Binocular flash-induced nystagmus in humans

Objective: The aim of this study was to demonstrate that binocular flash-induced nystagmus (B-FIN) can be evoked in humans. Design: The study evaluated the presence of B-FIN by stimulation with a stroboscopic flash. Setting: The study was conducted with 12 healthy patients in the Otorhinolaryngology Department of the University of Genoa (Italy), between April 2008 and January 2009. Methods: Patients underwent binocular flashing light stimulation, in the dark, by stroboscopic flash presented through a photostimulator at frequencies of 4.7 and 7.69 cycles/second for 120 seconds, with their eyes covered by a homogeneous field hollow opal hemisphere. The photostimulator was placed in three different positions with respect to the anterior-posterior axis: 0u, 45u to the right, and 45u to the left. Main Outcome Measures: Eyemovementswere recorded by electronystagmography (ENG). ENGrecording started 30 seconds before the stimulation and stopped 60 seconds after the end of the luminance stimuli to test the presence of flash induced after nystagmus (FIAN). Results: B-FIN was clearly evoked from 10 of the 12 healthy adults, whereas FIAN was evoked from 4 of the 12 subjects. The best stimulation of B-FIN was obtained through an intermittent luminance stimulus presented at a frequency of 4.7 cycles/second and the photostimulator placed at 0u to the optic axis. Conclusions: Our investigation demonstrates that B-FIN can be evoked in humans and its possible value in the differential diagnosis between central and peripheral vertigo.