Effect of ethanol on dynamic visual acuity during vertical body oscillation in healthy volunteers

Visual orientation is the most important sensory input during locomotion (e .g. walking, driving a car, riding a bicycle). We investigated dynamic visu al acuity (DVA) during vertical body-oscillations (amplitude 5 cm; frequenc y 1.5 Hz) in 12 healthy subjects before and twice after ethanol consumption . During oscillation, vertical eye movements were recorded under two test c onditions: with eyes closed (EC) and during DVA testing. A significant incr ease in vertical eye-amplitude after ethanol ingestion occurred only during EC tests, as a possible sign of vestibular hyperreaction. During vestibula r stimulation alone (EC), ethanol did not affect the phase shift between st imulus and eye movements. However, when the subjects were given an addition al visual stimulus (DVA), the post-alcohol phase shift rose significantly. Surprisingly, the post-alcohol phase shift values for the two test conditio ns showed no significant differences. After ethanol ingestion we found no c hanges in static visual acuity but a significant loss of DVA. Volunteers wi th a change of DVA threshold (DVAT) showed significantly (P = 0.004) higher post-alcoholic changes in the phase shift. In summary, low doses of ethano l disturbed the visually guided oculomotor response during fixation of an e arth-fixed target while the observer was subject to linear vertical acceler ation. This effect led to an increasing delay between the beginning of body and eye movements. The consequence was an increasing phase shift and thus a decrease in DVA during whole-body oscillation which was comparable to mov ements during human locomotion.