If you see Marilyn Monroe in the picture below, you probably need glasses.
According to Daily Mail, students at the Massachusetts Institute of Technology created an optical illusion several years ago that also acts as a test to determine vision impairment.
The image features a blurry picture of Marilyn Monroe superimposed over a lightly drawn picture of Albert Einstein.
A healthy pair of eyes will see only Albert Einstein if they view the picture from a normal distance.
Marilyn Monroe, on the other hand, will be seen if your eyes process close-up images as if they're much farther away.
Healthy eyes can therefore only see Marilyn Monroe by backing away from the screen:
The illusion shows that high spatial frequency features like the fine lines of Einstein are visible from up close whereas blurry, low spatial frequency features can only be seen from a distance.