Exposure to High Altitude Alters Tear Film Osmolarity and Breakup Time

High altitude provides environmental conditions with dry air and cold temperatures that may facilitate the development of dry eye symptoms. This study investigated, for the first time, the quality of the tear film during high altitude exposure in healthy subjects. This study is related to the Tübingen High Altitude Ophthalmology (THAO) study.Tear film osmolarity (TFO), tear film breakup time (TBUT), and Schirmer I and II were used to assess tear film properties under standardized conditions in 14 healthy subjects on day 1, 2, and 4 during exposure to high altitude at the Capanna Margherita (CM; 4559 m, Italy) compared to baseline measurements in Tübingen (341 m, Germany) before (BL1) and after (BL2) exposure.Upon arrival at CM, a significant increase in intra-individual TFO (309.1 ± 19.3, 332.2 ± 24.1, 335.5 ± 28.7, 329.7 ± 19.0, and 308.5 ± 15.3 mOsms/L at BL1, day 1, 2, 4, and BL2, respectively) and a significant decrease of TBUT (11.2 ± 5.2, 7.3 ± 5.2, 7.2 ± 11.6, 4.5 ± 2.3, and 8.7 ± 4.6 seconds at BL1, day 1, 2, 4, and BL2, respectively) were found. Schirmer test changes at high altitude remained statistically nonsignificant compared to baseline. Comparisons of parameters between BL1 and BL2 showed no statistically significant differences and recordings of right and left eyes for TBUT and Schirmer did not differ significantly on any day measured.High altitude exposure leads to an altered tear film resulting in an increased TFO and a reduced TBUT. These changes were fully reversible after descent. This is of clinical importance to populations living in high altitude areas and to trekkers and mountaineers exposed to high altitude due to their ever-increasing number.