First Author: M.Cozzi ITALY
Co Author(s): A. Clarke C. Imray S. Pagliarini
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Structural and functional changes of the human macula have been described after acute exposure to high altitude. Acetazolamide is known to reduce the incidence of acute mountain sickness. We report the effect of a gradual altitudinal ascent on retinal segmentation and subfoveal choroidal thickness (SCT) on a group of mountaineers who were randomized to acetazolamide vs placebo.
this is a longitudinal observational case/control study
20 healthy mountaineers who undertook an ascent from the base at Gressonay (1,640m) to Margherita Hut (4,559m) on Monte Rosa, Italy were randomized to treatment with acetazolamide 250mg BD vs placebo. Acclimatization was pursued with a first day 1,000 ascent and return to base followed by approximately 1,000 progressive ascent per day to Mount Rosa over 3 days (from 1,640m at base to 2,646m, 3,647m and 4,559m). OCT Spectralis (Heidelberg Engineering) was carried out at 1640m and at 4,599m. Fast volume 20x20° cube scans centreed on the fovea and vertical and horizontal 9mm EDI crosslines scans were acquired. Changes in overall retinal thickness and 8-retinal layers segmentation were calculated using the Eyex software (Version 6.3.2). SCT was obtained as an average of vertical and horizontal manual measurements of the distance from the RPE/BM complex to the choroidal-scleral junction. All measurements were taken late afternoon-evening to minimize diurnal variation.
The right eye of 20 subjects (mean age 36.4 SD±19.9 years) was included in the analysis. There was no significant difference between intervention and control groups for any retinal layer or SCT. A statistically significant all-participant ETDRS grid mean thickness increase was seen only for RNFL 2.36µm (p = 0.006), GCL 1.18 µm (p = 0.050) and OPL 2.31µm (p = 0.028). When ETDRS areas were grouped into larger and smaller vessel sectors the larger vessel group saw a significantly greater increase in mean RNFL thickness with altitude than the less vascularized group (% change 3.1 vs 0.24, p = 0.048). This difference was not present for other layers. The mean SCT decreased significantly by 8.8µm (p = 0.008).
Acetazolamide seems not to affect retinal and choroidal thickness changes after gradual ascent to high altitude. The RNFL contribution to increased altitudinal retinal thickness appears to be greater in sectors with larger retinal vessels. This is not the case for OPL expansion.