Intense physical exertion is known to reduce intraocular pressure (IOP). However, the effect of physical exertion on IOP in the first few seconds after beginning exertion has not been studied previously. IOP was determined twice within 15 s in 32 healthy, young men. Seventeen performed six deep knee bends within 8–10 s preceding the second IOP measurement, while 15 did not. The mean reduction in IOP immediately after such brief and moderate exertion was 1.9 ± 0.3 mmHg, compared with 0.8 ± 0.2 mmHg in the control group. The difference between both groups was statistically significant. Thus, even moderate physical exertion may reduce TOP. As the relative decrease in IOP correlated with the relative increase in heart rate, the observed reduction in TOP after brief, moderate physical exertion may be due to sympathetic activity.