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Intermittent photic stimulation (IPS) is a common procedure performed in the electroencephalography (EEG) laboratory in children and adults to detect abnormal epileptogenic sensitivity to flickering light (i.e., photosensitivity). In practice, substantial variability in outcome is anecdotally found due to the many different methods used per laboratory and country. We believe that standardization of procedure, based on scientific and clinical data, should permit reproducible identification and quantification of photosensitivity. We hope that the use of our new algorithm will help in standardizing the IPS procedure, which in turn may more clearly identify and assist monitoring of patients with epilepsy and photosensitivity. Our algorithm goes far beyond that published in 1999 (Epilepsia, 1999a, 40, 75; Neurophysiol Clin, 1999b, 29, 318): it has substantially increased content, detailing technical and logistical aspects of IPS testing and the rationale for many of the steps in the IPS procedure. Furthermore, our latest algorithm incorporates the consensus of repeated scientific meetings of European experts in this field over a period of 6 years with feedback from general neurologists and epileptologists to improve its validity and utility. Accordingly, our European group has provided herein updated algorithms for two different levels of methodology: (1) requirements for defining photosensitivity in patients and in family members of known photosensitive patients and (2) requirements for tailored studies in patients with a clear history of visually induced seizures or complaints, and in those already known to be photosensitive., (Wiley Periodicals, Inc. © 2011 International League Against Epilepsy.)

Wind turbines are known to produce shadow flicker by interruption of sunlight by the turbine blades. Known parameters of the seizure provoking effect of flicker, i.e., contrast, frequency, mark-space ratio, retinal area stimulated and percentage of visual cortex involved were applied to wind turbine features. The proportion of patients affected by viewing wind turbines expressed as distance in multiples of the hub height of the turbine showed that seizure risk does not decrease significantly until the distance exceeds 100 times the hub height. Since risk does not diminish with viewing distance, flash frequency is therefore the critical factor and should be kept to a maximum of three per second, i.e., sixty revolutions per minute for a three-bladed turbine. On wind farms the shadows cast by one turbine on another should not be viewable by the public if the cumulative flash rate exceeds three per second. Turbine blades should not be reflective.

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 >or=20 cd/m2, occurs at a frequency of >or=3 Hz, and occupies a solid visual angle of >or=0.006 steradians (approximately 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 >or=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.

Purpose: This report summarizes background material presented to a consensus conference on visually provoked seizures, convened by the Epilepsy Foundation of America., Methods: A comprehensive review of literature was performed., Results: Photosensitivity, an abnormal EEG response to light or pattern stimulation, occurs in approximately 0.3-3% of the population. The estimated prevalence of seizures from light stimuli is approximately 1 per 10,000, or 1 per 4,000 individuals age 5-24 years. People with epilepsy have a 2-14% chance of having seizures precipitated by light or pattern. In the Pokemon cartoon incident in Japan, 685 children visited a hospital in reaction to red-blue flashes on broadcast television (TV). Only 24% who had a seizure during the cartoon had previously experienced a seizure. Photic or pattern stimulation can provoke seizures in predisposed individuals, but such stimulation is not known to increase the chance of subsequent epilepsy. Intensities of 0.2-1.5 million candlepower are in the range to trigger seizures. Frequencies of 15-25 Hz are most provocative, but the range is 1-65 Hz. Light-dark borders can induce pattern-sensitive seizures, and red color also is a factor. Seizures can be provoked by certain TV shows, movie screen images, video games, natural stimuli (e.g, sun on water), public displays, and many other sources., Conclusions: Recommendations on reducing risk of seizures have been developed by agencies in the United Kingdom, Japan, and the International Telecommunications Union, affiliated with the United Nations. The Epilepsy Foundation of America has developed a consensus of medical experts and scientists on this subject, reported in an accompanying work.

The use of guidelines to prevent the broadcast of epileptogenic television program content has reduced the incidence of seizures in Britain and Japan. Epileptogenic content includes both flicker and patterns. The guidelines for flicker were developed on the basis of a model that related stimulus parameters to the proportion of patients affected. We here extend the model to pattern stimuli. A set of rules is advocated that keeps the level of risk to a consistent minimum and simplifies compliance. We propose that striped patterns that last > 0.5 s, occupy more than one fourth the area of the screen, and have bright stripes > 50 cd/m2 in luminance be restricted as regards the number of cycles admissible. The guidelines are estimated to protect at least two thirds of susceptible patients.

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 photo stimulator, procedure of photic stimulation, and interpretation of EEG results, has been defined according to available scientific and clinical knowledge., 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.