LIGHT DIFFUSION IN PHOTOSENSITIVE EPILEPSY

Photosensitivity is usually tested by intermittent photic stimulation. Photoparoxysmal responses in the EEG are enhanced when the eyes remai n closed during stimulation. We tested the hypothesis that this is due to diffusion of light By the eyelids; In 25 photosensitive patients, conditions 'eye closure', 'eyes closed', 'eyes open' and 'eyes open wi th diffuser' were tested for frequencies of 2-60 Hz. Additional influe nces of a red filter and fixation were also examined. The photosensiti vity range was maximal in the condition 'eyes open with diffuser', due to an increase of the upper limit to a median 60 Hz (range 25-60), fr om 35 (15-50) Hz with eyes open, 37.5 (25-60) Hz with eyes closed and 40 (23-60) Hz with eye closure (P = 0.0002). This effect was attenuate d in patients on valproic acid and with the use of a red or white filt er. Testing with a diffuser was more sensitive than without, except fo r one patient who was photosensitive only in the eye closure condition . The influence of the eyelids on photosensitivity can be explained by diffusion of light, attentuated by an intensity loss. Use of a diffus er may simplify testing for photosensitivity in the EEG laboratory. Th e diffusion effect may explain seizure susceptibility in front of 50 a nd 60 Hz television screens. (C) 1998 Elsevier Science Ireland Ltd.