The deep-sea pearleye, Scopelarchus michaelsarsi (Scopelarchidae) is a mesopelagic teleost with a... more The deep-sea pearleye, Scopelarchus michaelsarsi (Scopelarchidae) is a mesopelagic teleost with asymmetric or tubular eyes. The main retina subtends a large dorsal binocular field, while the accessory retina subtends a restricted monocular field of lateral visual space. Ocular specializations to increase the lateral visual field include an oblique pupil and a corneal lens pad. A detailed morphological and topographic study of the photoreceptors and retinal ganglion cells reveals seven specializations: a centronasal region of the main retina with ungrouped rod-like photoreceptors overlying a retinal tapetum; a region of high ganglion cell density (area centralis of 56.1 x 10(3) cells per mm2) in the centrolateral region of the main retina; a centrotemporal region of the main retina with grouped rod-like photoreceptors; a region (area giganto cellularis) of large (32.2+/-5.6 microm2), alpha-like ganglion cells arranged in a regular array (nearest neighbour distance 53.5+/-9.3 microm with a conformity ratio of 5.8) in the temporal main retina; an accessory retina with grouped rod-like photoreceptors; a nasotemporal band of a mixture of rod- and cone-like photoreceptors restricted to the ventral accessory retina; and a retinal diverticulum comprised of a ventral region of differentiated accessory retina located medial to the optic nerve head. Retrograde labelling from the optic nerve with DiI shows that approximately 14% of the cells in the ganglion cell layer of the main retina are displaced amacrine cells at 1.5 mm eccentricity. Cryosectioning of the tubular eye confirms Matthiessen's ratio (2.59), and calculations of the spatial resolving power suggests that the function of the area centralis (7.4 cycles per degree/8.1 minutes of arc) and the cohort of temporal alpha-like ganglion cells (0.85 cycles per degree/70.6 minutes of arc) in the main retina may be different. Low summation ratios in these various retinal zones suggests that each zone may mediate distinct visual tasks in a certain region of the visual field by optimizing sensitivity and/or resolving power.
The retinal topography of cells within the ganglion cell layer of three teleost species is examin... more The retinal topography of cells within the ganglion cell layer of three teleost species is examined in Nissl-stained material in which all neuronal elements containing Nissl substance in the cytoplasm are counted. A topographic comparison is made with retrogradely labelled ganglion cells to differentiate the proportion of nonganglion cells not possessing an axon joining the optic nerve. In the three species studied 92%, 80%, and 66% were found to be the maximum proportion of true ganglion cells in the area centralis, horizontal streak, and periphery, respectively. The proportion of nonganglion cells in the total population of cells counted was 24%. The major contribution to this discrepancy is from peripheral nonspecialized regions of the retina. There is little difference in both topography and peak densities of retinal ganglion cells between the two techniques. The soma areas of both populations are analysed, with the homogeneous nonganglion cell population possessing cells between 5 and 15 μm2 and the heterogeneous ganglion cell soma between 5 and 68 μm2, increasing in size with eccentricity.
The deep-sea pearleye, Scopelarchus michaelsarsi (Scopelarchidae) is a mesopelagic teleost with a... more The deep-sea pearleye, Scopelarchus michaelsarsi (Scopelarchidae) is a mesopelagic teleost with asymmetric or tubular eyes. The main retina subtends a large dorsal binocular field, while the accessory retina subtends a restricted monocular field of lateral visual space. Ocular specializations to increase the lateral visual field include an oblique pupil and a corneal lens pad. A detailed morphological and topographic study of the photoreceptors and retinal ganglion cells reveals seven specializations: a centronasal region of the main retina with ungrouped rod-like photoreceptors overlying a retinal tapetum; a region of high ganglion cell density (area centralis of 56.1 x 10(3) cells per mm2) in the centrolateral region of the main retina; a centrotemporal region of the main retina with grouped rod-like photoreceptors; a region (area giganto cellularis) of large (32.2+/-5.6 microm2), alpha-like ganglion cells arranged in a regular array (nearest neighbour distance 53.5+/-9.3 microm with a conformity ratio of 5.8) in the temporal main retina; an accessory retina with grouped rod-like photoreceptors; a nasotemporal band of a mixture of rod- and cone-like photoreceptors restricted to the ventral accessory retina; and a retinal diverticulum comprised of a ventral region of differentiated accessory retina located medial to the optic nerve head. Retrograde labelling from the optic nerve with DiI shows that approximately 14% of the cells in the ganglion cell layer of the main retina are displaced amacrine cells at 1.5 mm eccentricity. Cryosectioning of the tubular eye confirms Matthiessen's ratio (2.59), and calculations of the spatial resolving power suggests that the function of the area centralis (7.4 cycles per degree/8.1 minutes of arc) and the cohort of temporal alpha-like ganglion cells (0.85 cycles per degree/70.6 minutes of arc) in the main retina may be different. Low summation ratios in these various retinal zones suggests that each zone may mediate distinct visual tasks in a certain region of the visual field by optimizing sensitivity and/or resolving power.
The retinal topography of cells within the ganglion cell layer of three teleost species is examin... more The retinal topography of cells within the ganglion cell layer of three teleost species is examined in Nissl-stained material in which all neuronal elements containing Nissl substance in the cytoplasm are counted. A topographic comparison is made with retrogradely labelled ganglion cells to differentiate the proportion of nonganglion cells not possessing an axon joining the optic nerve. In the three species studied 92%, 80%, and 66% were found to be the maximum proportion of true ganglion cells in the area centralis, horizontal streak, and periphery, respectively. The proportion of nonganglion cells in the total population of cells counted was 24%. The major contribution to this discrepancy is from peripheral nonspecialized regions of the retina. There is little difference in both topography and peak densities of retinal ganglion cells between the two techniques. The soma areas of both populations are analysed, with the homogeneous nonganglion cell population possessing cells between 5 and 15 μm2 and the heterogeneous ganglion cell soma between 5 and 68 μm2, increasing in size with eccentricity.
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