This optical illusion disappears completely when you focus on it

• This image fades away completely if you focus on it for 30 seconds.
• It happens due to something called the Troxler effect.
• The picture disappears because the brain filters out information and images that it deems unnecessary — when you focus on a fixed point, the background fades away.
  

An eye-care practice in Horsham, Pennsylvania, shared an optical illusion on their Twitter account that's making users rub their eyes in disbelief. The entire graphic disappears after 30 seconds, if you focus on just one fixed point.

How does this happen? You can turn to a famous optical illusion, Troxler's fading circle, for answers. The Troxler effect was discovered in 1804 by Ignaz Troxler, a Swiss physician and philosopher. 

Troxler discovered that your eyes (and your brain) filter out information that is constant, and relatively unimportant. So if you focus on a fixed point in the image, which isn't moving or changing, all other stimuli in your peripheral vision will fade away.

There are many other classic optical illusions that demonstrate the Troxler effect, such as the Lilac Chaser. These also known as disappearing images.

So the next time you think your eyes are playing a trick on you, remember that your brain is just doing its job.

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