From Alzheimer's and diabetes to brain tumours and hypertension, the eyes offer a window into the body that is helping doctors spot a wide range of conditions.
What makes looking for disease in the eye particularly convenient is that it is non-invasive – there is no cutting of skin, bleeding, swallowing of cameras, or anything like that.
Unless something vile is suspected, your eye will just be peered into by an optometrist, ophthalmologist, or in some cases your GP. An ophthalmoscope (basically a sophisticated magnifying glass with a light) may be used, and you may be given some drops to dilate your pupils.
Literally like windows
The key to what makes the eyes such an excellent diagnostic tool is that not only can you see out of them, but also in. Doctors can look through the clear lens and cornea, all the way to the retina. And the area at the back of the eye is the one place in the body where blood vessels can be examined without first having to cut through skin. And if you thought you could tell a lot by looking into an eye, wait till you see a blood vessel.
It may help to imagine a building with only two windows. Through these windows you may see a few pipes (some of which may be leaking), or you may see some trash lying around. And by putting all this information together, you may get a general (or quite specific) idea of how well the building is maintained.
Similarly, the blood vessels at the back of the eye can offer invaluable clues to the body's health and help doctors spot a number of chronic systemic diseases.
Reading the vessels
Peering into your eyes, optometrists would probably see a branching network of veins and arteries – the veins being darker and thicker, while the arteries are thinner with a brighter red colour.
Certain changes in the appearance of this thin webbing of arteries suggest that the patient may have arteriosclerosis (hardening of the arteries) or hypertension (high blood pressure.)
There are also suggestions that small plaque deposits in the eye could indicate a cholesterol build-up elsewhere in the body.
Similarly, small haemorrhage (bleeding) spots may indicate that a patient has diabetes – such vascular damage is a typical result of diabetes. There are reports of patients having no idea that they were diabetic, until diagnosed in this way.
Certain signs in the eye can also be indicative of brain tumours. Thus, doctors may be looking for a swelling of the optic disk (known as papilloedema,) which in turn may be the result of a tumour pressing on the optic nerve.
Apart from these diseases and conditions, sickle cell anaemia, leukaemia, and brain aneurisms also leave their marks on the eye.
On the cutting edge
US researchers are experimenting with cutting edge technologies that help them detect beta amyloid protein in the lens of the eye, using short light pulses. Beta amyloid protein is a telltale sign of Alzheimer's. The hope is that these tests may help with the early diagnosis of this devastating neurological disease.
Early research also suggests that a deadly form of malaria known as cerebral malaria may be diagnosed through the eye. Researchers say that cerebral malaria leaves opaque spots on the retina and whitens certain arteries at the back of the eye.
The way in which the eye tracks movement may be used to diagnose a range of psychological conditions. Research conducted at the University of Illinois is trying to spot patterns of eye movement that may help diagnose conditions like schizophrenia.
Connected to the body
The fact that so many diseases leave traces in the eyes makes it clear that the eyes are integrally connected to the rest of the body.
For this reason researchers are increasingly linking the health of the eye to that of the rest of the body. There are strong suggestions that poor nutrition, lack of exercise, and smoking can have a detrimental effect on the eyes.
(Sources: www.reviewjournal.com; http://meded.ucsd.edu/clinicalmed/eyes.htm; www.healthdaynews.com; US National Cancer Institute)
South African Optometric Association
Tel: 011 805 4517
South African National Council for the Blind
Tel: 012 452 3811
Retina South Africa
Tel: 011 622 4904