Corneal Ulcers in Horses 

Updated December 15, 2023  | By: Jamie Whittenburg, DVM
A horse's eye with a corneal ulcer and accompanying conjunctivitis.
A corneal ulcer with accompanying conjunctivitis. Image courtesy of Dr. Andy Kaneps.

Corneal ulcers are a very common ailment in horses that require prompt veterinary attention. A horse’s eyes are often easily damaged due to their placement on the outer sides of the head. Horse eye ulcers are a specific type of injury that can range from simple to severe. 

What are Eye Ulcers in Horses? 

“Eye ulcer” is a term used to describe an injury to the corneal epithelium of a horse’s eye. The cornea is the clear outer layer of cells that covers the entire front part of the eye that faces outwards toward the environment. The cornea acts as a protective cover for the eye and aids the eye in focusing light onto its inner portions for vision.  

The cornea is unique in the fact that, in its healthy state, it does not have blood or lymphatic vessels within. It does, however, contain a high concentration of pain receptors and nerves, meaning that corneal injuries are extremely painful. 

A corneal ulcer is typically a small wound in the cornea. An ulcer may be the result of an injury or an infection. It is also common for ulcers that form in response to an injury to become infected secondarily, which further complicates the condition. 

The terminology can be confusing, but not all corneal injuries are ulcers. A scratch or abrasion to the cornea that is superficial and only affects the top layer of the cells of the cornea is not an ulcer. An ulcer occurs when the injury or infection goes deeper into the cornea. Additionally, there are different classifications of corneal ulcers. It is imperative that a veterinarian examine the eye to ascertain the extent and severity of any horse eye injury or infection

Classifying Horse Corneal Ulcers 

Having your veterinarian assess the eye and classify the extent of the injury or ulcer correctly is the first and most vital step in ensuring a speedy and complete resolution of the issue.  

There are a number of different types of horse eye ulcers. Your veterinarian will determine which type your horse has via an ophthalmic examination which will typically include a fluorescein staining of the cornea. Ulcers range from simple and superficial to deep and non-healing (referred to as “indolent”).  

Complications with Corneal Injuries 

Any ulcer can be complicated by infection. Bacterial infection is common, but a fungal infection can also occur. Equine ulcerative keratomycosis occurs when a fungus that is often a normal inhabitant of the horse’s eye colonizes the corneal injury and overgrows. The resulting inflammation and scarring are severe and often lead to blindness in the affected eye. A rapid diagnosis and prompt treatment are essential in avoiding severe complications. 

Another condition that can occur with equine corneal ulcers is keratomalacia. This is the medical term for a melting ulcer. A melting ulcer occurs when a corneal ulcer or injury becomes infected with bacteria that release enzymes which break down the structure of the cornea. Often, this condition progresses rapidly and may lead to severe destruction of the cornea as well as rupture of the eye itself. If not treated properly, the horse may require surgery to remove the affected eye. 

Signs of Corneal Ulcers in Horses

A veterinarian examining a horse's eyes.

 It is important to be able to quickly recognize the signs of a corneal ulcer in a horse as they are common and can have serious consequences. Signs that may indicate an eye ulcer include: 

  • Squinting (eye pain) 
  • Red conjunctiva (the inner lining of the eyelids) 
  • An abnormal amount or frequency of tearing 
  • Colored (yellow or green) discharge 
  • Swollen eyelids 
  • A cloudy (milky white to blue) appearance to the cornea 

If any of the above signs are seen, a veterinarian should be contacted right away. 

Treatment for Horse Eye Ulcers 

Due to the possibility of severe and long-lasting complications of corneal ulcers, it is imperative to have the issue correctly diagnosed and treated as soon as possible. Owners should not delay calling their veterinarian in hopes that the eye will heal itself. Though very superficial scratches may be able to heal successfully on their own, there is an extremely high likelihood that a secondary infection will arise, and delaying appropriate treatment could result in prolonged treatment, additional pain and discomfort, and even permanent blindness. Treatment of a corneal ulcer will depend on the severity and presence of bacterial or fungal infection. Typically, treatment will involve the administration of: 

  • anti-inflammatory medications,  
  • atropine eyedrops to dilate the pupil and relieve pain,  
  • antibiotics that target the organisms infection the ulcer, and  
  • antifungal medication, if necessary.  

Your veterinarian may also treat the eye with the horse’s own blood serum or ethylenediaminetetraacetic acid (EDTA) to speed and enhance healing. More advanced or non-healing ulcers may require debridement, which is a procedure where the cornea is anesthetized, and the damaged tissue is removed. 

It is essential that owners do not self-treat a horse eye ulcer, as serious complications may arise. The incorrect antibiotic or the application of a medication that contains a steroid can have catastrophic and irreversible consequences.  

Healing and Management of Equine Corneal Ulcers 

The length of time required to completely heal an ulcer in a horse’s eye depends on the severity and the presence of any secondary complications. Simple superficial abrasions and ulcers may heal in 5-7 days. Deeper and more complicated ulcers may require weeks of treatment administered multiple times throughout the day. 

If an ulcer is not healing properly, it is often diagnosed as an indolent, or non-healing ulcer. These stubborn ulcers are often seen in older horses but can be caused by a number of factors. Debridement of the dead and injured corneal tissue may help the healing process. Many indolent ulcers will require a referral to a veterinary ophthalmologist for advanced treatments and care. 

Care Owners and Barn Managers Can Provide

Bay horse wearing the Kensington Uviator Catch fly mask

During the healing process, the horse’s affected eye needs to be carefully looked after. If atropine is being used, the horse must be kept inside, out of direct sunlight because the pupil will be constantly dilated. A fly mask is often helpful as well to protect the eye and keep insects away.  

Medications must be delivered into the eye according to the veterinarian’s directions. If the horse is reluctant to allow treatment, a sub-palpebral lavage system should be inserted to ease the procedure for both the horse and the owner. 

A corneal ulcer will likely cause some vision loss in that eye to a degree, depending on size and severity. Hopefully, with appropriate treatment and time, the horse will regain full vision.  

Can you ride a horse with an eye ulcer? 

It is not advisable to ride or otherwise work a horse with a healing corneal ulcer. Firstly, they are in pain, and the horse should be allowed to rest and heal. Additionally, horses treated with atropine must be kept indoors in low light. Riding a horse with a decreased vision can also be dangerous to both the horse and the rider. 

Preventing Damage to Your Horse’s Eyes 

The anatomy of the eyes being on the sides of the head makes them vulnerable to injury. Horses are also notoriously curious and injury prone. To prevent corneal injuries and ulcers, it is important to check your horse’s environment and try to remove anything that could potentially injure them. A few things to look for are sharp ends on buckets, protrusions on stall walls, fence boards with sharp ends or protruding nails, and sharp edges on hay feeders.

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.