Histopathologic and ultrastructural features of the choriocapillaris in dogs with sudden acquired retinal degeneration syndrome and progressive retinal atrophy.

Dogs with sudden acquired retinal degeneration syndrome (SARDS) have rapid onset visual dysfunction and subsequent outer retinal atrophy. The pathophysiology of SARDS is poorly understood. This study's objective was to examine the histologic features of choriocapillaris perfusion and Bruch's membrane morphology in eyes from dogs with SARDS. Archived, paraffin-embedded, sagittal eye sections of dogs with SARDS (n = 12), age/breed-matched healthy control dogs (n = 24), and age-matched dogs with progressive retinal atrophy (PRA, n = 12) were evaluated. Choriocapillaris density and patency were estimated using light microscopy and immunofluorescence to quantify patent vessels containing luminal erythrocytes and nonpatent vessels with empty lumens. The outer nuclear layer (ONL) nuclei density was quantified to determine the extent of atrophy. The thickness of Bruch's membrane was measured from transmission electron microscopy images (n = 5 SARDS, 5 PRA, 6 controls). Statistical analyses were performed using 1-way analysis of variance (ANOVA) and the Spearman rank correlation. Both SARDS and PRA samples had lower patent vessel densities compared with controls (P = .006 and .04, respectively). ONL nuclei density and choriocapillaris vessel density were associated in samples from dogs with PRA (r = 0.94-1.00, P < .05), but not SARDS (r = 0.14-0.66, P > .05). Eyes with SARDS had thicker Bruch's membrane than controls and dogs with PRA (P < .0001). Outer retinal disorders in dogs, including SARDS and PRA, are associated with alterations in choriocapillaris characteristics and Bruch's membrane thickness. Whether these findings are causative or correlative with disease is unknown.