New insights into changes in ocular structural parameters in simulated hypobaric hypoxia

Purpose High altitude is the main area for human exploration, and human eye is an important organ for obtaining visual signals. The changes of ocular structural parameters in a simulated hypobaric hypoxia environment need to be clarified. Methods Measurements were taken at five altitudes ((1) ground, (2) 3500 m, (3) 4000 m, (4) 4500 m and (5) ground). Refractive values were measured with the IOL Master (Carl Zeiss Shanghai Co. Ltd.). Data analysis was performed using the Kolmogorov-Smirnov (K-S) test, paired sample T-test and Wilcoxon test. Results Subjects' axial length (AL) increased with altitude, peaking at 4500 m, then decreased. Significant AL differences were observed across altitudes (p<0.05), except between 2-5 and 3-5. Central corneal thickness (CCT) thickened then thinned with elevation changes, significantly thicker at altitudes 2-5 compared with the baseline (p<0.05). Lens thickness (LT) followed a similar pattern, increasing up to altitude 4, then decreasing at 5. Correlations were found between AL and LT at altitudes 1 (r=0.375, p<0.05) and 5 (r=0.341, p<0.05), and between AL and CCT at altitude 4 (r=0.337, p<0.05), but not elsewhere. Conclusions As altitude increases and acute low-pressure hypoxia worsens, changes in AL, CCT and LT may affect pilots' visual function, information acquisition, decision-making and flight safety.