The effects of betaxolol hydrochloride ophthalmic solution on intraocular pressures during transient microgravity

Background: Intraocular pressure (IOP) has been found to increase during mi crogravity. After peaking in the first few hours of orbital flight, IOP slo wly decreases to a level that is slightly elevated above baseline IOP's. Th ese modest elevations in IOP do not require treatment. just as in 1-G, a cl inically significant elevation of IOP that occurred during spaceflight woul d require treatment. We are not aware of previous studies of the efficacy o f IOP lowering agents under conditions of microgravity. Methods: This doubl e-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 a ircraft, and postflight. One eye of each of the subjects was treated with b etaxolol hydrochloride ophthalmic solution 0.5%, while the contralateral ey e was treated With normal saline placebo, for 7 d prior to parabolic flight . IOP's were measured by the Tone-Pen 2, a gravity independent tonometer. R esults: A modest, but statistically significant reduction of 2.4 mmHg in me an IOP was noted in betaxolol treated eyes at the time of preflight measure ment. During zero-C, the mean IOP's of both betaxolol treated eyes and plac ebo treated eyes increased approximately 20% over preflight levels. Postfli ght IOP's were similar to preflight IOP's. Conclusions: The effect of betax olol on the IOP of eyes treated with for 1 wk prior to exposure to microgra vity was statistically significant, but may lack clinical significance in n ormal eyes. Further research needs to be done to determine the efficacy dur ing microgravity of betaxolol and other agents, in subjects who have upper normal to slightly elevated IOP's at 1 G.