Intraocular pressure and axial length changes during altitude acclimatization from Beijing to Lhasa

Purpose To investigate changes in intraocular pressure (IOP) and axial length (AL) on the ascent to high altitude from Beijing to Lhasa. Patients and methods Twenty volunteers (17 men, 3 women) who had been sent to work in Lhasa, Tibet for more than 6 months were enrolled. One of their journeys from Beijing to Lhasa was chosen as the time for the examination. IOP, AL, corneal curvature (K), and blood pressure (BP) were measured in Beijing (altitude 43 m) and Lhasa (altitude 3658 m). Their first examination was conducted at least 1 day before arriving in Lhasa and the second examination after they had stayed in Lhasa for 7 days. The data from the highland and lowland examinations were analyzed with a paired-sample T test and Pearson's correlation coefficient was calculated for the association between IOP and average BP. Results The mean IOP was 12.65 +/- 2.34 mmHg in Beijing and 14.85 +/- 3.1 mmHg in Lhasa. The mean AL was 24.61 +/- 1.50mm in Beijing, and 24.98 +/- 1.45 mm in Lhasa. The IOP and AL showed a significant elevation in highland compared with lowland (P<0.05). The mean K was 43.58 +/- 2.25 D in Beijing and 43.56 +/- 2.21 D in Lhasa and no significant difference was found in this study (P>0.05). A positive correlation between variance of IOP and ACD was found (r = 0.475, P<0.05) and no correlation between IOP and average BP was noted. Conclusions High altitude may lead to a small but significant change in IOP and axial length. However, the shape of the corneal surface was not influenced by the hypobaric and hypoxic conditions.