The Importance of Photosensitivity for Epilepsy

The photoparoxysmal response (PPR), also referred to as photosensitivity, is defined as the abnormal occurrence of cortical spikes or spike-and-wave discharges on EEG recording in response to intermittent photic stimulation (IPS). Rate of PPR occurrence strongly depends on the rigor of the IPS testing protocols employed. Determination of photosensitivity range and feature makes it possible to define the likelihood of occurrence of reflex seizures in daily life. Type 4 PPR with generalized spike-and-wave discharges that outlast the duration of the stimulus train are highly related to clinical active visually induced epileptic seizures. Moreover, individuals presenting with type 1 photosensitivity often have a history of photo-induced seizures, which can be subtle or unusual and may go unnoticed or be mistaken. Very important, when PPR appears triggered by low-frequency stimulation, it is highly suggestive of severe neurological disorders.