Eyes see the world upside down, and the brain flips the image for you.

The longer version

The lens projects a real image onto the retina, and because the lens is a converging element, that image is inverted both top to bottom and left to right. Light from above the eye lands on the lower part of the retina, and light from the right lands on the left.

The brain does not literally rotate a picture; instead, the visual system learns the mapping during development and simply treats activity in a given retinal location as coming from the corresponding direction in space. Experiments with inverting prisms have found that people adapt to flipped input, showing how flexible the mapping is. Orientation is therefore something the system constructs rather than something it receives.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.