A team of researchers using Magnetic Resonance Imaging has found that most astronauts exhibit optical abnormalities after long-duration spaceflights.

An online article in the journal Radiology reports on a study of 27 astronauts who spent an average of 108 days on a Space Shuttle or International Space Station mission. Eight of the 27 astronauts also undertook a second mission lasting an average of 39 days. The study was headed by Dr. Larry Kramer, professor of diagnostic and interventional imaging at the University of Texas Medical School at Houston. (Press release here.)

The MRI study found that 33% of astronauts with more than 30 days of cumulative microgravity exposure showed expansion of the cerebral-spinal fluid space around the optic nerve. 22% shows flattening of the rear of the eyeball. 15% showed bulging of the optic nerve and 11% showed changes in the pituitary gland and its connection to the brain.

These changes are similar to symptoms seen in cases of intracranial hypertension (increased blood pressure). The authors hypothesize that the changes may be due to microgravity-induced intracranial hypertension. (Microgravity is known to cause fluid shifts from the lower extremities toward the upper body and head.)

This is not the first time optical abnormalities have been noted. A paper published in the October 2011 issue of Ophthalmology reported similar results. Dr. Robert Gibson, one of the authors of the Ophthalmology paper, said “We think it is intracranial pressure related, but we’re not sure; it could also be due to an increase in pressure along the optic nerve itself or some kind of localized change to the back of the eyeball.”

NASA is concerned about vision changes which have been reported by astronauts returning from long-duration missions. A post-flight survey of 300 Shuttle and ISS astronauts showed that 60% of ISS astronauts reported a decline in far and near visual acuity. Only 29% of Shuttle astronauts (who experienced shorter missions) reported such a decline.

How serious these changes will be is still unknown. Such changes are unlikely to be a problem for suborbital spaceflights due to their very short duration, but could become a limiting factor for interplanetary flights and other long-duration missions unless countermeasures such as artificial gravity are employed.


Written by Astro1 on March 13th, 2012 , Space Medicine and Safety

Leave a Reply

Your email address will not be published. Required fields are marked *