Regional specialization in the golden hamster's retina.

Ganglion cell swere counted and measured in whole mounts of the hamster's retina, stained with methylene blue. Their density varies between about 1,000/mm2 at the edge of the retina to about 5-6,000/mm2 in a broad area centralis centred about 1.9 mm(39 deg) directly temporal to the optic disk. Maps of cell density show a long horizontal extension of the dense area in the nasal direction. The sizes of ganglion cell somata fall into two main groups--small cells (5-11 mum diameter) and large cells (greater than 11 mum), the latter including a small proportion of giant cells (greater than 17 mum). All three classes of cells are maximal in density in the area centralis, although the small cells are relatively more numerous there. The total number of cells is about 114,000 with about 63,000 small cells and about 51,000 large. The optic nerve contains about 69,000 unmyelinated axons and about 50,000 myelinated axons, suggesting that the latter are the fibres of the larger ganglion cells. It is likely that the projections of the centres of the areae centrales of the two eyes are normally divergent in space; they are therefore not on "corresponding retinal points."