Pupil constriction and angle widening observed following short-term hypobaric hypoxia exposure.

Short-term exposure to hypobaric hypoxia induces pupil miosis and widens the anterior chamber angle, potentially offering a safer environment for individuals with narrow angles, according to a study.

In this study, swept-source anterior segment optical coherence tomography (SS AS-OCT) was used to measure anterior chamber parameters in 50 eyes from 25 healthy young individuals at baseline sea-level conditions, during a 3-hour exposure to a simulated altitude of 4,000 meters, and immediately after leaving the hypobaric environment. Key measurements included anterior chamber depth (ACD), lens vault (LV), angle opening distance (AOD500), trabecular-iris space area (TISA500), iris curvature (IC), pupil diameter (PD), and intraocular pressure (IOP).

Significant changes were observed in pupil diameter and intraocular pressure following exposure to hypobaric hypoxia. Pupil size decreased notably from 5.36 mm to 4.78 mm, and IOP dropped from 16.4 mm Hg to 14.9 mm Hg. In addition, there was a significant widening of the anterior chamber angle, reflected by changes in AOD500, TISA500, and angle recess area. Although iris volume increased slightly, the curvature of the iris decreased.

These anterior segment changes were not associated with acute mountain sickness symptoms or reduced arterial oxygen levels, highlighting a direct link between hypoxia and ocular structural alterations rather than overall systemic effects.

Reference
Xie Y, Sun Y, Shao Y, et al. Impact of Acute Short-term Hypobaric Hypoxia on Anterior Chamber Geometry. J Glaucoma. 2024;doi: 10.1097/IJG.0000000000002498. Epub ahead of print. PMID: 39311802.