Related Experiment Video
Updated: Jun 24, 2026
Retinal Vascular Reactivity as Assessed by Optical Coherence Tomography Angiography
Published on: March 26, 2020
Retinal vessel diameters in relation to hematocrit variation during acclimatization of highlanders to sea level
Peter Kristian Kofoed1, Birgit Sander, Gustavo Zubieta-Calleja
1Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Copenhagen, Denmark. peter.k@dadlnet.dk
Purpose:
To examine variations in retinal vessel diameters during acclimatization of native highlanders to normobaric normoxia at sea level.
Methods:
Fifteen healthy residents of the greater La Paz region in Bolivia (3600 m above sea level) were examined thrice over a 72-day period, after having traveled by airplane to Copenhagen, Denmark, near sea level.
Results:
In the study subjects, hematocrit decreased from 49.6% (day 2) to 45.9% (P = 0.0066, day 23) and 41.7% (P < 0.0001, day 72); from days 2 to 23, retinal vein diameter increased by 2.68% (P = 0.0079); whereas retinal artery and vein diameters were indistinguishable from baseline after 72 days. No funduscopic signs of retinopathy were observed. Arterial blood pressure remained stable throughout the study.
Conclusions:
Although a 16% reduction in hematocrit occurred between days 2 and 72 after arrival at sea level, the only significant excursion observed was that the diameter of the veins was larger at day 23 than at days 2 and 72. Retinal vessel diameters demonstrated a wide homeostatic range during acclimatization-driven hematocrit variation.
