CORRELATES OF ACUTE EXERCISE-INDUCED OCULAR HYPOTENSION

Purpose. To understand those factors that determine the decrease in in traocular pressure (IOP) that occurs during acute dynamic exercise. Me thods. Three aspects of the exercise-IOP relationship were studied. Th ese included graded exercise, with and without CO2 addition for isocap nia; comparison of the IOP response of trained and sedentary subjects to a fixed external work load; and exercise after ocular beta-adrenoce ptor blockade. Graded exercise consisted of 7 minutes each at 30 and 9 0 watts on a cycle ergometer, then progressive work to exhaustion. Tra ined and sedentary subjects were defined on the basis of the blood lac tate response to fixed external work (10 minutes at 90 watts). Selecti ve beta 1-adrenoceptor blockade (betaxolol) and nonselective beta-adre noceptor blockade (levobunolol) were superimposed on graded exercise. Intraocular pressure was measured using applanation tonometry. Results . Graded exercise: Intraocular pressure decreased in proportion to exe rcise intensity. Hypocapnia developed in the last minutes of exhaustin g work, but preventing hypocapnia with CO2 addition failed to lessen t he decrease in IOP. Response to fixed external work load: Intraocular pressure decreased significantly more in sedentary than in trained sub jects; this decline was correlated with elevations in blood lactate bu t not with changes in metabolic rate or plasma osmolarity. Selective a nd nonselective beta-adrenoceptor blockade: Both drugs lowered IOP at baseline and throughout graded exercise; the drugs and exercise had ap parently additive ocular hypotensive effects. Conclusions. Acute dynam ic exercise lowers IOP in a graded fashion proportional to relative, n ot absolute, work load. The IOP decline is correlated with blood lacta te but not with PCO2 of plasma osmolarity changes, and exercise potent iates the ocular hypotensive effects of beta-adrenoceptor blockade.