Retinal vascular changes in response to hypoxia

Abstract

AbstractPurpose: Increased tortuosity and engorgement of retinal vasculature are recognized physiological responses to hypoxia. This can lead to high‐altitude retinopathy (HAR), which is a pathology seen in unacclimatised individuals at altitude. It typically features asymptomatic flame haemorrhages, but incidence reports are highly variable and our understanding of the aetiological mechanisms remains incomplete. This study aimed to evaluate retinal vascular changes throughout an expedition to 4167 metres.Methods: 10 healthy participants summitted Mount Toubkal, Morocco. Fundus images were taken on a handheld camera pre‐departure, daily throughout the expedition, and one‐month post‐return. Diameter and tortuosity of four vessels was assessed, in addition to vessel density and the presence of HAR.Results: Significant (p ≤ 0.05) increases in tortuosity and diameter were observed in some vessels on high‐altitude exposure days. There was a significant increase in vessel density on summit day only.Conclusions: This is the first study to report increased vessel density and no incidence of HAR. These results are likely attributable to relatively low altitude exposure, a conservative ascent profile, and the young, healthy demographic profile of participants. However, the study is limited by its small sample size, environmental confounding factors and semi‐subjective diameter measurements. Physiological but not pathological changes were seen in this cohort, which gives insight to the state of the cerebral vasculature throughout this expedition and builds on current understanding of retinal vascular changes in hypoxia. Future work must include daily retinal images of larger sample sizes at higher altitude and take steps to mitigate against environmental confounders. This work is relevant to altitude tourists, patients with diabetic retinopathy or retinal vein occlusion, and critically ill patients at sea level.