Eye implant could end the daily burden of diabetic blood tests

By Pat Hagan
The Daily Mail UK
14th July 2008

A tiny sensor implanted in the eye could banish the agony of daily blood tests for millions of people with diabetes. The sensor – smaller than a grain of rice – contains a special chemical that gives off a fluorescent light when it comes into contact with glucose. If blood glucose levels are high, the fluorescent light shines more powerfully.
This type of light, called near infra-red, cannot be seen by the human eye but can be easily picked up by a handheld device that converts the measurements into glucose readings. Diabetics would simply have to hold the device up to their eye for a few seconds to get a glucose reading.

Diabetes affects at least two million people in Britain, but experts suspect another one million people have the disease without realising it.

The condition develops when the pancreas either stops producing insulin altogether or its output drops sharply. Insulin is needed to help muscle cells absorb glucose from food and use it as fuel for energy.

Without the right levels of insulin, glucose levels can build up – a condition called hyperglycaemia. This can cause long-term irreversible damage to the kidneys, eyes, nerves, heart and major arteries.

Diabetics can also suffer episodes of hypoglycaemia when blood sugar levels drop too low. This can occur if there is too much insulin compared to the amount of glucose circulating in the blood. While type two diabetes, which tends to affect people from middle-age onwards, can often be controlled through diet, those with type one diabetes often end up needing daily insulin jabs for the rest of their lives. Insulin-dependent diabetics have to take blood samples up to four times a day to make sure their glucose levels are stable. Although most get used to this routine, many complain that the constant need for finger-prick tests is a major burden.

In recent years, attention has turned to whether glucose levels can be accurately measured through something called interstitial fluid – a liquid that bathes and surrounds most of the body’s cells. The advantage of using interstitial fluid is it can be found in accessible parts of the body, such as the skin and the eyes. A device called GlucoWatch, which measures sugar levels in fluid in the skin, was launched in the UK a few years ago, but it was hampered by batteries that took three hours to charge and patients’ complaints of skin irritation.

Now scientists hope the eye sensor, which is being pioneered by a German company called EyeSense, will be more successful. 

The sensor is made from a water-based gel and contains lectin, a protein which binds to sugar, and another chemical called fluorophore. A doctor applies a few anaesthetic drops to the corner of the eye and uses a needle to implant the sensor inside the eye just below the surface. The procedure takes just three minutes. As glucose levels in the eye increase, they seep into the implant and ‘stick’ to the lectin inside. This displaces the fluorophore that is also inside. When the molecules in this chemical are displaced, they give off a fluorescent light. Every few hours, the patient holds up a matchbox-sized gadget – called a fluorophotometer – which instantly converts the light reading into blood glucose levels.
Each implant lasts about a year, after which it can be replaced with a new one. Five volunteers have so far had the sensor implanted, and test results show the light readings accurately reflect blood glucose levels. In a statement, EyeSense said: ‘The biggest advantage is the patient can measure glucose levels as often as he or she wants simply by placing the small photometer in front of the eye. It takes no longer than 20 seconds.’
Jemma Edwards, from Diabetes UK, said the eye implant could be an option for some people with diabetes if further studies prove it is effective and safe. But she warned: ‘This technology is at a very early stage and has been tested on only five people. ‘It is also a very invasive way of monitoring blood glucose levels. Some people may be uncomfortable about having a device in their eye.’

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