Corneal Ulcers

The clear front covering of the eye, known as the cornea, is a delicate structure. As such, corneal ulcers can result from trauma to the eye or one of many medical conditions that affect the eye. Both dogs and cats can get a corneal ulcer. If your pet blinks excessively, squints, paws at his eyes, seems sensitive to light, or has redness or swelling in one or both eyes, he could have this condition. Most corneal ulcers respond to drops or ointment put right in the eye. Sometimes surgery is indicated to help protect the cornea as it heals.


The cornea is the thin, transparent layer of cells on the front of the eye. The cells that make up the cornea are very fragile so that anything that rubs, scrapes, or irritates the eye can damage them or rub some of them off. When this happens, we refer to it as corneal ulceration. Corneal ulceration can occur if the eye is irritated by chemicals, dust, or inadequate tear production. Trauma, such as scratching, can also cause a corneal ulcer. In addition, some viral infections, such as feline herpes virus infection, can cause corneal irritation and ulceration.

Corneal ulceration is also caused by two very common conditions worth mentioning at the outset:

Entropion is a medical condition in which the pet’s eyelids roll inward and the eyelashes or other hairs (which are normally on the outside of the eyelid) are pulled underneath, where they can scrape against the cornea. This can lead to corneal ulceration.

Dry eye: Tears are a natural lubricant for the eye. When the eye doesn’t produce enough tears, the cornea can become irritated, and eventually, a corneal ulcer can form. This condition is commonly called dry eye, but the medical term is keratoconjunctivitis sicca (KCS).

There are two types of ulcerations: superficial, which affects only a small amount of the top layer of the cornea, and deep, which extends deeper into the layers of the cornea and can result in severe scarring and even eye rupture.

Most cases of corneal ulceration heal without complication when treated promptly. If treatment is delayed, bacteria and other pathogens, such as viruses and fungi, get an opportunity to cause infection, which can further complicate the condition.

Without proper treatment, or with severe injury, corneal damage can lead to vision-compromising scarring or even blindness. If the eye is severely damaged, surgical removal of the eye may be recommended to prevent the pet from suffering constant pain and chronic infection.

Symptoms and Identification

Corneal ulcers are extremely painful. Animals with this condition may squint, rub their eyes, or tear excessively. Sometimes, a thick mucous discharge can develop. Clinical signs of corneal ulceration also include:

  • Closed eyelids
  • Tearing, swelling, redness of the eyes
  • Conjunctivitis (inflammation of the membranes lining the eye)
  • Sensitivity to light
  • Pawing or rubbing at the eye

If the ulceration is severe, permanent damage to the cornea or rupture can occur so that blindness results.
Diagnosis of corneal ulceration is usually based on physical examination findings. If a pet is squinting because his/her eyes hurt, a veterinarian will often begin the examination by applying a drop of liquid topical anesthetic directly to the eye. This is not painful, and after a few minutes, it numbs the surface of the eye so the examination can proceed. During the examination, the veterinarian will also look for foreign material, abnormal hairs, or other causes of irritation. Entropion can also be diagnosed during the physical examination.

While examining the pet’s eyes, the veterinarian will often instill fluorescein stain. Fluorescein is a green-tinted dye that fluoresces (glows) under blue light. If the surface of the cornea is intact, the fluorescein dye will not stick to the eye. However, if there is a scratch, ulcer, or wound on the cornea, the dye adheres to the defect and can show your veterinarian where and how serious the injury is. Fluorescein staining is not painful and can provide valuable information about the condition of a pet’s eye.

Testing to determine if tear production is adequate is typical in cases where dry eye (keratoconjunctivitis sicca) is suspected.

Affected Breeds

Any dog or cat can develop a corneal ulcer. Dog breeds predisposed to dry eye (keratoconjunctivitis sicca) include Boston Terriers, Bull Terriers, English Bulldogs, and English and American Cocker Spaniels.

Entropion can be an issue for many dog breeds including Akitas, American Staffordshire Terriers, Pekingese, Pomeranians, pugs, Shih Tzus, Great Danes, Saint Bernards, and Newfoundlands.


Most corneal ulcers respond well to specially formulated antibiotic eye drops or ointment applied directly to the patient’s eye. If the underlying problem is dry eye (KCS), additional therapy can be initiated to help improve the condition. If the underlying cause is entropion, surgical correction may be recommended.

If the corneal ulcer is very deep or very large, other measures may be recommended, including an eye patch or surgery to temporarily cover (and protect) the surface of the cornea.


Some cases of corneal ulceration are preventable. For example, monitoring pets during play and exercise to reduce the risk of trauma to the eye, and keeping pets current on vaccinations against diseases like feline herpesvirus can reduce the likelihood of developing corneal ulceration associated with these causes.

This article has been reviewed by a Veterinarian.

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