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Abstract
PURPOSE: To understand those factors that determine the decrease in intraocular pressure (IOP) that occurs during acute dynamic exercise. METHODS: Three aspects of the exercise-IOP relationship were studied. These included graded exercise, with and without CO2 addition for isocapnia; comparison of the IOP response of trained and sedentary subjects to a fixed external work load; and exercise after ocular beta-adrenoceptor blockade. Graded exercise consisted of 7 minutes each at 30 and 90 watts on a cycle ergometer, then progressive work to exhaustion. Trained and sedentary subjects were defined on the basis of the blood lactate response to fixed external work (10 minutes at 90 watts). Selective beta 1-adrenoceptor blockade (betaxolol) and nonselective beta-adrenoceptor blockade (levobunolol) were superimposed on graded exercise. Intraocular pressure was measured using applanation tonometry. RESULTS: Graded exercise: Intraocular pressure decreased in proportion to exercise intensity. Hypocapnia developed in the last minutes of exhausting work, but preventing hypocapnia with CO2 addition failed to lessen the decrease in IOP. Response to fixed external work load: Intraocular pressure decreased significantly more in sedentary than in trained subjects; this decline was correlated with elevations in blood lactate but not with changes in metabolic rate or plasma osmolarity. Selective and nonselective beta-adrenoceptor blockade: Both drugs lowered IOP at baseline and throughout graded exercise; the drugs and exercise had apparently additive ocular hypotensive effects. CONCLUSIONS: Acute dynamic exercise lowers IOP in a graded fashion proportional to relative, not absolute, work load. The IOP decline is correlated with blood lactate but not with PCO2 or plasma osmolarity changes, and exercise potentiates the ocular hypotensive effects of beta-adrenoceptor blockade.