Well-crafted optical illusions will challenge your brain and eyes. And while we've seen quite a few designs, from black-and-white patterns hiding cats to illusions with "curvature blindness," there's still room for surprise. A new black-and-white optical illusion showing different sets of numbers for different people has been posted on Twitter. Or, to be more precise, it depends on a person's eyesight.
Most viewers commented on seeing "45283" hidden within the hypnotic vortex. It's not, but it's not a complete set. The round illusion actually has "3452839" stamped on it, only "3" and "9" are hard to see for some people. This phenomenon is related to contrast sensitivity, which refers to the eye's ability to distinguish an object from its background in a variety of situations, including darkness, fog, and bright light.
A common way people measure contrast sensitivity is, for example, by trying to read a letter as it moves from black to lighter and lighter shades of grey. Thus, a person with high contrast sensitivity is likely to see all the numbers, while someone with low contrast sensitivity can only see the most visible number, "528". However, if you are unable to recognise the signs of the optical illusion, it may indicate the need for an eye exam by a healthcare professional.