Intraocular pressure changes at high altitude

Abstract

AbstractPurpose: The effect of altitude on Intraocular Pressure has been debated for decades. The literature is unclear, encompassing exertional and non‐exertional ascents, as well as simulated ascents, with most finding a decrease in IOP, but some finding no change or an increase. Additionally, several papers have previously corrected IOP for Central Corneal Thickness, further confounding efforts to draw conclusions from the literature. The Imperial Remote Medicine BSc's Morocco expedition aimed to assess changes in IOP and CCT during an exertional winter ascent of Mount Toubkal (4167 m) which to our knowledge is the first exertional study conducted partially in sub‐zero temperatures.Methods: IOP, CCT, clinical parameters and Lake Louise Score (LLS) were recorded daily in 9 participants before, 1 month after and during the expedition. Participants flew into Marrakesh, ascended to Imlil (1886 m) by car, and ascended from there on foot, stayed at the Nelter refuge for 3 nights (3037 m). All measurements were taken in the evening. IOP was measured using an iCare ic200 tonometer. Total IOP and CCT per participant per day was used to assess more fully the overall change in IOP and CCT across the expedition. Differences between eyes were also assessed.Results: No significant change in IOP was seen. CCT increased significantly at altitude. IOP was significantly positively correlated with LLS and headache, and significantly negatively correlated with SpO2. In line with current clinical practice, IOP was not adjusted for CCT. There was no difference in IOP or CCT between contact users and non‐contact users.Conclusions: The increase in CCT is in line with the existing literature. The lack of significant change in IOP has precedence, and we propose that it is the interplay of physiological changes at altitude, alongside other factors such as exertion and temperature that alter IOP rather than IOP changes simply being a function of altitude.