Summary
The number, cell morphology and retinal distribution of rods and cones were determined in the retina of the toad, Bufo marinus. Adult animals were sacrificed, both eyes were removed and prepared for either tangential section across the outer segments of the photoreceptor layer, or transverse section across the whole retina.
Cone densities increased from an average of 7000/mm2 in the peripheral to a maximum of 25000/mm2 in the central retina. The high cone densities extended across the naso-temporal axis of the retina corresponding to the position of the visual streak in the ganglion cell layer. The total number of cones in the retina was estimated to be 1.1 million. Rod density of 21000/mm2 in the central retina decreased to 17000/mm2 at 1.5–4 mm eccentricity, and then increased to 29000/mm2 in the peripheral retina. The total number of rods amounted to about 2 million. The mean of the crosssectional area of rod outer segments was 11.2 ± 1.5 μm2 (mean ± SD) in the highest and 17.9 ± 4.7 μm2 in the lowest density areas of the retina. The length of the rod outer segments extended from 28 μm in the ventral peripheral retina to a maximum of 89 μm in the dorsal retina, dorsal to the visual streak of the ganglion cell layer.
The results of the present study showed a differential retinal distribution of photoreceptors, with a peak density in the retinal centre and a higher density along the naso-temporal axis of the eye. We conclude that the area of high photoreceptor density, matched by high neuron densities of the INL and GCL, corresponds to the site of acute vision of the Bufo retina.
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On leave from Department of Biology, Fujian Teachers University, Fuzhou, Fujian, People's Republic of China.
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Zhang, Y., Straznicky, C. The morphology and distribution of photoreceptors in the retina of Bufo marinus . Anat Embryol 183, 97–104 (1991). https://doi.org/10.1007/BF00185840
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DOI: https://doi.org/10.1007/BF00185840