Light in, picture built
How Do Your Eyes See?
Eyes turn light into nerve signals, and the brain assembles the picture from them.
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Step 1 of 5
The pupil controls how much light gets in.
It is a hole, not a part. Muscles in the iris widen it in dim light and shrink it in bright light, adjusting continuously.
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Step 2 of 5
A flexible lens focuses the image.
Muscles squeeze the lens fatter for close objects and let it flatten for distant ones. Sharp focus means the image lands exactly on the retina.
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Step 3 of 5
The retina turns light into signals.
Millions of light-sensitive cells fire when struck. Rods work in dim light but see no colour; cones need brighter light and give colour.
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Step 4 of 5
The image arrives upside down.
A lens flips whatever it focuses. Every image on your retina is inverted, and your brain simply works with it — you never notice.
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Step 5 of 5
Your brain fills in a great deal.
There is a blind spot where the nerve leaves the eye, and only the very centre is sharp. The brain patches the gaps so convincingly you never see them.
Your eyes flick several times a second, and vision is suppressed during each flick — so you are briefly blind, constantly.
The short version
Eyes focus light onto light-sensitive cells, and the brain assembles a patched, corrected picture from their signals.
Try it yourself
Search for a blind spot test. One eye closed, a dot vanishes — and your brain fills the hole with background.
Topics
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