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.