Mechanism of exercise-induced ocular hypotension

PURPOSE. Although acute dynamic exercise reduces intraocular pressure (IOP) , the factors that provoke this response remain ill-defined. To determine w hether changes in colloid osmotic pressure (COP) cause the IOP changes duri ng exercise, standardized exercise was performed after dehydration and hydr ation with isosmotic fluid. METHODS. Progressive cycle ergometer exercise to volitional exhaustion was performed after 4 hours' dehydration, and after hydration with 946 mi isosm otic liquid (345 mOsM). In each experiment, venous blood taken before and i mmediately after exercise was analyzed for hematocrit, plasma protein conce ntration, total plasma osmolality, and plasma COP. RESULTS. Exercise in both experiments significantly reduced IOP and elevate d COP (each P < 0.01). Dehydration, compared with hydration, also significa ntly reduced IOP and elevated COP, when measured before and after exercise (P < 0.05). The correlation of mean IOP with mean COP, over the entire rang e created by varying exercise and hydration statuses, was statistically sig nificant (r = -0.99; P < 0.001). In contrast, other indexes of hydration st atus, including hematocrit, total plasma osmolality, and plasma protein con centration, failed to change as IOP changed and failed to correlate with IO P, on either a group or individual basis, in conditions of varying levels o f exercise and hydration. CONCLUSIONS. Acute dynamic exercise and isosmotic fluid ingestion each seem to change IOP through changes in COP.