CONDITION
Corneal Ulcers
A corneal ulcer is a break in the surface layer of the cornea — the clear dome at the front of the eye. These injuries can occur from a scratch, a foreign body like a grass seed, friction from an in-turned eyelid, or irritation from abnormal hairs. The ulcer itself may be tiny or cover a larger area, shallow or deeper, and the severity of what the eye looks like does not always match the size of the damage. Owners often notice their dog or cat holding one eye partly or fully closed, producing tears or discharge, and sometimes pawing at the face. The white of the eye may look red, and in some animals the third eyelid slides partway across. The discomfort can range from mild sensitivity to light through to pronounced squinting, and some pets become quieter or less willing to play. The appearance of the cornea itself may be hazy, cloudy, or look unchanged to the naked eye. This page explores the signals that suggest a corneal ulcer may be present, what happens beneath the surface when the cornea is damaged, how the injury is identified and assessed, and the range of approaches used depending on depth, cause, and how the ulcer is responding. It also describes situations in which healing does not follow the expected pattern.
Why this matters now
Corneal ulcers are among the most common eye problems in dogs and cats. Certain breeds with prominent eyes (Pugs, French Bulldogs, Shih Tzus, Persian cats) are particularly susceptible due to increased corneal exposure. Ulcers can develop at any age and may result from trauma, foreign material, abnormal eyelid or eyelash conformation, or dry eye.
A corneal ulcer represents a break in the corneal surface that can range from superficial to deep. Simple ulcers often heal within days with appropriate treatment. However, ulcers can progress rapidly, particularly if infection develops. Deepening ulcers risk perforation, which can result in loss of the eye. Conversely, some ulcers fail to heal despite treatment, becoming chronic or indolent.
Signals & patterns
Early signals
Squinting or holding the eye closed
Pain causes the animal to hold the affected eye partially or fully shut.
Increased tearing
Excessive tear production is a reflex response to corneal injury.
Rubbing at the eye
Animals may paw at or rub the affected eye due to discomfort.
Redness of the eye
The white of the eye and surrounding tissues often appear red and inflamed.
Later signals
Cloudiness of the cornea
Swelling and cellular infiltration cause the normally clear cornea to appear hazy or white.
Visible defect in the eye surface
Deeper ulcers may appear as a visible divot or depression in the corneal surface.
Yellow or green discharge
Purulent discharge suggests secondary bacterial infection.
Loss of vision or altered appearance
Severe or perforated ulcers may cause obvious structural changes to the eye.
Click to read about the biological mechanisms
How this is usually investigated
Assessment involves examining the eye and using specialised tests to confirm the ulcer and assess its characteristics.
Ophthalmic examination
Fluorescein staining
Schirmer tear test
Intraocular pressure measurement
Bacterial culture and cytology
Options & trade-offs
Treatment aims to control pain, prevent infection, and promote healing. Approach varies based on ulcer depth, presence of infection, and underlying cause.
Topical antibiotics
Eye drops or ointments to prevent or treat bacterial infection.
Trade-offs: Standard treatment for most ulcers. Frequency of application varies based on severity. Ointments provide longer contact time but may blur vision.
Pain management
Oral pain relief and sometimes topical atropine to dilate the pupil and reduce pain.
Trade-offs: Atropine reduces painful pupil spasm. Some animals require additional oral pain medications.
Protective collar
Elizabethan collar to prevent the animal rubbing and worsening the ulcer.
Trade-offs: Essential to protect the eye during healing. May be cumbersome but prevents self-trauma.
Debridement for indolent ulcers
Removal of loose, non-adherent epithelium to promote proper healing.
Trade-offs: Required when ulcers fail to heal despite standard treatment. Often performed with grid keratotomy or similar techniques.
Surgery for deep or complicated ulcers
Conjunctival grafts, corneal grafts, or other surgical repair.
Trade-offs: Considered for deep ulcers at risk of perforation or those that have already perforated. May save the eye when medical treatment is insufficient.
Common misconceptions
"Eye problems can wait until the next available appointment"
Corneal ulcers can progress rapidly, particularly if infection develops. Early assessment allows treatment before complications arise.
"Squinting will resolve on its own"
Squinting indicates eye pain and typically has an underlying cause. Corneal ulcers are common and benefit from prompt treatment.
"Human eye drops are suitable for animals"
Some human eye drops contain ingredients that can impair corneal healing or be harmful to animals. Veterinary assessment determines appropriate treatment.
Related conditions
Entropion
Entropion can be an underlying cause of corneal ulcers, as the inward-rolling eyelid brings fur and skin into repeated contact with the cornea, creating friction and injury to the surface. In some animals, addressing the entropion becomes part of allowing a corneal ulcer to heal.
Ectopic Cilia
Ectopic cilia that grow through the inner eyelid surface can irritate the cornea continuously, leading to corneal ulceration in the area where the hair makes contact. The ulcer may recur or fail to heal until the abnormal eyelash is identified and removed.
Keratoconjunctivitis Sicca (Dry Eye)
Keratoconjunctivitis sicca reduces the tear film that normally protects and lubricates the cornea, leaving the surface vulnerable to drying, friction, and ulceration. Dogs with dry eye may develop corneal ulcers that are slow to heal or that recur, sometimes requiring management of both the tear deficiency and the ulcer itself.
Distichiasis
Distichiasis can cause corneal ulcers when the extra eyelashes growing from abnormal locations along the lid margin make repeated contact with the corneal surface. In some animals the hairs cause only mild irritation, while in others they lead to persistent or recurrent ulceration.
Canine Parvovirus
Canine parvovirus can occasionally be associated with corneal ulceration in severely affected puppies, either through direct viral effects on the eye or secondary to immune suppression and opportunistic infection. The ulcers in these cases form part of a wider pattern of illness affecting multiple systems.
Noting when squinting or eye discharge started provides helpful context. Observing whether the animal is rubbing at the eye indicates whether protective measures are needed. Tracking whether signs are improving or worsening helps assess response to treatment. Keeping the living area free of sharp objects or vegetation reduces injury risk for predisposed breeds.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS