When to see a vet urgently
Contact a vet promptly if you notice any of the following:
- Your cat keeps an eye closed, squints strongly or rubs it constantly.
- The eye's surface suddenly becomes cloudy or develops visible damage.
- Your cat bumps into objects or its vision seems to deteriorate rapidly.
- A sharp object or irritating chemical has contacted the eye.
- Eye pain or redness increases despite treatment having started.
You can find a vet near you. Progression of a deep corneal injury can threaten the eye itself.
Overview
The cornea is the transparent layer of the eye through which light passes. Keratitis disrupts its structure and causes inflammation and swelling. Depending on the inflammation, a corneal problem may be superficial or deep and affect one or both eyes.
The corneal surface consists of the epithelium, a protective cell layer. Beneath it is a thicker supporting layer. Inflammation can occur without an open surface defect or involve an ulcer in which protective tissue is missing. These situations need partly different treatment, even if both look like a cloudy eye to you.
The cornea also helps focus light entering the eye. Swelling, inflammatory cells, scarring or abnormal surface tissue can reduce transparency. However, outward cloudiness does not reveal the depth of damage. An eye is therefore not treated solely from a photograph or discharge colour.
Causes
The main causes of keratitis in cats include:
- Viral infections, such as feline herpesvirus FHV-1 and calicivirus.
- Bacterial infections, such as staphylococci and streptococci.
- Eye injuries, including scratches and foreign objects.
- Chemical burns.
- Autoimmune diseases, such as eosinophilic keratitis.
- Dry eye due to low tear production.
- Tumours.
The exact cause of eosinophilic keratitis is unknown, so calling it an autoimmune disease is a simplification. Eosinophils, a type of inflammatory cell, accumulate in the cornea. An association with herpesvirus has been observed, but this alone does not explain every case. The lesion may be a pale, pink or chalky raised area on the eye's surface.
After the initial infection, herpesvirus can remain dormant in the body and reactivate later. Recurrence can cause eye symptoms without severe respiratory illness. Stress and changes in the immune response can be associated with reactivation. On the other hand, not every cat previously infected with herpesvirus has ongoing corneal problems.
Risk factors
Keratitis develops more often in:
- Kittens and young cats with weakened immune systems.
- Cats living in boarding catteries and shelters, where infection risk is higher.
- White cats and cats prone to immune disorders.
- Cats with chronic viral infections.
Risk factor information depends on the form of keratitis, and a white coat alone has not been established as a general risk for all corneal inflammation. Viral eye disease in a young cat does not automatically mean immune deficiency either. Infection conditions, eye structure and previous diseases are assessed separately. Some breeds, for example, have a higher risk of a dark area of dead corneal tissue.
Main symptoms
Typical signs of keratitis include:
- Red eyes.
- Excessive tearing.
- Light sensitivity, with squinting and avoidance of bright light.
- Corneal cloudiness, a film-like or white area.
- Eyelid spasms, called blepharospasm.
- Eye discharge that is watery, mucus-like or contains pus.
- Impaired vision, including blindness due to ulcers.
Your cat may rub the eye with a paw or against a carpet, blink rapidly and avoid touch. Discharge sometimes accumulates around the eye even when the actual lesion is difficult to see. In eosinophilic keratitis, new blood vessels may initially appear at the corneal edge, followed by a spreading, raised, film-like area.
A brown or black patch may instead be a corneal sequestrum, an area of dead tissue. The surrounding inflammation can be painful. Do not try to wipe the patch away like discharge. Even lesions with different appearances may need assessment by a vet with expertise in eye disease.
Complications and consequences
Keratitis can lead to:
- Corneal ulcers.
- Chronic inflammation and scarring.
- Corneal perforation.
- Blindness and loss of the eye.
As an ulcer deepens, the wall protecting the eye's internal structures becomes thinner. Perforation can allow the eye's contents to escape and cause permanent visual damage. Not every case of keratitis progresses this way, but increasing pain or cloudiness cannot safely be watched at home for long.
A secondary bacterial infection can complicate a corneal ulcer even if the original cause was a virus or scratch. After healing, scarring or blood vessel growth can still reduce transparency. The prognosis therefore depends on both the original disease and the amount of tissue damaged.
Diagnosis at the vet
Diagnosis is based on:
- Slit-lamp eye examination.
- Fluorescein testing to detect corneal damage.
- The Schirmer tear test to assess tear production.
- Cytology and bacterial culture.
- Viral samples for FHV-1 and calicivirus.
A slit lamp magnifies the corneal surface and deeper layers. Your vet also checks the eyelids and any rubbing caused by a foreign object or hair. Redness can be associated with other eye diseases too, so examination is not limited to the visibly cloudy area.
Fluorescein is a dye that helps show a corneal surface defect. A small ulcer may become visible only with staining, even when the eye is clearly painful. The test also helps guide medicine selection and later confirm healing. Tear testing assesses whether insufficient tears have helped predispose the surface to damage.
Eosinophilic keratitis is confirmed with a cell sample examined for characteristic inflammatory cells. Your vet takes the sample from the eye's surface using an appropriate method. A deep or persistent ulcer may require a bacterial sample. The timing of samples in relation to staining and medication is planned at the appointment.
A herpesvirus PCR result is interpreted alongside symptoms and the rest of the examination. A positive finding alone does not prove that the virus explains the current lesion, because dormant and symptom-free infections are common. A negative result does not always rule out infection either, for example because shedding is intermittent.
Treatment according to the cause and damage
For ulcerative keratitis, treatment controls pain, protects the surface and prevents or treats additional bacterial damage. Herpes-related disease may need a medicine that inhibits viral replication. An antibiotic and an antiviral act on different targets, so they are not interchangeable simply because both are used for eye diseases.
Eosinophilic keratitis is often treated with medication that suppresses the inflammatory response. However, an eye medicine containing a corticosteroid can worsen a corneal ulcer, so the surface is examined before starting it. Do not use another animal's eye drops or those from a previous illness on your own initiative. The same cloudy-looking eye may need a very different medicine in different situations.
A deep, progressive or poorly healing lesion may need surgery and a tissue graft to support the cornea. Treating a sequestrum may require removal of the diseased tissue. The need for a procedure depends on the lesion's nature and depth. Your vet also assesses when care from a professional experienced in eye surgery is needed.
Giving medicine and home care
Ask to be shown how to give the prescribed eye medicine. Gently clean away loose discharge around the eye as instructed. Wash your hands before handling and make sure the bottle tip does not touch the eye's surface. Store and handle the product according to the packaging and clinic's instructions.
If needed, your cat can be calmly wrapped in a towel with another person helping, but do not press on the painful eye. If you cannot give the medicine, contact the clinic to adapt the technique or treatment plan. A collar can prevent rubbing and further damage. Agree its need and suitability with your vet.
Some eye medicines taste bitter and can cause brief drooling when they pass through the tear ducts into the mouth. If eye pain, redness or rubbing increases, ask the clinic for instructions before the next administration. Do not dismiss a severe or continuing reaction as an ordinary response to the medicine's taste.
Healing and follow-up
Symptoms improving does not, by itself, confirm that an ulcer has closed. Fluorescein staining may be repeated at follow-up, and medication is changed according to the findings. Herpes-related problems can recur, and eosinophilic keratitis often needs long-term treatment and repeated checks. Do not stop medication yourself because the eye looks better.
Prevention
To reduce the risk of keratitis:
- Keep vaccinations against viruses up to date.
- Protect your cat from eye injuries, including dangerous toys and fights.
- Manage chronic eye diseases.
- Treat conjunctivitis and upper respiratory infections promptly.
- Take your cat for a veterinary eye examination as soon as the first symptoms appear.
Vaccination reduces the severity of herpesvirus disease, but does not guarantee complete protection against infection, carrier status or further eye symptoms. A vaccinated cat's painful eye still needs examination. Managing a confirmed herpes infection includes hygiene, contacts with affected animals and reduction of stressful situations as advised by your vet.
Important for cat owners
Keratitis is a serious condition that can lead to sight loss without treatment. Remember that cloudy eyes, increased tearing and light sensitivity are reasons for an immediate examination by a veterinary ophthalmologist. The earlier treatment begins, the better the chances of preserving eye health.
This material is for information and does not replace treatment advice. Contact a vet as soon as the first signs of illness appear.
Frequently asked questions
Is keratitis always an ulcer?
No. Inflammation can also occur without an open surface defect. Fluorescein staining and other eye examinations help distinguish situations that may need different medication.
Can I use old steroid eye drops?
Do not use them without examination of the new problem. Corticosteroids can worsen a corneal ulcer, even if they helped with previous inflammation.
Why can herpesvirus eye symptoms return?
The virus can remain dormant in the body and reactivate. A new episode is assessed by examining the eye because other diseases can cause similar signs too.
Is the eye healed when my cat stops squinting?
Not necessarily. Ulcer closure can be confirmed at follow-up, and medication for long-term inflammation is adjusted according to examination findings.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Disorders of the Cornea in Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Eosinophilic Keratitis in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Guideline for Feline Herpesvirus Infection, European Advisory Board on Cat Diseases, accessed 2026-11-03.
- Corneal Ulcers, Cornell Feline Health Centre, accessed 2026-11-03.
- Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Corneal Ulcers in Cats, VCA Animal Hospitals, accessed 2026-11-03.