Romantics may say the eyes provide a window into the soul but medical experts claim they provide a portal into our inner health, enabling us to spot the early signs of health conditions from minor to life threatening - in the blink of an eye.
Ophthalmologists can detect and diagnose a range of medical conditions just by looking at the retina - the light sensitive tissue at the back of the eye.
These conditions aren't always restricted to eye diseases like cataracts and glaucoma, but systematic illnesses like diabetes, cardiovascular disease and liver disease, too.
Crucially, these early signs can be picked up before the symptoms appear, which is why it's important to have regular eye tests.
"The most important thing you can do to protect your eyes - and your general health - is to have regular eye tests. This is because most eye diseases can only be seen with specialist equipment that can look at the back of the eye," advises Larry Benjamin from The Royal College of Ophthalmologists.
Apart from maintaining good eye health with regular visits to the optician, there are diet changes you can make that will help improve your eyesight and general eye health:
Eat leafy greens, kale and spinach
Studies show that eating foods rich in carotenoids reduce the risk of age-related eyesight degeneration. Foods rich in the antioxidant include leafy green vegetables like spinach, collard greens and kale.
Add peas and pulses to your diet
Foods high in lutein and zeaxanthin reduce the risk of cataracts. Foods high in these compounds include broccoli, corn, green peas, turnips and zucchini.
Get a blueberry boost
Blueberries have long been linked to the reduction in eye fatigue.
Eat more fruit
Apricots in particular are a rich source of beta-carotene and lycopene - both great antioxidants that promote good eye vision.
Now, take a look to see what your eye could be trying to tell you about your inner health…
The pupils (the black circle in the centre of the eye) in normal people are usually symmetrical, the same size and react in the same way when exposed to sunlight. If one pupil is bigger or smaller than the other, there could be an underlying medical problem. Experts claim that differences in pupil size could indicate that the person is at a higher risk of having a stroke, brain or optic nerve tumour, or brain aneurysm. If you spot any changes to your pupils, raise this with your GP, optometrist or ophthalmologist.
If your eyes are always dry and ultra sensitive to light, it could signal an immune system disorder, Sjogren, which impairs the glands in the eyes and mouth. The condition affects women over 40 with autoimmune disorders, such as rheumatoid arthritis or lupus. Seek advice from your GP if this sounds like you, as artificial lubricant can be prescribed and you'll be advised to drink plenty of water. "Dry eyes are more common in women over 50 due to hormonal changes," adds Larry Benjamin from The Royal College of Ophthalmologists.
If your eye is covered in a 'cloud' and your vision is impaired because of it, you may have a cataract. This causes a clouding of the lens inside the eye and can be corrected with surgery. This condition mainly occurs in older people but in younger people, it is commonly caused as a side effect of diabetes, tumours and some medication.
Although there are many things that can cause itchiness around the eyes, the most common reason could be pinpointed to an allergic reaction. The eye, and the area around it, is delicate and sensitive and more vulnerable to infections and allergies. Triggers could be anything from airborne pollens, dust or animal fur. If you suffer from red itchy eyes, try antihistamines to ease the redness, or visit your GP to organise an allergy test. If your eye and eyelids become puffy and sore, this could be a sign that you're sleep deprived. "Fluid moves around your head when you sleep and normally disperses when you wake from a good night's sleep. "However, lack of sleep causes this fluid to retain around the eye area for longer," explains Larry Benjamin from The Royal College of Ophthalmologists.
If your eye has a light grey ring around the cornea (the coloured circle in your eye), you may have a condition called arcus senilis, which is often linked to high cholesterol levels and triglycerides - fatty acids found in the blood. These are linked to higher risk of heart disease and strokes, so if you spot a grey ring circling your eye, visit your GP to discuss changing your diet.
Although it's natural for eyebrows to become thinner as we age, if you notice your brows literally 'disappearing' from the outer third of the eyebrow, this could signal a thyroid dysfunction. Loss of eyebrow hair from the outer edges of your face is a common sign of hyperthyroidism (overactive thyroid) or hypothyroidism (under active thyroid). Thyroids help regulate the metabolism and thyroid hormones are vital for hair production. If in doubt, book an appointment with your GP.
"Watery eyes can indicate infection," explains Larry Benjamin from The Royal College of Ophthalmologists. "If the eye is watery, you've most likely got an infection caused by a virus. If it's sticky, you might have a bacterial infection." If your vision becomes blurry, this could also be the result of Computer Vision Syndrome (CVS), caused by eyestrain from lack of contrast on a computer screen. This makes the eyes work harder focusing on the pixels on the screen. If in doubt, speak to your employer about booking an eye test, which is free if you use visual display units (VDU) for long periods of time.
Yellow lumps, also known, as xanthelasma palpebral, which appear on your eyelids could be a warning signal that your cholesterol levels are sky high. These are fatty deposits, which clump together and live in the eyelid. These are very often mistaken for a stye. Although these are quite common, it's best to get them checked by your optician or GP, as it can sometimes be an early sign of coronary artery disease. If you spot any coloured spots on your eyelids, in particular brown spots, visit your GP immediately as it could be an early sign of skin cancer. These usually appear on the lower part of the eyelid and will look a brownish colour with tiny blood vessels.
If your eyes are always blood-shot with broken blood vessels making them look blotchy and sore, this could be a sign that you have high blood pressure. Your optician will be able to confirm this by looking at your retina (the inner part of the eye). High blood pressure causes the blood vessel in the retina to 'kink and twist', causing them to break and look red. This could increase your risk of a stroke, so raise it with your GP as soon as possible.
If the whites of your eyes have a yellow tint rather than pearly white, you may have jaundice, which is linked to various liver and gall bladder problems. A simple blood test will confirm this, so if you're in doubt, book an appointment with your GP.