Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures

• Published in: Physiological reviews Vol. 98; no. 1; pp. 59 - 87
• Main Authors: Zhang, Li-Fan, Hargens, Alan R
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01-01-2018
• Subjects: Adaptation; Animals; Cerebrospinal fluid; Gravity; Hemodynamics; Humans; Hypertension; Intracranial Hypertension - etiology; Intracranial Hypertension - pathology; Intracranial Hypertension - physiopathology; Intracranial Pressure - physiology; Intraocular Pressure - physiology; Optic nerve; Pathogenesis; Pathology; Posture; Posture - physiology; Pressure; Space Flight; Subarachnoid space; Vision Disorders - etiology; Vision Disorders - pathology; Vision Disorders - physiopathology; Visual impairment
• ISSN: 0031-9333; 1522-1210
• DOI: 10.1152/physrev.00017.2016

Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.