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Title	The eye at high altitude
Abstract Nr.	2077

Purpose	To investigate the response and recovery of retro-bulbar, choroidal and retinal circulations to exposure to normobaric hypoxia in healthy individuals.
Methods	Participants were examined with Optical Coherence Tomography (OCT), angio-OCT, retinography and colour Doppler imaging before, during and after a six-hour exposure to a simulated height of 4000m in a high-altitude chamber. Retinal nerve fiber layer (RNFL) and choroidal thickness (CT) were measure and vessel density was quantified as the mean gray value on angio-OCT images. Central retinal arteriolar (CRAE) and venular (CRVE) equivalent were measured on retinographies. Repeated measures ANOVA was used to assess the changes within patients over time.
Results	18 eyes of 18 healthy individuals aged 34.5±16.4 years were analyzed. RNFL, CT, peripapillary vessel density and CRVE showed a significant increase after six hours of hypoxia exposure (p = 0.036, p < 0.001, p = 0.040 and p <0.001 respectively) that was accompanied by a decrease in resistive and pulsatility indexes (both p<0.001) and an increase in ophthalmic artery flow velocities (p < 0.001). After one hour of recovery at sea level, all these changes returned to baseline values.
Conclusion	To the best of our knowledge, this study stands as one of the most exhaustive studies on changes in ocular blood flow in response to prolonged hypoxia. We demonstrate that in healthy individuals the decrease in ambient oxygen saturation at high altitudes is compensated at the retrobulbar, choroidal and retinal micro- and macrocirculatory levels and that these changes quickly recover back to baseline.
Conflict of interest	No

Authors 1

Last name	VAN KEER
Initials	K
Department	UZ Leuven
City	Leuven

Authors 2

Last name	Barbosa Breda
Initials	J
Department	UZ Leuven
City	Leuven

Authors 3

Last name	De Jongh
Initials	R
Department	ZOL
City	Genk

Authors 4

Last name	Nijs
Initials	I
Department	ZOL
City	Genk

Authors 5

Last name	Wirix
Initials	M
Department	ZOL
City	Genk

Authors 6

Last name	Abegão Pinto
Initials	L
Department	Centro Hospitalar Lisboa Norte
City	Lisbon

Authors 7

Last name	Stalmans
Initials	I
Department	UZ Leuven
City	Leuven

Authors 8

Last name	Vandewalle
Initials	E
Department	UZ Leuven
City	Leuven