Introduction to Visual Impairment and Intracranial Pressure

Abstract

As the spaceflight community prepares for long-duration exploration class missions of distant objects beyond low Earth orbit, a new and perplexing spaceflight-induced ocular syndrome has emerged. Vestibular dysfunction, loss of mechanical weight bearing, subjective sensation of a headward fluid shift, reduction in muscle volume, and bone loss were intensely studied in the past five decades. These spaceflight adaptations are obvious to most of us now, reduced muscle activity results in muscle atrophy, and reduced mechanical loading of bone results in bone loss. Body fluid redistribution and cardiovascular adaptations during spaceflight result in postflight orthostatic intolerance, but are now mostly met with effective countermeasure strategies.Our International Space Station, home to more than 200 crew members to date, provides novel data that challenge the scientific community to elucidate the mechanisms responsible and to provide effective countermeasures for spaceflight-induced ocular adaptations. Recent ophthalmic evaluations of astronauts after their sixmonth missions to the International Space Station reveal unexpected vision problems (Mader et al., 2011). While there are many possible explanations for these vision problems in astronauts, altered posterior ocular fluid volume and pressure (above levels in the upright posture) due to a headward fluid shift during microgravity (Watenpaugh and Hargens, 1996) is proposed as the leading mechanism for the observed disc edema, globe flattening, choroidal folds, and hyperopic shifts (Mader et al., 2011