Hypobaric hypoxia: effects on intraocular pressure and corneal thickness.

Objective: The purpose of this study has been to better understand the mechanisms underlying ocular hydrodynamics and the changes that occur in the eyes of subjects exposed to hypobaric hypoxia (HH) to permit the achievement of more detailed knowledge and a better clinical approach in glaucomatous disease. Methods: Twenty male subjects, aged 32 ± 5 years, attending the Italian Air Force aerophysiological basic courses, required to carry out the designed training in hypobaric chamber, went through this study. The research were derived by hypobaric chamber using helmet and mask usually supplied to jet pilots, connected to oxygen cylinder, equipped with a preset automatic mixer. Results: The baseline values of tonometry measurements, recorded at T1, showed a mean intraocular pressure (IOP) of 16 ± 2.23 mmHg, while climbing up to 18,000 feet IOP mean value was 13.7 ± 4.17 mmHg (T2). Comparing T2 value with T1, the resulting difference was not statistically significant. The last assessment was performed returning to sea level (T4) where the mean IOP value was 12.8 ± 2.57 mmHg, with a significant change (p <0.05) compared to T1. Pachymetry values related to corneal thickness in conditions of hypobarism revealed a statistically significant increase (p <0.05). Conclusions: This work shows how IOP variations are mild and not very significant, while most studies gathered corresponding results regarding corneal edema. The pathophysiological basis by which these changes occur under conditions of HH, are not completely understood. Probably behind this phenomenon seems to be the increasing outflow of aqueous humor (AH) in the trabecular meshwork (TM). The data collected in our study seem to confirm this outcome.