Histological study of choroidal melanocytes in animals with tapetum lucidum cellulosum

The distribution and morphology of choroidal melanocytes in dogs and cats which have a tapetum were compared with those of humans who do not. In dogs or cats, tapetal cell-like melanocytes were arranged in layers on the scleral side of the tapetum and underneath the choriocapillaris in the non-tapetal area. Although the tapetum of the dog occupied a smaller area than that of the cat, the tapetum plus the area of tapetal cell-like multilayered melanocytes occupied most of the fundus in the dog in almost the same way as in the cat. These multilayered melanocytes contained few intracytoplasmic organelles except for melanin granules, and some had regularly arranged melanin granules. In human eyes tapetal cell-like melanocytes were not found anywhere. It was concluded that the morphology and structural architecture of choroidal melanocytes of dogs or cats are different from those of human eyes and closely correspond to the tapetum.