Hypoxia challenge test and retinal circulation changes - a study using ocular coherence tomography angiography

Previous studies report that the response of retinal vessels to a decrease in oxygen (hypoxia) is vasodilation, thus increasing blood flow. We aimed to characterize the changes in retinal microvasculature induced by a mild hypoxia stress test in a healthy population, using ocular coherence tomography angiography (OCT-A) technology.

Interventional repeated-measures study. The standardized hypoxia challenge test (HCT) was performed to all volunteers, according to the British Thoracic Society protocol. Ocular coherence tomography angiography (OCT-A) was performed at three time-points (baseline, during HCT and 30' posthypoxia). Macular and peripapillary vessel densities were assessed using the built-in software. To minimize bias, analysis was performed separately in right (OD) and left (OS) eyes. Repeated-measures anova and mean comparison analysis were used as statistical tests (stata v13).

Studied population included 30 healthy subjects (14 women), with a mean age of 28.8 ± 4.2 [range 22-37] years. Baseline vessel density increased in hypoxic conditions and subsequently decreased to near-baseline values in posthypoxia conditions. This pattern was observed for both eyes in both parafovea (OD: 55.3 ± 2.3 to 56.7 ± 1.9 to 55.8 ± 1.9, p < 0.05; OS: 56.9 ± 2.1 to 57.9 ± 1.9 to 57.3 ± 1.7, p < 0.05) and peripapillary (OD: 60.5 ± 0.5 to 62.6 ± 0.5 to 60.1 ± 0.4, p < 0.05; OS: 60.4 ± 0.4 to 62.3 ± 0.5 to 60.7 ± 0.4, p < 0.05) areas.

To our knowledge, there are no published data specifically addressing mild hypoxia conditions and retinal microvasculature changes, using OCT-A. This pilot study may pave way to better understand vascular responses in disease setting.