The effects on vision of prolonged missions
The National Aeronautics and Space Administration (NASA) is conducting the VIIP (Vision Impairment and Intracranial Pressure) study to identify the causes of eye changes reported by American astronauts during space missions lasting more than six months.
Some astronauts complain of visual disturbances after missions, in some cases even after several years.
Initial data, presented at the American Glaucoma Society congress, showed, using modern imaging tests: hypermetropic shift, choroidal folds, optic nerve sheath distention, optic nerve torsion, flattening of the eyeball, disc oedema and cotton wool spots.
Investigation into the causes of these ocular changes seems to have identified the variation in brain pressure under zero gravity conditions as a relevant factor.
In fact, in a microgravity situation, there is a shift of about 2 litres of fluid from the lower limbs to the thorax and then to the head, which leads to a rebalancing of intra-body pressure, both arterial and venous. It can be assumed that this redistribution of fluids can lead to a pathological condition similar to the intracranial hypertension that occurs on earth
The outcome in some cases may be a reduction in visual acuity, but this does not occur in a significant number of astronauts, suggesting a different biological response to the space environment.
This assumption imposes the need to identify existing risk factors. In addition, the standardisation of qualitative and quantitative criteria for imaging tests will be helpful in detecting even asymptomatic changes and will allow countermeasures to be taken to reduce the damage to vision that may arise in the long term.
For updates see the NASA study VIII
Dr. Carmelo Chines
Direttore responsabile
English 
Italian