They help us navigate the world, see what’s around us and experience the joy that smiles bring. Our eyes are often taken for granted, and often they don’t get a look-in when it comes to taking care of ourselves. But for such small objects, the eyes are amazing.
Light reflects off objects and travels to the eye where it passes through the cornea — the transparent outer covering of the eye. This bends rays of light so these can pass through the pupil — that’s the dark hole of the eye — and on through the lens whose function is to focus light on to the back of eye, the retina. Cloudy patches that occur in the lens are called cataracts. They’re more common with age and cause blurry vision.
The retina of each eye is home to around 125 million photoreceptors, or sensors, that convert light into electrical signals. This is achieved when chemicals within the photoreceptors change in response to light exposure, triggering an electrical signal. Two types of photoreceptors are present. Cones are concentrated at the centre of the retina, called the macula, and help us to see colours and fine detail, and so are responsible for sharp and clear vision. When the macula becomes damaged (age-related macular degeneration or AMD), loss of central vision occurs such that people’s faces, for example, look blurry and are sometimes unrecognisable, and reading and watching TV becomes problematic too. With AMD, peripheral vision is maintained so a person can see what’s to the side, just not what’s in front of them. The other type of photoreceptor, the rods, are located outside the macula and over the rest of the retina, and help us see in dim light and at night. They detect motion and supply us with our peripheral vision.
The electrical messages travel from the retina along the optic nerve to the brain. The optic nerve consists of more than a million nerve fibres, and is why we have a blind spot since the area of the retina where the optic nerve emerges from the back of the eye lacks any photoreceptors. In the visual cortex at the rear of the brain these nerve messages are interpreted — this is how we see.
The iris is the coloured part of the eye and regulates the size of pupil to control how much light passes through. In bright light the pupil is smaller, and in dim light — and, it is said, when we are attracted to someone — it is bigger. The white part of the eye is the sclera and has six small muscles attached to it that control eye movements, allowing us to see what’s going on and track movements. Fluid called aqueous humour fills the eye and keeps it inflated. This liquid is produced by the eye and drains from the eye in a continuous process. When fluid within the eye can’t drain properly but is still being produced, pressure within the eye increases, called glaucoma. This results in optic nerve damage and loss of peripheral vision unless treated.
Short-sightedness, called myopia, is caused by the eye being too long from front to back such that light doesn’t reach the retina, instead being focused in front of it. So while close-up vision is clear, distant vision is blurred. Genes play a large part in why someone becomes short-sighted. Close-up work such as frequent use of computers, and reading for long periods of time, also increase the risk.
Long-sightedness, also known as hyperopia or hypermetropia, occurs when the eyeball is too short, meaning that light is focused behind the retina with distant vision being clear but it’s difficult to see clearly close-up. If the lens is not thick enough, or the cornea is not curved enough, it’s the same result. Once again, genes play a part, but so does the ageing process, so after the age of 40 many people develop age-related long-sightedness, or presbyopia. There are rare instances when an underlying medical condition is responsible for causing long-sightedness, such as may occur with diabetes.
Astigmatism affects vision, causing it to be distorted or blurred. It happens when the lens or cornea is irregular and not perfectly curved. This means light isn’t focused properly and what we see is blurred.
Making vision clearer in these circumstances is relatively straightforward with corrective lenses in the form of glasses or contact lenses, or laser eye surgery.
There’s much more to an eye test nowadays than just checking whether a person can read letters of ever-decreasing sizes — and wearing eye contraptions that are more at home on a Mad Max movie set. Eye tests also include examination of the outside and inside of the eye, assessment of eye movements and often measurement of pressure within the eye. Some optometrists also offer photographs of the retina, which can be helpful to identify changes when photographs and examination findings are compared.
How often someone should have an eye test very much depends on individual circumstances. Optometrists recommend at least every two years for people over 40, and for those of African-Caribbean and Asian descent as there is an increased risk of, for example, diabetes in these groups. More frequent checks may be recommended if changes in vision or in the eyes are noted that need monitoring.
Obviously an eye test can help establish how good a person’s vision is and whether corrective measures might make things clearer. But establishing whether glasses or contacts may be necessary is not the only reason to be tested. It’s said the eyes are the windows to the soul, but they are also a window to help detect major health conditions before these cause symptoms. For instance, high blood pressure (hypertension) and diabetes cause specific changes of the retina and detecting these conditions early on means steps can be taken sooner to treat them and lessen the risk of the problems they can cause such as heart disease and stroke.
To see us through a lifetime we have to take care of our eyes from the outside and from within. Eye injuries are all too common but easily avoided. Protective glasses, ideally with side protection too, worn while doing DIY, gardening, sport or other hobbies help protect the eyes from flying objects. UV light exposure can damage the eyes too, increasing the risk of cataracts, and of melanoma that can develop on the retina. So wearing sunglasses that carry a CE mark and the British Standard BS EN 1836:2005 is recommended, particularly on very sunny days and when near water or snow where UV can reflect. Talking of reflection, most sunglasses only protect from UV entering the eye from in front. Wrap-around sunglasses help block UV creeping into the eye from the side. Some glasses now also have a UV protective coating on the inside of the lens too, to protect against UV that enters behind the lens being reflected off it into the eyes.
Smoke gets in your eyes, so no prizes for guessing that not smoking is essential for eye health — smoking increases the risk of cataracts and AMD. A healthy balanced diet rich in fruit and vegetables is essential, in particular to help provide the nutrients that specifically help support the eyes, notably vitamins A, C and E, the mineral zinc and the carotenoid antioxidants lutein and zeaxanthin. Avoiding excessive amounts of alcohol is wise since overconsumption increases the risk of AMD and of suffering accidents that may involve the eyes. Keeping active is another helpful step as this helps avoid high blood pressure, diabetes and blood vessel damage that can in turn detrimentally affect vision.
As we spend more and more time fixed in front of computer screens so eyestrain, or eye fatigue, is becoming increasingly common in modern society. It can also occur as a consequence of intense use of the eyes when reading or driving. The eyes may feel tired or tight, may itch, burn or feel sore. Dryness is often a problem from using computer screens since we blink less so the eyes are refreshed less often. So blinking consciously when in front of a screen helps lubricate the eyes.
When performing intense close-up work such as using a computer screen practise the 20-20-20 rule — every 20 minutes look at an object 20 feet away for at least 20 seconds — to give your eyes a break, and to enjoy what’s going on around you. After all, as the world passes by, you want to see it.