TMS-induced blinking assessed with high-speed video: optical disruption of visual perception

It is known that TMS can induce blinking, but it is unknown to what extent and at what time TMS-induced blinking can cover the pupil. We applied single-pulse TMS with a leftward and rightward monophasic current through a round coil over the occipital pole in 8 healthy subjects, using high-speed video to monitor left or right eye with a spatial resolution of 0.1 mm and a temporal resolution of 2 ms. We plotted eyelid position relative to upper and lower pupil borders as a function of time after TMS for each subject and current direction. We found 2 blinks in every subject, an isolated late blink with one current direction and a superimposed early and late blink with the other current direction, in accordance with our previously reported association between a leftward and rightward lower coil rim current and an early blink in right and left eye, respectively. Blink extent varied, but 4 subjects showed total pupil covering with both current directions. Blink timing varied, but pupil covering was initiated as early as 32 ms after TMS and pupil uncovering was completed as late as 200 ms after TMS. We found no saccades. We conclude that TMS can cause an important optical disruption of visual perception.