Forschungsdatenbank der Universitt Zrich Medizinische Fakultt by mikesanye


									Forschungsdatenbank der Universität Zürich
Medizinische Fakultät > Augenklinik > Prof. Dr. Klara Landau

Ophthalmologic findings at high altitude

Summary / Zusammenfassung
Climbing to very high altitudes is associated with exposure to hypobaric atmospheric conditions
that cause an altitude-dependent decrease in arterial oxygen content. The degree of arterial oxygen
saturation ranges from near-normal values at altitudes up to 2’500m (8’200ft) to severe
desaturation with values less than 65% at altitudes higher than 6’500m (21’320ft). Mountaineers
exposed to low barometric pressure can acquire altitude-associated illnesses such as acute
mountain sickness (AMS) and the rare and potentially lethal high-altitude cerebral edema,
depending on the degree of hypoxia, ascent rate, and individual susceptibility.
In the summer of 2005 a large-scale Swiss medical expedition to Muztagh Ata (7’546m, 24,751ft)
in the Western Xinjiang Province, China aimed at exploring the effects of very high altitude on the
human body. The expedition was initiated by two experienced physicians and climbers interested
in high altitude medicine. Preparations of this multidisciplinary prospective study, which was
funded by the Swiss National Science Foundation, took over a year. The ophthalmological part
received an additional unrestricted grant from a private sponsor.
The ambitious goal of the researchers was to collect data on physiological changes in the human
body that were thus far unavailable under the extreme conditions of a very high altitude
expedition. With major improvements in medical instrumentation and hardware equipment this
endeavour was successfully accomplished. Moreover, a major feature of the described expedition
was the collaborative effort of multiple disciplines that allowed acquiring important basic data (e.
g. oxygen saturation, signs and symptoms of acute mountain sickness), and cross-correlate them
with findings of various disciplines such as pneumology, hematology, neurology and
The eye was the target of several investigations during the high altitude expedition, with two
ophthalmologists on board. Parameters such as the appearance of the ocular fundus, visual
function, refraction, intraocular pressure, corneal topography, choroidal and retinal circulation
were carefully documented at each heights, using the appropriate instruments for each task. Many
novel findings could be derived from this large scale study. The main goal was to evaluate eye
findings as a means to predict acute mountain sickness and at the same time to examine the ocular
response to hypoxia.
34 healthy mountaineers (27 men and 7 women) participated in the study and were divided into
two different ascent groups. The logistic challenges involved in the realization of a project of this
scale will be described in detail in the talk. All subjects underwent thorough medical and
ophthalmological examinations one month prior to the expedition in Zurich 490m (1’607ft), as
well as during ascent at 4’497m (14’750ft = base camp), 5’533m (18’148ft), 6’265m (20’549ft),
6’865m (22’517ft), after redescent to base camp, and 4.5 months after completion of the
expedition in Zurich.
What did we learn about functional and structural changes that occur in the eye under hypobaric
hypoxic conditions at very high altitude?
1. Corneal changes:
Central corneal thickness (CCT) increased in both groups with increasing altitude and decreased
after descent. In group 1 with short acclimatization CCT increased from 537 to 572 μm. CCT in
group 2 (longer acclimatization) increased from 534 to 563 μm. Amount of decrease in oxygen
saturation paralleled the increase in CCT. No significant decrease in visual acuity was observed. A
significant correlation was seen between CCT and acute mountain sickness score when controlled

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for oxygen saturation and age.
We concluded that corneal swelling during high altitude climbs is promoted by low oxygen
saturation. Systemic delivery of oxygen to the anterior chamber seems to play a greater role in
corneal oxygenation than previously thought. Adhering to slower ascent profile results in less
corneal edema. Visual acuity in healthy corneas is not adversely affected by edema.
2. Intraocular pressure changes:
Intraocular pressure in both groups revealed small but statistically significant changes: an increase
during ascent from 490m (1’607ft) to 5’533m (18’148ft), followed by a continuous decrease
during further ascent to 6’265m (20’549ft) and upon descent to 4’497m (14’750ft) and to 490m.
Differences between groups were not significant. It seems that hypobaric hypoxia at very high
altitude leads to small but statistically significant changes in IOP that are modulated by systemic
oxygen saturation. Climbs to very high altitudes proved to be safe with regard to intraocular
pressure changes.
3. Choroidal and retinal blood flow:
In order to gain insight into retinal and choroidal autoregulatory properties during hypoxia under
high altitude conditions, examinations were performed including fundus photography and
measurements of retinal and choroidal blood flow using blue-field simulation and laser-Doppler
flowmetry, respectively. The initial increase in retinal blood velocity was followed by a decrease
despite further ascent, whereas choroidal flow increase occurred later, at even higher altitudes. The
sum of all adaptational mechanisms resulted in a stable oxygen delivery to the retina and the
choroid. Parameters reflecting retinal circulation and optic disc swelling correlated well with the
occurrence of AMS-related symptoms. We demonstrated that sojourns at high altitudes trigger
distinct behavior of retinal and choroidal blood flow. Increase in retinal but not in choroidal blood
flow correlated with the occurrence of AMS-related symptoms.
4. Optic disc swelling:
59% of study subjects exhibited optic disc swelling during their stay at high altitudes, with
complete regression on return to lowlands. Significant correlation was noted between optic disc
swelling and lower arterial oxygen saturation, younger age and higher cerebral acute mountain
sickness scores. We concluded that optic disc swelling occurs frequently in high-altitude climbers,
and is correlated with peripheral oxygen saturation and symptoms of acute mountain sickness. It is
most likely the result of hypoxia-induced brain volume increase.

Publications / Publikationen
Barthelmes D., Bösch M.M., Merz T.M., Petrig B., Truffer F., Bloch K.E., Holmes TA, Cattin P,
Hefti U, Sellner M, Sutter FKP, Maggiorini M,, Landau K.: Delayed Appearance of High Altitude
Retinal Hemorrhages. PLoS ONE, 17. 2. 2011
Bösch M.M., Barthelmes D., Merz T.M., Knecht P.B., Truffer F., Bloch K.E., Thiel M.A., Petrig
B., Turk A.J., Schoch O.D., Hefti U., Landau K: New insights into corneal thickness changes in
healthy mountaineers during a very high altitude climb to Mt. Muztagh Ata. Arch Ophthalmol,
Bösch M.M., Barthelmes D., Merz T.M., Truffer F., Knecht P.B., Petrig B., Bloch K.E., Hefti U.,
Schubiger G., Landau K.: Intraocular Pressure During a Very High Altitude Climb. Invest
Ophthalmol Vis Sci, 2010;51:1609-1613. Epub 2009; October 29.
Bosch M.M., Merz T.M., Barthelmes D., Petrig B., Truffer F., Bloch K.E., Turk A.J., Maggiorini
M., Hess T., Schoch O., Sutter F.K.P., Pichler J., Huber A., Landau K.: New insights into ocular
blood flow at very high altitudes.
J Appl Physiol; 2009; 106: 454-60
Bosch M.M., Barthelmes D., Merz T.M., Bloch K.E., Turk A.J., Hefti U., Sutter F.K.P.,

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Maggiorini M., Wirth M.G., Schoch O.D., Landau K.: High incidence of optic disc swelling at
very high altitudes. Arch Ophthalmol, 2008; 126:644-650
Schnetzler G, Barthelmes D, Bosch MM; High Altitude Retinopathy (HAR): Fundusbefunde bei
einem Expeditionsteilnehmer auf 6800m Höhe. Schweiz Med Forum. 2006;6(46):1039

Keywords / Suchbegriffe
Hypoxia, high altitude, high altitude retinopathy, high altitude cerebral edema, retinal blood flow,
choroidal blood flow

Project Leadership and Contacts / Projektleitung und Kontakte
Prof. Dr. med. K. Landau (Project Leader)                             
Dr. med. M. Bösch (Project Leader)                                 
Dr. med. D. Barthelmes                                          

Other Links to external Webpages / Andere Links zu externen Webseiten

Funding Source(s) / Unterstützt durch
SNF (Personen- und Projektförderung), Others

In Collaboration with / In Zusammenarbeit mit
Dr. B. Petrig, L'institut de recherche ophtalmique, Sion                                 Switzerland
PD Dr. med. Konrad Bloch, Department of Internal Medicine,                               Switzerland
Pneumology, University Hospital
Prof. Dr. med. Marco Maggiorini, Intensive Care Unit,                                    Switzerland
University Hospital Zurich

Duration of Project / Projektdauer
Mar 2005 to Dec 2011

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