Ever wondered how your eyes let you see the world around you? This page will take you on a simple journey through the parts of the eye and show how they work together to help you focus, perceive colour, and take in everything you see every day. 

The eye parts and what they do 

Cornea 

The clear, curved front layer that performs the initial focusing of light onto the lens. The cornea bends incoming light to help it pass through the pupil. 

Iris 

The coloured part of the eye that controls how much light enters through the pupil (the black circular opening in the centre of the iris) 

Lens 

Adjusts by changing shape to focus light onto the retina. 

Retina 

A thin layer at the back of the eye with cells that change light into signals for the brain. It contains photoreceptor cells called rods and cones: 

• Rods are responsible for vision in low-light conditions

• Cones detect colour and provide sharpness in bright light

Optic Nerve 

Carries these signals to the brain for interpretation 

All of these parts work together to focus on and process light, but how do we see things? 

How do we see things? 

1. Light passes through the cornea, pupil and lens. The cornea helps to bend the light for it to travel through the pupil. 

2. The iris adjusts the size of the pupil based on the light's intensity. In bright light, the pupil constricts and in dim light, it dilates. 

3. The lens adjusts to focus light precisely onto the retina. It does this by becoming thicker for nearby objects and thinner for distant ones. 

4. The retina captures the light and forms an inverted image of the object. 

5. Photoreceptor cells in the retina convert the light into electrical signals. These signals travel through the optic nerve to the brain. 

6. The optic nerve sends signals to the brain, which flips and interprets the image, allowing us to perceive it correctly. 

How do we see in colour? 

Our eyes can perceive depth and colour. 

Colour vision 

As mentioned above, cones detect colour and provide sharpness in bright light. Cones in the retina detect red, green and blue light. Their combination allows us to perceive a wide spectrum of colours. 

Depth perception 

Depth perception is the slight differences in the images captured by each eye help the brain judge distances. It uses images from both eyes to understand how near or far objects are. 

What happens if the eye doesn’t focus correctly? 

Common vision problems can occur if the eye doesn’t focus correctly. Some of these are: 

• Myopia – myopia typically starts during childhood and is the medical word for short-sightedness. Myopia makes seeing objects at a distance appear out of focus, e.g. when watching the TV, the screen may seem blurry compared to when reading a book. 

• Hyperopia (long-sightedness): Difficulty focusing on nearby objects due to a shorter eyeball or a flatter cornea. 

• Astigmatism: Blurred vision caused by an irregularly shaped cornea or lens. This can occur with both myopia and hyperopia. 

• Presbyopia: Age-related reduction of near vision caused by decreased lens flexibility.

Glasses and contact lenses can help many of these issues

Getting your eyes tested regularly protecting eyes from UV rays and reducing strain from screens can help keep your eyes working at their best. You can find out more on how to keep your eyes healthy with our top tips here.