Quantification of Optic Disc Edema during Exposure to High Altitude Shows No Correlation to Acute Mountain Sickness

Abstract

BackgroundThe study aimed to quantify changes of the optic nerve head (ONH) during exposure to high altitude and to assess a correlation with acute mountain sickness (AMS). This work is related to the Tuebingen High Altitude Ophthalmology (THAO) study.Methodology/Principal FindingsA confocal scanning laser ophthalmoscope (cSLO, Heidelberg Retina Tomograph, HRT3®) was used to quantify changes at the ONH in 18 healthy participants before, during and after rapid ascent to high altitude (4559 m). Slitlamp biomicroscopy was used for clinical optic disc evaluation; AMS was assessed with Lake Louise (LL) and AMS-cerebral (AMS-c) scores; oxygen saturation (SpO2) and heart rate (HR) were monitored. These parameters were used to correlate with changes at the ONH. After the first night spent at high altitude, incidence of AMS was 55% and presence of clinical optic disc edema (ODE) 79%. Key stereometric parameters of the HRT3® used to describe ODE (mean retinal nerve fiber layer [RNFL] thickness, RNFL cross sectional area, optic disc rim volume and maximum contour elevation) changed significantly at high altitude compared to baseline (p<0.05) and were consistent with clinically described ODE. All changes were reversible in all participants after descent. There was no significant correlation between parameters of ODE and AMS, SpO2 or HR.Conclusions/SignificanceExposure to high altitude leads to reversible ODE in the majority of healthy subjects. However, these changes did not correlate with AMS or basic physiologic parameters such as SpO2 and HR. For the first time, a quantitative approach has been used to assess these changes during acute, non-acclimatized high altitude exposure. In conclusion, ODE presents a reaction of the body to high altitude exposure unrelated to AMS.

Hypoxia in the Eye: A Two-Sided Coin

“…Studies in mountaineers revealed that an ascent to high altitude may cause morphological and functional changes of the retina, such as optic disc swelling, changes of macular function including color discrimination, altered retinal and choroidal blood flow, and retinal hemorrhages (Frayser et al, 1970;Wiedman, 1975;Pavlidis et al, 2005;Morris et al, 2007;Bosch et al, 2008Bosch et al, , 2009Willmann et al, 2010Willmann et al, , 2011Ho et al, 2011;Fischer et al, 2012). While some of these changes present physiological adaptive mechanisms to high altitude exposure such as increased blood flow and increased tortuosity of blood vessels, others present potentially pathological changes to hypoxia, such as optic disc swelling or retinal hemorrhages.…”

High Altitude Retinal Hemorrhages–An Update

“…Also, the higher the ascent and the longer the duration at high altitudes, the higher the occurrence of retinal hemorrhages. Further studies have implicated that HARH may be seen more often in young and physically well-trained mountaineersespecially in those who undergo strenuous exercise at high altitudes (Brinchmann-Hansen et al, 1989;Arora et al, 2011)-such as in the report by Willmann et al (2011) where mountaineers rapidly ascended to an altitude of 4559 m.…”

“…Whether high altitude retinopathy shows a clear correlation with cerebral dysfunction at high altitude and thus may be utilized as a predicting sign, is still a matter of debate (Clarke and Duff, 1976;Wiedman and Tabin, 1999;Barthelmes et al, 2011;Willmann et al, 2011). Hence, we suggest to discuss HARH separately from optic disc swelling, which has been included in the current classification of high altitude retinopathy (Wiedman and Tabin, 1999).…”

“…Optic disc swelling has been reported to occur in up to 79% at altitudes of 4560 m (Willmann et al, 2011) and up to at least 59% of mountaineers at altitudes of 6800 m above sea level, increasing in incidence with ascent to higher altitudes and regressing quickly upon descent (Bosch et al, 2008). A correlation between optic disc swelling, peripheral oxygen saturation, and symptoms of acute mountain sickness has been reported in 27 climbers, concluding that optic disc swelling is most likely the result of hypoxia-induced brain volume increase (Bosch et al, 2008).…”

Ocular Problems in High-Altitude Traveling: A Review With Focus on Management

“…The incidence rate of this condition among climbers varies from 59% to 79% depending on the altitude above sea level and the speed of ascent. 37,38 There is a correlation between optic disk swelling, low arterial oxygen saturation, and the signs and symptoms of acute mountain disease. Hypoxia-induced brain volume increase is considered the most common cause of disk swelling at high altitudes.…”