Intraocular Pressure Changes of Healthy Lowlanders at Different Altitude Levels: A Systematic Review and Meta-Analysis

Abstract

Background: High altitude, characterized by hypobaric hypoxia, low temperature, and intensive ultraviolet radiation, is identifiably one of the examples of scientific enquiry into aviation and space analogs. However, little is known about the ocular physiological response, especially intraocular pressure (IOP) changes at high altitude.Objectives: This study aimed to systematically review of high altitude exposure on IOP for healthy lowlanders with unoperated eyes.Methods: A comprehensive systematic literature search was conducted in the electronic databases until September 1st, 2019. A meta-analysis was performed following the preferred reporting items for systematic review and meta-analysis statement (PRISMA). We systematically searched the studies conducted over 2,000 m above sea level (a.s.l) in healthy lowlanders with measurements of IOP. Meta-analyses (random effect model and heterogeneity tests), subgroup analyses (altitude, duration, type, and pattern of exposure), sensitivity analysis, funnel plot, Begger's and Egger's test for publication bias were performed. Quality assessment was conducted using the Newcastle–Ottawa scale. The meta-analysis was registered in the PROSPERO database (CRD42019136865).Results: Of 9595 publications searched, 20 publications (n = 745) qualified for inclusion, with non-significant decrease in overall IOP [standardized mean difference (SMD): 0.14, 95% CI: −0.12–0.40; p = 0.30] with high heterogeneity (p < 0.001, I2 = 82%). However, subgroup analyses revealed significant decrease of IOP at high altitude of 3,000–5,500 m a.s.l (SMD: 0.57, 95% CI: 0.07–1.06; p = 0.03) whereas increase of IOP at extreme altitude of over 5,500 m a.s.l (SMD: −0.34, 95% CI: −0.61–0.06; p = 0.02). And the duration of exposure more than 72 hours (h) was likely to induce a decrease of IOP bordering on statistical significance at the 5% level (SMD: 1.29, 95% CI: 0.02–2.56; p = 0.05). Simultaneously, we also observed significant decrease of IOP for active exposure (e.g., physical activity and hiking, SMD: 0.81, 95% CI: 0.05–1.57; p = 0.04).Conclusion: Our analysis shows exposure to the altitude over 3,500 m a.s.l, duration of exposure more than 72 h and active exposure pattern may have modest, but significant effects on IOP. The higher altitude, the duration of exposure as well as physical activity seem to play crucial roles in the effects of high-altitude exposure on IOP.

New insights into refraction and intraocular pressure in simulated plateau environment

“…In a previous study, Bruttini et al [7,8] found a statistically signi cant decrease in mean IOP at 3466 m compared to sea level in the moderate altitude range of 1300 m (19°C) to 3466 m (-1.4°C), which is inconsistent with our observations. We speculate that this may be due to a signi cant decrease in temperature at 3466 m resulting in IOP changes.…”

Impacts of heatwaves and cold spells on glaucoma in rural China: a national cross-sectional study

“…A few (10%) of the cold receptors were silenced when the temperature increased, and the firing rate of the cold receptors was increased when the surface temperature of the cornea decreased (Patel et al 2021 ). So sudden physiological responses are consistent with the steep increase in risk that was associated with extreme temperature events (Mansouri et al 2022 , Yang et al 2019b ).…”

Influence of hypobaric hypoxic conditions on ocular structure and biological function at high attitudes: a narrative review

“…Overall, the studies relating altitude and IOP were mixed; therefore, it was necessary to summarize the relevant results. Yang et al (2019) conducted a meta-analysis on IOP changes at different altitudes. The data showed that IOP significantly decreased with the increase in altitude between 3,000 and 5,500 m, whereas IOP increased at extreme altitudes of over 5,000 m. They also found that a duration of exposure of more than 72 h was likely to induce a decrease in IOP.…”

“…The high-altitude hypobaric hypoxia environment clearly effects intraocular pressure (IOP) (Albis-Donado et al, 2018;Najmanova et al, 2018). Yang et al (2019) and Bruttini et al (2020) illustrated that within the moderate altitude range of 1,300 m (19°C) to 3,466 m (−1.4°C), the average IOP at 3,466 m was statistically lower than that at sea level, and altitude significantly correlated with IOP. Subsequently, Willmann et al ( 2017) studied IOP at 4,559 m after 3 days and found no significant change compared with baseline levels.…”