In the more advanced stages of diabetes, the patient has a real risk of going blind. While there are treatments to help keep this from happening, they're invasive and often painful. There may be new hope, though, in the form of glowing contact lenses.
When diabetics do lose their vision, it's the result of a condition known as diabetic retinopathy. This occurs when the disease damages tiny blood vessels in the eye, reducing blood flow to nerve cells in the retina, starving them of oxygen and causing them to die.
The body tries to compensate by growing new blood vessels in the retina, although the diabetes often causes these to be imperfectly formed, resulting in their bleeding and damaging the retina. That damage is repaired via the growth of scar tissue – not new nerve cells – so over time, the patient loses their sight.
Existing treatments for diabetic retinopathy center around reducing the retina's oxygen demands. One approach involves using a laser to burn away nerve cells in the peripheral part of the retina. By eliminating those cells, the oxygen that would have been used by them can instead now be used by nerve cells in the retina's more important central area.
Another approach involves giving the patient an injection in the eyeball, introducing medication that reduces the growth of new blood vessels.
Yet another approach that has been tried before involves using lighted eye masks to illuminate the retina while the patient sleeps. This causes the retina's rod cells, which provide vision in low-light conditions, to remain inactive. Ordinarily, when we make things dark by closing our eyes, the rod cells become very active, consuming about twice as much oxygen as they do in bright conditions. In fact, scientists have hypothesized that much of the damage caused by diabetic retinopathy occurs when the rod cells are consuming oxygen at night.
Unfortunately, however, patients who tried the masks didn't like them, as they saw flickers of light every time they moved their eyes, making sleep difficult … and that's where the glowing contact lenses come in.
Developed by a Caltech team led by graduate student Colin Cook, they incorporate tiny vials of tritium, the same radioactive (but apparently safe) form of hydrogen gas used in glow-in-dark wristwatch dial markers. As the tritium gradually decays, it emits electrons that are converted into light by a phosphorescent coating.
The vials are arranged on each lens in a ring, which falls outside of the wearer's vision when their pupil is constricted while exposed to light. When they shut their eyes and the pupil expands, however, the glow emitted by the vials is able to be detected by the rod cells, keeping them from firing up.
Unlike the lights in the sleep masks, the glowing vials in the lenses move with the user's eyes, so they don't see any annoying flickers of light. "There's neural adaptation that happens when you have a constant source of illumination on the eye," says Cook. "The brain subtracts that signal from the vision."
In early tests of the lenses, they were found to reduce rod cell activity by up to 90 percent when worn in the dark. The team now plans on conducting research to determine if that reduction in activity will result in the prevention of diabetic retinopathy. FDA approval and clinical trials could follow.
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