Relationship between spatial resolution and effective retinal ganglion cell separation in macaque monkeys

Abstract

Abstract: : Purpose: To investigate the relationship between spatial resolution and effective retinal ganglion cell separation in macaque monkeys. Methods: We used previously published data from the literature of spatial resolution thresholds (mean of 7 monkeys (Macaca nemestrina)) obtained using gratings of 90% contrast at eccentricities from 0 to 24 deg and ganglion cell densities (from 1 monkey (Macaca fascicularis)) at eccentricities from 3 to 25 deg. Ganglion cell densities were transformed to effective ganglion cell separations. Results: There is a very good correspondence between measured spatial resolution (Kiorpes, L. and D. C. Kiper (1996). Vision Res 36(2): 239–47) and effective ganglion cell separation (Wässle, H., U. Grünert, et al. (1990). Vision Res 30(11): 1897–911) in the studied eccentricity range. A linear regression with origin constraint yields a regression coefficient of 1.39 (r² = 0.98). Assuming that only midget cells mediate spatial resolution, and that they make up 80% of the ganglion cell population in macaque retina, it is possible to calculate the contribution of ON and OFF midget ganglion cells. A direct proportionality between resolution and effective ganglion cell separation should yield a regression coefficient of one. To account for an ON/OFF midget population in which the cells act as complementary encoders (ON and OFF) it is necessary to divide the regression coefficient based on the whole ganglion cell population by 1/sqrt(0.8) = 1.12, and for a population in which the cells act as individual encoders (ON or OFF) the divisor will be 1/sqrt(0.4) = 1.58. This yields coefficients of 1.25 (r² = 0.98) for a population of complementary encoders and 0.88 (r² = 0.98) for a population of individual encoders. Conclusions: Several factors might have affected our results: maturation of the visual system, methodological issues relating to the measurements of central spatial resolution performance, and the fact that the ganglion cell density data were only obtained from one macaque. Nonetheless, we present results that are comparable to theoretical limits of resolution.

Keywords: visual acuity • ganglion cells