Critical frequency of photic driving: which part of the visual pathway do we examine?

Studies on critical frequency of photic driving were performed on patients with optic atrophy, moderately expressed suprachiasmal lesions and normal subjects. A reduction was present only in optic atrophy patients. The critical frequency of photic driving showed significant correlations with visual acuity and differential light sensitivity of the areas located within 15 degrees from the fixation point. The correlation proved higher for foveal sensitivity expressed in non-logarithmic rather than in logarithmic units, the opposite being the case for the sensitivity of parafoveal areas. It may be concluded that critical frequency of photic driving is conditioned by the cortical projection zones and visual pathways corresponding to the central 15 degrees of the visual field, but with predominant role of foveal projections.