A vision exam is one of the easiest tests you’ll ever take in your life—or, at least, it should be. All you have to do is cover one eye at a time and look at a chart! It might seem simple, but some eyesight tests are far trickier than others…

For instance, a large number of people who try these particular vision-based tests have more trouble than they expected—even if they think they’re sportin’ the best eyesight in town. Check out the tricky tests below. Do you have what it takes to pass them?

When it comes to eyesight, some people want you to know how good their vision is, while others brag about wearing glasses. That’s why people go crazy for these online eye tests. Eyesight’s status symbols…sort of.

That’s why, on February 26, 2015, Twitter users shared a picture of a dress over 10 million times in a single week. The dress raised serious questions about the hidden talents of our eyeballs—and drove the world into a social media frenzy. Ready to test your vision?

1. See, some people who saw the overexposed, crummy photo (left) of the dress on the right saw a simple blue and black dress. Others looked at the exact same photo and observed a just-as-fashionable white and gold dress. How could this be?

Unbelievably, scientific communities never reached consensus as to how people saw two different dresses in the same photo. Neuroscientist Jay Neitz, right, offered a good theory, though.

Seattle Times / Ken Lambert
His jargon-heavy theory boiled down to this: we see the overexposed photo of a dress, and our brains eliminate what we perceive to be the color of light. Some brains see a white and gold dress lit with a blue light; others see a blue and black dress lit with gold light.

As Neitz put it, “Our visual system is supposed to throw away information about the illuminant and extract information about the actual reflectance.” So it depends what you saw as the color of the light. But what color was the dress really?

Blue and black according to Roman Originals, the dress’s retailer (who saw a huge spike in sales after the photo went viral!) But this wasn’t the only “vision experiment” that captured the internet. Check out the 7-second test, for instance…

2. Are you ready to take an exam? All you have to do is spot the letter hidden in this picture in under seven seconds and you win. It’s not as easy as you think. Go ahead and give it a shot…

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Did you find it? It’s the letter “C,” tucked between the bottom right corner and center of the puzzle! See, not all eye exams are as easy as the others. Just take a look at the Magic Eye Picture…

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3. Stare at the Magic Eye Picture below. Relax your vision, like you’re staring into an open book you’ve already stopped reading. Give it a few seconds. Do you see anything?

Most people who stare down that Magic Eye Picture see three-dimensional penguins in the lower third of the picture—that’s because there’s some cool visual science at play here.

Magic Eye photographs started with the 1959 work of Bela Julesz. He tested peoples’ abilities to see in 3D with what he called a random dot stereogram. Then, in 1991, engineer Tom Baccei, 3D artist Cheri Smith, and programmer Bob Salitsky went further…

Rebecca / Flickr

They created images that looked 3D by putting darkening points that were “further away” and lightening the “close” points. Then, they overlay the two-dimensional pattern over it—the snow, in the case of the above photo.

When we look at the repeating pattern, our brain interprets the hidden, depth image—though it takes a few moments to parse through the weeds. But not everyone is so lucky.

Some people might look at the Magic Eye photos and never see the 3-dimensional figures hidden within them—they might as well have their eyes closed! Some people see the proverbial black and gold dress. But how?

To see a three-dimensional image, your eyes have to work together. They’ve got to be teammates. Partners. When that partnership fails, though, so does your stereo vision. In other words?

Out of sync eyes mean it’s tough for your brain to merge and blend the separate images they’re picking up (your eyes do view the world from slightly different positions, after all). No 3D vision for you. How about one more test?

4. The below image, posted on Twitter by professor Akiyoshi Kitaoka, contains no red. Engineers scrubbed every trace of red from the pixels composing the photo—so why do so many people still see red strawberries?

Just as with the blue and black dress, viewers eyes process both the color of the object and the color of the light—and it often ignores the color of the light. Similarly, our brains know strawberries are redso they do some inferring.

“Your brain says, ‘the light source that I’m viewing these strawberries under has some blue component to it'” neuroscientist Bevil Conway, below, said. “‘So I’m going to subtract that automatically from every pixel.” The end result?

“When you take grey pixels and subtract out this blue bias, you end up with red,” he added. Undoubtedly, our eyes are unbelievable tools—even when we think our vision’s bad, they’re still working overtime!

Some people boast the vision of a hawk; others are happy Benjamin Franklin invented the bifocal. How did you fair in these tests of visionary prowess?

Share these vision tests with your friends below!