Waves of light bounce off whatever you’re looking at and enter your eye through the cornea. Once light passes through the cornea, it has to go through the pupil – that’s the little black dot at the centre.
The pupil is a smart fellow, helping you see more when it gets dark. In low light, the pupil dilates. This allows more light to pass through the eye, giving you a better idea of what’s going on.
The muscles that control the pupil are found in the iris, that’s the coloured part of the eye surrounding the pupil. You probably think of yourself as having blue or green or brown eyes, but in fact you’re far more unique than that. That’s because each iris has a pattern of ridges and folds that are specific to you.
This bit is important, so focus. The flexible lens that sits behind the iris changes its shape to allow you to see clearly. It flattens so you can see things at a distance and, when you look at something up close, it becomes thicker. This focuses light waves on their target – the retina at the back of your eye.
The highway to the retina is made up of vitreous humour, a kind of gel that consists of 99% water and fills your eye, maintaining its shape, like air in a beach ball. Although of course your eye is only about an inch in diameter, making it a little bit smaller than a squash ball.
The retina consists of millions of light sensitive rods and cones. They convert light waves into electrical signals that pass through the optic nerve. Your eye has three different types of cones, allowing you to see different colours. Rods are more sensitive than cones, but they can’t detect colour. That’s why colours are hard to see when the light is low.
The optic nerve is like cable TV for your head. It transmits electrical signals created by the millions of rods and cones on the surface of your retina. Your brain then interprets these signals as the object you see in front of you.
Ta-dah! Now you see it.