You step from bright sunshine into a dim cinema and notice the black centres of your eyes look bigger. Your iris changes the size of your pupils to control how much light enters.
Quick quiz
Which part controls how much light enters your eye?
- A. The iris
- B. The retina
- C. The optic nerve
Correct answer: A, the iris. It changes the size of the pupil, which is the opening where light enters your eye.
How your eye handles light
The pupil is the dark opening in the centre of the eye. The coloured ring around it is the iris. In a dim place, the iris makes the pupil larger so more light can enter. In bright light, it makes the pupil smaller.
The iris works a little like a camera shutter by adjusting the opening for light. Unlike a camera, your eye then changes light into signals for your brain.
The cornea and lens help focus light onto the retina at the back of the eye. The retina sends signals to the brain through the optic nerve. Learn more from the National Eye Institute’s How the Eyes Work guide.
Remember
The pupil is the opening; the iris is the coloured part that adjusts it.
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This article is for general education and does not replace personalised advice from a qualified healthcare professional.