To determine whether there was a simple relationship between levels of ocular pigmentation and the number of mitotic and pyknotic profiles, animals from each pigmentation phenotype were bred and collected on D1 and D3 (D1: albino, n = 3; Himalayan, n = 3; Beige, n = 6; C57Bl, n = 3; D3: albino, n = 8; Himalayan, n = 3; Beige, n = 7; C57Bl, n = 8). These were killed as described, and their eyelids opened. The heads were then placed in 2% paraformaldehyde and 2% glutaraldehyde in PBS (pH 7.2) and left overnight. The following day, the heads were dissected, leaving the eyes attached through the pallet. The tissue was then dehydrated as described and embedded in resin (Historesin; Leica). These blocks were sectioned horizontally at 5 μm, with every fifth section being saved. Sections were mounted on clean slides, left on a hot plate overnight, and then stained with cresyl violet. In each case, three sections close to the horizontal meridian were selected for analysis from three animals from each pigmentation phenotype, and the number of mitotic and pyknotic profiles were counted in these. Mitotic figures were identified as clear meta- or anaphase profiles adjacent to the RPE, which represents the ventricular margin where cell division takes place. Pyknotic profiles were present throughout the depth of the developing retina and were clearly identified as dense, round profiles that were heavily stained. Mitotic and pyknotic profiles were counted in complete retinal sections from one edge of the periphery to the other.