Background
The visual system undergoes profound changes when exposed to hypoxia or high altitude. Although some of these changes, such as increased blood flow and increased tortuosity of blood vessels, present physiological adaptive mechanisms to high altitude exposure, others present potentially pathological changes due to hypoxia, for example, optic disc swelling or retinal hemorrhages, which in part have previously been correlated with AMS.
Objective
These visual system changes are of special interest or study as the retina is a directly visible part of the central nervous system, and thus may be able to give insight into a possible underlying pathologic mechanism of AMS.
Methods
With a long history of high altitude research focusing on ocular changes during mountaineering expeditions, the Tübingen High Altitude Ophthalmology study investigated retinal changes in 14 healthy subjects during acute high altitude exposure in a controlled study setting at the Capanna Margherita (Italy) at 4559 m using state-of-the-art equipment to study morphological and functional changes of the retina in regard to AMS. Retinal function was assessed in psychophysical tests and in objective measurements such as microperimetry (MP1, Nidek, Japan). Morphological changes using spectral domain optical coherence tomography, fluorescein angiography, and Heidelberg retinal angiography (Spectralis optical coherence tomography plus Heidelberg retinal angiograph and Heidelberg retinal tomograph, Heidelberg Engineering, Heidelberg, Germany]) during acute high altitude exposure were tested for the first time.
Results
Fluorescein angiography showed considerable dye leakage in the periphery of the retina and increased vessel diameters. Optical coherence tomography and Heidelberg retinal tomograph measurements demonstrated swelling of the optic disc as well as distinct foveal changes with perifoveal thickening of the retinal nerve fiber layer and vascular arcades.
Conclusions
No correlation between these changes and central retinal function and AMS was found.