Abstract
Purpose :
Conventional perimetric stimuli have been reported to evoke neuronal firing of retinal ganglion cells in magnocellular pathway (M-RGCs). The author hypothesized that the firing rates may correspond to the so-called "stimulus energy" in Ricco's law.
Methods :
To test this hypothesis, the author calculated the reciprocal of firing rates at detection threshold as estimates of local M-RGC density. The firing rates to threshold intensity were simulated by a Michaelis-Menten equation. Validation of estimates was done by predicting the mean M-RGC density in regions with glaucomatous damage as a weighted average of local density estimates. The weights, representing the spatial irregularity of surviving M-RGCs, were derived from the slope of empirical frequency-of-seeing curves (ARVO 2021 E-abstract #3532912).
Results :
In simulations, the firing rates of M-RGCs increased with threshold intensity until they reached an asymptote (Fig.1a). The corresponding estimates of local M-RGC density decreased and eventually plateaued at approximately 17% of normal (Fig.1b). The predicted mean M-RGC density in regions with glaucomatous damage decreased with retinal sensitivity from 98.4% at 32dB to 3.0% at 1dB (Fig.1c).
Conclusions :
The reciprocal of firing rates yielded reasonable estimates of M-RGC density, supporting the equivalence of firing rates of M-RGCs and "stimulus energy".
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.