What exactly is happening to a cat's eye when it has a corneal ulcer?

The cornea is the clear, dome-shaped window covering the front of the eye, built from three layers: an outer epithelium, a thick middle stroma, and Descemet's membrane sitting above the endothelium. A corneal ulcer means at least the epithelium has been breached, exposing tissue underneath, and veterinary ophthalmologists grade ulcers by how many layers are involved, since a shallow epithelial defect behaves very differently from a deep stromal ulcer or a descemetocele where only the thinnest inner membrane remains intact (Merck Veterinary Manual, 2023).

Because the cornea has no blood vessels of its own, it depends on tear film and the blood supply at the limbus (the rim where cornea meets sclera) to deliver the cells and growth factors needed for repair. Cornell University's veterinary ophthalmology service notes that this avascular structure is why even small epithelial defects can take three to seven days to close, while ulcers that reach the stroma often need topical antibiotics and pain control for one to two weeks or longer (Cornell University College of Veterinary Medicine, 2022).

What are the first signs an owner usually notices?

Cat owners typically notice a change in how the eye looks and behaves before they notice a physical wound: the cat squints or holds the eye partly closed (blepharospasm), the eye looks red or has a bluish-white haze over the cornea, and there is excessive blinking or pawing at the face. The American Association of Feline Practitioners lists ocular pain signs in cats as including avoidance of light, reduced appetite, and hiding, since cats mask pain more subtly than dogs (American Association of Feline Practitioners, 2021).

Discharge is inconsistent — some ulcers produce thick mucoid or pus-like drainage from secondary bacterial infection, while others, especially early or sterile ulcers, produce only watery tearing. A third eyelid (nictitating membrane) that partially covers the eye is another common early clue, and it often gets mistaken for allergies or a minor irritation rather than a corneal injury (Merck Veterinary Manual, 2023).

What actually causes corneal ulcers in cats?

Trauma accounts for the majority of feline corneal ulcers — cat fights, scratches from another animal, running into brush outdoors, or self-trauma from rubbing an already-itchy eye. Foreign material like a grass awn or plant material lodged under the eyelid is a frequent culprit that owners rarely see without a vet's eyelid eversion exam (Cornell University College of Veterinary Medicine, 2022).

Feline herpesvirus-1 (FHV-1) is a leading non-traumatic cause and can produce a distinctive branching dendritic ulcer visible with fluorescein stain; the virus is estimated to infect the majority of cats at some point in their lives and can reactivate during stress, according to the Cornell Feline Health Center (Cornell Feline Health Center, 2021). Eyelid abnormalities such as entropion (an inward-rolling eyelid) and inadequate tear production from dry eye (keratoconjunctivitis sicca) also chronically irritate the cornea, particularly in brachycephalic breeds like Persians and Himalayans whose shallow eye sockets already put the cornea at greater mechanical risk.

How do veterinarians confirm and grade a corneal ulcer?

The core diagnostic test is fluorescein staining: a vet applies an orange dye strip to the eye, then examines it under blue light, and any area where the epithelium is missing turns bright green because the dye binds to the exposed stroma underneath. This simple in-clinic test, described by the Merck Veterinary Manual, distinguishes a true ulcer from surface irritation and helps map the ulcer's size and depth (Merck Veterinary Manual, 2023).

Vets also check tear production with a Schirmer tear test strip, measure intraocular pressure to rule out concurrent glaucoma or uveitis, and evert the eyelids to search for foreign bodies or eyelash abnormalities rubbing the cornea. For ulcers that look unusually deep, slow to heal, or infected, referral to a veterinary ophthalmologist for corneal cytology or culture and sensitivity testing is common so the antibiotic choice matches the actual bacteria present (Cornell University College of Veterinary Medicine, 2022).

What treatments do vets actually use, and does every ulcer need surgery?

Most superficial ulcers are treated medically with topical broad-spectrum antibiotic drops or ointment applied multiple times daily, an oral or topical pain reliever since corneal ulcers are intensely painful, and an Elizabethan collar to stop the cat from rubbing or scratching the eye further. Atropine drops are sometimes added short-term to relieve painful ciliary muscle spasm, though they temporarily dilate the pupil and increase light sensitivity (Merck Veterinary Manual, 2023).

Deep ulcers, descemetoceles, or ulcers that are actively melting from bacterial collagenase enzymes are surgical emergencies — a veterinary ophthalmologist may perform a conjunctival graft or corneal transplant to reinforce the eye before it perforates. Steroid-containing eye medications are avoided or used only under specialist supervision because steroids can worsen an active ulcer and are dangerous if herpesvirus is the underlying cause, which is why owners should never reuse old prescription eye drops without a fluorescein check first (Cornell Feline Health Center, 2021).

How do I care for my cat at home while the ulcer heals?

Strict compliance with the medication schedule matters more than almost anything else — missing doses of antibiotic drops is one of the most common reasons a straightforward ulcer turns into a non-healing or infected one. The Elizabethan collar needs to stay on essentially all the time, including overnight, since a single bout of scratching can reopen a healing defect in seconds.

Keep the cat in a calm, dim, low-traffic room during recovery, since bright light is uncomfortable with an inflamed eye, and separate the cat from other pets if trauma or fighting was the cause. Most uncomplicated ulcers are rechecked with repeat fluorescein staining every three to seven days until the stain no longer takes up, and owners should expect a recheck schedule rather than a single follow-up visit, since ulcers that look better on the surface can still be deeper than they appear (Merck Veterinary Manual, 2023).

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

Simple superficial ulcers treated promptly typically heal within about a week with no lasting vision impact. Deeper stromal ulcers can leave a permanent corneal scar (visible as a cloudy or white patch) that may cause mild vision changes but rarely blindness if the eye itself was not ruptured (Cornell University College of Veterinary Medicine, 2022).

Cats with underlying FHV-1 are prone to recurrent ulcers during stress flare-ups such as boarding, new pets, or household moves, and long-term management may include antiviral medication or L-lysine supplementation discussed with a vet, even though evidence on lysine's effectiveness is mixed (Cornell Feline Health Center, 2021). Cats with anatomical risk factors like entropion or breed-related shallow orbits may need corrective eyelid surgery to prevent repeated injury to the same eye.