Development of the hamster retina: a morphologic study.

Hamster retinas were examined by light and electron microscopy during the first 15 postnatal days and at the adult stage. At birth, these retinas were more primitive than those of other rodents, but eventually they became very similar. Initial postnatal growth and development were more rapid than in other rodents of comparable ages. Mitotic figures were present throughout the first 9 days. The primitive inner plexiform layer formed during days 2 to 4; on day 7, several developmental changes became apparent: outer segment disks of the photoreceptor cells formed from flattened, smooth vesicles, horizontal cells became readily identifiable, the outer plexiform layer appeared, and ribbon synapses formed in the receptor cell axon terminals. By day 11, there were numerous conventional synapses in the inner plexiform layer, and ribbon synapses were beginning to appear in the terminal portions of the bipolar axons. The retinal tissue was progressively invaded by developing vasculature. The first photoreceptor outer segment disks formed from smooth membranous vesicles flattening radially around the ends of the connecting cilium. After the outer segment assumed a more mature appearance, with a stacked disk arrangement, further disk formation occurred by plasma membrane infoldings at the outer segment base. The adult hamster retinas were similar to those of other rodents.