Glow-in-the-dark contact lenses can fight blindness

Scientists have developed glow-in-the-dark contact lenses that can painlessly fight blindness caused by diabetes. Hundreds of millions of people suffer from diabetes worldwide, putting them at risk for a creeping blindness, or diabetic retinopathy, that comes with the disease in its more advanced stages. Existing treatments, though effective, are painful and invasive, involving lasers and injections into the eyeball.

Researchers from California Institute of Technology (Caltech) in the US developed a potential treatment that could be a lot less scary and invasive, in the form of a glow-in-the-dark contact lens. The loss of vision that accompanies diabetes is the result of the damage the disease causes to tiny blood vessels throughout the body, including those in the eye.

That damage results in reduced blood flow to the nerve cells in the retina and their eventual death. As the disease progresses, the body attempts to counteract the effects of the damaged blood vessels by growing new ones within the retina. In diabetes patients, however, these vessels tend to be badly developed and bleed into the clear fluid inside the eye, obscuring vision and compounding eyesight problems.

As the blood vessels bleed, they cause additional damage to the retina that the body repairs with scar tissue rather than new light-sensing cells. Over time, a diabetic patient's vision becomes blurry and patchy before fading away completely. However, damage to the retina begins with an insufficient supply of oxygen, it should be possible to stave off further eyesight loss by reducing the retina's oxygen demands.

Until now, that has been achieved by using a laser to burn away the cells in the peripheral parts of the retina, so the oxygen those cells would have required can be used by the more important vision cells in the centre of the retina. Another treatment requires injecting medication that reduces the growth of new blood vessels directly into the eyeball.

The lenses reduce the metabolic demands of the retina, but in a different fashion. Key to their success are the eye's rod cells, which provide vision in low-light conditions. "Your rod cells, as it turns out, consume about twice as much oxygen in the dark as they do in the light," said Colin Cook, a graduate student at Caltech.

For that reason, the contact lenses are designed to reduce the retina's night-time oxygen demand by giving the rod cells the faintest amount of light to look at while the wearer sleeps. 

"If we turn metabolism in the retina down, we should be able to prevent some of the damage that occurs," he said. To provide light to the retina throughout the night, the lenses borrow technology from wristwatches that have glowing markers on their faces. The illumination is provided by tiny vials filled with tritium, a radioactive form of hydrogen gas that emits electrons as it decays.
In the dark, the pupil expands, and the faint glow from the vials can illuminate the retina.