Your dog or cat suddenly seems bothered in one eye. You can’t get a closer look as they keep blinking. What if it’s a corneal ulcer?
The Cornea
The cornea is the transparent front part of the eye. In dogs and cats, its thickness ranges from 0.5 to 0.8 millimeters. This tissue is avascular, meaning it does not receive oxygen and nutrients through the bloodstream—unlike most other organs—but primarily through the tear film and aqueous humor.
What Is a Corneal Ulcer?
This involves a loss of corneal tissue. Since the cornea's superficial layers are more innervated than the deeper layers, an ulcer is more painful the more superficial it is—that is, when it affects less than one-third of the corneal thickness. Medium or deep ulcers therefore tend to be less painful, but the risks of perforation and eye loss are increased.
When a corneal ulcer is present, the animal exhibits signs of ocular pain: it may rub the area with its paw, frequently or constantly close its eyelids, and the eye appears red and watery. If the pain is severe, your dog or cat may become less active than usual or even eat less.
How Does a Corneal Ulcer Occur?
A corneal lesion can occur for various reasons. The most obvious one is trauma: a scratch from a fellow animal or a bush branch rubbing against and damaging this fragile surface. An ulcer can also develop following repeated aggression, such as in cases of tear deficiency, for example, or when the eyelids fail to perform their function. Indeed, it may happen that they do not close properly.
- due to a neurological issue,
- because they are too "short" relative to the eyeball—known as lagophthalmos—or because the eyeball itself is too large, referred to as buphthalmos (which differs from exophthalmos, where the eyeball is normal in size but protrudes abnormally from the orbit),
- or because a mass or eyelashes are present on their free edge or inner surface, rubbing against the cornea with every blink, ...
Finally, in cats, the development of a corneal ulcer may occur following infection with the feline herpesvirus. This virus is frequently responsible for recurrent conjunctivitis as well as dendritic corneal ulcers (so named because of their distinctive, highly characteristic branching pattern). The virus can also cause keratoconjunctivitis sicca in affected cats, which weakens the cornea.
My dog or cat seems to have an eye injury—is it urgent to see a vet?
If you suspect a corneal injury in your four-legged companion, it’s best not to delay consulting your vet. Indeed, an untreated ulcer can lead to bacterial or fungal infection. What’s more, if the injury worsens, the eye may perforate.
To determine if the corneal surface is damaged, your veterinarian will perform a fluorescein test. They will apply a drop of green dye (which appears orange before instillation) directly to the eye, rinse it with saline solution or a suitable eye cleanser, and check—using a blue light—whether the dye has adhered to the corneal stroma, the cornea’s second layer. If so, a corneal ulcer is indeed present.
How to Heal a Corneal Ulcer?
If your pet has a corneal lesion, your veterinarian will prescribe:
- an antibiotic gel or eye drop to manage or prevent bacterial superinfection,
- an ocular lubricant to lubricate and hydrate the corneal surface—depending on the molecules used in the formulation, a lubricant may also support corneal surface regeneration in case of injury,
- a pain reliever in syrup or tablet form—in cases of severe pain, the local use of atropine eye drops is essential.
Your vet will also recommend using an Elizabethan collar to prevent any scratching or rubbing, which could obviously delay wound healing.
A check-up is usually scheduled a week later: a superficial, uncomplicated ulcer should not take longer to heal.
