Spatial summation properties for magnocellular and parvocellular pathways in glaucoma.

PURPOSE: To examine the spatial summation properties for the magnocellular (M) and parvocellular (P) visual pathways in participants with glaucoma and approximately age-matched controls in central and midperipheral retinal eccentricities.
METHODS: Contrast discrimination thresholds were measured for six different stimulus array sizes, using steady- and pulsed-pedestal paradigms designed to measure function of the M and P pathways, respectively. This study involved 15 participants with glaucoma and 17 approximately age-matched controls. All participants completed trials foveally and at 12.5 degrees eccentricity. The peripheral stimulus location for each glaucoma participant was within a quadrant of early visual field loss, and locations were matched for the control group.
RESULTS: The glaucoma group demonstrated significantly elevated thresholds compared with the control group (F((1,30)) = 16.29; P < 0.001). Thresholds were also significantly dependent on the stimulus sizes, testing location, and pedestal condition. Data obtained for the steady-pedestal paradigm were fit with an exponential decay function, whereas the pulsed-pedestal data were fit with a linear function, demonstrating different spatial summation properties for the M and P pathways, consistent with previous studies using this methodology. Analyses of the curve parameters obtained from the curve fits indicated no significant difference in the shape of the curves between glaucoma and control participants.
CONCLUSIONS: Although spatial summation properties are different for presumed M- and P-mediated pathways, the underlying spatial summation properties associated with these pathways are similar in the control and glaucoma participants in this study, centrally and midperipherally.