Normobaric hypoxia induces changes in mean ocular perfusion pressure

Purpose It is still unclear how a normobaric hypoxic stimulus affects mean ocular perfusion pressure (MOPP) in healthy subjects. The Hypoxia Challenge Test (HCT), performed according to the British Thoracic Society (BTS) protocol, mimics the hypoxia levels in medium/long‐haul flights, in which cabins are pressurized to a value of around 565 mmHg, equivalent to breathing 15.1% oxygen at sea level. We aimed to study the relationship between hypoxia and MOPP. Methods Prospective cohort study. All volunteers answered a health questionnaire and HCT was performed, according to the BTS protocol. Oxygen desaturation index (ODI) was assessed using the built‐in software. Intraocular pressure was measured in three timepoints (baseline, hypoxia, post‐hypoxia) using iCare ® tonometer. The MOPP was calculated as MOPP = 2/3(mean arterial pressure) − IOP. To guarantee data independence, right and left eyes were compared separately. Statistical analyses were performed using STATA 13.0. Results Studied population included 30 subjects (14 women), with a mean age of 28.8 ± 4.2 [range 22–37] years. There was a within‐subject statistically significant difference in MOPP for both right and left eyes (p < 0.01). Paired analysis confirmed a significant difference (p < 0.05) in MOPP values (in mmHg): baseline (OD = 46.6 ± 6.7, OS = 47.0 ± 6.6), hypoxia (OD = 43.5 ± 6.7; OS = 43.1 ± 6.6) and post‐hypoxia (OD = 46.7 ± 6.2, OS = 47.3 ± 5.9). Controlling for age and axial length, a multivariate linear regression model analysis revealed a relationship between MOPP and ODI, for right (p = 0.01) and left (p = 0.07) eyes. Conclusions To our knowledge, there is no published data specifically addressing flight cabin hypoxia and MOPP. These results in healthy subjects may help to establish normality responses to a hypoxic stress.