Advances in Photoreception Proceedings of a Symposium on Frontiers of Visual Science (1990) / Chapter Skim
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The Distribution of Cones in the Primate Retina
The Distribution of Cones in the Primate Retina
Pages 105-116
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From page 105... ...
The use of whole-mounted retinas greatly reduces many of the problems associated with using sectioned retinas and allows accurate estimates of retinal shrinkage. The identification of rods and cones in the primate retina poses few problems (Figure 1~.
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From page 106... ...
In these preparations the shrinkage was minimal. Estimates of the foveal cone density were made from horizontal sections that passed through the inner segments.
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From page 107... ...
There was a clear nasotemporal asymmetry in the cone distribution outside the central 10 deg or so of the retina; the cone density declined more slowly along the nasal horizontal meridian of the retina than along the other axes. The asymmetry in cone density was somewhat smaller than that seen for the ganglion cells (Perry et al., 1984~.
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From page 108... ...
The cone distribution in the human eye has a similar but not as pronounced nasotemporal asymmetry as described for the monkey with the higher densities in the nasal retina. The large variation in foveal cone density cannot be readily attributed to differential tissue shrinkage.
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From page 109... ...
~ _ ~) - #_ ~ ~ ~ 4~-~ Y<\ 2 it,/ ff i' · ~ FIGURE ID, E Analysis of cone mosaics to demonstrate the local triangular lattice at the fovea and how it degenerates with eccentricity.
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From page 110... ...
A sample of our data is shown in Figure 2, where the cone density along the temporal horizontal meridian in eight retinas is plotted. In six of the retinas there is a rapid decline in cone density with eccentricity, as we
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From page 111... ...
showed quite clear reductions in density within the central 0.5 deg. In these animals we could observe no pathology or distortion of the tissue, and indeed it was clear that the inner segments of the cones were themselves larger than in the retinas with higher densities.
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From page 112... ...
The anatomical data suggest that we can give no single value as the cone spacing at the human fovea. Ideally, we would like to look at the cone separation in the living eye and compare the results obtained with those found in whole-mount preparations.
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From page 113... ...
has shown that in the human eye, again using interference fringes, the orientations of the moire patterns observed are of a form consistent with triangular packing of the cones with local but not long-range order. The extent of the regular packing predicted by his studies is in good agreement with the size of the largest islands and the rapid degeneration of the regularity with distance from the foveal center.
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From page 114... ...
GANGLION/FOVEAL CELL RATIO From our knowledge of the length of the fibers of Henle or by taking into account the fact that cone pedicles are at least twice the diameter of the cone inner segment (Boycott et al., 1987) , it is possible to estimate the numerical relationship of ganglion cells to cones for the foveal retina.
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From page 115... ...
This information should prove useful in showing the extent to which cone density limits visual performance across the visual field. The next important task is to discover from anatomical and physiological experiments how the information from the cones is used to construct the receptive field characteristics of the different types of ganglion cells.
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From page 116... ...
1985 Aliasing in human foveal vision. Vision Research 25:195-205 1988 Topography of the foveal cone mosaic in the living human eye.
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