Effects of a Hyperbaric Normoxic Environment on the Retina and Choroid

Divers and individuals working in submarines and other underwater environments are exposed to normoxic hyperbaric conditions frequently. The aim of this study was to evaluate the effects of hyperbaric normoxia on the retina and choroid.

Healthy participants with no prior diving experience were exposed to 2.4 atmospheres absolute pressure in a normoxic hyperbaric chamber (HC). Optical coherence tomography was used to measure retinal thickness, the peripapillary retinal nerve fiber layer, and choroidal thickness (CT) before and within 30 minutes after HC exposure.

The right eyes of 42 participants (mean age, 23.88 ± 2.85 years) were included in the study. The retinal nerve fiber layer thickness significantly decreased in the central 1-mm Early Treatment Diabetic Retinopathy Study (ETDRS) subfield after HC exposure (P < 0.05). The outer plexiform layer showed significant thickening in the central 1-mm ETDRS subfield (P < 0.05). The retinal pigment epithelium (RPE) thickness in the 3-mm ETDRS subfield significantly decreased after HC exposure (P < 0.01). Furthermore, nasal CT (P < 0.05), temporal CT (P < 0.05), and mean CT (P < 0.01) significantly increased after HC exposure.

This study is the first in which the effects of a hyperbaric normoxic environment on the retina and choroid were examined. The observed increases in outer plexiform layer and CTs may result from elevated intracranial perfusion pressure, likely owing to increased venous pressure with unchanged cerebral arterial blood flow under hyperbaric normoxic conditions. Elevated intracranial perfusion pressure may also contribute to venous stasis in the retinochoroidal circulation, potentially explaining the structural changes observed in this study.