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HomemifeatureAstronaut Vision Research: The Dangers to the Eyes of Living in Microgravity

Astronaut Vision Research: The Dangers to the Eyes of Living in Microgravity

The International Space Station (ISS), which has been orbiting the Earth for nearly 15 years, is an enormous satellite which, like all other artificial satellites can be seen from Earth with the naked eye. In size, the Space Station is as long as a football field. It’s as big as a house with five bedrooms, two bathrooms and a gym and is home to six permanent crew members. On this giant microgravity research lab crew members conduct experiments in biology, human biology, physics, astronomy, meteorology and other fields, including optics.

Research is currently being conducted to determine why weightlessness alters vision. There is a permanent risk to the vision of astronauts who live with microgravity. By collecting data before, during and after space expeditions, researchers hope to design future studies to mitigate, and hopefully eliminate the dangers of living without gravity.

“What we are seeing is flattening of the globe, swelling of the optic nerve, a far-sighted shift, and choroidal folds,” said Dr. C. Robert Gibson, a therapeutic optometrist from Houston, who consults to the NASA Flight Medicine Clinic and one of authors of the study.

Dr. Gibson who specialises in the diagnosis and treatment of ocular diseases and contact lenses has received awards from NASA for his contributions to the space program.

Swelling of the optic nerve is a serious problem. If it’s chronic, that could cause some permanent damage to the eyes…

“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 localised change to the back of the eyeball,” he said.

The study identified new risks for those who live in space for at least six months. Blurred vision was the primary issue reported by the seven astronauts who were tested for the study.

“After a few weeks aboard the (station),” said Astronaut Bob Thirsk, a Canadian Space Agency physician who spent six months as a member of the Expedition 20 and 21 crews in 2007, “I noticed that my visual acuity had changed. My distant vision was not too bad, but I found that it was more difficult to read procedures. I also had trouble manually focusing cameras, so I would ask a crewmate to verify my focus setting on critical experiments.”

The NASA-conducted post-flight survey included in the paper polled about 300 shuttle and station astronauts, documenting various vision changes. About 29 per cent of shuttle astronauts and 60 per cent of station astronauts reported a decline in distant – and near – vision clarity.

“Swelling of the optic nerve is a serious problem. If it’s chronic, that could cause some permanent damage to the eyes,” said Dr. Gibson. “We do see some change to the anatomy, to the structure of the eye; we see little wrinkles to the retina and the back of the eye, and change in the shape of the eyeball that may be permanent for some individuals.”

Researchers are specifically looking at changes to the refraction of the eye (i.e. the way light rays focus inside the eye before images transfer to the brain). In microgravity, alteration to the shape of the eyeball may occur, which would indicate a shift in vision. While the swelling of the optic nerve seems to resolve over time, the flattening of the back of the eye does not appear to return to normal.

Monitoring eye health is a routine activity for crews of the ISS. Until recently, NASA treated vision changes as a temporary problem to work around. However, the increase in reports of diminished focus in near-vision has prompted NASA into more extensive testing.

“Our medical support team on the ground was superb,” said Dr. Thirsk. “They launched an electronic ophthalmoscope on the next shuttle flight to the station. The retinal imagery from the ophthalmoscope, as well as ultrasound images of the backs of our eyes, helped our medical team determine the extent of our visual problems. I was really impressed with the responsiveness.”

The astronauts now undergo a pre- and post-flight eye test which includes taking pictures of the back of the eye, fully dilated eye exams, and an ultrasound of the optic nerve and eyeball to look for changes in the shape of the eyeball. An OCT (optical coherence tomography) is used to measure swelling and other anatomical changes in the back of the eye, and a MRI scan is done of the brain and eye.

In-flight diagnosis and treatment also are critical aspects when planning for future long-duration spaceflight missions, particularly those leaving low-Earth orbit, or extreme environment missions – this would include trips to Mars or an asteroid, where communication may be delayed and where returning home in a short amount of time is not possible.

To help meet the vision needs of an astronaut while in orbit, NASA provides reading glasses for crew members over the age of 40 who are on the verge of presbyopia. The crew also has access to SuperFocus adjustable glasses, which are kept aboard the ISS. These revolutionary glasses can be easily refocused, by sliding a knob on the bridge of the glasses, like turning a dial on a pair of binoculars. While astronauts will have their regular prescription glasses, the SuperFocus glasses eliminate the issue of prescription changes while in orbit.

“During the first half century of spaceflight, we have encountered and addressed many medical problems associated with orbital missions,” said Dr. Thirsk. “However, as we extend human presence further into the solar system and expand the scope of our activities, we can anticipate that new medical issues will arise.”

The microgravity optical research will help NASA prepare astronauts for living on space stations for long periods of time, and could also help advance the development of new treatments for vision problems here on Earth.

References

Dr. C. Robert Gibson, is one of authors of the study published in the October 2011 issue of Ophthalmology, the journal of the American Academy of Ophthalmology.

Further information about the astronaut vision research is available at NASA mission news, Astronaut Vision Research, www.nasa.gov.

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