Sight is one of our five main senses and an incredibly valuable one—yet it’s easy to take it for granted. Whether due to ageing or health problems, our vision can deteriorate over time. Understanding how the human eye works can help us better appreciate and protect this vital sense.
Structure of the Eye
At the front of the eye is the cornea, a clear, dome-shaped layer that helps to focus incoming light. Behind the cornea sits the iris — the coloured part of the eye — which controls the amount of 
light entering through the pupil, the black circular opening in its centre.
Between the cornea and iris is a fluid-filled space containing the aqueous humour, which helps to nourish the eye and maintain pressure.
Just behind the iris is the lens, held in place by ciliary muscles. These muscles adjust the shape of the lens to focus light:
- When the muscles relax, the lens flattens to focus on nearby objects.
- When the muscles contract, the lens thickens to focus on more distant objects.
After passing through the lens, light travels through a clear, jelly-like substance called the vitreous humour, which fills the main chamber of the eyeball and gives it shape.
Finally, light reaches the retina at the back of the eye. The retina contains millions of specialised cells:
- Rods help detect light and dark, making them crucial for low-light (night) vision.
- Cones detect fine detail and colour, functioning best in bright light.
These cells convert light into electrical signals that travel via the optic nerve to the brain, where they are instantly interpreted as images.
Common Eye Problems
Given how many parts are involved in vision, it’s no surprise that things can occasionally go wrong. If any component is damaged or malfunctions, it can affect how we see.
Some common vision problems are:
- Age-related degeneration: Cells in the retina gradually deteriorate and are not replaced, affecting central or night vision.
- Floaters: Clumps or strands in the vitreous humour that cast shadows on the retina, appearing as small dark spots in your field of vision.
- Focusing issues: Problems with the ciliary muscles can interfere with the lens’ ability to focus light correctly, leading to blurry vision.
Regular eye tests with an optometrist can catch early signs of issues and help manage or even prevent more serious problems.
Human Eyes vs Animal Eyes
Not all animals see the world as we do. Some have better vision in low light, while others excel at detecting movement or viewing a wider field.
Take cats, for example:
- Cats have excellent peripheral and night vision, allowing them to detect small movements in dim light.
- However, they don’t see colour as vividly and are not as good at spotting objects over long distances.
- These traits evolved to support their role as nocturnal hunters.
Another fascinating example is the Tarsier, a tiny primate with enormous eyes:
- Each eye is bigger than its brain!
- These oversized eyes allow it to gather as much light as possible in darkness, helping it hunt at night.
Learn more about the Tarsier at Britannica.com.
Then there are creatures like spiders, which can have multiple pairs of eyes. Each pair serves a slightly different purpose:
- Some detect light and shadows.
- Others are better at detecting movement or judging distance.
This multi-eye setup helps them survive in environments where danger and prey could appear from any direction.
Conclusion
The human eye is an amazing and complex organ. From filtering and focusing light to sending detailed images to the brain, it does an incredible job every second of the day. Understanding how it works—and how it compares to the vision of other creatures—can help us appreciate just how precious our eyesight is.
Protecting our eyes through regular check-ups, proper eye care, and eye protection where needed is one of the best ways we can preserve this vital sense for years to come.