Vision — How Eyes Work
SEEING starts with LIGHT entering your eye. Light passes through the CORNEA (clear front layer) and PUPIL (the dark hole in the middle — the iris adjusts its size). The LENS focuses light onto the RETINA at the back. The retina contains millions of light-sensitive cells (RODS for dim/black-white, CONES for color and detail). They convert light to electrical signals.
From eye to brain. The OPTIC NERVE carries those signals to your brain's VISUAL CORTEX. The brain processes the signals — recognizing edges, colors, motion, faces, written words. Most "seeing" actually happens in the BRAIN. Optical illusions trick the brain's processing. People with healthy eyes but a damaged visual cortex can't see, even though their eyes work fine.
When you walk from a bright room into a dark closet, your pupils:
Common vision conditions. NEARSIGHTED (myopia): can see close, can't see far — the eye is too long, focusing light in front of the retina. FARSIGHTED (hyperopia): the opposite. ASTIGMATISM: irregular cornea shape distorts vision. COLORBLIND: missing or weak color cones — most commonly red-green. Glasses, contacts, or surgery can correct most of these. Eye exams catch issues early.
Pupil Test
Look in a mirror in a bright room. Notice your pupil size. Now slowly cover both eyes with your hands for 30 seconds. Open quickly and look — for a moment, your pupils are LARGE before they shrink back. You just saw your iris adjust to changing light.
Vision is a marvel — millions of cells, instant focus, color, depth, motion. Take care of your eyes: regular check-ups, breaks from screens, sun protection. Most people don't fully appreciate vision until they lose some of it.
Want to keep learning?
Sign up for free to access the full curriculum — all subjects, all ages.
Start Learning Free