The aim of the study was to determine the thickness of choroidal layers in mixed breed dogs suffering from retinal atrophy (RA) and showing symptoms of progressive retinal atrophy (PRA), with the use of SD-OCT. The study was performed on 50 dogs divided into two groups: 25 dogs diagnosed with retinal atrophy (RA) with PRA symptoms aged 1.5-14 years and 25 healthy dogs aged 2-12 years. The dogs were examined using slit-lamp biomicroscopy, tonometry, ophthalmoscopy, fundus camera and SD-OCT (Topcon 3D OCT 2000). Measurements of the choroidal layers: RPE-Bruch membrane-choriocapillaris complex (RPE-BmCc) with tapetum lucidum in tapetal fundus, medium-sized vessel layer, (MSVL), large vessel layer with lamina suprachoroidea and (LVLS) whole choroidal thickness (WCT) were taken manually with the use of the caliper function integrated with the SD-OCT software. The measurements were performed dorsally (D) and ventrally (V) at a distance of 5000-6000 μm, and temporally (T) and nasally (N) at a distance of 4000-7000 μm from the optic disc with enhanced depth scans. The measurements were conducted temporally and nasally both in the tapetal (TempT, Nast) and nontapetal (TempNT, NasNT) fundus. Statistical analysis was performed using Statistica 10 software (Mann Whitney U Test). In all dogs affected by retinal atrophy (RA) with PRA symptoms, a statistically significant (p≤0,05) reduction in thickness of MSVL was observed in all the measured regions. A statistically significant reduction in thickness of LVLS and WCT was found in all nontapetal areas (p≤0,05). RA in mixed breed dogs with PRA symptoms was accompanied by choroid disorders such as reduction in thickness of the large vessel layer and decreased whole choroidal thickness in the nontapetal fundus as well as the medium vessel layer in all fundus regions.