Diagnostic approach and grading scheme for canine allergic conjunctivitis

In humans, allergic conjunctivitis is a well described disease. In contrast, allergic conjunctivitis has not received much attention from the veterinary community so far. Canine allergic conjunctivitis (cAC) is one of the possible manifestations associated with canine atopic dermatitis (cAD), being often underdiagnosed and undertreated. Our aim is to contribute to disease characterization and clinical stagingfor cAC severity.

A retrospective observational study including 122 dogs that underwent a complete ophthalmological and dermatological examinations and diagnosed with allergic conjunctivitis was conducted. A total of six ophthalmic clinical signs were considered for disease characterization and clinical staging: conjunctival hyperemia, chemosis, ocular pruritus, epiphora, seromucoid to mucopurulent discharge and keratitis, classified from 0 (absent) to 3 (severe). Scores comprised between 1-5 were considered mild, 6-10 moderate and 11-18 severe. The majority of dogs (64%) presented with moderate cAC followed by 24% of mild stages and only 12% of severe presentations. The severity of allergic conjunctivitis was not correlated to sex or age at the time of diagnosis and all presented with a bilateral form of the disease. Chemosis (84%), hyperemia (83%) and ocular pruritus (79%) was observed in 55% of the cases. Seromucoid to mucopurulent discharge (62%) and epiphora (69%) were less frequent, with keratitis being the least encountered clinical sign (15%). The degree of keratitis showed a positive correlation with both severity and chronicity of cAC (rho = 0.21-0.29, p ≤ 0.02)). Severity of cAD and cAD were not significantly correlated (p-value = 0.4).

The triad hyperemia, chemosis and ocular pruritus, already known in human medicine to be a reliable way of diagnosing human allergic conjunctivitis, also proved to be important in cAC Mild forms of the disease may pass unnoticed, ocular pruritus being hard to assess in canine patients.The proposed standardized diagnostic approach and novel grading scheme for cAC may be of value for both veterinary ophthalmologists and dermatologists, as well as general practitioners.