S4.5.3 For the adult
The eye
How does your eye let in the right amount of light, and how does it see near things and far things clearly?
What this chapter teaches
Light enters through the cornea and pupil, is bent by the cornea and the lens, and falls on the retina. In bright light the circular muscles of the iris make the pupil smaller. In dim light the radial muscles make it wider. The ciliary muscle and the suspensory ligaments change the shape of the lens for near and far objects.
Three questions to ask
There is no one right wording. Listen for the idea.
- What does each part of the eye do, from the cornea to the optic nerve?
- What happens to your pupils when you come out of a dark room into the light, and why?
- How does the lens change when you look from a near object to a far one?
After the chapter, the learner can
- Label the eye and give the job of each part
- Explain how the pupil changes in bright and dim light
- Explain how the lens focuses on near and far objects
What they copy into their notebook
Light goes in through the cornea and pupil, and the lens focuses it on the retina. Bright light: pupil small. Dim light: pupil wide. Near: ciliary muscle contracts, lens fatter. Far: muscle relaxes, lens thinner.