Reconsideration of Bell's phenomenon using a magnetic search coil method.

The exact direction, amplitude and time course of Bell's phenomenon is still controversial. We evaluated the eye movements associated with spontaneous blinks, voluntary blinks and prolonged eyelid closure using a magnetic search coil method. Spontaneous blinks were accompanied by transient downward and nasalward eye movements, and similar movement accompanying voluntary blinks were often followed by upward movements. The eye positions occurring immediately after blinks often differed from the initial positions and were followed by corrective saccades, which disappeared when the subjects did not fixate. Prolonged eyelid closure was accompanied by tonic eye elevation and voluntary blinks were accompanied by marked transient eye elevation when eyelid closure was mechanically impeded. Under normal conditions Bell's phenomenon does not occur during blinks.