Background/aims The study aims to investigate changes in the optic nerve sheath diameter (ONSD) at high altitude and to assess correlation to optic disc oedema (ODE) and acute mountain sickness (AMS). This investigation is part of the Tübingen High Altitude Ophthalmology study.
Methods Fourteen volunteers ascended to 4559 m for 4 days before returning to low altitude. Ultrasonography of ONSD, quantification of optic disc parameters using a scanning laser ophthalmoscope and fluorescein angiography were performed at 341 m and at high altitude. Pearson’s coefficient was used to correlate changes in ONSD with the optic disc and AMS. Assessment of AMS was performed using the Lake Louise (LL) and AMS-cerebral (AMS-C) scores of the Environmental Symptom Questionnaire-III. All volunteers were clinically monitored for heart rate (HR) and oxygen saturation (SpO2).
Results The mean ONSD at high altitude (4.6±0.3 mm, p<0.05) was significantly increased compared with baseline (3.8±0.4 mm) and remained enlarged throughout high-altitude exposure. This change in ONSD did not correlate with AMS (AMS-C, r=0.26, p=0.37; LL, r=0.21, p=0.48) and high-altitude headache (r=0.54, p=0.046), or clinical parameters of SpO2 (r=0.11, p=0.72) and HR (r=0.22, p=0.44). Increased ONSD did not correlate with altered key stereometric parameters of the optic disc describing ODE at high altitude (r<0.1, p>0.5).
Conclusion High-altitude exposure leads to marked oedema formation of the optic nerve independent of AMS. Increased ONSD and ODE reflect hypoxia-driven oedema formation of the optic nerve at high altitude, providing important pathophysiological insight into high-altitude illness development and for future research.
- optic nerve
- high altitude; acute mountain sickness; AMS; eye
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Contributors AS, GW and VG had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of data analysis. Study concept and design: GW and FG. Acquisition, analysis or interpretation of data: all authors. Drafting of the manuscript: AS and GW. Critical revision of the manuscript for important intellectual content: all authors. Administrative, technical or material support: all authors. Study supervision: GW.
Funding This work was supported by the Wilderness Medical Society with the Charles S Houston Award. The supporting source had no role in study design; collection, analysis and interpretation of data; writing the report; and the decision to submit the report for publication.
Competing interests None declared.
Patient consent Obtained.
Ethics approval The study was approved by the local IRB (Ethik-Kommission der Medizinischen Fakultät/Universitätsklinikum Tübingen, IEC project number: 258/2010B01).
Provenance and peer review Not commissioned; externally peer reviewed.
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