How the eye works​

One of the best ways of understanding vision problems is learning how the eye works. It's a complicated little organ, which works by detecting light which bounces off objects, and sending signals to your brain. 



Light rays enter the front of our eye through the clear cornea and lens. It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina.The cornea and lens bends light so that it can focus on the retina at the back of our eye. This gives us a clear, precise image. The cornea focuses the light towards our retina. The lens fine tunes the focussing of this light. Our tears form a protective layer at the front of the eye and also help to direct the light coming into our eye. The iris, the coloured circle at the front of our eye, changes the size of the pupil which allows different amounts of light into our eye. The pupil is the dark hole in the middle of the iris. The pupil gets smaller in bright conditions to let less light in, and bigger in dark conditions to let more light in.



The middle of our eye is filled with a jelly-like substance called the vitreous. The vitreous is clear and allows light to pass directly from the front to the back of our eye.



The retina at the back of the eye is a light-sensitive layer which consists of rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye. Rod cells are concentrated around the edge of the retina. They help us to see things that aren't directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around by stopping us from bumping into things. They also enable us to see things in dim light and to see movement. Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading, watching TV, sewing and looking at people's faces. They are also responsible for most of our colour vision. Finally, the optic nerve is made up of thousands of nerve fibres. These fibres pass the electrical signals along to our brain where they are processed into the image we are looking at.



Seeing can be likened to the process of taking pictures on a film with a camera which you then get developed. The retina is like a camera film which stores an image of what we are looking at. The image directed onto the retina is then sent along to the brain where it is processed, like developing a camera film. Therefore we actually "see" in our brain with the light information sent to it from our eyes. This whole process happens very quickly so that everything we see is in focus.

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How to look after your eyes

Although it's true that some sight loss is inevitable for some people, 50% can be avoided. There are a few simple steps everyone can take to improve their eye health, and therefore decrease the chances of devloping problems with their peepers. 



• Go for regular eye tests. It's an obvious one, but it's a really important one, and many people don't get their eyes tested as often as they should (every two years, FYI). It is, however, the best way of catching conditions early, and this means they can be treated much more effectively. You might even be eligible for free tests, and if you use a screen regularly at work your employer might offer them free too - it's worth enquiring about.  
• Stop smoking. Smoking can double the risk of developing age-related macular degeneration, which is the UK's leading cause of sight loss. In fact, the link is as strong as the link between smoking and lung cancer. That, coupled with all the other million (just an estimation) reasons to stop should be enough for anybody.
• Eating a diet low in saturated fats but rich in green leafy vegetables such as spinach and broccoli may help protect against cataracts and AMD. Oranges, kiwis, nuts, seeds and oily fish may also help prevent and slow down some eye conditions. It is also important to maintain a healthy weight: obesity can increase the risk of developing diabetes, which in turn could lead to sight loss.
• Protecting your eyes from the sun. UVA and UVB rays in sunlight can harm your eyes and may increase the risk of cataracts and AMD. Wearing sunglasses, glasses or contact lenses with built in UV filter will protect your eyes. Only buy sunglasses that have a CE mark or carry British Standard BSEN 1836:1997
• Finally, be careful with your DIY and sport! DIY causes thousands of eye related injuries each year. Always wear safety goggles (European Standard BS EN 166) to protect your eyes from flying debris and fine particles. Sport (especially racquet-based sports) also causes lots of eye related injuries each year. Investing in a good pair of protective sports goggles will help prevent serious damage to your eyes.​

Conditions

As eyes are such fiddly little organs, there are understandably a lot of things which can go wrong with them. Fortunately many of these things are minor, or treatable. Here is the RNIB's guide to eye conditions.



Get to a hospital if any of these apply to you.

• You have a sudden serious change in your vision
• You lose all or part of your vision in one eye or both eyes
• You have an accident involving your eyes
• Or you suddenly start seeing flashing lights or floaters in your vision.