Controlled systemic hypoxia induces consistent and reversible changes in retinal tissue oxygen saturation measured by ocular oximetry.

PURPOSE: To quantify changes in retinal tissue oxygen saturation (StO₂) during systemic hypoxia assessed with ocular oximetry in healthy subjects. METHODS: Twenty healthy volunteers were studied in a prospective, single-site study. Retinal tissue StO₂ was measured at the optic nerve head (ONH) and the peripapillary retina using the Zilia Ocular device at baseline, during breathing of 12% oxygen in 88% nitrogen for 30 min (hypoxia), and after reoxygenation with ambient air for 30 min (recovery). Retinal blood flow was assessed with Laser Speckle Flowgraphy (mean blur rate, MBR), and capillary blood gas parameters were obtained from the arterialized earlobe. RESULTS: Gas breathing significantly reduced arterial oxygen saturation (SaO₂; from 97.1 ± 0.9% to 89.6 ± 2.5%, p < 0.001) and partial pressure of oxygen (pO₂; from 89.2 ± 6.6 mmHg to 56.4 ± 5.1 mmHg, p < 0.001) indicative of systemic hypoxia. StO₂ decreased significantly at both measurement sites during hypoxia (ONH: -6.3 ± 3.8%, p < 0.001; retina: -11.7 ± 13.4%, p < 0.001) and recovered following reoxygenation. Retinal blood flow indices (mean tissue MBR, mean area MBR, mean vessel MBR) increased significantly during hypoxia (all p < 0.01) and returned to baseline during recovery. CONCLUSION: Ocular oximetry with the Zilia Ocular detected consistent and reversible changes in retinal tissue oximetry during controlled systemic hypoxia. These findings, together with the expected compensatory increase in retinal blood flow, support the validity of the Zilia Ocular as a tool for non-invasive assessment of retinal tissue oxygenation and encourage its further evaluation as a potential biomarker in diseases characterized by altered retinal oxygen metabolism.