Topical 1% cyclosporine eyedrops for the treatment of crystalline corneal dystrophy in dogs

Crystalline corneal dystrophy (CCD) is the most common type of corneal lipidic deposition in dogs. CCD is a primary metabolic disorder of the corneal fibroblast featuring an accumulation of extracellular and intracellular lipid deposits. Corneal lipid deposits create a corneal opacity and modify the interfibrillar collagen distance, inducing light scattering. Corneal vascularization is not usually associated with the disease, but, in case of chronicity, cell death may produce inflammation, and new corneal vessels are developed. To the best of the authors' knowledge, this is the first report of a medical approach for CCD treatment in veterinary medicine. To evaluate the efficacy of topical 1% cyclosporine eyedrops (1% CsA) for the treatment of CCD in dogs. Medical records of dogs with CCD were retrospectively reviewed (2009-2020). Corneal opacification description (COD) [size (mm), depth, and opacification degree (0-3)] was evaluated at 0, 3, 6, 9, 12, and 15 months postinitial diagnosis. Dogs were classified into three groups: the control group (G), the group receiving topical 1% CsA once per day (G), and the group receiving topical 1% CsA twice daily (G). Ninety-two client-owned dogs (163 eyes) of different breeds, ages, and gender fulfilled the inclusion criteria. When compared to G, where the eyes significantly increased COD (p < 0.001), G and Gsignificantly decreased COD (p < 0.001). In fact, the probability of reducing COD was about three times higher in G than in G, being nearly the same for the right [odds ratio (OR) = 2.94; 95% confidence interval (95% CI) = 0.55-15.78] and left eye (OR = 2.92; 95% CI = 0.49-17.26). In addition, for each additional month of treatment in G, the probability of reducing COD increased significantly (OR = 1.12; 95%CI = 1.00-1.26 for the right eye and OR = 1.16; 95%CI = 1.02-1.32 for the left eye). Long-term treatment with topical 1% CsA eyedrops significantly improved CCD in dogs, being the probability of reducing COD higher when applying the treatment twice daily.