Scotopic threshold of the human retina during dynamic physical effort

The scotopic threshold of 7 subjects was measured with a 1 degree circular white light located 15 degrees below fixation during 45 min at rest followed by 10 min of running on an exercise treadmill. The slope of the treadmill was adjusted individually so that the effort extended by each subject required 60-75% of his maximum oxygen uptake. Thresholds showed a sudden elevation of about 0.55 nLa (logarithmic scale) at the onset of the exercise period, and remained at this level throughout the following 10 min. It was concluded that the head movements and consequent eye instability imposed by the run were the main cause for the increase in scotopic threshold.