Central Corneal Thickness Measurements at Very High Altitudes

Abstract

Purpose: : High altitude mountaineering is a very popular recreational sport in healthy lowlanders. Since the tragic and often quoted experience of Dr. Beck Weathers, a climber on Mt. Everest who had undergone prior corneal refractive surgery, a keen interest in the consequences of this procedure at high altitudes has developed. But, not many publications have addressed the changes of normal untouched corneas in such environmental conditions as present at high altitudes, i.e. hypobaric and hypoxic. The purpose of our study was to evaluate acute and chronic central corneal thickness (CCT) changes during a climb to very high altitudes.

Methods: : Thirty-two healthy mountaineers were randomly assigned to two different ascent profiles during a medical research expedition to Mt. Muztagh Ata (7546m/ 24,757ft). CCT measurements were performed at 400m (1,300ft), 4497m (14,754ft=base camp (BC)), 5533m (18,153ft=C1), 6265m (20,554ft=C2). Ultrasound pachymetry was utilized for measurements. Vital parameters such as oxygen saturation (SpO2) were measured at each altitude. Climbers with incomplete data and ophthalmic disease were excluded. Contact lens wearers and climbers post refractive surgery were analyzed separately.

Results: : CCT [µm; mean±SD] increased from 550±43=BC to 572±40=C2 during ascent. Corneal thickness did not vary significantly during initial ascent from base camp to C1 (p=0.112). Central corneal thickness measurements were highest at C2 (p<0.05) compared to all other altitudes. Upon return to BC CCT decreased (560±28), and remained tendentially higher compared to initial values at the same height (p=0.11). Corneas at 400m were significantly thinner (534±36) than during the expedition (p<0.001). There was a significant time*group (i.e. ascent profile) interaction regarding the mean CCT changes (p= 0.048). Multiple regression analysis showed that a decrease of SpO2 correlates with a CCT increase.

Conclusions: : Corneal thickness parameters show an increase during ascent to very high altitudes which tendentially persists even after redescent to lower altitudes. Acclimatization and thus systemic hypoxia seems to play a significant role in the occurrence of central corneal thickening.

Keywords: cornea: clinical science • hypoxia • cornea: endothelium