The eye is a lens instrument
The eye is like a camera. It has a lens and a light-sensitive screen. Light-sensitive means it reacts to light. The screen is where the picture forms. Rays are thin beams of light.
- Light enters the eye from the left.
- The iris is a ring of muscle. It sets the size of the pupil, the opening for light.
- The eye lens bends the rays. Muscles hold it in place.
- The rays cross on the retina, the screen at the back. That is the image.
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Read each job. Tap the part that does it.
The rule
The eyeball is about 2.3 cm across. The cornea is a clear bulge at the front. The cornea does most of the bending. The lens then makes a small final change to the focus. To focus is to bring rays to one point.
Light enters through the cornea. The lens forms a real, upside-down image on the retina. The optic nerve carries the signal to the brain.
A real image is one that forms where rays meet.
| Part | Job |
|---|---|
| Iris | A ring of muscle that sets the size of the pupil |
| Pupil | The opening that lets light in |
| Ciliary muscles | Change the shape of the lens |
| Retina | The light-sensitive screen where the image forms |
| Optic nerve | Carries signals from the retina to the brain |
Watch out!
The image on the retina is upside down. Nothing is wrong. The brain reads the signals, so you see things as they are.