The lens in your eye throws an upside down picture onto the retina, and your brain flips it.

What it means

Any simple lens inverts the image it forms, and the eye is no exception. What reaches the retina is upside down and reversed left to right. The correction happens entirely in the visual system, and it is learned rather than built in. People fitted with prism goggles that flip the world adapt within days, and then have to adapt all over again when the goggles come off.

The claim comes from National Eye Institute.

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