What actually happens to a dog's eye when it has a corneal ulcer?

The cornea is a clear, multilayered dome covering the front of the eye, made up of an outer epithelium, a thick middle stroma, and an inner Descemet's membrane and endothelium. A corneal ulcer, also called ulcerative keratitis, occurs when trauma, infection, or an underlying disease erodes through the epithelium and exposes or damages the stroma beneath it (Merck Veterinary Manual, 2023). Veterinary ophthalmologists classify ulcers by depth, since a superficial erosion carries a very different prognosis than a descemetocele, where only the innermost membrane separates the eye from rupture (American College of Veterinary Ophthalmologists, n.d.).

Because the cornea has no direct blood vessels, it heals more slowly than skin and relies on tear film, oxygen diffusion, and migration of epithelial cells across the defect (Cornell Riney Canine Health Center, n.d.). This is also why flat-faced, brachycephalic breeds such as Pugs, French Bulldogs, and Shih Tzus are overrepresented in corneal ulcer cases: their prominent, shallow eye sockets and reduced blink reflex leave the cornea more exposed to drying and direct trauma (Merck Veterinary Manual, 2023).

What are the first signs an owner is likely to notice?

Owners typically catch a corneal ulcer because their dog is squinting or holding one eye partly or fully closed, a reflex called blepharospasm that signals pain rather than mere irritation. Excess tearing or thick, yellow-green discharge, redness of the white part of the eye, and pawing or rubbing at the face are also common early signs (American Veterinary Medical Association, n.d.). Some dogs develop a visible cloudy or bluish haze over the cornea as the surrounding tissue swells with fluid (corneal edema), and a third eyelid may partially cover the eye as a protective response.

A key clue that distinguishes an ulcer from simple conjunctivitis is asymmetry: one eye looks and behaves differently than the other, and the dog resists having that side of the face touched. Sudden light sensitivity, where a dog seeks out dark rooms or squints hard outdoors, often accompanies deeper ulcers because inflamed intraocular structures become more sensitive to bright light (Merck Veterinary Manual, 2023).

What actually causes eye ulcers in dogs?

Blunt or sharp trauma is the leading cause, from a scratch by another animal's claw, a stick or thorn during off-leash play, or self-inflicted rubbing after an initial irritation. Chemical exposure to shampoo, dust, or lawn chemicals can also erode the epithelium. Underlying eye conditions frequently set the stage: dry eye (keratoconjunctivitis sicca), in which insufficient tear production leaves the cornea unprotected, and entropion, where the eyelid rolls inward and eyelashes chronically rub the surface, are both well-documented predisposing factors (Cornell Riney Canine Health Center, n.d.).

Infectious causes matter too. Bacterial contamination, often with Pseudomonas or Staphylococcus species, can turn a simple scratch into a rapidly progressing melting ulcer within 24 to 72 hours because bacterial and host-derived enzymes literally digest stromal collagen (American College of Veterinary Ophthalmologists, n.d.). Indolent ulcers, sometimes called Boxer ulcers, are a distinct chronic form seen most often in middle-aged and older dogs, where the epithelium fails to properly adhere to the stroma and the erosion won't heal despite weeks of standard treatment.

How does a veterinarian confirm it's actually a corneal ulcer?

The standard diagnostic test is fluorescein staining, in which a vet applies an orange-green dye to the eye's surface; the dye binds exposed stroma and glows green under blue light wherever the epithelium is missing, confirming both the presence and rough size of the ulcer (Merck Veterinary Manual, 2023). A Schirmer tear test is often run alongside it to measure tear production and rule out dry eye as an underlying cause, since normal tear production in dogs is generally above 15 millimeters per minute on that strip test.

Vets also examine the eyelids, third eyelid, and eyelashes for anatomical problems like entropion or ingrown lashes that could keep causing damage, and they'll assess anterior chamber depth and clarity to check whether the ulcer has progressed toward a descemetocele or perforation. Referral to a board-certified veterinary ophthalmologist is common for deep, non-healing, or rapidly worsening ulcers, since specialized magnification and surgical options may be needed (American College of Veterinary Ophthalmologists, n.d.).

How are dog eye ulcers actually treated?

Simple, superficial ulcers are usually managed medically with a topical broad-spectrum antibiotic, often applied four to six times daily, plus an oral or topical pain reliever, since corneal injuries are considered among the most painful ocular conditions in veterinary medicine (Merck Veterinary Manual, 2023). Atropine drops are sometimes added short-term to relieve the muscle spasm that causes deep aching pain, though they can noticeably dilate the pupil and increase light sensitivity during use. Topical corticosteroids and many over-the-counter human eye drops are avoided or used only under close supervision, since steroids can worsen an ulcer and accelerate melting if infection is present.

Deeper ulcers, melting ulcers, or descemetoceles typically require surgery, such as a conjunctival graft or corneal-conjunctival transposition, to physically reinforce and protect the eye while it heals (American College of Veterinary Ophthalmologists, n.d.). Indolent, non-healing ulcers often respond to a diamond burr debridement or grid keratotomy procedure performed under sedation, which removes the loose, non-adherent epithelium and encourages proper reattachment; healing rates after these procedures are reported in the range of 80 to 90 percent within a few weeks.

What can be done at home while an ulcer heals?

An Elizabethan collar (e-cone) is non-negotiable for essentially every dog being treated for a corneal ulcer, since a single episode of pawing or rubbing can convert a healing superficial scratch into a ruptured globe. Owners need to give every prescribed medication on schedule and in the correct order when multiple drops are involved, typically waiting several minutes between different eye medications so each has time to absorb (Cornell Riney Canine Health Center, n.d.).

Follow-up rechecks, often at 5 to 7 day intervals, are used to re-stain the eye and confirm the ulcer is shrinking rather than staying the same size or worsening; a lack of measurable improvement at a recheck is one of the main triggers for escalating to surgery or specialist referral. Dogs with chronic dry eye also need long-term tear-stimulating medication such as cyclosporine, since the underlying deficiency will keep producing new ulcers if left untreated.

What's the long-term outlook, and can this happen again?

Most uncomplicated superficial ulcers heal within 3 to 7 days with appropriate treatment and leave no lasting vision impairment, though a faint scar or pigment change on the cornea can persist (Merck Veterinary Manual, 2023). Deeper ulcers and those requiring surgical grafts carry a longer recovery, generally several weeks, and a higher chance of a visible corneal scar, but most dogs retain functional vision in the affected eye.

Dogs with anatomical risk factors, brachycephalic breeds, entropion, or unmanaged dry eye, are prone to recurrence unless the underlying issue is corrected, which is why vets often recommend addressing entropion surgically or committing to lifelong tear-replacement therapy rather than treating each ulcer as an isolated event (Cornell Riney Canine Health Center, n.d.).