Visual disturbances during prolonged space missions.

PURPOSE OF REVIEW: During prolonged spaceflight, astronauts often experience ocular changes, due to constant head-ward fluid shifts in space as compared with Earth. This article reviews symptoms, likely causes, and potential solutions, such as lower body negative pressure, to counteract space-associated neuroocular syndrome (SANS).

RECENT FINDINGS: Low gravity conditions and other aspects of spaceflight affect the eye detrimentally, causing SANS which is characterized by optic disc edema, choroidal thickening, cotton wool spots, and a hyperopic shift. SANS is probably caused by altered hemodynamic flows in the head and neck as well as mildly elevated intracranial and intraocular pressures. Carbon dioxide and other chemicals in space-craft may influence SANS as well. SANS may be counteracted by using lower body negative pressure, thigh cuffs, spacecraft engineering, and/or artificial gravity by a centrifuge.

SUMMARY: Prolonged space missions are associated with optic disc edema, choroidal thickening, cotton wool spots, and a hyperopic shift. Possible causes and countermeasures are currently being researched to reduce the risk of SANS. Although many countermeasures to SANS are under investigation lower body negative pressure exhibits great promise in counteracting the headward fluid shifts in space. Understanding and prevention of SANS is critical to future space exploration, especially to long-duration missions to the moon and Mars.