Evidence for My-cell Involvement in the Spatial Frequency Doubled Illusion as Revealed by a Multiple Region PERG for Glaucoma

Recent evidence suggests that glaucoma leads to early loss of large retinal ganglion cells1,2 projecting to the Magnocellular layers of the dLGN: the so called "M" retinal ganglion cells. It is necessary for the present study, to appreciate that there are two subgroups of M-cells, the Mx-cells which are quite linear, and the nonlinearly responding My-cells, where the subscripts indicate physiological similarities with cat X and Y-cells3. In particular the retinal gain control described by Shapley and Victor4 for cat X and Y cells is strongly expressed in primate M- cells5. Except at very low temporal frequencies the quadratic response of Y-cells is larger than the linear response, especially at low spatial frequencies6, and the gain control effects Y-cells more, especially their quadratic response7. At least three studies indicate that My-cells are larger than Mx- cells8,9,10. Therefore, methods for glaucoma diagnosis should perhaps appeal to My-cell physiology, e.g. the strong effects of gain control upon their nonlinear responses.