Idiopathic uveitis is a common presentation in cats, with a reported incidence of 37% to 70%.1-3 Diagnosis can be made only after excluding other ocular or systemic causes; however, empirical or supportive treatment for uveitis is often instituted because of the cost or time restraints of ruling out causative disease.
The goals of treatment are to stabilize the blood-aqueous barrier, control pain, and prevent secondary complications (eg, glaucoma). Glaucoma results from accumulation of inflammatory cells, fibrin, and other debris in the iridocorneal angle; this causes decreased outflow of aqueous humor.4 Posterior synechiae from uveitis also can prevent outflow of aqueous humor through the pupil and cause glaucoma and iris bombé.
Mydriatics are useful in preventing synechiae and aid in pain control by reducing ciliary body spasm. Tropicamide and atropine are commonly used mydriatic agents, but tropicamide is less commonly employed for cycloplegia because most of its action is at the iris dilator muscle as opposed to the ciliary body.5 Likewise, tropicamide’s effect in pupil dilation is blunted by the presence of uveitis, wherein prostaglandins bind to receptors in the iris sphincter muscle, resulting in miosis. Atropine is a more potent cycloplegic and mydriatic with a longer duration of action; therefore, its use is preferred for uveitic eyes.5,6
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Care should be taken to monitor corneal health and IOP; use of parasympatholytics may cause a decrease in tear production,7 and use of mydriatic and cycloplegic agents has been associated with an increase in IOP.8,9 Immunosuppressive medications can cause recrudescence of latent feline herpesvirus 1 with subsequent corneal ulceration. Additionally, dilating agents can occasionally induce profound salivation, as the drug flows through the nasolacrimal system and is licked by the cat as it exits the nose. Use of an ointment rather than drops may ameliorate this side effect.
Corticosteroids (topical or oral) can be used for immunosuppression, inhibition of arachidonic acid metabolism, antifibrotic therapy, and inhibition of neovascularization. Prednisolone acetate, although less potent than dexamethasone, is formulated to have better penetration and is therefore preferred over dexamethasone. Topical treatment with steroids is ideal to limit systemic effects and has not been shown to exacerbate systemic disease.10 Contraindications include presence of a corneal ulcer or active superficial infection. Topical NSAIDs (eg, diclofenac, flurbiprofen) may be used if ulceration is present, but these alone may be insufficient in controlling active uveitis. Dosing frequency will typically correlate with uveitis severity (eg, every 6 hours for 2+ flare, every 6-8 hours for trace-1+) and can be tapered accordingly as uveitis subsides.
Setting an appropriate recheck period is an important part of managing uveitis, as it allows for assessment of patient response to treatment and of secondary complications. If uveitis improves, anti-inflammatory drugs can be continued until the eye is free of clinical signs, at which point the drugs can be slowly tapered. Mydriatics can be continued until the pupil is dilated and then tapered to the lowest dose necessary to maintain effect. The owners should be prepared for what to expect if uveitis does not improve or if systemic disease goes undiagnosed. They should also be made aware that long-term therapy may be needed.
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