Dogs get eye ulcers when the outer surface of the cornea is damaged, exposing the sensitive layers underneath. The most common cause is simple trauma, like a scratch from another animal, a thorn, or debris picked up on a walk. But ulcers can also develop from underlying conditions like dry eye, eyelid abnormalities, or bacterial infections that weaken the cornea over time.
What a Corneal Ulcer Actually Is
The cornea is the clear dome covering the front of your dog’s eye. It has several layers: a thin outer skin called the epithelium, a thicker structural layer called the stroma, and a deep inner membrane. A corneal ulcer forms when the epithelium breaks down and the stroma beneath it becomes exposed or inflamed. Shallow ulcers affect only the surface. Deep ulcers penetrate into the stroma and, in the worst cases, can eat through nearly the entire cornea, creating a risk of the eye rupturing.
Trauma Is the Most Common Cause
The majority of corneal ulcers in dogs result from physical injury. A scratch from a cat’s claw, a branch that catches the eye during a walk, rough play with another dog, or sand and grit blown into the eye can all break through the corneal surface. Even something as simple as your dog rubbing its face against carpet or furniture can cause enough friction to damage the epithelium.
Foreign bodies are a related problem. Small pieces of plant material, grass seeds, or dirt can lodge under the eyelid and scrape the cornea with every blink. If an ulcer develops after your dog has been running through brush or hedges, your vet will check for embedded debris that may need to be removed.
Dry Eye Strips Away the Cornea’s Defenses
Tears do far more than keep the eye moist. The tear film lubricates the cornea, delivers nutrients, flushes away debris, and contains antibacterial compounds that fight infection. It has three distinct layers: a mucus layer that sits against the corneal surface, a watery middle layer produced by the tear glands, and an oily outer layer from glands in the eyelids that prevents evaporation.
When tear production drops, a condition called keratoconjunctivitis sicca (commonly known as dry eye), all of those protections disappear. The cornea dries out, becomes inflamed, and grows increasingly vulnerable to damage. Dogs with chronic dry eye often develop recurring corneal ulcers because the surface never fully heals before the next injury occurs. Left untreated, the cornea can become so scarred, pigmented, and blood vessel-laden that the dog loses vision entirely, or a deep ulcer can perforate the eye.
Eyelid Problems That Rub the Cornea Raw
Some dogs develop ulcers not from a single injury but from constant, low-grade irritation caused by eyelid abnormalities. Entropion is a condition where the eyelid rolls inward, pressing fur and lashes directly against the corneal surface with every blink. Distichiasis is a separate problem where extra eyelashes grow from abnormal locations along the eyelid margin, typically from or near the oil gland openings. These rogue lashes rub against the eye and cause watering, redness, and discharge. In severe cases, especially in dogs with prominent eyes, the ongoing friction leads to corneal ulceration and blood vessel growth across the cornea.
Trichiasis, where normally positioned lashes grow in the wrong direction, produces similar damage. All of these conditions create a cycle: the lashes or eyelid irritate the cornea, a shallow ulcer forms, it partially heals, and then the same mechanical irritation opens it up again.
Why Flat-Faced Breeds Are at Higher Risk
Brachycephalic breeds (Pugs, Bulldogs, Shih Tzus, Boston Terriers, Pekingese, and similar flat-faced dogs) are significantly more prone to corneal ulcers because of how their skulls are shaped. Their shallow eye sockets cause the eyes to sit forward and protrude, leaving more corneal surface exposed to the environment. Many of these dogs also have excessively wide eyelid openings that can’t provide adequate coverage or lubrication.
Some flat-faced dogs have lagophthalmos, meaning their eyelids physically cannot close all the way. This leaves a strip of cornea permanently exposed, especially during sleep. On top of that, brachycephalic breeds tend to have reduced corneal sensitivity, so they don’t blink or react as quickly when something touches the eye. Their meibomian glands (the oil-producing glands in the eyelids) also show higher rates of dysfunction, which degrades the tear film’s protective oily layer and speeds up evaporation. The combination of bulging eyes, incomplete blinking, and poor tear quality makes these breeds especially vulnerable.
Bacterial Infections and Melting Ulcers
Bacteria are the most common infectious cause of corneal ulcers in dogs, though viral and fungal infections play a smaller role. The bacteria most frequently identified in canine ulcers are Staphylococcus species, which account for roughly 46% of isolates in studies. Pseudomonas aeruginosa, found in about 21% of cases, and Streptococcus species are particularly concerning because they tend to appear in the most aggressive, tissue-destroying ulcers.
These bacteria don’t always start the ulcer. More often, they colonize an existing wound. Once established, they release enzymes (including collagenases and matrix metalloproteinases) that actively dissolve the corneal stroma. This creates what’s called a “melting ulcer,” where the cornea takes on a gelatinous, liquefied appearance and can deteriorate rapidly toward perforation. Melting ulcers are emergencies. Without aggressive treatment, the eye can rupture within days.
How Vets Diagnose an Ulcer
The primary diagnostic tool is a fluorescein stain test. Your vet places a drop of bright yellow-green dye on the eye’s surface. Healthy corneal epithelium is water-repellent, so the dye slides off. But where the epithelium is missing, the exposed stroma absorbs the dye and glows bright green under a blue light. The size, shape, and depth of the stained area tell the vet exactly how severe the ulcer is. If the dye doesn’t stain a spot in the center of an otherwise stained area, it can indicate the ulcer has penetrated so deep that only the innermost membrane remains, a dangerous situation called a descemetocele.
Your vet will also examine the eyelids for abnormal lashes or rolling, measure tear production if dry eye is suspected, and check for trapped foreign material.
Why Steroid Eye Drops Make Ulcers Worse
One critical thing to know: corticosteroid eye drops, which are commonly prescribed for other eye conditions, are contraindicated when a corneal ulcer is present. Steroids slow down the regeneration of the corneal surface and, worse, amplify the activity of the same collagenase enzymes that cause melting ulcers. Using steroid drops on an ulcerated eye can turn a manageable wound into a rapidly deteriorating emergency. This is true for both topical and oral steroids. It’s the reason vets always perform a fluorescein stain before prescribing steroid-containing eye medications.
Healing Timelines and What to Expect
Simple, shallow corneal ulcers caused by minor trauma typically heal within one to two weeks with appropriate treatment, which usually involves antibiotic eye drops to prevent infection and pain management. Your dog will likely wear an Elizabethan collar (cone) to prevent pawing at the eye, which is one of the most common reasons ulcers worsen or recur.
Deep ulcers, infected ulcers, and melting ulcers require more intensive care and sometimes surgery to save the eye. Procedures range from placing a protective tissue graft over the ulcer to, in extreme cases, removing the eye entirely if it has ruptured or become unsalvageable.
Some dogs develop “indolent” or slow-healing ulcers where the surface epithelium refuses to reattach to the underlying stroma, even though there’s no infection or ongoing irritation. These are most common in middle-aged and older dogs and often require a minor procedure where the vet removes the loose edges of the epithelium and makes shallow scratches in the stroma to encourage the new surface layer to grip and stick.