A high-intensity, goggle-mounted flash stimulator for short-latency visual evoked potentials.
The few studies that have been done on short-latency, subcortical visual evoked potentials (SVEPs) have all used stroboscopic flashes as the evoking stimulus. The dimensions of the stimulator, the acoustical artifacts and the photic spread to the examination room limited the use of SVEPs to research laboratories. With the advent of high-efficiency light-emitting diodes (LEDs), high-intensity flashes can now be generated from goggle-mounted LEDs. In this study, a goggle-mounted high-intensity stimulator was constructed and its flashes used to evoke SVEPs. The reproducibility of SVEPs across subjects and the ease of using the high-intensity LED flash stimulator make them a promising candidate for testing subcortical visual pathway function in the operating room.
Visual potentials evoked by light-emitting diodes mounted in goggles.
Ronald P. Lesser, M.D. Hans Lüders, M.D. G. Klem, R. EEG T . Dudley S. Dinner, M.D. The authors compared, in 20 subjects, the occipital potentials following pattern reversal stimulation to those following stimulation by light-emitting diodes (LEDs) mounted 5 mm apart in 4 X 4 arrays inside goggles. The resulting waveform resembled that evoked by flash and varied between subjects, with the most useful measurements being those of differences between leftand righteye stimulation. Not all peaks occurred in each control. Thus the method appears to have only limited advantages over those previously available, although it may have applications in young, uncooperative, comatose, or anesthetized patients. Awareness of the limitations of the method should stimulate the search for more reliable techniques for use when pattern stimulation cannot be employed.
Effect of eye blink on the visual evoked response in children.
Abstract The frequency of reflex blinking to flash and its effect on the visual evoked response (VER) were studied in thirty-one normal children, ages 5–11 years. Recordings were made from electrodes located at the orbit, the mastoid and at Fz, Cz and Oz. The scoring of reflex blink frequency, the averaging of evoked responses and the development of triggers for averaging involuntary blinks (not flash-associated) were done off-line. The average probability of reflex blinking to moderately intense flash under alert, eyes open conditions was 0.62, with a significant trend to increased blinking during continued testing. In eight subjects who blinked to approximately half the flashes, segregation and separate averaging of blink and blink-free responses demonstrated a substantial difference in the potentials recorded at all locations. Specifically, a positive component at the occiput (scalp to mastoid) occurring approximately 200 msec after flash was enhanced in trials that included reflex blinks. Averages of EEG time-locked to the peak of involuntary blink potentials (no flash) showed penetration of artifact into posterior scalp as well. These findings suggest that many children in this age group exhibit persistent reflex blinking, and that there is a high probability of artifact in the VER therefrom.