Intraocular pressure at a simulated altitude of 9000 m with and without 100% oxygen.

INTRODUCTION: Exposure to high altitude may affect intraocular pressure (lOP). This study aimed to determine how IOP was altered by two different inspired oxygen tensions at altitude. METHODS: There were 34 healthy male pilots, ages 26-39 yr (mean 31.9 yr), who were studied at the Air Health Examination and Physiological Training Centre in Eskisehir, Turkey. They were studied at ground level, which is 792 m (2414 ft), and during a training session in a hypobaric chamber at a simulated altitude of 9144 m (30,000 ft). IOP was measured with a Tone-pen XL tonometer before subjects entered the chamber, at altitude while breathing 100% oxygen by mask and after removing the mask, and again 30 min after leaving the chamber. RESULTS: Ground level values for IOP (mean +/- SD) were 12.31 +/* 2.98 mmHg. Levels increased significantly at altitude on oxygen (16.75 +/- 4.14 mmHg) and decreased slightly on breathing ambient air (14.37 +/- 3.44 mmHg). In 30 min after leaving the chamber, IOP was 12.81 +/- 1.74 mmHg, indistinguishable from pre-test values. DISCUSSION: Healthy subjects whose baseline IOP is in the normal range experience only a small, temporary elevation of IOP during passive exposure to high altitude with either normoxia or acute hypoxia.