Researchers recently found a possible link between hypoxia-triggered reduction in plasma bicarbonate ion, decreased aqueous humor production and intraocular pressure (IOP) at high altitudes (4,000m above sea level).

This prospective study evaluated 25 healthy young patients who did not live in a high-altitude environment. The team exposed the participants to a simulated high-altitude environment for two hours using a hypobaric chamber and measured IOP in both eyes and analyzed arterial blood gas parameters. They took measurements at sea level (T1), the 15-minute mark (T2), the two-hour mark (T3) and again at sea level (T4).

The investigators discovered that partial oxygen pressure significantly decreased at T2 and T3 and resolved at T4, while pH significantly increased at T2 and returned to baseline at T3. They noted that IOP was not correlated with pH but dropped with actual and standard bicarbonate ion at T3 and T4, with IOP significantly decreasing from 16.4±3.4mm Hg at T1 to 15.1±2.1mm Hg at T3 and remaining lower (14.9±2.4mm Hg) at T4. They added that lower IOP was also associated with lower standard bicarbonate ion when adjusted for actual bicarbonate and diastolic blood pressure.

“These findings may shed light on the mechanism of IOP regulation at high altitude,” the study authors concluded. “Hypobaric hypoxia at high altitude is an environmental factor that can reduce IOP and, therefore, deserves further study.” 

Xie Y, Yang Y, Han Y, et al. Association between arterial blood gas variation and intraocular pressure in healthy subjects exposed to acute short-term hypobaric hypoxia. Trans Vis Sci Tech. 2019;8:22.