The Eye

In order for us to see objects, light reflects off the object and enters our eye.

Let’s look at the structure of the eye in more detail:

Structure of the eye

Ciliary body – Contains the ciliary muscle that relaxes and tightens to allow the lens to change shape for focusing.

Iris – The coloured part of the eye, which contains muscles that control the size of the pupil. The purpose of the iris is to regulate the amount of light that enters the eye.

For example, if you are in a dim environment, your iris will make the pupil large and dilated to take in as much light as possible. However, if you are in a bright environment, the iris will shrink the pupils to prevent too much light from entering the eye, as this can damage the eye.

Pupil – The pupil is a hole at the centre of the iris. Its function is to let in light and focus it on the retina.

Cornea – The cornea is the eye’s outer lens. It is transparent, so it transmits light and its purpose is to control and focus the entry of light into the eye.

Lens – The purpose of the lens is to focus light on the retina.

The thickness of the lens can be adjusted to correctly focus light on the retina. When this process doesn’t happen correctly, glasses can help this process.

Suspensory ligament – Helps to control the shape of the lens.

Sclera – The tough supporting wall of the eyeball and its purpose is to protect the eye.

Retina – A thin layer of tissue at the back of the eye that contains cells which are sensitive to light. This is where the image is formed and the retina sends this information to the brain through the optic nerve.

Optic nerve – Carries impulses from the retina to the brain.

The Process of Taking In Light

Light hits the lens, which focuses light onto the retina

1. When light hits the lens, it is refracted, which means it is bent slightly as it reaches the lens.

  • How much the light bends depends on the shape of the lens

2. The refracted light rays are focused onto the retina, which is the focal point in the diagram above.

  • The eye’s lens is convex, which means it bends out

3. The information is passed along the optic nerve to the brain.

  • Although the image formed is upside down, due to the bending of light in the eye, the brain eventually turns the image the right way