A corneal ulcer in a dog typically makes the eye look cloudy or hazy, often with visible redness, squinting, and sometimes a discharge. The cloudiness happens because fluid builds up in the damaged layers of the cornea, which is normally crystal clear. Depending on severity, you might notice anything from a faint whitish film over part of the eye to an obviously swollen, weeping, red eye your dog can barely keep open.
What You’ll See on the Eye
The most recognizable sign is a loss of transparency on the surface of the eye. Instead of a clear, glossy cornea, you’ll see a cloudy, whitish, or bluish-gray patch. This cloudiness can cover a small spot or spread across much of the eye, and it results from fluid soaking into the corneal tissue where the protective outer layer has broken down.
You may also notice tiny blood vessels creeping across the white of the eye toward the damaged area. This is the body’s healing response: new blood vessels grow from the sclera (the white part) inward toward the ulcer to deliver nutrients and immune cells. In a healthy eye, the cornea has no blood vessels at all, so any visible red lines crossing onto the clear surface are a strong indicator something is wrong.
The conjunctiva, the pink tissue lining the inner eyelids, often turns an angry red and can puff up or swell around the eye. This swelling, called chemosis, can make the eye look puffy or like the tissue is bulging slightly around the edges. A mucus or pus-like discharge may collect in the corner of the eye or run down the face, particularly if the ulcer has become infected.
Behavioral Signs That Accompany the Appearance
Dogs with a corneal ulcer almost always squint or hold the affected eye partially shut. This reflexive squinting, called blepharospasm, is a pain response and is often the first thing owners notice before they get a close look at the eye itself. Your dog may also paw at the eye, rub their face along furniture or carpet, or shy away from bright light. Some dogs become reluctant to play or seem unusually subdued because the discomfort is constant.
How Different Types of Ulcers Look
Not all corneal ulcers look the same. The appearance changes significantly depending on depth and whether infection is involved.
Superficial Ulcers
A simple superficial ulcer affects only the outermost layer of the cornea. It may be hard to see with the naked eye, appearing as a subtle haze or a slightly dull patch on the surface. Your vet can confirm it by applying a fluorescein stain, a bright green-yellow dye that sticks to damaged corneal tissue but not to the intact surface. Under a blue light, the ulcerated area glows green, making even tiny erosions easy to spot. Simple superficial ulcers typically heal within five to seven days with appropriate treatment.
Deep or Infected Ulcers
A deeper ulcer looks more dramatic. The cloudiness is more intense, the surrounding redness is more pronounced, and there’s often a visible crater or indentation on the corneal surface. Thick, yellow or green discharge suggests bacterial infection. If an ulcer hasn’t healed within seven days, it’s considered complicated, meaning there’s likely an underlying problem such as dry eye, abnormal eyelash growth irritating the surface, or an infection that’s preventing recovery.
Melting Ulcers
The most alarming type is a melting ulcer, which looks exactly as the name suggests. Enzymes from bacteria or the dog’s own immune cells break down the structural proteins in the cornea, causing the tissue to liquefy. The corneal surface takes on a sagging, gelatinous, oozing appearance. The affected area may look like it’s literally dissolving. This is a true emergency because the cornea can perforate, meaning it ruptures completely. Melting ulcers can progress from bad to catastrophic within hours.
Why Some Dogs Are More Prone
Most corneal ulcers in dogs result from trauma: a scratch from a thorn on a walk, a claw swipe during play, or a foreign body like a grass seed getting trapped under the eyelid. Dry eye, where the eye doesn’t produce enough tears to keep the surface lubricated, is another common cause. Eyelid abnormalities, where the lid rolls inward and pushes lashes against the cornea, can also create chronic irritation that leads to ulceration.
Flat-faced (brachycephalic) breeds face dramatically higher risk. Research from the Royal Veterinary College found that brachycephalic dogs have over 11 times the risk of corneal ulcers compared to dogs with normal skull shapes. Pugs specifically have more than 19 times the risk of crossbred dogs. Their protruding eyes and wide eyelid openings leave the cornea more exposed to injury and make it harder for the eyelids to spread tears evenly across the surface. Spaniel breeds also carry about three times the average risk.
One particular concern with flat-faced breeds is how quickly ulcers can deteriorate. A superficial ulcer in a pug or bulldog can progress to a deep or melting ulcer faster than in other breeds, making early detection especially important. If your brachycephalic dog is squinting, tearing up, or has any cloudiness in the eye, treating it as urgent rather than waiting to see if it resolves on its own can make the difference between a simple recovery and a surgical emergency.
What Happens at the Vet
Your vet will examine the eye closely, often with a magnifying lens and a bright light. The key diagnostic step is the fluorescein stain test. A drop of orange-green dye is placed on the eye’s surface. Healthy corneal tissue repels the dye, but damaged areas absorb it and glow bright green under blue light. This reveals the exact size, shape, and location of the ulcer. The stain also helps determine depth: it sticks to the middle layers of the cornea but not to the deepest membrane, so if a very deep ulcer shows a ring of green stain around a dark center that doesn’t absorb dye, that signals the ulcer has nearly penetrated the full thickness of the cornea.
Your vet will also check for underlying causes. They may test tear production to rule out dry eye, examine the eyelids for abnormal lash growth or inward rolling, and look under the third eyelid for trapped foreign material. Identifying and addressing the root cause is essential, because even a properly treated ulcer will come back if the thing that caused it is still there.
What Recovery Looks Like
For a straightforward superficial ulcer, you can expect to use antibiotic eye drops several times a day, and possibly pain-relieving drops. Your dog will likely wear an Elizabethan collar (cone) to prevent rubbing, which can dramatically worsen an ulcer. Most simple ulcers heal within a week, and your vet will want to recheck with another fluorescein stain to confirm the surface has closed.
Deeper ulcers, infected ulcers, or melting ulcers may need more intensive treatment, including more frequent medication, and in some cases surgery to protect or repair the cornea. Recovery from surgical repair takes longer, often several weeks, but many dogs regain good vision. Even after healing, you may notice a faint scar or slight cloudiness where the ulcer was. In many cases this fades over time, though deep ulcers can leave a permanent mark that doesn’t significantly affect the dog’s quality of life.