Corneal Ulcer in Horses

Updated Aug. 24, 2022
Eye of Arabian horse

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What Is an Eye Ulcer in Horses?

Eye ulcers are abrasions or scratches of the clear part of the eye called the cornea. The cornea is the clear part of the eye that covers the iris and pupil. It allows light through so your horse can see. There are no blood vessels in the cornea, which slows down healing because there is no way for white blood cells and other healing cells to reach injuries.

The eye is extremely sensitive, so a corneal ulcer can be very painful. They are often caused by trauma (such as scratching the eye) or an inflammatory condition known as uveitis. There is a high risk of infection with corneal ulcers, so it’s important to visit the vet as soon as you see any signs of a ulcer or injury to your horse’s cornea.

If you notice any signs related to corneal ulcers, contact your veterinarian immediately.

Symptoms of Eye Ulcer in Horses

Signs that may indicate an eye ulcer include:

  • Squinting

  • Excessive tearing

  • Discharge from the eye

  • Swelling of the eyelids

  • Redness of the conjunctiva (the inside of the eyelids)

  • Corneal edema (a cloudy or bluish tinge to the surface of the eye)

  • Constriction of the pupil

Squinting is the most common symptom of a corneal ulcer. This occurs because ulcers are very painful and the body automatically tries to protect itself and cover the defect. In addition, the pupil also constricts and becomes very small to protect the eye, but this causes additional discomfort. 

Healing is very slow in this part of the body. During the healing process, blood vessels will migrate from the white part of the eye, called the sclera, into the cornea. This allows the immune system to carry healing cells into the cornea. When healing is complete, these vessels will regress, the pupil will relax, and the horse will appear significantly more comfortable.

Depending on the severity of the ulcer, a scar can sometimes be seen on the cornea’s surface as a white/slightly bluish patch.

Causes of Eye Ulcer in Horses

Some of the more common causes of eye ulcers in horses include:

  • Trauma

  • Foreign body

  • Equine Recurrent Uveitis (ERU): this is an autoimmune condition that causes inflammation within the eye. In certain cases, infection with leptospirosis may initiate uveitis.

  • Immune mediated keratitis (IMMK): inflammation of the cornea caused by an overactive immune system.

  • Eosinophilic Keratitis (EK): an immune-mediated corneal disease that has been associated with parasitic infections or allergies, resulting in inflammation and plaque formation on the cornea that may ulcerate.

Complications of Corneal Ulcers

Since corneal ulcers appear in such a delicate area, common complications include:

  • Indolent ulcers: An indolent ulcer is one that doesn’t heal. In most cases, simple ulcers begin to heal almost immediately. Depending on the size of the ulcer, it should take no more than 1-2 weeks. When ulcers show little or no progress in this time frame, veterinarians consider it a non-healing or “indolent” ulcer.

  • Corneal mineralization: Treatment for ERU often requires management of inflammation
    with topical steroids. The long-term use of steroids can cause areas of the cornea to
    mineralize, which increases the risk of an ulcer. To prevent this, vets may remove
    the mineralized tissue.

  • Infection: One of the most common and potentially most severe complications of corneal ulcers is infection. The cornea has limited immune system capabilities and infection can take over and destroy tissue quickly.

  • Keratomalacia: This is the disintegration or “melting” of the corneal structure secondary to an infection. This is a medical emergency.

  • Corneal perforation: This can occur after a penetrating foreign body or because of an infection that results in keratomalacia.

  • Reflex uveitis: Not only can ERU cause ulcers, but ulcers can cause short-term uveitis by the amount of inflammation they cause in the eye.

How Veterinarians Diagnose Eye Ulcer in Horses

If your horse is squinting or has a lot of discharge from their eye, you should be suspicious of an eye ulcer and call your veterinarian immediately. To diagnose an ulcer, your veterinarian will perform a full ophthalmic examination. A tool called an ophthalmoscope may be used to magnify the structures within the eye. Often, veterinarians will turn off other lights so the horse’s pupil will dilate and they can get a better look in the back of the eye.

A fluorescein stain strip will also be recommended to help diagnose. Fluorescein stain strips are special paper strips with dye on them. During the test, the strip will be gently placed on the cornea to transfer dye to the eye. Afterward, the vet will use a light to detect issues. If there is an ulcer present, the dye will turn green and adhere to the ulceration areas. By using this stain, your veterinarian can tell that there is an ulcer present, where it is and how big it is.

Additionally, your veterinarian may take swabs or scrapings if they suspect that the ulcer is already infected to help determine the best course of treatment.

Treatment of Eye Ulcer in Horses

Corneal ulcer treatment typically starts with a topical antibiotic and possibly a topical antifungal. Because the cornea does not have much of an immune system, it is important to protect the eye from infection while it heals. A topical ointment or drop is used because a stronger dose can be administered directly to the site as compared to oral medications that travel through the horse’s bloodsteam.

Veterinarians may also recommend atropine, a medication that helps to dilate the pupil and decrease the pain associated with the tightening of the muscle that closes the pupil.

Oral pain medications and anti-inflammatories such as phenylbutazone or Banamine are also often used to help relieve discomfort.

During the initial exam, the veterinarian may determine that the edges of the ulcer are thickened or raised. This will make it difficult for new healthy tissue to close the defect. A sterile cotton-tipped applicator or a specialized burr can be used to remove these interfering cells to help encourage the ulcer to heal more quickly.

If the ulcer is particularly deep or goes all the way through the cornea, surgical intervention may be necessary. This often involves a referral to an ophthalmologist who can close the ulcer through corneal or conjunctival grafting.

Recovery and Management of Eye Ulcer in Horses

During the treatment process and recovery, your horse’s eye may stay dilated from the medication, making them much more sensitive to bright light. You can use a fly mask, even indoors, to help decrease the amount of light the eye is exposed to, and also protect against rubbing or other trauma.

Most small ulcers will heal within 1-2 weeks. Larger ulcers or ulcers in the very center of the cornea may take longer to heal. Ulcers secondary to uveitis or other underlying conditions may take longer as well because the inflammation associated with them slows the healing process.

Once the ulcer is healed, the underlying cause may still need to be treated. If the ulcer was caused by trauma, there may be no follow-up required. If an underlying disease such as uveitis or IMMK caused the ulcer, then long-term anti-inflammatories or other treatments may be needed to prevent recurrence.

Eye Ulcer in Horses FAQs

What is the difference between a corneal abrasion and a corneal ulcer?

Both terms refer to the same process and can be used interchangeably.

What is an indolent corneal ulcer?

Indolent corneal ulcers are non-healing ulcers. There are a number of reasons that an ulcer might not heal properly. Your veterinarian may debride the ulcer (remove damaged tissue) to encourage it to heal more quickly. Some of these cases will require referral to an ophthalmologist.


  1. Brooks, Dennis E. Wait and See Won't Work for Equine Corneal Problems. AAEP.
  2. Young, Amy. Equine Recurrent Uveitis. UC Davis School of Veterinary Medicine. 2022.


Featured Image: Khruscheva


Kaela Schraer, DVM


Kaela Schraer, DVM


Dr. Kaela Schraer graduated from Tufts Cummings School of Veterinary Medicine in 2017 with her doctorate in veterinary medicine. After...

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