Structural and Functional Changes of the Human Macula during Acute Exposure to High Altitude

Abstract

BackgroundThis study aimed to quantify structural and functional changes at the macula during acute exposure to high altitude and to assess their structure/function relationship. This work is related to the Tuebingen High Altitude Ophthalmology (THAO) study.Methodology/Principal FindingsSpectral domain optical coherence tomography and microperimetry were used to quantify changes of central retinal structure and function in 14 healthy subjects during acute exposure to high altitude (4559 m). High-resolution volume scans and fundus-controlled microperimetry of the posterior pole were performed in addition to best-corrected visual acuity (BCVA) measurements and assessment of acute mountain sickness. Analysis of measurements at altitude vs. baseline revealed increased total retinal thickness (TRT) in all four outer ETDRS grid subfields during acute altitude exposure (TRTouter = 2.80±1.00 μm; mean change±95%CI). This change was inverted towards the inner four subfields (TRTinner = −1.89±0.97 μm) with significant reduction of TRT in the fovea (TRTfoveal = −6.62±0.90 μm) at altitude. BCVA revealed no significant difference compared to baseline (0.06±0.08 logMAR). Microperimetry showed stable mean sensitivity in all but the foveal subfield (MSfoveal = −1.12±0.68 dB). At baseline recordings before and >2 weeks after high altitude exposure, all subjects showed equal levels with no sign of persisting structural or functional sequels.Conclusions/SignificanceDuring acute exposure to high altitude central retinal thickness is subject to minor, yet statistically significant changes. These alterations describe a function of eccentricity with an increase in regions with relatively higher retinal nerve fiber content and vascular arcades. However, these changes did not correlate with measures of central retinal function or acute mountain sickness. For the first time a quantitative approach has been used to assess these changes during acute, non-acclimatized high altitude exposure.

Impact of Acute Exposure to High Altitude on Anterior Chamber Geometry

“…11,12 To minimize diurnal variation, all subjects (only right eyes) were assessed once a day at 9:00 AM, approximately 2 hours after awakening. All recordings were performed by the same investigator.…”

“…[7][8][9][10] However, measurements acquired any time after descent or in chambers may not necessarily reflect the changes during exposure to high altitude-related hypoxia. 7,11 These difficulties may account for some of the variability in results and conflicting conclusions drawn from those studies.…”

“…11,12 As such, the study design and location provided ideal logistical solutions to such an undertaking with the additional benefit of an established ascent profile already used in numerous previous studies on high altitude medicine especially in regard to acute mountain sickness (AMS) and high altitude pulmonary edema. 13,14 This study aimed to quantify changes of individual layers in the central cornea and anterior chamber angle (ACA) and anterior opening distance (AOD) as measures of anterior chamber geometry during acute exposure of healthy volunteers to high altitude using high-resolution anterior segment optical coherence tomography (AS-OCT).…”

Hypoxia in the Eye: A Two-Sided Coin

“…Studies in mountaineers revealed that an ascent to high altitude may cause morphological and functional changes of the retina, such as optic disc swelling, changes of macular function including color discrimination, altered retinal and choroidal blood flow, and retinal hemorrhages (Frayser et al, 1970;Wiedman, 1975;Pavlidis et al, 2005;Morris et al, 2007;Bosch et al, 2008Bosch et al, , 2009Willmann et al, 2010Willmann et al, , 2011Ho et al, 2011;Fischer et al, 2012). While some of these changes present physiological adaptive mechanisms to high altitude exposure such as increased blood flow and increased tortuosity of blood vessels, others present potentially pathological changes to hypoxia, such as optic disc swelling or retinal hemorrhages.…”

Effects of refractive surgery in extreme altitude or space

“…[1][2][3] As refractive surgery changes the properties of the cornea and the lens, concerns about refractive or intraocular lens (IOL) procedures in humans exposed to extreme situations have been raised.…”