Abstract
The retinal ganglion cells (RGCs) are radially displaced from their receptive field locations, with the magnitude varying by eccentricity and polar angle. Drasdo and colleagues (2007) proposed that the degree of displacement along a given polar angle may be derived by taking the difference between retinal eccentricities with matching cumulative counts of midget RGCs and receptive fields (RFs). We are developing a fully analytic solution for RGC displacement at every retinal location, building upon similar prior work (Drasdo et al., 2007, Watson 2014, Turpin et al, 2015). We model RF and RGC density across eccentricities for a given polar angle with functions that can be integrated. We used a two-term exponential for RF, and the Fréchet (a gamma-like) distribution for RGC. Parameters for the density functions for the cardinal meridians (e.g., nasal, temporal) are obtained from fits to existing data (Drasdo et al., 2007) or models (Watson 2014). Parameters for intermediate polar angles are given by the interpolation of these values. The density functions are integrated and summed to yield cumulative counts (RFs or RGCs) per solid degree of retina as a function of eccentricity. The analytic solution for displacement is then the difference in eccentricities for which the two integrated functions have the same cumulative count. Our result does not yet match empirical measures of displacement; this may be corrected by improvements in the functional form for RGC density. If successful, this approach may be tailored to account for individual variation as measured by psychophysics and retinal imaging.