A regional specialization in the opossum's retina: Quantitative analysis of the ganglion cell layer

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Abstract
The distribution of ganglion cells in the opossum's retina was determined from flat-mounted preparations stained with cresyl-violet. The retinal area is 109 mm2 (SD = 16 mm2). Maps of ganglion cell density were made from retinae of seven animals. in all maps iso-density lines were approximately concentric, showing a slight elongation towards the nasal region. Cell density varied from 400 cells/mm2 at the extreme periphery to 2,900 cells/mm2 in the region of highest count, the are centralis. The center of this region lies 1.85 mm (26.3°) temporal to the center of the optic nerve head. The average total number of ganglion cells is 77,384 (SD = 10,173). Based upon soma diameter histograms ganglion cells were classified into three groups, showing at area centralis peaks at 7 μm, 12 μm and 15 μm respectively. Cell soma diameter ranged from 6 μm to 21 μm, larger values being observed at the periphery.