Intraocular pressure after exposure to moderate altitude.

Background: To study intraocular pressure (IOP) alteration in healthy individuals following a rapid effortless increase in altitude from 1900 m above sea level (ASL) to 3740 m ASL.

Methods: Intraocular pressure, blood pressure, pulse rate, and arterial oxygen tension were determined in both eyes of healthy volunteers at the lower altitude. Participants were taken to a higher altitude of 3740 m ASL (1840-m altitude gain) via gondola lift, which took 30 minutes. All measurements were repeated at the higher altitude. Pearson and Spearman correlation analysis was conducted to assess the correlations among the variables. A paired t-test and linear regression were also used to compare IOP before and after ascending. The accepted level of significance for all tests was p <0.05.

Results: Fifty-four healthy volunteers participated in the study. Four eyes of three subjects with IOP higher than 21 mmHg were excluded. Intraocular pressure ± SD (range) decreased from 14.9 ± 2.6 mmHg (9-21 mmHg) to 14.3 ± 2.4 mmHg (11-20 mmHg) (p = 0.02) after the ascent. Arterial oxygen saturation decreased from 95.4 % to 91.5 % (p < 0.001). Neither of the participants complained of any ocular or systemic symptoms during or after ascending to the higher altitude. Mean IOP, before and after ascending, was positively correlated with systolic blood pressure before and after the increase in altitude (Pearson correlation coefficient, 0.41, p = 0.002 and Pearson correlation coefficient, 0.37, p = 0.006, respectively). Intraocular pressure changes did not correlate with age, pulse rate, or arterial oxygen saturation.

Conclusion: A rapid, effortless increase in altitude (over a moderate range in altitude) decreases IOP in healthy individuals. The observed decrease may not be clinically significant; however, it shows the versatility of IOP control mechanisms in response to alteration in altitude and temperature.