In 2011, American astronaut Andrew Feustel got a flake of anti-fogging solution in his eye, five hours into a seven-hour spacewalk. Although he managed to rub his eye against a sponge inside his helmet (normally used to plug an astronaut’s nose, during pressure readjustment), the experience illuminated a happenstance scientific discovery.
Crying, although possible, is not recommended because it actually causes physical discomfort. Tears well up in the eyeball, unable to drop because of the lack of gravity; the resulting moisture remains stuck.
To quote current International Space Station (ISS) commander Chris Hadfield, ‘Space tears don’t shed.’
When afloat inside the ISS, tears simply collect until they get too big. At that point they break free and float out into the interior of the station. The spacewalk scenario, however, is truly challenging. With no way to reach into their enclosed helmets, astronauts would have to find another way (i.e. the sponge) to excise the fluid.
Speculation as to this phenomenon, which has not been thoroughly studied, is that fluids may collect in the head during spaceflight. This has been confirmed by the reports by some astronauts noting diminished eyesight during long stays in microgravity.
After 50 years of human spaceflight its fairly noteworthy that this has not been reported earlier, which probably is a testament to the machismo of astronauts.
Source: Garber M, ‘Why You Can’t Cry In Space,’ The Atlantic