According to Daily Mail, students at the Massachusetts Institute of Technology created an optical illusion that's also a test to determine vision impairment. Basically, if you see Marilyn Monroe in the picture below from a reasonable distance (about a foot away), you need glasses.
See Albert Einstein? You probably have good vision. Crazy, right?
ASAP Science explained the illusion, saying:
"Depending on how well you're able to focus or pick up contrast, your eye will only pick out details. Up close, we're generally able to pick up fine details like Einstein's moustache and wrinkles. But as the distance increases, or if your vision is poor and creates a more blurred image in the first place, your ability to pick up details fades away."
Whatever it is, it just saved (or inspired) a trip to the optometrist.