of the human eye
Your eyes are something that you probably don’t give much thought to – as long as they’re working properly. They may only be about the size of a ping-pong ball, but your eyes are among the most amazing parts of your body.
Every moment that you’re awake, your eyes are in constant motion – gathering vast amounts of visual information and helping you make sense of the world around you. They also help communicate your emotions to other people – not bad for two blobs of jelly that each weigh about 8g (about the same as two credit cards).
Let’s look at five eye facts that sum up just how amazing your eyes are:
Your eyes “cry” continuously
In a normal day, your eyes produce around 1.2ml of tears – enough to fill a 1-litre cool drink bottle in just over two years. Tears are your eyes’ way of self-cleaning – they flush out dust and bacteria, help your eyes move smoothly, and prevent them from drying out. Visible crying happens when you produce more tears than can discreetly drain away – typically when you’re upset, or your eyes are irritated.
Your eyes have natural ‘windscreen wipers’
Your eyelids are also pretty amazing – they block out light when it’s time to sleep and help move tears around your eyes, keeping them moist and clean. They also protect your eyes from foreign objects – you may have noticed how quickly they can close when something approaches your eyes. Without really noticing it, we blink a lot – on average, around 10 times per second. That can add up to half a billion blinks in the average lifetime. Incidentally, if someone doesn’t blink when you ask him or her a question, then blinks a lot after answering, it could mean that he or she is not telling the truth…
Your eyes have more cones than any highway
It’s the photo-sensitive (or light-detecting) cells in your eyes that help you see, and you have an awful lot of them – on average, about 130 million in each eye! Around 10 million of those cells are cones (named for their shape); they detect colour and help us appreciate and understand everything from flowers to fashion and traffic lights. The majority are rods – they make a real difference in low-light conditions or at night. These rods require Vitamin A to function effectively, so there might just be some truth in the story that eating carrots helps your night vision (carrots are a great source of Vitamin A).
You actually see upside down
Your eyes work by detecting light that’s reflected back from objects around you. The curvature of the front part of each eye actually bends the light waves that enter it, which means that upside-down images are projected on to your retina. Fortunately, your brain can make sense of these signals and turns the image the right way up. This works whichever way you turn – even if you’re standing on your head – give it a try if you don’t believe us!
Your eyes contain clues about your overall health
Doctors are increasingly using patients’ eyes as diagnostic tools – that’s because changes in the appearance of your eyes, or the way that they move, can provide early indications of quite serious health conditions. For example, pale spots on your retinas can be a sign of diabetes, while the retinal arteries can provide clues about hypertension. Proteins linked to dementia can be detected in the retina before other symptoms appear – this may act as an early warning for diseases like Alzheimer’s.