Intermittent photic stimulation was performed in 21 photosensitive epileptic patients and the relation of the photoparoxysmal response (PPR) to the epilepsy syndrome was determined in a study at the National Epilepsy Center, Shizuoka Higashi Hospital, Shizuoka, Japan. The PPR was dependent on the quantity-of-light in 4 of 6 patients with photosensitive myoclonic epilepsy in infancy, and in 2 of 7 with symptomatic generalized epilepsy. Wavelength dependent PPR was elicited in 5 of 8 patients with photosensitive localization-related epilepsy, and in 4 of 7 with symptomatic generalized epilepsy. The type of pathophysiologic mechanism for eliciting PPRs by low-luminance photic stimulation was correlated with the epilepsy syndrome classification. [1]

COMMENT. The high frequency of photosensitivity in patients with severe myoclonic epilepsy of infancy might be related to the quantity-of-light-dependent (OLD) mechanism. In the above study, patients with QLD-PPRs have PPRs at frequencies from 6 to 33 Hz, whereas patients with wavelength-dependent (WLD) PPRs show responses at a narrower range (12-20 Hz). This suggests a higher level of photosensitivity in patients with QLD than WLD PPRs. Some photosensitive patients are thought to undergo an evolution and a change in mechanism with age.