Retinal Vessel Diameter at High Altitude

Abstract

Purpose: This study aimed to quantify the impact of acute high altitude exposure on retinal vessel diameter and to assess possible correlations to symptoms of acute mountain sickness (AMS) and high altitude headache (HAH). This work is related to the Tuebingen High Altitude Ophthalmology (THAO) study.

Methods: VesselMap 1 analyzer (Imedos Systems, Germany) was used to quantify changes of retinal vessel diameter within one diopter distance of the papilla in 18 healthy subjects during acute high altitude exposure to 4559 m compared to baseline recordings (341 m) using infrared fundus images obtained from a Spectralis® device (Heidelberg Engineering, Germany). Intra-individual differences were calculated using ANOVA with a significance level of p < 0.05. Pearson’s correlation was used to assess a possible linkage between retinal vessel diameter and scores of AMS and HAH.

Results: Analysis of intra-individual differences revealed a significant (p < 0.05) increase of mean arterial (MAD; increased MADaltitude = 13.6 μm) and venous diameter (MVD; increased MVDaltitude = 26.7 μm) at high altitude in healthy subjects compared to baseline recordings. Average arterial and vein diameters at baseline and high altitude were: MADbaseline = 122.72±14.78 μm vs. MADaltitude = 136.36±19.84 μm; MVDbaseline = 148.02±15.32 μm vs. MVDaltitude = 171.74±22.09 μm; mean±sd) Changes were completely reversible upon descend. Pearson’s coefficient showed neither a correlation between increased retinal vessel diameter and AMS (MAD vs. AMS-c score: r = 0.02, p = 0.95; MVD vs. AMS-c score: r = -0.17, p = 0.51) nor with HAH (MAD vs. headacheAMS-c score: r = -0.17, p = 0.50; MVD vs. headacheAMS-c score: r = -0.10, p = 0.71).

Conclusions: A significant increase in central retinal vessels for both arteries and veins occurs in response to acute exposure to high altitude in healthy subjects. This may be attributed to the physiologic response to the effects of hypoxia during acute high altitude exposure in non-acclimatized subjects. The missing correlation of retinal vessel diameter and symptoms of AMS or HAH is of special interest as restricted cerebral and retinal venous outflow is currently debated to be associated with a greater headache burden in response to high altitude hypoxia. Our findings may provide a novel basis for this debate.

Keywords: 548 hypoxia • 688 retina