THE ANATOMY OF YOUR EYE
Your eyes are complex, delicate and expressive ‘windows to your soul’. But how do they see?
Your eyes receive light and transmit detailed messages to your brain, which interprets them as images. Each part of your eye has a different specialised role in recording and transmitting these images.
The parts of the eye
Your eye is a small sphere consisting of an outer skin protecting clear gel within. The skin has three distinct layers, each with its own set of functions:
Outer layer: Sclera
The sclera is the tough, protective ‘white of your eye’. Most of the sclera is opaque, but at the front there is a transparent window. This window is your cornea, through which light travels into your eye. A thin, clear membrane called the conjunctiva helps to protect the front of your eye and the inside surfaces of your eyelids.
Middle layer: Choroid
Behind the sclera is the middle layer, the choroid. This is dark to prevent light reflecting within your eyes and contains mostly blood cells, which nourish your eyes.
When you look at someone’s eyes, usually you first notice their iris. The iris is at the front of the choroid and gives eyes their colour. Your pupil is the circular opening that looks like a black dot, at the centre of your iris. Muscles in your iris control the size of your pupil to let in more or less light.
Inner layer: Retina
Your retina’s job is to capture light information that the main nerve in your eye (your optic nerve) sends as nerve impulses to your brain. Your brain then translates these messages into images.
On your retina, two types of light-sensitive cells capture light rays. These are called rods and cones. Rods are sensitive to light and movement, and help you to see in dim light. Cones enable you to see detail and colour.
The lens of your eye is transparent and flexible. It focuses light onto your retina. For precise tasks, light is focused on the centre of your retina, in an area called the macula. Muscles around your lens control its shape, allowing you to see objects at different distances.
The rest of your eye
The cavity between your lens and cornea contains a liquid called aqueous humour. A jelly-like substance, called vitreous humour, fills the cavity behind your lens.
The aqueous and vitreous humours help to give your eyes their shape.
How your eyes work
When you see something, this is what happens:
- Light enters your eye through your cornea, which bends the light.
- Your pupil adjusts in size according to the brightness of the light, getting bigger in dim light and smaller in bright light.
- Light passes through your pupil and onto the lens of your eye.
- The lens of your eye changes shape to focus the light onto your retina, according to whether you are looking at a near or far object.
- Rod and cone cells in your retina absorb the light and send messages to your brain via your optic nerve.
- Your brain then interprets these messages into an image.
It’s amazing that your eyes have so many working parts and are so complex. But when you consider how difficult a task it is to provide you with vision, perhaps it's not so amazing!