Background: Intraocular pressure (IOP) has been found to increase during microgravity. After peaking in the first few hours of orbital flight, IOP slowly decreases to a level that is slightly elevated above baseline IOP's. These modest elevations in IOP do not require treatment. Just as in 1-G, a clinically significant elevation of IOP that occurred during spaceflight would require treatment. We are not aware of previous studies of the efficacy of IOP lowering agents under conditions of microgravity.
Methods: This double-masked, placebo-controlled study measured the IOP's of 11 adult subjects (22 eyes) at baseline, preflight, and zero-gravity aboard the NASA KC-135 aircraft, and postflight. One eye of each of the subjects was treated with betaxolol hydrochloride ophthalmic solution 0.5%, while the contralateral eye was treated with normal saline placebo, for 7 d prior to parabolic flight. IOP's were measured by the Tono-Pen 2, a gravity independent tonometer.
Results: A modest, but statistically significant reduction of 2.4 mmHg in mean IOP was noted in betaxolol treated eyes at the time of preflight measurement. During zero-G, the mean IOP's of both betaxolol treated eyes and placebo treated eyes increased approximately 20% over preflight levels. Postflight IOP's were similar to preflight IOP's.
Conclusions: The effect of betaxolol on the IOP of eyes treated with for 1 wk prior to exposure to microgravity was statistically significant, but may lack clinical significance in normal eyes. Further research needs to be done to determine the efficacy during microgravity of betaxolol and other agents, in subjects who have upper normal to slightly elevated IOP's at 1 G.