Purpose: Assessment of long-term effects of high altitude on choroidal thickness.
Methods: This prospective cross-sectional study included 88 and 79 age- and sex-matched healthy individuals who were living at sea-level (SL group) and high-altitude (HA group), respectively. Participants were required to have resided in the same place for at least 10 years. Spectral-domain optical coherence tomography (SD-OCT) scans were conducted in two different and were performed within the same time (08:00 am to 10:00 am). Central macular thickness (CMT) and choroidal thickness were measured at five different points (i.e., at the central fovea and 1 mm and 2 mm temporal and nasal of the fovea). Blood hemoglobin (Hb), red blood cell (RBC), hematocrit (Htc) levels, blood oxygen saturation, heart rate, and body mass index (BMI) were compared between groups statistically.
Results: The HA group had a mean age of 47.5 ± 13.3 years, whereas the SL group was 48.7 ± 13.4 years (P = 0.57). There was no significant difference between the groups in terms of CMT. Subfoveal choroidal thickness (SCFT) was 282.73 ± 87.82 μm in the HA group and 310.49 ± 74.73 in the SL group (P = 0.02). The choroid was found to be thinner at all the measured locations in the HA group except the 2 mm nasal point of the fovea. However, only the difference at an SFCT was statistically significant. Furthermore compared with the SL group statistically significant higher Hb, RBC, Htc levels were determined in the HA group. In the multiple linear regression model analysis, age was found an only effective confounder factor for SCFT (P = 0.001, 95% CI 4.132-2.476).
Conclusion: The systemic adaptive changes due to chronic high altitude exposure may cause structural changes in the choroidal vascular network. The current study results revealed significant thinning only at SFCT. Large-scale longitudinal studies are needed to obtain more definitive data on this subject.
Keywords: Altitude; choroid; hypercapnia; hypoxia; optical coherence tomography.