Photic Stimulation: Standardization of Screening Methods

Abstract

Summary: Purpose: Differences in methodology of intermittent photic stimulation within and between countries in Europe make collaborative research and interpretation of results difficult.Method: Experts in the field of photic stimulation from European countries have given an overview of methods used in routine photic stimulation. A consensus meeting was organized in May 1996 in the Netherlands.Results: Methodology, including specification of a photoDuring intermittent photic stimulation (IPS), subtle seizures such as myoclonic jerks and absence seizures can be evoked, and even tonic-clonic seizures if no precautions are taken. The pathologic responses to IPS, consisting of generalized (poly-) spike and wave discharges, are strongly related to a history of epilepsy. In populations of patients undergoing EEG examination for clinical purposes, if the response outlasts the stimulus train, the prevalence of overt epilepsy is >90% (1,2). IPS can also evoke a number of normal, non-pathologic responses such as photic driving, often with supra-or subharmonics. The "photomyoclonic response" consists of rhythmic action potentials from the orbital and other facial muscles synchronous with the flashes, possibly with a frontal cortical component. Occipital spikes timelocked to the flash may be seen in both photosensitive and other subjects and have no strong association with epilepsy. Other ill-defined reactions to IPS, such as occipital slow waves and generalized spikes at the stimulus frequency, have no known specific significance. Responses to IPS, which are "atypical" in the sense of differing from photic following at the flash rate, are found in 510% of normal adults and 15% of normal children In many EEG laboratories in Europe and elsewhere, IPS is not performed routinely. In those laboratories that (3-5). Conclusions: Consensus was reached in setting up a safe, quick, simple and reliable method to determine whether or not patients are photosensitive. A specification of an international standard for intermittent photic stimulation in the routine EEG examination is given with the purpose of improving patient care and facilitating collaborative research.do undertake photic stimulation routinely, considerable variation exists with respect to the type of photostimulator, the test procedure, and the interpretation of the EEG response. As a result of these variations, findings are inconsistent from one laboratory to another, and this has unfortunate consequences for both patient care and collaborative research.Until now, manufacturers of EEG apparatus and photic stimulators have shown little interest in producing an optimal photostimulator. Lack of knowledge concerning important aspects of methodology can cause a misunderstanding of the photic stimulation procedures and lead to an over-, but mainly an underestimation of photosensitivity.Experts' in the field of photic stimulation from European countries came to a consensus during a meeting in May 1996 held at the instituut voor Epilepsiebestrijding,

Headache, epilepsy and photosensitivity: how are they connected?

“…[51]. During IPS in the EEG laboratory, an epileptiform EEG reaction or so-called PPR can be elicited in these patients with the highest prevalence in adolescents.…”

Human photosensitivity: from pathophysiology to treatment

“…In particular specific cognitive activities associated with decision making and hand movements and non-specific emotional factors associated with playing (anxiety, excitement) may increase the risk of a seizure (Bureau et al, 2004). In effect, Kasteleijn-Nolst Trenite´et al (1999b) showed that subjects know to have seizures induced by VGs, were more sensitive to playing rather simply to viewing the game under test conditions, and 14% could not be shown to be photosensitive. In daily life, extrinsic non-specific factors such as sleep deprivation, drug or alcohol use, prolonged exposure to the stimulus, may also play a role in reflex seizure occurrence (De Keyser et al, 1984;Zifkin and Inoue, 2004).…”

IPS Interest in the EEG of Patients after a Single Epileptic Seizure

“…Takahashi and Tsukahara [29] noted that flicker frequency of 20–15 Hz was most effective in eliciting generalized PPR. Other surveys found that most patients are sensitive between 10 and 30 Hz [30] and peak sensitivity is between 16 and 20 flashes/s [16]. Fisher et al, 2005, reported that frequencies of 15–25 Hz are the most provocative.…”