Uveitis is defined as inflammation of the vascular intraocular uveal tract, which is composed of the iris, choroid, and ciliary body. Anterior uveitis (iridocyclitis) refers to inflammation in the middle layer of the eye (anterior segment) affecting the iris and ciliary body. Posterior uveitis (choroiditis) describes inflammation of the back part of the uvea called the choroid, while chorioretinitis is a type of posterior uveitis that includes neighboring retinal involvement. Panuveitis (Diffuse uveitis) describes inflammation of all uveal tissues with no particular site of major inflammation.
Uveitis can be either acute or chronic and can be unilateral (one eye) or bilateral (both eyes). Systemic causes can result in both unilateral and bilateral uveitis. In general, there are numerous and often elusive causes for uveitis. uveitis treatment is dependent on the possible underlying cause as it is necessary for the preservation of comfort and vision.
The Etiologies also depend on the dog’s environment, geographic location, breed, age, sex, and even travel history. To help further classify underlying causes of uveitis, several grouping categories have been proposed. Etiologies may be classified based on systemic or endogenous causes (e.g. neoplastic, infectious) and external or exogenous causes (e.g. traumatic, toxic, radiation).
In general, exogenous causes can be immediately identified (e.g. accidental bleach, cleaning products or penetrating ocular injury, etc.) While unseen trauma is often a most plausible “reason” for the owner and vet, this is a rare cause of uveitis, particularly if there are no other systemic or periocular symptoms of trauma.
Exogenous causes of uveitis are far more common than Endogenous and, per se, can be difficult to figure out. Endogenous causes can be further classified depending on primary ocular disease (e.g. pigmentary uveitis, intraocular neoplasia, lens-induced uveitis) versus systemic disease (e.g. immune-mediated, infectious, metabolic, toxic, neoplastic, idiopathic).
The most common underlying etiology is Systemic causes, which pose a diagnostic challenge for the vets. The leading cause of secondary glaucoma in dogs is Anterior uveitis and it is often a globe-threatening and vision-threatening condition.