Ocular hypotension after exercise: Role of colloid osmotic pressure

Purpose. Acute exercise reduces intraocular pressure via unknown mechanisms. We investigated the possibility that increased plasma colloid osmotic pressure (COP) in exercise mediates the ocular hypotensive effect. Methods. Four separate series of experiments each involved 12 healthy subjects; one series compared hydration with dehydration, while the other three series involved different forms of exercise. IOP (Goldmann applanation tonometer) and COP (Wescor 4100 colloid osmometer) were measured before and after each condition. Experimental series' included cycle ergometer exercise, and isometric exercise performed using both hand-grip and arms+legs variations in muscle mass. Results. Both dehydration and dynamic exercise elevated COP as they lowered IOP (each p<0.05); the COP-IOP correlation coefficient was close to 1.0 (p<0.05). In contrast, both forms of isometric exercise significantly lowered IOP (p<0.05) without changing COP. Conclusions. Colloid osmotic pressure changes in the plasma may underlie the ocular hypotension that results from either dehydration or dynamic exercise; however, isometric exercise reduces IOP apparently through a separate mechanism.