When to see a vet urgently
Contact a vet immediately if your cat develops:
- eye pain, marked squinting or holding an eye closed;
- a suddenly altered pupil shape or unequal pupils with other eye symptoms;
- rapid clouding, redness or visible blood in the eye;
- impaired vision, bumping into objects or obvious eye enlargement.
Do not wait until an adhesion is clearly visible at home. You can find a vet near you.
Overview
Inflammation of the iris and front of the eye causes tissue swelling and damage. The iris can then stick to the cornea or lens. Lasting connective tissue adhesions, or synechiae, subsequently form. They disrupt pupil function, fix it in place and impair normal circulation of fluid inside the eye.
Not every adhesion obstructs flow equally. A small local posterior synechia may mainly cause an irregular pupil shape. Extensive adhesion or one encircling the entire pupil margin differs because it may block the fluid pathway. Effects are assessed from eye structure and pressure, rather than the presence of an adhesion alone.
The fluid inside the eye, called aqueous humour, is produced in the ciliary body behind the iris. It passes through the pupil into the anterior chamber and drains mainly through the angle between the iris and cornea. This differs from tears moistening the outer surface. Increased tearing therefore does not mean internal eye pressure is being relieved normally.
If posterior synechiae seal the whole pupil circumference, fluid can collect behind the iris and push it forwards. This is called iris bombé. The bulging iris can also narrow the drainage angle. This structural problem may raise pressure and requires urgent assessment by a vet experienced in eye disease.
Causes
- Uveitis from various causes, including infections such as FIP, toxoplasmosis or feline leukaemia virus, immune-mediated disease and trauma.
- Eye injuries.
- Complications of eye surgery.
- Chronic inflammation at the front of the eye.
Uveitis can also accompany lens damage, a tumour or systemic disease. An adhesion alone does not establish infection, immune-mediated inflammation or injury as the cause. Sometimes the original cause remains unclear despite investigation. Active inflammation and eye pressure are then treated according to findings while the condition is monitored.
Risk factors
- Cats that have had uveitis.
- Cats with viral infections, including FeLV, FIV or FIP.
- Cats after eye surgery or injury.
- Elderly cats with more severe inflammation.
There is little research on separate risk factors for synechiae in cats. Old age alone does not mean worse inflammation, and significant adhesions can also form in a young cat. Risk relates above all to the cause, intensity and duration of uveitis and any other eye injuries. A viral diagnosis alone does not reveal which adhesions will develop.
Typical symptoms
- Abnormal pupil shape, including distortion or narrowing.
- A pupil that does not move as lighting changes.
- Corneal or lens cloudiness at adhesion sites.
- Uveitis signs, including tearing, light sensitivity, pain and redness.
- Raised eye pressure and glaucoma with extensive synechiae.
- Impaired or lost vision.
The pupil may remain asymmetrical or seem to have one edge that does not dilate with the rest. Eye medicines also change pupil size, so report every drop being used. Changing lighting or a photograph alone cannot assess adhesion extent or vision.
Pain may appear as light avoidance, closing the eye, face rubbing or hiding. Not every cat rubs its eye or cries in pain. Glaucoma does not always mean a wide pupil either: adhesions may keep it small despite high pressure. Pressure is therefore measured regardless of the signs' appearance.
Complications and consequences
- Secondary glaucoma, the most dangerous complication.
- Cataracts.
- Chronic uveitis.
- Eye shrinkage and blindness.
Some listed changes result from the same long-standing uveitis rather than adhesions alone. High pressure can damage the retina and optic nerve, and lost vision may not return. Conversely, severe chronic inflammation can reduce fluid production and lead to a low-pressure, shrinking eye. The same cat's condition can change during the illness.
Diagnosis at the vet
- Eye examination using a slit lamp and examination of the back of the eye.
- Eye pressure measurement.
- Fluorescein staining to assess corneal damage.
- Eye ultrasound if cloudiness prevents visualisation of structures.
- Investigations into the underlying cause of uveitis.
The vet examines both eyes and assesses pupil reactions, vision-related responses and inflammation. A slit lamp helps locate adhesions and identify inflammatory cells or protein in anterior chamber fluid. Examination of the back of the eye assesses the retina and optic nerve, for example, if visibility allows.
Eye pressure is often lower than normal with uveitis but may be normal or high if drainage is disrupted. One measurement therefore does not replace other examination, and repeat measurements may be needed. Fluorescein staining looks for a corneal ulcer, which affects the safety of anti-inflammatory treatment among other decisions.
If the pupil does not open or the eye is cloudy, ultrasound can help assess the lens, iris and back of the eye. It can also establish whether a bulging iris resembles a mass or reflects fluid accumulation. Shining a light into the eye at home cannot reliably assess these structures.
A general examination matters because another illness may underlie uveitis. The vet selects blood and urine tests, infection testing and chest or abdominal imaging when needed. Symptoms, findings and infection risks determine the extent. Not every cat receives the same test package, and an adhesion is not automatically interpreted as a sign of one viral infection.
Treatment
Treatment aims to relieve pain, control active uveitis, maintain fluid flow and treat any underlying cause. Anti-inflammatory or immunosuppressive medication is chosen according to suspected infection and corneal integrity. An infection needs treatment targeting its cause. Ordinary antibiotic drops alone do not treat every cause of inflammation inside the eye.
In some uveitis cases, the vet uses a pupil-dilating medicine to preserve iris movement and reduce painful muscle spasm. Do not start it at home based on pupil shape, because pressure and fluid flow affect the choice. Relief of inflammation cannot guarantee disappearance of an established permanent adhesion.
If pressure is raised, reducing it is an urgent part of treatment. Medicines may reduce aqueous humour production or improve drainage, and some patients need surgical assessment. The method depends on eye structure, remaining vision and the cause. Removal of a blind, persistently painful eye may sometimes be recommended to end pain.
Home care and monitoring
Follow medication prescribed for the particular eye. Do not try old corticosteroid, pupil-dilating or pressure-lowering drops for a new symptom without instructions. Corticosteroids can delay corneal ulcer healing and cause serious complications. If you cannot give drops, tell the practice so a workable plan can be found.
Wash hands before and after handling and avoid touching the dropper tip to the eye or eyelids. Prevent rubbing with protection recommended by the practice. Record changes in how the eye is held open, cloudiness and behaviour. If pain or redness clearly increases after medication, contact the practice before continuing.
Check-ups remain necessary after symptoms settle. Inflammation can decrease while scarring in drainage pathways sustains glaucoma. Medication needs may also change during recovery. Normal appetite or little tearing at home does not confirm safe eye pressure; assessment depends on examination and agreed measurements.
Prognosis
Prognosis depends on the underlying cause, adhesion extent and whether structures supporting vision have permanent damage. A small adhesion may remain visible without the same effects as extensive pupil obstruction and glaucoma. The goal is a comfortable eye with the best possible sight. Complete structural recovery or prevention of further inflammatory episodes cannot be promised.
Prevention
- Treat uveitis and eye inflammation promptly.
- Protect eyes from injury, particularly in outdoor cats.
- Arrange regular eye examinations for cats with viral infections.
- Use a protective collar after surgery to prevent eye injury.
Infection prevention and safe surroundings reduce some uveitis-related exposure, but not every synechia can be prevented. Postoperative protection does not replace anti-inflammatory medication or check-ups. Report eye symptoms promptly even when a cat already receives treatment for another illness.
Important for cat owners
Synechiae are a complication of eye inflammation rather than an independent disease. Remember that every sign of uveitis, including tearing, redness, light sensitivity and pain, is a reason for urgent veterinary assessment. Early inflammation treatment prevents synechiae and preserves vision.
Early treatment reduces complication risk but does not guarantee absence of adhesions or preservation of sight in every case. Response therefore needs repeated assessment, and worsening pain or visual changes require prompt re-examination.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Can a small adhesion remain permanently?
Yes. Settling inflammation does not guarantee an existing adhesion disappears. Its effects depend on location, extent and eye pressure. Monitoring may be needed even if the cat seems pain-free at home.
Can pressure be high despite a small pupil?
Yes. Uveitis and adhesions may keep a pupil small or irregular while drainage is obstructed and pressure rises. Pupil appearance does not replace pressure measurement.
Can cleaning the eye treat an adhesion?
No. A synechia is inside the eye, and surface cleaning cannot release it. Treatment targets inflammation, pain, any raised pressure and underlying disease. Do not choose medication yourself.
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
- Diagnostic Ophthalmology: Anterior uveitis and secondary glaucoma, The Canadian Veterinary Journal, accessed 2026-11-05.
- The Anterior Uvea in Animals, Merck Veterinary Manual, accessed 2026-11-05.
- Anterior Uveitis in Small Animals, Merck Veterinary Manual, accessed 2026-11-05.
- Uveitis in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Uveitis in Dogs and Cats, American College of Veterinary Ophthalmologists, accessed 2026-11-05.
- Glaucoma in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Corneal Ulcers in Cats, VCA Animal Hospitals, accessed 2026-11-05.
- Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-05.