Spaceflights lasting 6 months or longer can cause a spectrum of changes to the astronauts’ visual systems, says a new NASA-sponsored study.
Some of these problems linger even after their return to Earth, affecting plans for manned space voyages to places like Mars.
So a team of researchers led by Thomas Mader of Alaska Native Medical Center studied 7 astronauts, all about 50 years old and all of whom reported that their vision became blurry, to varying degrees. Changes began around 6 weeks into the mission and some persisted for months after coming back. In-depth exams revealed several abnormalities:
- Flattening of the back of the eyeball
- Folds in the light sensitive area in the back of the eye
- Excess fluid around and swelling of the optic nerve.
The abnormalities appear to be unrelated to launch or re-entry, and none of these astronauts experienced symptoms usually associated with pressure inside the head.
The researchers believe other factors are involved, such as abnormal flow of spinal fluid around the optic nerve, changes in blood flow behind the retina, or changes related to chronic low pressure within the eye. These sorts of changes may result from the fluid shifts toward the head that occur when astronauts spend extended time in microgravity. But confirming this won't be easy, since tests to keep track of pressure changes in the eye are difficult to do on a spacecraft.
So, NASA has been sending astronauts up with ‘space anticipation glasses’ with amped-up power that astronauts could switch through if their sight begins to decline, Popular Mechanics reports.
Discovery's final spaceflight carried Superfocus adjustable glasses, now kept aboard the International Space Station. They can be easily refocused by sliding a knob on the bridge of the glasses, like turning a dial on a pair of binoculars.
The glasses were created for people over 40 with presbyopia, a condition that sets in with age and the lenses of the eyes lose their youthful flexibility – making it difficult to adjust focus from near to far. (Bifocals leave part of the field of view perpetually blurry, and constantly switching back and forth between regular glasses and reading glasses can be a hassle.)
Superfocus glasses have 2 lenses: a conventional firm lens on the front and a flexible lens near the eye. The pocket between them holds a clear fluid, and when you move the slider on the bridge, it pushes the fluid. The flexible lens bubbles out, changing the shape and correction of the glasses.
The report was published in Ophthalmology.