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down to EARTH

An up-close interview with NASA's Former Chief Optometrist

Can you envision being in space? Then imagine trying to wear eyeglasses there. Your eye drops don't drop. Your specially tinted glasses float. But, if you look at the sun for more than a couple of seconds without them, you'll burn your retina.

And, what about day and night? In space, you experience sunrises and sunsets every 45 minutes. How's that for a strain on your visual system? These are just a few of the “routine” challenges addressed by former Astronaut Corps' chief optometrist Keith Manuel, O.D. We recently sat down with Dr. Manuel and asked him about some of the visual challenges of astronauts and how they apply to those of us who consider driving to the office a long commute.

VISION IN SPACE “Of all the resources astronauts have at their disposal, vision has to be one of the most important. Most things in human space flight are dependent upon visualization of targets; and tolerances for error are minimal at best.”

EYEWEAR = PROTECTION “Astronauts operate above the protective ozone of earth, thereby exposing themselves to harmful levels of UV and IR wavelengths. There is no total shielding by the Shuttle, International Space Station (ISS) or space walking suits. We provide this protection via their personal eyewear.”

BRIGHT LIGHT “In addition to the invisible wavelengths, there is exposure to extremely bright visible light. The sun is estimated to be 40% brighter in space, and appears larger, than on earth.”

“SUN” BURN “Our calculated safe-look time for direct viewing of the sun is estimated at less than 2.4 seconds. Beyond that we expect to see retinal thermal burns. We rely entirely on tinted lenses for this protection.”

A DIFFERENT UV “UV-C, which is virtually nonexistent on earth due to ozone protection, is a much higher energy wavelength with a much more extreme threat to the eye than UV-A and UV-B. One window on both the Shuttle and the International Space Station is UV transparent. The astronauts' eyes must be protected with lens coatings and materials when working there.”

EXTREME ENVIRONMENTS “In addition to glare from both direct and reflected sunlight exposure, astronauts work in constantly changing environments—going from extreme brightness to extreme darkness. They make a complete earth revolution every 90 minutes—that means a rapid sunset and sunrise every 45 minutes.”

IN-SPACE Rx “My statistics indicate 34% of astronauts experience vision changes during space flight. Their vision will generally change back within approximately an hour of returning to earth. This creates a challenge in setting the Rx for flight.”

ASTRONAUT EYES “Though all astronauts wear tinted lenses for eye protection in space, approximately 90% of the Astronaut Corps requires actual vision correction, vs. 55% of the general adult population.”

SHUTTLE LANDING “The pilot/commander is flying and landing the Shuttle after having been weightless for 2+ weeks. He is now pulling 2-3 G's of load and may be experiencing a slight nystagmus [an involuntary jittery movement of the eyes]. Because the Shuttle has no engines and is a glider as it returns to earth, he has only one shot at landing. He must make all decisions perfectly, and that requires not only clear thinking, but excellent vision.”