Corneal Ulcers in Dogs: Causes, Treatment, and When to Seek Urgent Care
A squinting, tearing dog with a red eye is not something to wait on. Corneal ulcers range from minor scratches that heal in a week to deep infected craters that can rupture an eye within days. Knowing which type your dog has – and how that changes treatment – is what this guide is for.
What Is a Corneal Ulcer?
The cornea is the clear dome at the front of the eye. It has distinct layers: the outermost epithelium, the underlying stroma (which makes up most of the corneal thickness), and the innermost Descemet’s membrane and endothelium. A corneal ulcer is a defect in these layers – a wound that penetrates at least through the epithelium.
Ulcers matter because the cornea is densely innervated. Even a small superficial scratch causes significant pain – often described by ophthalmologists as disproportionate to the size of the wound. A dog with a corneal ulcer is in genuine discomfort and will show it through squinting, pawing at the eye, and light sensitivity.
The danger of corneal ulcers is twofold: infection and progression. An uninfected superficial ulcer in an otherwise healthy cornea heals quickly with antibiotic support and protection. A deep ulcer, or one infected with proteolytic bacteria like Pseudomonas, can progress to corneal perforation within 24 to 72 hours. Depth and infection status are the two most critical variables a vet assesses when examining a corneal ulcer.
Common Causes
- Trauma: The most common cause. Cat scratches, running through brush, rough play with other dogs, foreign bodies (grass seeds, grit), or rubbing against rough surfaces. The eye is the most exposed organ on the face.
- Dry eye (KCS): Keratoconjunctivitis sicca reduces tear film, leaving the corneal surface poorly lubricated and vulnerable to epithelial breakdown. Dogs with KCS develop recurrent ulcers until the underlying tear deficiency is managed.
- Entropion: Inward rolling of the eyelid causes the eyelashes or lid skin to rub constantly against the corneal surface, producing chronic mechanical trauma and ulceration.
- Distichiasis / ectopic cilia: Abnormally placed eyelashes grow from unusual locations and rub the cornea, causing recurring ulcers.
- Chemical exposure: Shampoo, household cleaners, or other irritants that contact the eye can cause epithelial burns.
- Infection: Bacterial or viral (herpesvirus in some species) primary infections, though purely infectious corneal ulcers without a predisposing cause are less common in dogs than cats.
- Brachycephalic breed anatomy: Dogs with prominent, shallow eye sockets (brachycephalic breeds) have eyes that protrude further, increasing exposure and trauma risk and reducing blink reflex effectiveness.
Depth Classification: From Scratch to Perforation
How Vets Diagnose a Corneal Ulcer
Diagnosis is made by staining the eye with fluorescein dye. The dye adheres to exposed corneal stroma but is repelled by intact epithelium and Descemet’s membrane. Under blue light, an ulcer lights up bright green. The pattern and location of stain uptake gives the vet information about ulcer type, size, and depth.
Additional diagnostic steps may include:
- Schirmer tear test: Measures tear production. Done before any topical anesthetic is applied. Identifies underlying KCS.
- Tonometry: Measures intraocular pressure. Important to rule out glaucoma, which can accompany or cause eye pain.
- Cytology and culture: For deep, infected, or rapidly progressing ulcers. Swabs from the ulcer edge are examined for bacterial type and tested for antibiotic sensitivity to guide targeted treatment.
- Slit-lamp biomicroscopy: For detailed evaluation of ulcer depth and edges, usually performed by a veterinary ophthalmologist.
Corticosteroid eye drops are contraindicated in any dog with corneal ulceration. Steroids impair epithelial healing, suppress immune defenses against infection, and activate corneal collagenases – enzymes that can dramatically accelerate stromal dissolution. A dog whose eye looks worse after starting a compounded or leftover steroid eye drop may have an underlying ulcer that the steroid is rapidly deepening. If a dog is squinting and you are not certain what medication is safe, use saline only until a vet can examine the eye.
Standard Treatment Protocol
Triple antibiotic (neomycin/polymyxin/bacitracin), tobramycin, or ciprofloxacin are commonly used. Applied every 6 to 8 hours. Purpose is to prevent secondary bacterial infection while the epithelium regenerates – most uncomplicated ulcers are not primarily infected. For infected ulcers, culture-guided antibiotic selection is preferred.
Atropine 1% eye drops are used once or twice daily to dilate the pupil and paralyze the ciliary muscle, which is the source of much of the deep aching pain associated with corneal ulcers. Atropine relieves reflex uveitis (intraocular inflammation) and makes the dog significantly more comfortable. It also reduces tearing and photophobia.
Mandatory while the ulcer is healing. Self-trauma from pawing at a painful eye is one of the most common reasons ulcers deepen and become complicated. The e-collar should be worn at all times until the vet confirms the ulcer has healed – not removed at night or during meals, when supervision lapses and rubbing often occurs.
A simple ulcer should show clear improvement – smaller stain uptake area – within 3 to 5 days. If the ulcer is the same size or larger at the first recheck, the vet should reassess for underlying causes (KCS, entropion, indolent ulcer type), change antibiotics based on culture, or refer to a veterinary ophthalmologist.
Treating the ulcer without addressing the cause (dry eye, entropion, distichiasis) guarantees recurrence. Tear production testing, eyelid evaluation, and lid margin examination should be part of every corneal ulcer workup, especially for recurrent cases.
Indolent Ulcers: The Non-Healing Type
An indolent ulcer – also called a boxer ulcer, SCCED (spontaneous chronic corneal epithelial defect), or refractory ulcer – is a superficial corneal ulcer that refuses to heal despite weeks of appropriate antibiotic treatment. The characteristic finding is loose epithelium at the ulcer edge that can be swept off with a cotton swab, revealing that the epithelial cells cannot adhere to the underlying basement membrane.
Indolent ulcers do not respond to antibiotics because they are not caused by bacteria. They are caused by a structural defect in the corneal basement membrane that prevents normal epithelial adhesion. The treatment is mechanical:
- Debridement: Loose epithelium is removed with a dry cotton swab under topical anesthesia, stimulating a fresh healing response.
- Grid keratotomy: A needle or blade creates a superficial grid pattern across the ulcer to stimulate fibroblast activation and new basement membrane formation. Performed under sedation at the vet clinic.
- Diamond burr debridement: A rotating diamond-tipped burr removes loose epithelium and the abnormal basement membrane more completely than manual debridement. Often achieves healing in a single treatment session.
After debridement, most indolent ulcers heal within 3 to 6 weeks with continuing antibiotic drops and e-collar use. Dogs that do not respond may be referred to a veterinary ophthalmologist for additional options including superficial keratectomy.
Breeds Predisposed to Indolent Ulcers
Deep Ulcers and Surgical Options
When a corneal ulcer involves deeper stromal layers, or when a descemetocele (deep crater leaving only the thin inner Descemet’s membrane intact) is identified, surgery is needed to prevent perforation. Surgical options include:
- Conjunctival pedicle graft: A flap of conjunctiva (the pink tissue lining the eyelid) is sutured over the ulcer. The graft provides structural support, blood supply, and a scaffold for healing. It is the most common surgical treatment for deep stromal ulcers.
- Corneoconjunctival transposition: Used for deep or full-thickness ulcers. A section of healthy cornea is rotated to cover the defect.
- Therapeutic soft contact lens: A bandage lens can be placed over a painful superficial ulcer to reduce discomfort and protect the healing surface. Used in selected cases where surgery is not immediately available.
- Enucleation: Removal of the eye is rarely needed but considered when a perforated eye has lost all vision potential and cannot be repaired, or when chronic painful conditions cannot otherwise be managed.
Take your dog to a vet the same day if you observe: the eye is held tightly shut, the eye appears cloudy or has a visible white or yellow spot on the cornea, the eye appears smaller than the other or the pupil is not visible, there is a dark or black mass visible at the edge of the cornea (iris prolapse indicating perforation), the dog is in obvious pain and will not let you examine the eye, or the eye seems to have changed significantly over a few hours. These signs indicate a potentially sight-threatening emergency.
Frequently Asked Questions
The E-Collar Is Not Optional
The single most common reason a corneal ulcer in a dog fails to heal or deepens is self-trauma. Dogs paw at their painful eye the moment the owner’s back is turned – at night, during meals, during walks. The e-collar stays on for the full healing period. Removing it to “give the dog a break” is when damage most often occurs. A week of wearing the cone is a small price for preserving vision.