Role of intolerance to hypoxia in the occurrence of anterior bilateral ischaemic optic neuropathy at high altitude

The pathophysiology of nonarteritic anterior ischemic optic neuropathy (NA-AION) is still imperfectly understood, but arterial hypertension seems to play a decisive role. Intolerance to hypoxia is defined as desaturation of hemoglobin more than 15% at rest and/or elevation of blood pressure at rest or after exercise over 20 mmHg in hypoxia. We report the case of a 66-year-old woman who presented bilateral NA-AION during a trek at high altitude (>2500 m). The etiological check up was negative. Due to the circumstances of occurrence, we requested a tolerance to hypoxia test, which was positive. In this case, the combined effects of altitude and effort probably led to prolonged desaturation of oxyhemoglobin associated with an excessive blood pressure increase upon exercise leading to ischemia of the optic nerve head. This case showed the value of a systematic search for hypoxia tolerance in patients with nonarteritic anterior ischemic optic neuropathy occurring during a situation of prolonged hypoxia (long-distance flight, high altitude). (C) 2010 Elsevier Masson SAS. All rights reserved.