The Eye

For us to see objects, light reflects off them and enters our eyes.

Illustration showing the journey of visible light from the Sun, passing through space, depicted with a rocket and planets against a dark blue backdrop. The wavy light spectrum travels through raindrops in a cloudy atmosphere before reaching a stylised human eye that is nestled on a green leaf. The term "VISIBLE LIGHT" is labelled near the eye, emphasising the type of light spectrum shown. The overall imagery blends concepts of space, nature, and human perception on a panoramic horizontal layout.

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

Structure of the eye

The diagram below details the structure of the eye.

A detailed cross-sectional illustration of a human eye. From the exterior moving inwards: the sclera is a protective outer layer, with the clear cornea in front, covering the iris and pupil. Behind the pupil is the lens, held in place by suspensory ligaments and the ciliary body. The interior of the eye is filled with a reddish hue representing the choroid layer which is adjacent to the retina, containing vital structures such as the fovea centralis, optic disc (blind spot), and an intricate network of blood vessels. Finally, at the back, the optic nerve extends out, responsible for transmitting visual information to the brain.

Ciliary body – Contains the ciliary muscle, which relaxes and contracts 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’re in a dim environment, your iris will enlarge the pupil to take in as much light as possible. However, if you’re in a bright environment, the iris will constrict the pupil to prevent too much light from entering the eye, which could be damaging.

Illustration depicting the eye's response to different lighting conditions. Starting with an eye in normal light, showing a medium-sized pupil and labelled iris. Above, influenced by the representation of the sun, the eye adjusts to bright light by constricting the pupil. Below, influenced by a dimly lit candle, the eye responds to dim light by dilating the pupil.

Pupil – The pupil is the hole located 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.

Illustration showing an eye with a healthy lens, effectively focusing light onto the retina. An apple in the foreground represents the object of vision, with a beam of light passing through the eye's lens and converging sharply onto the retina, highlighting clear vision.

The lens can adjust its thickness to focus light correctly on the retina. If this process is faulty, glasses can correct it.

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

Sclera – This is the tough outer wall of the eyeball, serving to protect the eye.

Retina – This is a thin layer of tissue at the back of the eye containing cells that 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 then focuses the light onto the retina

Illustration featuring a detailed close-up of a human eye labelled 'Normal vision'. Below, there's a representation of an eyeball, demonstrating how light rays converge directly onto the retina, signifying clear and normal vision.

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

  • The degree to which the light bends depends on the shape of the lens

2. The refracted light rays focus onto the retina. In the diagram above, you’ll see the retina serving as the focal point, which is the point where converging light rays meet.

  • The lens of the eye is convex, meaning it curves outward

3. This information is then relayed to the brain via the optic nerve.

  • Although the image formed on the retina is upside-down due to the bending of light in the eye, the brain flips the image the correct way.