Uveitis in dogs: diagnosis and treatment
Uveitis in dogs is one of the main causes of eye disease and blindness.1
Introduction and anatomical review
The term uveitis refers to inflammation of the uvea, which is made up of the iris, the ciliary bodies and the choroid.2,3 Uveitis in dogs can be divided into anterior uveitis (which affects the iris and ciliary body, causing iritis and/or cyclitis), posterior uveitis (inflammation of the choroid, i.e., choroiditis) and panuveitis (affects all three components of the uvea).
Clinically speaking, it is hard to differentiate between iritis and cyclitis, so they are normally grouped under the term “anterior uveitis”.
Aetiopathogenesis
Uveitis in dogs usually presents as an independent entity or as a complication of diseases in other ocular structures. Furthermore, it may be a primary disease or secondary to an infectious, neoplastic or immune-mediated disease (Table 1). A recent study showed that most cases of panuveitis were idiopathic/immune-mediated, although other causes, such as blastomycosis or lymphomas, should be included in the list of differential diagnoses.4 Ehrlichiosis is reported to be the infectious disease most commonly associated with uveitis in dogs,1 but it is probably related to the prevalence of the disease in each region. It is estimated that the cause of uveitis cannot be determined in about 50% of cases.1
Uveitis always originates from tissue damage, secondary to trauma, an infectious agent or an immune-mediated process. Thereafter, the sequence of events includes increased blood supply, increased vascular permeability and leukocytes migrate to the point of injury.2 The inflammatory process of uveitis is made up of three phases: active (acute), subacute and chronic. The acute phase is typically exudative, and the exudate may be serous, fibrous, bloody or purulent. The immune reaction begins in the subacute phase and may result in scarring, necrosis, recurrence or chronicity.
Uveitis in dogs: clinical signs
Uveitis may cause specific signs (turbidity of the aqueous humour with Tyndall effect or hypopyon), as well as signs common to other eye conditions (tearing, blepharospasm, hyperaemia or photophobia). Further clinical signs of uveitis in dogs include pain (especially in acute cases), congestion of the ciliary vessels, hyphaema, enophthalmos, miosis, perikeratic precipitates, decreased intraocular pressure, corneal oedema, rubeosis and changes in the colour of the iris, synechiae and iris bombé, decreased vision and conjunctival hyperaemia. Patients with posterior uveitis can have vitreous opacity, chorioretinal granulomas, retinal detachments and haemorrhages, choroidal effusion and optic neuritis. In addition, cataracts, glaucoma, lens luxation, endophthalmitis/panophthalmitis and phthisis bulbi are possible sequela of uveitis.2,3 A study in Golden Retrievers with pigmentary uveitis found that blindness may occur in 46% of eyes due to the development of secondary glaucoma.5 In such cases, glaucoma develops because drainage of the aqueous humour is obstructed by waste products of the inflammatory process, iris bombé or extension of earlier synechiae.2
Diagnosis
Whenever possible, it is important to try and identify the cause of uveitis. Therefore, in most cases, a complete physical examination and general laboratory tests (haematology and blood chemistry profile) are indicated.2,3 Other diagnostic tests, such as infectious disease serologies or imaging tests, may be performed on a case-by-base basis according to the clinical suspicion.2 In cases with marked cellular infiltration, cytology of the aqueous humour may be diagnostic (e.g., in case of lymphoma). On the other hand, the role of certain infectious diseases as an active cause of uveitis (aqueous humour antibodies/antibodies in blood > 1) may be established by aqueocentesis and subsequent serological titration of the resulting fluid.3 Finally, a fluorescein test should be performed in all patients with suspected uveitis to rule out the existence of (neurogenic) reflex uveitis secondary to ulcerative keratitis. 3
Treatment
Treatment of uveitis in dogs aims to control inflammation, stabilise the blood–aqueous barrier, minimise sequelae, reduce pain and preserve vision. Topical mydriatics, corticosteroids (topical or sometimes systemic) and nonsteroidal anti-inflammatory drugs are used to this end. And if the primary cause is identified, it must also be addressed.3 Topical treatment of uveitis should be initiated at the time of diagnosis, even before fully assessing the possibility of systemic diseases. This reduces the chance of sequelae.2
Thanks to their mydriatic and cycloplegic effects, parasympatholytic agents (1% atropine, tropicamide) play an important role in the treatment of uveitis. Atropine may be given up to 4 times a day for mydriasis and every 12–24 hours thereafter for maintenance.3 It is contraindicated in patients with a high intraocular pressure (IOP) (except in iris bombé), in which case it may be better to resort to tropicamide, which despite having a weaker parasympatholytic effect, also has less effect on IOP.2
Topical corticosteroids are a key element in the management of anterior uveitis, unless the patient has specific contraindications (corneal ulcer). 1% prednisolone acetate or, failing that, 0.1% dexamethasone, 4–6 daily applications if eye drops are used, 3–4 if ophthalmic ointments are used.2,3 They may be accompanied by treatment with a subconjunctival triamcinolone acetonide or betamethasone injection.2 Systemic corticosteroids (1–2 mg/kg/day) should not be initiated until the possibility of systemic diseases has been assessed and the need for its use established (posterior or immune-mediated uveitis). Patients with immune-mediated uveitis and a contraindication or poor response to systemic corticosteroids can be treated with other immunomodulators, such as azathioprine or cyclosporine.2
Topical formulations of nonsteroidal anti-inflammatory drugs (NSAIDs) can be used 2–4 times a day, in monotherapy or combination therapy with topical corticosteroids, always with monitoring for collagenolytic effects on the corneal epithelium in patients with ulcers.2,3 The effects of systemic NSAIDs on the eye have not been studied in full, but possible side effects must be considered, e.g., etodolac is associated with keratoconjunctivitis sicca.2
In general, there are only a few indications for the use of topical antibiotics in the treatment of uveitis, except in cases of associated corneal ulcer. This is because primary bacterial uveitis is rare and topical antibiotics have poor intraocular penetration. So, systemic antibiotic therapy may be preferable, if this medication is required.2
Conclusions
Uveitis in dogs is a common reason for ophthalmologic consultations. Bear in mind that uveitis may be an ocular sign of systemic disease. So, a complicated diagnostic approach may be necessary. It is important to start treatment early to avoid the onset of severe sequelae that can lead to vision loss, even if the diagnosis is still ongoing.
