Sense organs and the eye

Coordination and response · Sense organs · note 1 of 4

Spec 14.2.1, 14.2.2, 14.2.3Download all Sense organs notes (PDF)Download all notes (PDF)6 pages

Sense organs and the eyeSpec 14.2.1, 14.2.2, 14.2.3

In short

The eye is a sense organ: a group of receptor cells responding to light. The cornea refracts light as it enters, the iris controls how much light enters the pupil, and the lens focuses light on to the retina. The retina contains light receptors, and the optic nerve carries impulses to the brain. The blind spot has no receptors.

Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals. The eye is a sense organ that responds to light.

Structures of the eye
Structure	Function
Cornea	Refracts (bends) light as it enters the eye
Iris	Controls how much light enters the pupil
Pupil	The hole in the centre of the iris through which light enters
Lens	Focuses light on to the retina
Retina	Contains light receptors, some sensitive to light of different colours
Optic nerve	Carries impulses to the brain
Blind spot	The place where the optic nerve leaves the eye. It has no receptors, so it is not sensitive to light

Horizontal section through the eye labelled cornea, iris, pupil, lens, retina, optic nerve and blind spot, with parallel light rays refracted by the cornea and lens and focused on the retina. — Structures of the eye. The **blind spot** is where the optic nerve leaves the eye.

Exam tip:

Give the job of each structure with the exact verb: the cornea refracts light, the lens focuses light, the iris controls how much light enters. The optic nerve carries impulses, not images, to the brain.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

How does the eye focus on near objects?

Supplement The eye focuses on near objects by accommodation. The ciliary muscles contract, so the tension in the suspensory ligaments decreases and they go slack. The lens becomes thicker and more curved, so it refracts light more and focuses the image on the retina. Remember: contracted muscle, slack ligaments, fat lens.

What does the cornea do?

The cornea refracts, or bends, light as it enters the eye. After the cornea, light passes through the pupil, and the lens focuses it on to the retina. The iris controls how much light enters. In exams use the exact verb: the cornea refracts light, while the lens focuses light.

Why does the pupil get smaller in bright light?

The pupil gets smaller in bright light to protect the retina from damage. This is the pupil reflex, an automatic response. Less light enters the eye when the pupil constricts. In the iris, the circular muscles contract and the radial muscles relax, which makes the pupil narrower. In dim light the reverse happens.

All 5 questions on Sense organs