A new adaptive temporal filter: application to photosensitive seizure patients

Visually sensitive seizures: An updated review by the Epilepsy Foundation

Light flashes, patterns, or color changes can provoke seizures in up to 1 in 4000 persons. Prevalence may be higher because of selection bias. The Epilepsy Foundation reviewed light-induced seizures in 2005. Since then, images on social media, virtual reality, three-dimensional (3D) movies, and the Internet have proliferated. Hundreds of studies have explored the mechanisms and presentations of photosensitive seizures, justifying an updated review. This literature summary derives from a nonsystematic literature review via PubMed using the terms "photosensitive" and "epilepsy." The photoparoxysmal response (PPR) is an electroencephalography (EEG) phenomenon, and photosensitive seizures (PS) are seizures provoked by visual stimulation. Photosensitivity is more common in the young and in specific forms of generalized epilepsy. PS can coexist with spontaneous seizures. PS are hereditable and linked to recently identified genes. Brain imaging usually is normal, but special studies imaging white matter tracts demonstrate abnormal connectivity. Occipital cortex and connected regions are hyperexcitable in subjects with light-provoked seizures. Mechanisms remain unclear. Video games, social media clips, occasional movies, and natural stimuli can provoke PS. Virtual reality and 3D images so far appear benign unless they contain specific provocative content, for example, flashes. Images with flashes brighter than 20 candelas/m² at 3-60 (particularly 15-20) Hz occupying at least 10 to 25% of the visual field are a risk, as are red color flashes or oscillating stripes. Equipment to assay for these characteristics is probably underutilized. Prevention of seizures includes avoiding provocative stimuli, covering one eye, wearing dark glasses, sitting at least two meters from screens, reducing contrast, and taking certain antiseizure drugs. Measurement of PPR suppression in a photosensitivity model can screen putative antiseizure drugs. Some countries regulate media to reduce risk. Visually-induced seizures remain significant public health hazards so they warrant ongoing scientific and regulatory efforts and public education.

Photosensitive epilepsy and image safety

Photosensitive epilepsy came to prominence in the 1950s with the advent of television. Photosensitive epilepsy occurs in 1 in 4000 of the population. The incidence is 1.1 per 100,000 per annum, however amongst 7-19 year-olds the incidence is more than five times as common. Photosensitive epilepsy is twice as common in females as in males. The onset is around puberty, but less than 25 per cent of patients lose their photosensitivity in their twenties. Patients are investigated in the EEG laboratory using intermittent photic stimulation. Peak sensitivity is between 16 and 20 flashes/s but 49 per cent of patients are sensitive to 50 flashes/s, explaining the sensitivity to PAL television systems. From 1993 the development of broadcast guidelines was developed restricting both flash rates and the areas of screen involved, as well as the use of long-wavelength red. Automatic analysis systems can now test material for compliance with guidelines in real time.

The photoparoxysmal response: the probable cause of attacks during video games

Photic stimulation is part of a typical EEG in most countries, especially to check on the photoparoxysmal response (PPR). Interest in this response was enhanced in 1997 when hundreds of Japanese children had attacks while viewing a TV cartoon called "Pokemon." The overall prevalence of the PPR among patients requiring an EEG is approximately 0.8%, but 1.7% in children and 8.87% in patients with epilepsy, more often in Caucasians and females. Autosomal dominant inheritance is indicated, and this response is seen especially at the wavelength of 700 nm or at the flicker frequency of 15-18 Hz. The PPR extending beyond the stimulus carries no increased risk of seizures. Prognosis is generally good, especially after 20 years of age. Attention to PPR has been increased with the advent of video games, and the evoked seizures from these games are likely a manifestation of photosensitive epilepsy. Drug therapy has emphasized valproic acid, but Levetiracetam has also been successful in eliminating the PPR.

Suppressive Efficacy by a Commercially Available Blue Lens on PPR in 610 Photosensitive Epilepsy Patients

PURPOSE

Photosensitivity can represent a serious problem in epilepsy patients, also because pharmacologic treatment is often ineffective. Nonpharmacologic treatment using blue sunglasses is effective and safe in controlling photosensitivity, but large series of patients have never been studied.

METHODS

This multicenter study was conducted in 12 epilepsy centers in northern, central, southern, and insular Italy. A commercially available lens, named Z1, obtained in a previous trial, was used to test consecutively enrolled pediatric and adult epilepsy patients with photosensitivity. Only type 4 photosensitivity (photoparoxysmal response, PPR) was considered in the study. A standardized method was used for photostimulation.

RESULTS

Six hundred ten epilepsy patients were tested. Four hundred (66%) were female patients; 396 (65%) were younger than 14 years. Three hundred eighty-one (62%) subjects were pharmacologically treated at the time of investigation. Z1 lenses made PPR disappear in 463 (75.9%) patients, and PPR was considerably reduced in an additional 109 (17.9%) of them. PPR remained unchanged only in the remaining 38 (6.2%) patients. The response of PPR to Z1 lenses was not significantly influenced by the patients' age, sex, or type of epilepsy. No difference was found between pharmacologically treated and untreated patients.

CONCLUSIONS

The Z1 lens is highly effective in controlling PPR in a very large number of photosensitive epilepsy patients irrespective of their epilepsy or antiepileptic drug treatment. The lens might become a valid resource in the daily activity of any clinician who cares for patients with epilepsy.

Human photosensitivity: from pathophysiology to treatment

Photosensitivity is a condition detected on the electroencephalography (EEG) as a paroxysmal reaction to Intermittent Photic Stimulation (IPS). This EEG response, elicited by IPS or by other visual stimuli of daily life, is called Photo Paroxysmal Response (PPR). PPRs are well documented in epileptic and non-epileptic subjects. Photosensitivity rarely in normal individuals evolves into epilepsy. Photosensitive epilepsy is a rare refex epilepsy characterized by seizures in photosensitive individuals. The development of modern technology has increased the exposition to potential seizure precipitants in people of all ages, but especially in children and adolescents. Actually, videogames, computers and televisions are the most common triggers in daily life of susceptible persons. The mechanisms of generation of PPR are poorly understood, but genetic factors play an important rule. The control of visually induced seizures has, generally a good prognosis. In patients known to be visually sensitive, avoidance of obvious source and stimulus modifications are very important and useful to seizure prevention, but in the large majority of patients with epilepsy and photosensitivity antiepileptic drugs are needed.

Photic- and pattern-induced seizures: a review for the Epilepsy Foundation of America Working Group

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.

Visual Reflex Seizures Induced by Complex Stimuli

Visual reflex seizures induced by complex stimuli may be triggered by patterned and flashing displays that are now ubiquitous. The seizures may be clinically generalized, but unilateral and bilateral myoclonic attacks also may be triggered, especially in patients with juvenile myoclonic epilepsy, and recently, clearly focal reflex occipital lobe seizures have been described. Some seizure-triggering properties of video displays can be identified, such as perceived brightness, pattern, flicker frequency, and color. Knowledge of these is useful in planning individual treatment and in designing regulations for screen content of television broadcasts or for other video displays. Some subjects will also be sensitive to cognitive or action-programming activation, especially when playing video games, and this can increase the chance of seizure triggering. Nonspecific factors such as sleep deprivation, prolonged exposure, and drug or alcohol use also may play a role in reflex seizure occurrence.

Regulations: What Next?

Television (TV) is the most provocative visual stimulus and evokes (first) seizures in susceptible children and adolescents, especially when flickering and patterned images are shown. This has led to the initiative to develop guidelines for broadcasters. The development of new types of TV screens will not remove the need for control of broadcast material. It could be argued that rather than protect the whole viewing audience by application of broadcasting guidelines, only those who are photosensitive should be protected. But maybe we should do both, because most known sensitive patients will benefit from greater safety and will not be dependent on fashionable ideas by commercial broadcasters that are not (yet) familiar with the guidelines. No such guidelines exist for video material, electronic screen games, and the Internet. It would be wise to adopt the guidelines for video material and electronic screen games.

Suppressive efficacies by adaptive temporal filtering system on photoparoxysmal response elicited by flickering pattern stimulation

PURPOSE

Based on our previous study that validated efficacies of an adaptive temporal filtering system (ATFS) suppressing a photoparoxysmal response (PPR) elicited by a chromatic flicker stimulation, we further studied ATFS efficacies on PPRs elicited by pattern-flicker stimulation in 13 photosensitive epilepsy patients.

METHODS

Subjects were 13 photosensitive epilepsy patients (two male and 11 female patients; mean age +/- SD, 20.9 +/- 8.9 years) who were all sensitive to a flickering geometric-pattern scene. We used a scene consisting of 15-Hz flickering 4 c/deg stripe images lasting for 4 s. With a 14-inch television set 2 m before a subject, we displayed the following video scenes: nonfiltered and filtered flickering-stripe scenes; for the latter, two kinds of ATFSs with mild efficacy and strong efficacy were used. Three flickering-stripe scenes altogether, each of which lasted for 4 s, were given at random with a 10-s interval.

RESULTS

A nonfiltered flickering-stripe scene elicited generalized PPRs in all patients; a filtered scene by use of an ATFS with mild efficacy elicited generalized PPRs in six patients (46%), whereas that by an ATFS with strong efficacy exhibited no PPRs.

CONCLUSIONS

This study, using an ATFS, again shows suppressive efficacy on PPRs elicited by flickering-pattern stimulation. Therefore a series of our studies suggested that ATFS may be useful as a preventive measure for photosensitive seizures triggered by stimulative flickering images from televisions or other displays.