What exactly is happening inside a cat's eye when it has uveitis?

Uveitis means inflammation of the uveal tract, the middle layer of the eye made up of the iris, ciliary body, and choroid, which together regulate light entry, intraocular fluid production, and blood supply to the retina (Merck Veterinary Manual, 2023). Anterior uveitis affects the iris and ciliary body at the front of the eye, while posterior uveitis involves the choroid deeper inside; many cats present with panuveitis, meaning the whole tract is affected at once. Because the uvea is heavily supplied with blood vessels, it's a frequent site where circulating infectious agents, immune complexes, or cancer cells first cause visible eye disease, which is why veterinary ophthalmologists treat uveitis as a signal to look for a body-wide problem, not just an eye problem (American College of Veterinary Ophthalmologists, n.d.).

The inflamed uvea leaks protein and inflammatory cells into the aqueous humor, the clear fluid filling the front chamber of the eye, which is what produces the hazy or 'flare' appearance a veterinarian sees during a slit-lamp exam (Cornell Feline Health Center, 2021). That same fluid shift can raise or, more often initially, lower intraocular pressure, and either direction of pressure change can damage the optic nerve and retina if it persists. Cats are considered especially prone to uveitis compared with dogs, and a large proportion of feline cases are classified as idiopathic even after a thorough workup, meaning no single cause is ever identified despite extensive testing (Cornell Feline Health Center, 2021).

What are the first signs an owner usually notices?

Early uveitis often looks subtle: a cat squinting more than usual in bright light, one eye that seems to tear excessively, or a slightly cloudy or reddish tint compared with the other eye. Owners frequently describe the affected eye as 'smaller' looking because the cat is holding it partly closed (blepharospasm) to guard against light sensitivity and pain (VCA Animal Hospitals, n.d.). A change in iris color, such as a normally green or gold iris turning a duller, muddier hue, is a classic early clue that inflammatory cells are settling on the iris surface.

Some cats show a miotic pupil, meaning the pupil stays small and doesn't dilate normally in dim light, or the two pupils appear uneven in size (anisocoria). Because cats mask pain well, behavioral signs can be the loudest signal: reduced interest in play, hiding, reluctance to be touched near the face, or eating less because head position affects eye discomfort. Veterinary ophthalmology sources note that any sudden change in eye appearance or behavior in a cat warrants same-day evaluation rather than a watch-and-wait approach, since uveitis can progress to secondary glaucoma within days (American College of Veterinary Ophthalmologists, n.d.).

What actually causes uveitis in cats?

Infectious causes are common and include feline herpesvirus-1 (FHV-1), feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), and the parasite Toxoplasma gondii, all of which can trigger inflammation either through direct infection of ocular tissue or through the immune response mounted against them (Cornell Feline Health Center, 2021). Bartonella henselae, the bacterium associated with cat scratch disease, has also been implicated in some feline uveitis cases, though its exact role is still debated among researchers.

Non-infectious causes include blunt or penetrating trauma, lens-induced uveitis from a ruptured or cataractous lens, intraocular tumors such as diffuse iris melanoma or lymphoma, and systemic hypertension, which is itself often secondary to chronic kidney disease or hyperthyroidism in older cats (Merck Veterinary Manual, 2023). Because so many systems can trigger the same eye finding, veterinarians typically recommend bloodwork, blood pressure measurement, and infectious disease testing rather than treating the eye in isolation, especially in cats over eight years old where hypertension and cancer become more likely culprits.

How do veterinarians actually diagnose the cause?

Diagnosis starts with a thorough ophthalmic exam using a slit lamp to grade aqueous flare, check for keratic precipitates (inflammatory cell clumps on the inner cornea), and measure intraocular pressure with tonometry, since pressure readings help distinguish uveitis from glaucoma or guide treatment when both occur together (Cornell Feline Health Center, 2021). A fundic exam looks for choroidal or retinal lesions that point toward FIP, toxoplasmosis, or lymphoma.

Beyond the eye exam, vets typically run a complete blood count, serum chemistry panel, blood pressure measurement, and FeLV/FIV testing as baseline screening, adding Toxoplasma titers, Bartonella testing, or FIP-specific bloodwork based on the cat's age, indoor/outdoor status, and other symptoms (Merck Veterinary Manual, 2023). Cats with no identifiable systemic disease after this workup are labeled idiopathic uveitis, which still requires ongoing anti-inflammatory treatment and monitoring even without a definitive underlying diagnosis.

What does treatment for feline uveitis involve?

Treatment centers on topical corticosteroid or NSAID eye drops to control inflammation, along with atropine drops to dilate the pupil, which reduces pain from ciliary muscle spasm and helps prevent the iris from sticking to the lens (a complication called synechiae) (VCA Animal Hospitals, n.d.). If an infectious cause like herpesvirus or toxoplasmosis is identified, vets add systemic antiviral or antiparasitic medication such as famciclovir or clindamycin alongside the eye drops rather than relying on topical treatment alone.

When intraocular pressure is elevated or the cat develops secondary glaucoma, additional pressure-lowering medications are added, and cats with lens-induced uveitis, tumors, or a blind painful eye that isn't responding to medical management may need referral to a veterinary ophthalmologist for surgery, including enucleation in severe, unsalvageable cases (American College of Veterinary Ophthalmologists, n.d.). Treating any underlying systemic disease, such as starting antihypertensive medication for a cat with high blood pressure, is just as critical as the eye drops themselves.

What does day-to-day care and medication management look like at home?

Most cats need eye drops multiple times daily during the active phase, and consistency matters because gaps in dosing let inflammation rebound and increase the risk of permanent scarring inside the eye. Owners should keep a written medication schedule, since it's common to be applying two or three different drops on staggered timing (commonly waiting five minutes between different drops so one doesn't wash out the other) (VCA Animal Hospitals, n.d.). An e-collar is often necessary short-term since cats that paw at an uncomfortable eye can cause corneal ulceration on top of the existing inflammation.

Follow-up rechecks, typically within one to two weeks of starting treatment and then periodically after, are how veterinarians confirm the inflammation is resolving and adjust drop frequency, since tapering too quickly is a common cause of relapse. Cats with recurrent herpesviral uveitis may benefit from long-term environmental stress reduction and, in some cases, L-lysine supplementation, though evidence for lysine's effectiveness has been questioned in more recent studies and it should be viewed as a secondary measure rather than primary therapy.

What's the long-term outlook for a cat diagnosed with uveitis?

Outlook depends heavily on the underlying cause and how quickly treatment started. Cats treated promptly for idiopathic or herpesviral uveitis often retain functional vision, though some develop chronic low-grade inflammation that flares periodically and requires intermittent drop therapy for life. Cats whose uveitis stems from FIP, lymphoma, or diffuse iris melanoma generally carry a more guarded prognosis tied to the systemic disease itself rather than the eye findings alone (Cornell Feline Health Center, 2021).

Secondary glaucoma is the complication that most often costs a cat vision permanently, so cats with a history of uveitis typically need intraocular pressure rechecked at every follow-up visit, sometimes for years afterward, even once the eye looks quiet. Cats that lose vision in one eye from chronic uveitis generally adapt well at home using scent, hearing, and memorized layouts, but owners should keep furniture and food/water locations consistent to help with that adjustment.