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M.M. Bosch, T. Merz, D. Barthelmes, F. Truffer, B.L. Petrig, K. Landau; High Altitude–Induced Changes in Retinal and Choroidal Circulation in Healthy Mountaineers–Preliminary Results . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1797.
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© ARVO (1962-2015); The Authors (2016-present)
To determine changes in retinal and choroidal circulation in healthy mountaineers at different altitudes during an expedition to very high altitudes.
A total of 32 participants in good physical condition completed this prospective study performed during a medical research expedition to Muztagh Ata (7546m). Five participants were excluded. The blue field simulation (BFS) technique was used to measure leukocyte velocity (V) in the perifoveal retinal capillaries. Laser Doppler flowmetry (LDF) was used to measure velocity (Vel) of red blood cells in the choriocapillaris behind the foveal avascular zone. Measurements were performed 1 month prior to the expedition in Zurich (ZH1, 400m), at basecamp (BC1, 4450 m), at camps (C) C1, 5450 m, C2 ,6250 m, upon return to BC (BC2) and in ZH 4.5 months after the expedition (ZH2). The average ascent rate was less than 320m per day. Duration of the stay above 4000m was maximally 24 days. Complete data records of 27 participants (54 eyes) were analyzed by repeated measure analysis (ANOVA). Statistical significance was defined as p < 0.01.
Retinal blood velocity parameter (BFS–V) increased continuously from ZH1 to C1 and then showed a steady decrease. Choroidal blood velocity (Ldf–Vel) was stable during the initial ascent to C1, increased markedly at C2 and went on to slightly increase at BC2. Both retinal and choroidal velocity parameters decreased significantly upon return to base level (ZH2).
Retinal and choroidal blood velocity parameters show distinct changes at high altitudes. Initial hypoxia–induced increase of retinal blood velocity decreases despite further ascent presumably due to acclimatization during prolonged stay at high altitude. Choroidal velocity alterations seem to occur later, at higher altitudes, compared to those during retinal circulatory adaptation. Choroidal blood flow may be ample enough to compensate the effects of medium elevation.
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