Structural and Functional Changes in the Macula During Acute Exposure to High Altitude

Abstract

Purpose: : This study aimed to quantify structural and functional changes of the macula during acute exposure to high altitude and to assess their structure/function relationship.

Methods: : Spectral domain optical coherence tomography, fundus controlled microperimetry and best-corrected visual acuity (BCVA) were used to quantify changes of central retinal structure and function in 14 healthy subjects between baseline recordings (341 m) and during acute exposure to high altitude (4559 m). Data from high-resolution macular volume scans and central microperimetry were analyzed for all 9 subfields of the ETDRS grid.

Results: : Detailed longitudinal analysis revealed increased total retinal thickness (TRT) in all four peripheral ETDRS grid subfields during acute altitude exposure (TRTperiphery = 2.80±2.16 μm; mean±95%CI). This change is inverted towards the central four subfields (TRTcentral = -1.89±2.05 μm) with significant reduction of TRT in the foveola (TRTfoveola = -6.62±1.92 μm) at altitude. BCVA revealed no significant difference compared to baseline (-0.04±0.10 logMAR). Microperimetry showed stable mean retinal sensitivity in all but the foveolar subfield (MSfoveolar = -1.38±1.15 dB). At baseline recordings before and >2 weeks after high altitude exposure, all subjects reached prior levels with no sign of persisting structural or functional sequels.

Conclusions: : Significant changes of TRT occur in the central retina of healthy subjects during acute exposure to high altitude. The gradient from central reduction to peripheral increase of TRT reflects the relatively higher contribution of nerve fibers and vessels to the TRT in peripheral ETDRS subfields. The observed structural changes did not have an overall impact on key functional outcome measures such as BCVA and retinal mean sensitivity. For the first time a quantitative approach has been used to assess these changes during acute, non-acclimatized high altitude exposure.

Keywords: macula/fovea • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • perimetry