How Does the Eye Work? Structure and Accommodation

The eye works by focusing light onto the retina, which detects light and converts it into electrical impulses. These impulses travel along the optic nerve to the brain. To keep objects at different distances in focus, the eye changes the shape of its lens. This is called accommodation.

This explanation assumes AQA GCSE Biology separate science and applies to both Foundation and Higher tiers.

What do the parts of the eye do?

Light first passes through the cornea, the clear front surface of the eye. The cornea refracts, or bends, light. Light then passes through the pupil, an opening whose size is controlled by the iris. In dim light, the pupil widens to let more light in.

The lens bends light further so that it focuses on the retina at the back of the eye. The retina contains light-sensitive receptor cells. The optic nerve carries their electrical impulses to the brain. The tough outer layer, called the sclera, protects the eye.

How does accommodation work?

The ciliary muscles and suspensory ligaments control the lens’s shape:

• Looking at a near object: the ciliary muscles contract, the suspensory ligaments loosen and the lens becomes thicker. It refracts light more strongly.
• Looking at a distant object: the ciliary muscles relax, the suspensory ligaments are pulled tight and the lens becomes thinner. It refracts light less strongly.

Worked example

Suppose you look up from a nearby book to a distant tree. Your ciliary muscles relax, so the suspensory ligaments tighten and pull the lens thinner. The thinner lens refracts light less strongly, allowing the tree’s image to focus on the retina.

Common exam mistake

Do not say the lens becomes thicker for distant objects. Always link distance to the ciliary muscles, suspensory ligaments and lens shape. Also remember that accommodation changes lens shape; it does not change the shape of the retina.