It's the same as "All w@"k and no play makes Jack a dull boy"....No seriously, it was a myth perpetuated by the church to put fear into young men (they didn't believe young ladies did such things) to stop what they seen as a heinious sin.
What about that report last week that it cuts the chances of prostrate cancer in half for those who conscientiously indulge in their 20s 30s....reason being that it flushes out the prostrate gland and doesnt allow nasty chemicals to lodge there.
THE REASON PEOPLE USED TO SAY THAT WAS BECAUSE IT WAS SUPPOSED TO TAKE THE WHITE FROM BEHIND YOUR EYES RESULTING IN BLINDNESS ITS AN OLD WIVES TALE .. KEEP DOING IT LOLOLOL .
Depending on aim and luck I would say it might be able to cause very temporary blindness in at least one eye. I've heard before that certain "projectiles" are more alkaline than others which would no doubt affect the irritation caused to the unfortunate person whose eye is affected.