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Anna Ter-Zakarian, Rustum Karanjia, Alfredo A Sadun; Oxygen, Atmospheric Pressure and Non-arteritic Ischemic Optic Neuropathy. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5088.
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To assess variations in aircraft pressurization for potential high altitude dangers in patients predisposed to non-arteritic ischemic optic neuropathy (NAION). As an airplane ascends, pressurization of the cabin partially offsets and limits the fall of air pressure. The United States Federal Aviation Administration (FAA) requires that the cabin pressure on commercial airplanes be maintained at levels equivalent to the atmospheric pressure below 8,000 feet – the maximum allowed. Most aircraft are pressurized to 6,000 and 8,000 feet, depending on the type of aircraft and composite materials of the fuselage. While this has little effect on most passengers, patients with a history of NAION may not tolerate a reduction of inspired oxygen pressure and may be at increased risk of a recurrent ischemic event.
As part of this study, altimeters were used to measure commercial aircraft pressurization at cruising altitude. A total of 13 planes were measured for pressure, including 6 narrow-body planes and 7 wide-body planes manufactured by Boeing and Airbus. Single-aisle aircraft with a fuselage cabin diameter of 10-13 ft. were considered narrow-body, while twin-aisle aircraft with a fuselage width of 16-20 ft. were qualified as wide-body.
Larger aircraft maintained a lower internal pressure altitude than the smaller aircraft, with average cruising altitude pressures of 5910 ft. and 7020 ft., respectively.
Consequences of high altitude include hypoxic depression of cerebral function and cerebral edema, manifesting as retinal hemorrhages and papilledema. NAION may also be exacerbated by several mechanisms induced by low oxygen pressure, leading to hypoperfusion of the optic nerve head. Patients with an underlying history of NAION may be at increased risk of fellow eye involvement, especially in unpressurized flights and narrow-body planes, which based on our study are on average 1110 ft. less pressurized relative to wide-body aircraft. Consequently, there may be a greater danger of optic neuropathy development in commercial flying in smaller aircraft for patients predisposed to AION.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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