Allergic conjunctivitis and conjunctival provocation tests in atopic dogs

Canine atopic dermatitis (cAD) is a very common disease, but little is known about eye involvement. The conjunctival provocation test (CPT) is used in human to study the ocular response to allergenic stimuli and to evaluate anti-allergic therapy. To our knowledge it has not been used in dogs.

To evaluate the prevalence of ocular signs in a population of atopic dogs and relate these with clinical cAD scores; and the usefulness of CPT for dust mites in atopic dogs with itchy eyes.

Sixty cAD patients were evaluated for (i) ocular signs of allergic conjunctivitis including conjunctival hyperemia, chemosis, epiphora, ocular discharge, pruritus and corneal involvement, graded 0 to 3 according to severity, and (2) cAD Extent and Severity Index (CADESI-03). Additionally, CPTs for Dermatophagoides farinae (n = 12) and Dermatophagoides pteronyssinus (n = 12) were performed in sensitized atopic dogs and 24 control dogs.

Periocular and ocular signs of allergy were present in 60% (36/60) of cases. Conjunctival hyperemia (90%) was the most common sign. Severity of ocular signs was significantly correlated with eye pruritus (r(s)  = 0.690, P = <0.001) and skin lesions score for head region (r(s) = 0.261, P = 0.04). A highly significant difference (P < 0.001, Fisher test) was found in CPTs between the test and the control groups.

Allergic conjunctivitis signs associated with cAD seem under valuated so these patients would benefit from an ophthalmologic evaluation. Furthermore, we found CPT to be a reliable, easy to perform and safe test for the etiologic diagnosis of allergic conjunctivitis in the dog.