Photic- and pattern-induced seizures: Expert consensus of the epilepsy foundation of america working group

Purpose: In August, 2004, the Epilepsy Foundation of America convened a workshop to begin to develop an expert consensus on photosensitive seizures. Methods: Literature and data were reviewed, and consensus was derived from discussion. Results: A flash is a potential hazard if it has luminance ≥20 cd/m², occurs at a frequency of ≥3 Hz, and occupies a solid visual angle of ≥0.006 steradians (∼10% of the central visual field or 25% of screen area at typical viewing distances). A transition to or from saturated red also is considered a risk. A pattern with the potential for provoking seizures contains clearly discernible stripes, numbering more than five light-dark pairs of stripes in any orientation. When the light-dark stripes of any pattern collectively subtend at the eye from the minimal-expected viewing distance a solid angle of >0.006 steradians, the luminance of the lightest stripe is >50 cd/m², and the pattern is presented for ≥0.5 s, then the pattern should display no more than five light-dark pairs of stripes, if the stripes change direction, oscillate, flash, or reverse in contrast; if the pattern is unchanging or smoothly drifting in one direction, no more than eight stripes. These principles are easier to apply in the case of fixed media, for example, a prerecorded TV show, which can be analyzed frame-by-frame, as compared with interactive media. Conclusions: A consensus view of stimuli likely to provoke visually evoked seizures can be developed.