Migraine phosphenes and the retino-cortical magnification factor

Quantitative observations on the shape and position of migraine phosphenes within the visual field were obtained by controlled "perimetric" drawings of the phosphenes performed every 1-2 min during the aura state. The visual field eccentricity of the "fortification" or zig-zag patterns scintillating at about 10 Hz was plotted as a function of observation time. It is well described by an exponential function of time. This exponential function is the product of a first-order linear differential equation determined by the distribution of the retino-cortical magnification factor across the visual field and a constant diffusion speed of the cortical pathophysiological process leading to the migraine phosphene patterns. The observed "particle" size of the phosphene pattern and the width of the scotoma trailing the scintillating phosphenes could also be easily predicted from these assumptions. A model in which the main components are an increase in extracellular potassium concentration, a decrease in extracellular calcium concentration and the constant speed diffusion of the ions along the extracellular space of the stripe of Gennari within the primary visual cortex explains the observations.