The comparative histology of the retinal pigment epithelium (RPE) of the following species was studied by examining bleached flat preparations and cross sections of the cells: human, monkey, rat, rabbit, sheep, cow, dog, and chicken. The variations noted among the cells of the different species involved cell size, nuclear size, number of nuclei per cell, and the distribution of pigment granules within the cells. The majority of the retinal pigment epithelial cells of the rat and rabbit were binucleate; binucleate RPE cells were common in primate eyes and were noted occasionally in other species. Normal and abnormal mitotic figures were observed in the retinal pigment epithelium of two apparently normal adult albino rats.
Ts'o MOM, Friedman E. The Retinal Pigment EpitheliumI. Comparative Histology. Arch Ophthalmol. 1967;78(5):641-649. doi:10.1001/archopht.1967.00980030643016