CONDITION

Corneal Ulcers

Why this matters now

Corneal ulcers can develop at any age in both dogs and cats, though certain factors increase their likelihood. Brachycephalic breeds with prominent, exposed eyes — such as Pugs, Shih Tzus, Persian cats, and Exotic Shorthairs — may be more prone due to their ocular anatomy. Trauma from vegetation, cat scratches, or foreign material is a common precipitant. Some ulcers develop secondary to underlying conditions such as dry eye (keratoconjunctivitis sicca), entropion, or ectopic cilia that create ongoing corneal irritation.

The trajectory of a corneal ulcer depends on its depth, cause, and whether complicating factors are present. Simple superficial ulcers in otherwise healthy eyes may heal within days to a week with appropriate management. However, ulcers can deepen if the underlying cause persists, if infection develops, or if the animal traumatises the eye further through rubbing. Deep ulcers that extend into the corneal stroma carry the risk of perforation — a breach of the full thickness of the cornea that can threaten the integrity of the eye. Some ulcers, particularly in older dogs, become indolent (spontaneous chronic corneal epithelial defects), where the epithelium fails to adhere properly and healing stalls despite the ulcer being superficial. Infected ulcers, sometimes called melting ulcers when enzymes from bacteria or the body's own inflammatory cells dissolve corneal tissue, can progress rapidly and represent a more serious trajectory.

Signals & patterns

Early signals

Squinting or holding the eye closed

Blepharospasm — the reflexive partial or complete closure of the eyelids — is often the earliest sign of corneal pain. The affected eye may appear narrower than the other, or the animal may hold it completely shut, particularly in bright light.

Excessive tearing

Reflex tearing is one of the cornea's immediate responses to injury. The eye may appear wet, with tears tracking down the face, particularly from the inner corner of the eye.

Pawing at the eye

Animals may rub the affected eye with a paw or against furniture and carpet in response to the discomfort. This behaviour can worsen the ulcer through additional mechanical trauma to the already damaged corneal surface.

Sensitivity to light

The animal may turn away from bright lights, prefer dimly lit areas, or show increased squinting when moving from indoor to outdoor environments. This photophobia reflects the inflammation within the eye triggered by the corneal injury.

Later signals

Visible cloudiness or white spot on the eye

As the ulcer develops an inflammatory response, the surrounding cornea may become oedematous (fluid-filled), producing a visible haze or white opacity. In deeper ulcers, a distinct divot or crater may be visible on the corneal surface.

Blood vessel growth across the cornea

The normally transparent cornea lacks blood vessels, but when healing requires additional resources, new vessels may grow in from the limbus (the junction of the cornea and sclera). This neovascularisation appears as fine red lines extending across the normally clear corneal surface.

Yellow or green discharge

Purulent discharge suggests that secondary bacterial infection may have complicated the ulcer. The discharge may be visible at the inner corner of the eye or may accumulate on the lids, causing them to stick together.

Change in eye shape or appearance

In severe cases, the cornea may appear to bulge (descemetocoele, where only the innermost corneal membrane remains intact) or the pupil may appear irregular. These changes suggest a deep ulcer that has compromised a significant portion of the corneal thickness.

Click to read about the biological mechanisms

How this is usually investigated

Investigation of a suspected corneal ulcer focuses on characterising the depth, extent, and any complicating factors present. Ophthalmic examination provides the foundation, with additional tests guided by the clinical findings.

Fluorescein staining

Purpose: A drop of fluorescein dye is applied to the corneal surface; it adheres to exposed stroma where the epithelium is absent, producing a bright green area under blue light that outlines the ulcer's size and shape.
Considerations: This is the primary diagnostic test for corneal ulcers and can be performed quickly. The staining pattern reveals whether the ulcer is superficial (uniformly staining), deep (with a darker centre), or has undermined edges (loose epithelium staining at the margins, characteristic of indolent ulcers). A negative fluorescein test does not completely exclude all corneal pathology.

Slit lamp biomicroscopy

Purpose: Provides magnified, cross-sectional illumination of the cornea, allowing assessment of the depth of the ulcer relative to total corneal thickness, the presence of stromal infiltrate, and any anterior chamber reaction.
Considerations: This examination can reveal details about ulcer depth that are difficult to assess with the naked eye. The presence of cells or protein flare in the anterior chamber suggests secondary uveitis, which influences management decisions.

Schirmer tear test

Purpose: Measures tear production to identify keratoconjunctivitis sicca (dry eye), which is a common underlying cause and complicating factor in corneal ulceration, particularly in dogs.
Considerations: Low tear production impairs the cornea's natural defences and healing capacity. Identifying dry eye as a contributing factor is important because the ulcer may not heal adequately or may recur if the underlying tear deficiency is not addressed.

Corneal cytology and culture

Purpose: Sampling the ulcer bed allows identification of the specific bacteria involved in infected ulcers and determination of their antibiotic sensitivity patterns.
Considerations: This is particularly valuable in deep, rapidly progressive, or melting ulcers where targeted antimicrobial therapy can be critical. The results guide the selection of the most appropriate topical antimicrobial agents.

Tonometry

Purpose: Measures intraocular pressure to identify concurrent glaucoma or, more commonly, the low intraocular pressure (hypotony) associated with reflex uveitis secondary to the corneal ulcer.
Considerations: Knowing the intraocular pressure helps contextualise other clinical findings and can influence management. Elevated pressure in the presence of a corneal ulcer may suggest concurrent disease, while low pressure reflects the degree of intraocular inflammation.

Options & trade-offs

Management of corneal ulcers depends on their depth, whether infection is present, and any underlying contributing factors. Approaches range from topical medical therapy for simple ulcers to surgical intervention for deep or complicated cases.

Topical antimicrobial therapy

Broad-spectrum topical antibiotics are typically the foundation of ulcer management, preventing or treating secondary bacterial infection while the cornea heals. The frequency of application often depends on the severity of the ulcer, with more frequent dosing for deeper or infected ulcers.

Trade-offs: Frequent topical application (sometimes hourly in severe cases) requires significant owner commitment and can be stressful for the animal. Some antimicrobials may be irritating to the eye. Treatment typically needs to continue beyond apparent healing to ensure the corneal surface has fully recovered.

Pain management and uveitis control

Topical atropine may be used to dilate the pupil and reduce the painful ciliary spasm that accompanies corneal ulceration. Systemic pain relief may also be incorporated depending on the degree of discomfort.

Trade-offs: Atropine reduces tear production, which can be counterproductive in patients with borderline tear production. It also causes pupil dilation and light sensitivity, which may be distressing in brightly lit environments. Certain systemic anti-inflammatory medications may need to be avoided as they can impair corneal healing.

Protective measures

Elizabethan collars (cone collars) prevent self-trauma to the healing eye. Contact lens bandages or third eyelid flaps may be placed to protect the corneal surface and promote healing.

Trade-offs: Elizabethan collars are restrictive and can affect the animal's quality of life during the healing period. Contact lens bandages require monitoring and may trap infection if not managed carefully. Third eyelid flaps prevent direct visualisation of the healing cornea, making it difficult to monitor progress.

Debridement for indolent ulcers

Indolent (non-healing) ulcers may require removal of the loose, non-adherent epithelial edges followed by procedures to promote adhesion, such as grid keratotomy (in dogs) or diamond burr polishing.

Trade-offs: These procedures address the specific pathology of indolent ulcers but may need to be repeated if adhesion fails to establish. Grid keratotomy leaves fine scars on the cornea, though these typically fade with time. The procedure is generally not performed in cats due to the risk of corneal sequestrum formation.

Surgical intervention

Deep ulcers, descemetocoeles, or perforated corneas may require surgical repair. Options include conjunctival grafts, corneoconjunctival transposition, or placement of biological tissue grafts to restore corneal integrity.

Trade-offs: Surgery carries general anaesthetic risks and requires specialist ophthalmic expertise. Grafted tissue is not transparent, so some degree of vision obstruction may persist, though the graft often contracts over time. Surgical intervention can be sight-saving for eyes that would otherwise be lost to perforation.

Common misconceptions

Misconception:

"A corneal ulcer is just a minor scratch that will heal on its own"

Reality:

While some superficial corneal abrasions do heal rapidly, corneal ulcers represent a spectrum from mild to potentially sight-threatening. Without appropriate management, even initially superficial ulcers can deepen, become infected, or progress to perforation. The cornea's intense innervation means that even small ulcers can be very painful, and the lack of blood supply means the eye has limited resources to combat infection without external support.

Misconception:

"You can tell how serious a corneal ulcer is just by looking at it"

Reality:

The severity of a corneal ulcer cannot be reliably assessed without proper ophthalmic examination, particularly fluorescein staining and magnified examination. An eye that appears only mildly irritated may harbour a deep ulcer, while dramatic redness and tearing may accompany a superficial abrasion. The depth of the ulcer relative to total corneal thickness, the presence of infection, and the involvement of underlying structures all require professional assessment to determine accurately.

Misconception:

"Eye drops from the medicine cabinet can be used to treat a sore eye"

Reality:

Some medications that are safe for intact eyes can be harmful to ulcerated corneas. Corticosteroid-containing eye drops, which are common in both human and veterinary formulations, can dramatically worsen corneal ulcers by suppressing the immune response and accelerating stromal degradation. Using inappropriate topical medications on an ulcerated eye can convert a manageable condition into a potentially sight-threatening emergency.

Corneal ulcers involve a tissue that is both highly sensitive and uniquely exposed, making them a condition where the speed and nature of the response can significantly influence the outcome. Understanding the difference between a simple surface abrasion and a deeper, potentially complicated ulcer requires professional assessment, as visual inspection alone cannot reliably gauge severity. Brachycephalic breeds and animals with underlying conditions such as dry eye may benefit from awareness of their increased susceptibility, and prompt attention to signs of ocular discomfort can make a meaningful difference in the trajectory of these cases.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS