Abstract: The total number, soma size, topographic distribution, and density of ganglion cells were studied in retinal wholemounts of the Steller sea lion (Eumetopias jubatus). Ganglion cell soma size varied from 6 to 37 μm, and the majority of cells were of a size from 10 to 25 μm. A distinct group were large ganglion cells of more than 25 to 37 μm, which were similar to the α-cells known in terrestrial mammals. The number of α-like cells constituted 8% of the total ganglion cell population. The topographic distribution of ganglion cells showed a definite area of high cell density similar to the area centralis of terrestrial carnivores. This area was located in the temporal retinal quadrant, 8 to 9 mm from the optic disk. In this area, the peak cell densities in six wholemounts ranged from 1,512 to 2,520 (mean 1,904) cells/mm2. With a posterior nodal distance of 19 mm (underwater), these densities corresponded to 166 to 277 (mean 209) cells/deg2. This predicts a mean retinal resolution of 4.15' of minimum visibility (7.2 cycle/deg) in water and 5.5' (5.5 cycle/deg) in air. Topographic distribution of α-like cells was qualitatively similar to that of the total ganglion cell population, but the density of α-like cells reached only 45 to 72 (mean 59) cells/mm2.

Key Words: STELLER SEA LION; EUMETOPIAS JUBATUS; MAMMALS; RETINA; GANGLION CELLS; RETINAL TOPOGRAPY; AREA CENTRALIS; VISUAL ACUITY; ALPHA-CELLS

Document Type: Research article

DOI: 10.1578/AM.31.4.2005.393

Page Numbers: 393 - 402

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