Double Vision

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By Jennifer Trueland (HWU Magazine)

A technique developed to allow armies to detect camouflaged vehicles could help doctors diagnose the most common diseases of the eye, potentially saving the sight of millions of people.

"The key is the chemical make-up of substances at specific wavelengths which translates into different colours in the image. These can then be analysed." Interview with Dr. Andrew Harvey

Researchers in Heriot-Watt's School of Engineering & Physical Sciences are working on a new way of taking pictures of the retina to study blood vessels in the eye to look for signs of disease.

They believe the technique, using spectral imaging, can detect the presence of the most common eye diseases, glaucoma, diabetic retinopathy and age-related macular generation.

If diagnosed at an early stage, glaucoma and diabetic retinopathy can be treated successfully so that the patient's sight can be saved. But current methods of detecting eye diseases are unreliable and, in some cases, even dangerous.

The Heriot-Watt technique involves using a standard ophthalmoscope which has been modified with a liquid crystal tuneable filter, which allows images to be taken of the retina at specific wavelengths. These images can then be analysed to show the level of oxygen in the blood vessels in the eye, which gives important information about how healthy you are.

Healthy vessels take oxygen and other nutrients from the blood as it pumps through, while diseased vessels will be less efficient at doing so, leaving the blood more highly oxygenated. Where the metabolism is lower due to disease, less oxygen is used.

"There's no other way of measuring the oxygenation other than through its spectrum," says Dr. Andrew Harvey, a senior lecturer and supervisor of the project. "Other techniques look at the flow of blood so they can tell if there are blockages. But they can't show the biochemistry of the blood. What we're providing is chemical imaging of the retina and that's very exciting."

Dr. Harvey and his colleagues developed the tool as a way of finding a medical application for technology being developed for the Ministry of Defence. They have found that spectral imaging allows armies to differentiate between different types of vehicle or between a tank and foliage, for example. The key is the chemical make-up of substances at specific wavelengths which translates into different colours in the image. These can then be analysed.

"The technique allows us to combine pictures at different wavelengths to give a true picture of what's going on," explains Dr. Harvey. "The retina is unique because we are able to look into living tissue, unlike other parts of the body where the skin gets in the way. That means there's greatly reduced clutter, which is quite attractive."

The team has shown that the concept works and have carried out preliminary trials, both on healthy people and on patients with glaucoma and diabetic retinopathy. So far, it has proved successful in helping doctors to detect and monitor the conditions. The next stage will involve testing it more widely. The team has made sure some of the aspects of the technology are under patent and has already attracted interest from a company keen to develop it commercially.

Dr. Harvey believes it has the potential to be a cost-effective tool which would be a vast improvement on current methods. "Retinal eye examinations can be very unpleasant and some, such as the Fluorescein Angiogram for diabetic patients, which involves injections of dye, can be dangerous. Some people have bad reactions to it and it can even be fatal. So it's no surprise that sometimes people don't go along for their treatments. But this technique is safe, simple and non-invasive, so we think people would be happier to attend for regular screening."

He is hopeful that, if all goes well, the technique will be widely available in the next three to four years.

But it doesn't stop at eye disease. Because spectral imaging of the retina gives a clear picture of vascular function, it may also give clues to how the vascular system in the rest of the body is working. That means it might give early warning of other problems which could lead to strokes, for example, giving an opportunity to take preventative action.

"I suppose you could say that in this case the retina is the window to the vascular system," says Dr. Harvey. "I think this technique has enormous potential."

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Article kindly reproduced with permission from Heriot-Watt University Magazine, Issue 15.