In vivo confocal microscopy of brachycephalic dogs with and without superficial corneal pigment

Objective To characterize canine superficial corneal pigment (SCP) in brachycephalic dogs using in vivo confocal microscopy (IVCM). Animals studied Fifty-seven client-owned brachycephalic dogs from breeds predisposed to SCP (i.e., Boston Terrier, Lhasa Apso, Pekingese, Pug, and Shih Tzu). Procedures Complete ocular examination, including slit-lamp biomicroscopy, was used to determine presence or absence of SCP, and IVCM examinations were then performed. Clinical and IVCM abnormalities were recorded using a standardized scoring system and statistically compared between dogs with and without SCP. Dogs were split into two groups for analysis; Pugs and non-Pug breeds. Results Of the 57 dogs examined, 32 were Pugs and 25 were non-Pug breeds. Twenty-three Pugs (71.8%) and 10 non-Pugs (40%) displayed SCP. Six of 13 evaluated IVCM features were significantly (P < 0.05) associated with SCP in both Pugs and non-Pugs and included superficial epithelial pigment, basal epithelial pigment, Langerhans cells, anterior stromal dendritic cells, epithelial disorganization, and vascularization. Additionally, superficial epithelial leukocytes and anterior stromal dendritic cells were significantly associated with SCP in Pugs only. Many of the IVCM features associated with SCP were also observed in SCP unaffected dogs; however, they were present at a reduced frequency and confined to the perilimbal region of the cornea. Conclusions By IVCM, SCP in dogs is characterized by microscopic features of chronic inflammation. Abnormalities were superficial and largely confined to the corneal epithelium. Superficial pigment in brachycephalic dogs appears morphologically as a centripetal corneal migration of microanatomic features normally confined to the perilimbal region of the cornea.