Refractive Changes and Corneal Thickness in Healthy Mountaineers at High Altitude: The Korzhenevskoi Experience (7105 m)

Purpose: The purpose of this study was to investigate the effect of hypoxia and hypobaric conditions on refraction and central corneal thickness on healthy corneas during an ascent without oxygen supplementation above 7000 m (23 000 ft). Methods: Twelve multinational mountaineers were included in a prospective observational cohort study during an expedition to the Korzhenevskoi Peak (7105 m). The two patients excluded from the study had a history with keratoconus or were current wearers of rigid contact lenses. None had a history of refractive surgery or ocular disease. The central corneal thickness (CCT), the oxygen saturation, and the refraction have been recorded for each patient using portable equipment. The highest measurement has been taken at 6356 m of altitude which is the highest ophthalmologic measurement ever done. Results: Longitudinal analysis revealed a significant increase of CCT during altitude exposure (CCT baseline = 542± 36 μm; CCT C3 = 633 ± 30 μm) due to stromal edema reversible upon descent. The amount of decrease in oxygen saturation paralleled the increase in CCT. The refraction measurements showed a myopic shift (−1.14D) with the altitude (R Baseline = −0.41 ±2.25D; R C3 = −1.55 ± 2.41D P < 0.05). Conclusions: Significant stromal edema was found during exposure to high altitude in healthy mountaineers. This is due to hypoxia and decreased atmospheric pressure leading to a deficiency of adenosine triphosphate. A significant and clinically relevant myopic shift, due to the stroma edema, appears above 6500 m which can explained the blurry far vision in high altitude for mountaineers without oxygen supplementation.