Epidemiology and clinical significance of canine distichiasis: A retrospective study of 291 cases.

Objective: To describe the epidemiological factors and clinical significance of canine distichiasis.

Animals Studied: Two hundred and ninety-one client-owned dogs.

Methods: Retrospective study of medical records for canine patients diagnosed with distichiasis between 2010 and 2019 in an ophthalmology specialty practice. The breed, sex, skull conformation, coat type, age at the time of diagnosis, reason for presentation, clinical examination findings, and affected eyelid(s) were reviewed.

Results: The prevalence of distichiasis was 5.5% (95% confidence interval (CI): 4.9-6.1) in the population of dogs presented to an ophthalmology specialty practice. The breeds with the highest prevalence were English bulldogs (35.2%, 95% CI: 26.7-43.7) and American cocker spaniels (19.4%, 95% CI: 8.3-30.5). The prevalence was significantly higher in brachycephalic dogs (11.9%, 95% CI: 9.8-14.0) than in non-brachycephalic dogs (4.6%, 95% CI: 4.0-5.3) and in short-haired dogs (8.2%, 95% CI: 6.8-9.6) than in dogs with other coat types (5.3%, 95% CI: 4.5-6.1). Most dogs were affected bilaterally (63.6%, 95% CI: 58.0-69.1). Among dogs with clinical signs, 39.0% (95% CI: 26.5-51.4) exhibited corneal ulceration, including superficial ulcers (28.8%, 95% CI: 17.3-40.4) and deep stromal ulcers (10.2%, 95% CI: 2.5-17.8). Distichiasis was non-irritating in 85.0% (95% CI: 80.6-89.4) of affected dogs.

Conclusion: This study reports the largest cohort of canine distichiasis to date. In a large proportion of dogs, distichiasis was a non-irritating condition. However, brachycephalic breeds, especially English bulldogs, were the most frequently and severely affected.