Published online Oct 26, 2019. doi: 10.12998/wjcc.v7.i20.3226
Peer-review started: September 5, 2019
First decision: September 23, 2019
Revised: October 13, 2019
Accepted: October 15, 2019
Article in press: October 15, 2019
Published online: October 26, 2019
Processing time: 51 Days and 0.3 Hours
High intraocular pressure (IOP) is a major risk factor for glaucoma. Previous studies suggested that high altitude affected intraocular pressure, but the results were inconsistent. Now many lowlanders ascend to high altitude by plane. The effects of such an acute, effortless exposure to different altitudes have rarely been reported.
This study is a longitudinal observation of intraocular pressure variation with acute, effortless altitude changes. Our findings may provide additional information on how altitude changes affect IOP.
To investigate changes in IOP after acute effortless exposure to high altitude in stages and compare it with systemic parameters.
This prospective study included three groups according to the place of residence: Low-altitude (LA) group [44 m above sea level (ASL)], high altitude (HA) group (2261 m ASL), and very high altitude (VHA)group (3750 m ASL). The LA group flew to HA first. Three days later, LA group flew with the HA group to VHA where both groups stayed for 2 d. Then, the LA group flew back to 2261 m ASL and stayed for 1 d before flying back to 44 m. IOP, vital values and hematological values were measured and compared before, during and after exposure to 2261 m and 3750 m ASL. The mixed linear model was used to compare repeated measurements and Bonferroni correction was applied for multiple comparisons. Spearman correlation was used to analyze the associations between IOP and systemic parameters. Different from previous studies, this is the first study to observe IOP changes in the same subjects from sea level to high altitude and then up to very high altitude, and then back to sea level. In addition, subjects flew from one altitude to another altitude. We also compared the IOP in ascending groups from low altitude with that in local highlanders.
The LA group had the highest IOP (18.41 ± 2.40 mmHg) compared with the HA (12.23 ± 2.38 mmHg) and VHA (11.53 ± 1.83 mmHg) groups. IOP in the LA group significantly decreased from 18.41 ± 2.40 mmHg at 44 m to 13.60 ± 3.68 mmHg at 2261 m ASL, and then to 11.85 ± 2.48 mmHg at 3750 m ASL and partially recovered to 13.47 ± 2.57 mmHg upon return to 44 m. IOP in the LA group at HA and VHA decreased to that in the native residents. IOP was positively associated with pulse oxygen saturation. Higher baseline IOP correlated with greater IOP changes in the LA group. The findings indicated that acute, effortless exposure to high altitude reduced IOP. It would be interesting to investigate the effects of long-term altitude exposure on IOP in the future. Furthermore, the mechanisms of IOP changes at high altitude deserve further study.
IOP in the lowlanders reduced as altitude elevated in stages and became comparable to IOP in native residents. The lower IOP was associated with hypoxia at high altitude. The higher the baseline IOP, the greater the decrease in IOP. The findings may provide a potential environmental factor to lower IOP, that deserves further study.
The results suggested that high and very high altitude residents have lower IOP than lowlanders had. The IOP in ascending groups from low altitude dropped to the level of local highlanders after acute, effortless exposure to higher altitude. Lower IOP is associated with hypoxia at high altitude. Larger sample studies are needed to investigate the normal range of IOP in native residents at high altitude. Furthermore, the mechanisms of IOP variation and IOP changes after long-term exposure to high altitude deserves further study.