When to see a vet urgently
Seek immediate care if your cat has:
- a suddenly painful, cloudy or markedly swollen eye;
- rapidly declining vision or new bumping into objects;
- an eye wound or foreign object after an injury;
- increasing pain, discharge or changed eye appearance after surgery;
- eye symptoms alongside marked weakness, refusal to eat or fever.
Do not wait for visible pus discharge. You can find a vet near you.
Overview
Endophthalmitis is rare but extremely dangerous. Inflammation affects the vitreous, iris, ciliary body and retina. Bacterial infection is the most common cause, with fungal or viral infection less common. In cats, it occurs as a complication of eye surgery or penetrating injury.
Bacteria and fungi are central causes of infectious endophthalmitis. Viruses may be associated with inflammatory eye diseases, but a viral infection alone does not establish a pus-forming bacterial infection inside the eye. Assessing uveitis, inflammation of the uveal tract, and endophthalmitis requires examination of eye structures.
The vitreous is a transparent, jelly-like substance filling the back of the eye. When inflammatory cells and discharge accumulate internally, light cannot pass normally. The retina and other structures essential for vision can also be damaged. Surface redness alone does not reveal the severity of internal injury.
Causes
- eye injuries, including bites, scratches and penetrating wounds;
- postoperative complications, for example after cataract surgery;
- infection spreading from adjacent tissue, including orbital cellulitis or abscesses;
- bacteria carried through the bloodstream during sepsis;
- chronic eye inflammation, such as uveitis or keratitis, becoming pus-forming.
Infection entering the eye from outside is called exogenous; infection arriving from elsewhere through the bloodstream is endogenous. In the latter, there may be no visible entry wound. Examination of the whole cat looks for a possible source, which sometimes remains unclear despite investigation.
A foreign object left in or near the eye can maintain infection. A poor response to medication may therefore lead to further investigations rather than simply mean an incorrect medicine amount. Unusual routes taken by foreign material have also been described in cats; individual cases do not establish their frequency.
Ordinary uveitis or superficial corneal inflammation does not inevitably become pus-forming. However, a deep ulcer or corneal perforation can open a route for microbes into the eye. The cause and integrity of the eye surface are checked before selecting treatment.
Risk factors
- outdoor cats that frequently suffer injuries;
- cats with chronic infections;
- older cats with weakened immune defences;
- cats whose postoperative eye care has been inadequate.
Information on individual risk factors for endophthalmitis in cats is limited. Old age or outdoor access alone does not explain the disease, which has also been described in young cats. A postoperative infection does not automatically indicate inadequate home care either: the possible cause is investigated individually.
Typical symptoms
Endophthalmitis in cats causes:
- severe pain, with eye rubbing and avoiding touch;
- marked eye redness and swelling;
- pus-containing discharge;
- cloudiness of the cornea and vitreous;
- reduced vision or complete sight loss;
- swelling of the eyeball;
- lethargy and refusal to eat with severe infection.
Your cat may keep the eye closed, avoid head contact or change eating habits. Vision in the other eye can hide the affected eye's problem at home. Do not test sight by startling your cat or pressing the eye. Home observations help the history, but do not replace examination of visual responses.
Visible discharge comes from the surface, while inflammation may lie deep within the eye. Little or no discharge therefore does not rule out serious disease. Explain when cloudiness, redness and behaviour changes began and how they have progressed.
Complications and consequences
- complete blindness;
- panophthalmitis, with infection extending throughout the eye;
- an orbital abscess;
- sepsis;
- a need for eye removal, or enucleation.
Pressure inside the eye can rise because of inflammation and increase pain. If the eye enlarges and the eyelids cannot close, the corneal surface can also be damaged. Treatment may therefore need to address pressure and surface injury alongside infection.
Not every eye is damaged in the same way, but resolving infection does not guarantee restored sight. A case has been described in cats where both eyes were preserved with treatment but blindness remained permanent. This illustrates different treatment goals rather than predicting every cat's outcome.
Diagnosis at the vet
- an eye examination with a slit lamp;
- eye ultrasound when cloudiness is severe;
- cytology and bacterial culture of pus-containing discharge;
- a complete blood count to assess signs of inflammation and sepsis.
The examination compares both eyes and assesses visual responses, the surface and visible internal structures. Eye pressure is measured when safe. Severe pain or injury may require sedation or anaesthesia for a detailed examination. Do not force your cat's eye open at home.
If cloudiness obscures the back of the eye, ultrasound can help assess the vitreous and retina. Suspected injury or foreign material may need other imaging too. An imaging change alone does not identify the bacterial cause. Sampling is planned around the question being investigated and the risks.
Surface discharge does not always reflect the cause of infection inside the eye. Your vet may consider an internal sample for cytology, culture and susceptibility testing. Samples can help target care, but you must not try to collect one yourself. Mention medicines already used too.
A normal complete blood count or biochemistry alone does not rule out bacterial infection inside the eye. Conversely, an abnormal white cell count alone does not confirm sepsis. Sepsis requires organ dysfunction associated with infection, assessed through general health and other findings. A source of infection elsewhere is investigated when needed.
Treatment and prognosis
Treatment is planned according to the suspected cause, eye damage and general health. It may include local and systemic antimicrobial medication and pain relief. A medicine's ability to reach internal eye tissues affects selection. An old, ordinary eye drop is therefore not adequate first aid to start yourself.
A foreign object maintaining inflammation must be removed through an appropriate procedure. Medication and surgical options are assessed with a vet experienced in eye disease. Uncontrolled pain and a permanently damaged blind eye may lead to removal. The decision depends on eye function and your cat's welfare.
Enucleation removes the eyeball and closes the skin over its place. It aims to remove pain and diseased tissue rather than restore vision. The removed eye can be sent for histopathology to clarify the cause. With serious infection, a cosmetic implant is unnecessary and generally inappropriate.
Do not add your own corticosteroid drops or another animal's medicine. Topical corticosteroids can be harmful with a corneal ulcer. Medication changes depend on findings and response; reduced redness alone is not proof that infection has gone.
Home care and monitoring
Follow prescribed medication and agreed checks. Wash hands before and after giving eye medicine, and do not touch the bottle tip to the eye or other surfaces. Report difficulty administering it so the practical approach can be changed.
Some eye drops taste bitter when they drain through the tear ducts into the mouth and may cause drooling. If rubbing continues or the eye becomes more inflamed, ask the practice for instructions before the next administration. Give the product name at the same time.
After surgery, prevent wound rubbing and licking by other animals. Use any protective collar as directed. Monitor swelling, discharge, pain and general health. New deterioration or heavy discharge or bleeding requires contact even if the previous check was satisfactory.
Provide quiet rest and monitor eating. Pain and nausea can reduce appetite; report inadequate intake promptly. Do not force food into the mouth. If the other eye sees, many cats adapt to life with one eye, but its condition also needs consideration.
Prevention
- Prevent injuries and fights between animals.
- Follow postoperative eye care carefully.
- Treat conjunctivitis, keratitis and uveitis promptly.
- Treat chronic infections and support immune defences.
Important for cat owners
Endophthalmitis is extremely dangerous, threatening sight and also life if infection becomes generalised. Remember that pus-containing discharge, pain and sudden vision loss require an immediate visit to a vet experienced in eye disease. The earlier treatment starts, the better the chance of preserving the eye and your cat's health.
This article provides general information and does not replace veterinary care. Contact your vet if you notice signs of illness in your cat.
Frequently asked questions
Can a normal blood test rule out endophthalmitis?
No. Internal eye infection can occur without obvious changes on routine blood tests. Eye examination and targeted samples when needed are essential.
Why does medication not help if there is a foreign object in the eye?
Foreign material can maintain injury and infection, so medication does not remove the whole cause. Suspicion requires detailed investigation and possible removal by your vet.
Does resolving inflammation mean sight returns?
Not always. Infection can be controlled even when tissues supporting vision are permanently damaged. Follow-up separately assesses pain, eye condition and remaining function.
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
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- Penetrating Intraocular Injuries in Small Animals, Merck Veterinary Manual, accessed 2026-11-05.
- Feline Corneal Ulcers: Diagnosis and Management, Today’s Veterinary Practice, accessed 2026-11-05.
- Enucleations, American College of Veterinary Ophthalmologists, accessed 2026-11-05.
- Eye removal (enucleation) in cats, PDSA, accessed 2026-11-05.
- 2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat, Journal of Feline Medicine and Surgery, accessed 2026-11-05.
- Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Sepsis in Dogs and Cats—Consensus Definition and Clinical Criteria, Journal of Veterinary Emergency and Critical Care, accessed 2026-11-05.
- Physical Examination of the Eye in Animals, Merck Veterinary Manual, accessed 2026-11-05.