The Anatomical Structure
It's a simple sphere, about 2.5cm in diameter, yet its power is awesome. It discerns colors and shapes. In bright or dim light. From near or far. It helps you read books, and situations, and people. It is a vital link to the world around you. And it succeeds through a complex ballet of muscles and nerves.
The Inner Workings
Light reflected off an object passes through the cornea. Muscles around the eye contract or relax to adjust the shape of the lens, focusing the light rays. The rays then reach the retina, where over 100 million light-sensitive cells read them and transmit the image through the optic nerve to the brain.
Because the light rays cross while going through the cornea, the retina reads the image upside down—but the brain readjusts so you stay properly oriented.