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Alexander Clarke, Mariano Cozzi, Charles Hand, Chris Imray, Sergio Pagliarini; The Impact of Imaging Modalities and Acetazolamide on Retinal Vessel Diameter at High Altitude. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4824. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Acute mountain sickness (AMS) is common at altitude, and can presage the more serious complication of cerebral oedema. One major hypothesis for the development of this condition is venous outflow insufficiency. This has in turn increased interest in the retinal vessels, with their accessibility to imaging and anatomical connections to the cerebral vasculature. However there remains major unanswered methodological questions in these studies. As part of an expedition to the Italian Alps we studied two major causes of study design heterogeneity; the use of disparate imaging modalities and the concurrent use of acetazolamide, an AMS prophylactic.
20 participants (mean age 36.3, SD 19.7) ascended Monte Rosa (4634m) over 4 days as part of a double-blind parallel RCT. Randomisation was between a twice daily 250mg acetazolamide capsule and placebo. All participants underwent evening fundus digital photography (Zeiss Visucam) and near-infrared retinal reflectance (Heidelberg Engineering Spectralis) in Gressoney (1600m) and the Capanna Margherita (4559m). Right eye retinal vessel diameter was measured using automated software (Imedos Vesselmap1).
A highly significant increase in mean venous diameter was seen at altitude on both digital camera images (10.6μm, p < .001) and infrared camera images (11.3μm, p < .001). This was also true for mean arterial diameter, with increases of 5.2μm (p < .001) and 5.1μm (p < .001) for digital and infrared cameras respectively. However, there was no significant difference between intervention and control groups in venous or arterial calibre in either imaging modality. Pearson correlation found a very strong association between digital and infrared images for both venous calibre (r = .772, p < .001) and arterial calibre (r = .813, p < .001).
In line with existing studies, arterial and venous retinal vessel diameter have been shown to increase significantly with altitude. Moreover it was shown that acetazolamide, commonly used by climbers to attenuate AMS, is unlikely to confound studies of retinal vasculature. Finally it was found that digital and near-infrared camera images correlate well when measuring altitude related vessel diameter changes.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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