Quantitative estimations of foveal and extra-foveal retinal circuitry in humans.

For an understanding of the basis for psychophysical measurement of visual resolution, quantitative morphological studies of retinal neuronal architecture are needed. Here we report on cell densities and retinal ganglion cell:cone ratio (RGC:C) from the foveal border to the peripheral retina (34 degrees eccentricity). Quantitative estimates of RGC and C densities were made using a modified disector method in three vertically sectioned human retinae and were adjusted for RGC displacement. In agreement with our previous data on humans, we found an RGC:C ratio close to 3 at 2-3 degrees eccentricity. Outside the foveal border, the ratio declined to 1.0 at 7.5 degrees eccentricity and to 0.5 at eccentricities larger than 19 degrees. Center-to-center separation of C and RGC in addition to center-to-center separation of estimated 'receptive fields' was calculated at corresponding locations along the superior and inferior hemimeridians. The center-to-center separation of estimated 'receptive fields' was found to be more closely related to resolution thresholds from the fovea to 19 degrees eccentricity than was the separation of RGC and C. On the basis of these quantitative estimates, models for neural circuitry involved in central and peripheral spatial vision can be discussed.