Retinal vessel regulation at high altitudes1

Area of Science:

• Ophthalmology
• Altitude Physiology
• Vascular Biology

Background:

• Hypoxia, encountered at high altitudes or simulated environments, can impact physiological systems.
• Understanding the effects of hypoxia on retinal vasculature is crucial for assessing altitude-related health risks.
• Endothelin receptor antagonists like macitentan may play a role in mitigating hypoxia-induced vascular changes.

Purpose of the Study:

• To investigate static and dynamic alterations in retinal vessels under normobaric hypoxia (NH) and hypobaric hypoxia (HH).
• To evaluate the efficacy of macitentan in modulating hypoxia-induced changes in retinal venous pressure.

Main Methods:

• Two studies were conducted: Study A involved 10 healthy individuals exposed to simulated 5500m altitude (NH).
• Study B included 17 individuals studied at 3000m altitude (HH), with and without macitentan treatment.
• Measurements included retinal vessel diameter, flicker light response, oxygen saturation, and venous pressure.

Main Results:

• Both NH and HH conditions led to increased retinal arterial and venous diameters.
• A decreased response to flicker light was observed in retinal vessels under both hypoxia types.
• Retinal venous pressure increased at 3000m and was normalized by macitentan; AMS correlated with decreased arterial constriction.

Conclusions:

• Retinal arteries and veins exhibit vasodilation and impaired dynamic response to NH and HH.
• Macitentan effectively normalized elevated retinal venous pressure at high altitudes.
• These findings highlight the impact of hypoxia on retinal vasculature and the potential therapeutic role of macitentan.