Figure 4: (a) Light microscopy (LM) of the inferior nontapetal retina of the 9-year-old ESS dog. Severe thinning of the entire retina is seen with complete degeneration of photoreceptor cells and inner retinal degeneration, disorganization, and gliosis. (b) LM of superior tapetal retina. A variation in retinal thickness is observed and some areas with a single row of photoreceptor nuclei that are still present. Toluidine blue staining; ×40.