye cases often change quickly, and a treatment plan may need adjustment within 24 to 72 hours. Tell your vet right away if the eye becomes cloudier, the horse starts squinting more, discharge increases, or the cornea develops a white, yellow, or gray spot.

Home care supports healing, but it does not replace an exam. Because horses are at real risk for infected and fungal corneal ulcers, a red eye deserves prompt veterinary attention even when the problem first seems small.