The first category of retinal cells are neurons: photo-receptors, bipolar cells, and ganglion cells. The intra-retinal nervous optic pathway consists of three consecutive neurons: rods and cones (first neuron), bipolar cells (second neuron), and ganglion cells (third neuron). These cells in human retina are: first neuron about 125 million; bipolar cells about 12.5 million; and ganglion cells about 1.25 million in the ratio 100:10:1.
The neuronal cells of the retina (Radnot, 1978), the inner and outer segments of photoreceptors (Antal, 1977), and the pigment epithelium and its relationships with the photo-receptors were well studied and well described (Leuenberger, 1971). Retinal thickness is known to vary between its central and peripheral regions (Follman and Radnot, 1979) as well as between temporal and nasal zones (Lewis et al., 1969). Moreover, large individual variations have been described in the numbers of neuronal cells localized in the different layers of the human retina
(Osterberger, 1935). Consequently, all retinal quantifications must be performed precisely considering the same topographical location for each sample of investigated retinas.
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