Frey MA. Research Progress Reports from the NASA Human Research Program: visual impairment intracranial pressure project. Aviat Space Environ Med 2013; 84:163–4.
These summaries are written for NASA and prepared for the journal by Mary Anne Frey, Ph.D., with the support of NASA’s Human Research Program Office and are intended to alert the scientific community to ongoing work in Space Medicine. Original sources for the material may include journal articles, NASA Technical Reports, internal NASA documents, and personal communications from Principal Investigators.
Since the earliest human spaceflights, it has been known that when exposed to the microgravity environment, astronauts experience a shift of fluids from their lower body (more than a liter from each leg) to the chest and head. Evidence includes signs and symptoms such as reduced size of the legs, puffy faces, distended jugular veins, increased stroke volume and cardiac output, headaches, nasal stuffiness, and a feeling of head fullness. This microgravity-induced fluid shift is reversed on return to gravity, causing orthostatic intolerance, a consequence that has been well studied. Recently, evidence is accumulating that the cephalad fluid shift may have more serious consequences for spaceflight crewmembers than previously recognized, especially for crewmembers on long-duration spaceflights. As mission duration on ISS has lengthened, reports of changes in astronauts’ vision during spaceflight have increased and NASA Space Life Sciences Medical Operations has instituted greater pre-, in-, and postflight visual testing. As a result, varying degrees of anatomic and functional changes were identified in 10 astronauts who completed long-duration missions. Degradation in near vision, which in some cases continued for longer than 1 yr post mission, has also been identified in other astronauts with long- and/or short-duration flights. The ophthalmic findings in the long-duration crewmembers may be related to idiopathic intracranial hypertension, a syndrome identified on Earth, which suggests that an increase in intracranial pressure (ICP), caused by the headward fluid shift that occurs with exposure to microgravity, may be involved. The syndrome has been designated “visual impairment intracranial pressure” (VIIP). This report describes the evidence for this syndrome and efforts to understand the causes and underlying physiology and to develop effective countermeasures and treatment.