Light therapy tackles eye injuries

    19:00 12 July 02



    People blinded by light could be treated with more light. Researchers
    have found that shining near-infrared radiation on damaged retinal
    cells can keep them alive and prevent permanent blindness.

                                                     (Photo: Corbis Sygma)
                                                     (Photo: Corbis Sygma)

    The US Defense Advance Research Projects Agency is funding research
    into the method and hopes to use it to treat people whose eyes are
    damaged by lasers. A number of US military personnel, including a
    helicopter pilot over Bosnia in 1998, have suffered laser eye
    injuries.

    If the infrared technique works in people, it could be used to treat a
    wide range of eye injuries and diseases. And it does not stop there.

    Other studies have shown that infrared light can help heal all sorts
    of injuries and sores, and it is already being used to treat severe
    mouth ulcers in children undergoing chemotherapy.

    Cell powerhouses

    In the late 1990s, lab studies on cells showed that near-infrared
    wavelengths can boost the activity of mitochondria, the crucial
    powerhouses in cells. That caught the attention of NASA, which hoped
    it could use the technique to treat astronauts in space, where
    injuries heal more slowly than on Earth, possibly because mitochondria
    do not function properly.

    The treatment requires high-intensity light, but instead of lasers,
    NASA has developed powerful light-emitting diodes for the job. Lasers
    tend to damage cells, whereas LEDs can deliver light in a way that is
    less harmful to tissue (New Scientist magazine, 25 September 1999, p
    20). Now Harry Whelan, a neurologist at the Medical College of
    Wisconsin in Milwaukee, and his colleagues have put the LEDs to the
    test on eye injuries.

    In a study that will appear in Proceedings of the National Academy of
    Sciences, Whelan blinded rats by giving them high doses of methanol,
    or wood alcohol. This is converted by the body into formic acid, a
    toxic chemical that inhibits the activity of mitochondria. Within
    hours, the rats' energy-hungry retinal cells and optic nerves began to
    die, and the animals went completely blind within one to two days.

    But if the rats were treated with LED light with a wavelength of 670
    nanometres for 105 seconds at 5, 25 and 50 hours after being dosed
    with methanol, they recovered 95 per cent of their sight. Remarkably,
    the retinas of these rats looked indistinguishable from those of
    normal rats. "There was some tissue regeneration, and neurons, axons
    and dendrites may also be reconnecting," says Whelan.

    Painful sores

    The results have raised the hope that the LED technique could be used
    to treat people for a range of eye diseases known to be caused by
    mitochondrial problems. Whelan also thinks it will help treat laser
    injuries to the retina, apart from areas where cells have been
    completely destroyed.

    Whelan has already tested the LEDs on 30 children suffering from
    mucositis, a painful side effect of cancer chemotherapy. The children
    had painful sores in their mouths and throats and were unable to eat
    or drink, he says.

    The LED treatment eliminated the mucositis and is now being used to
    prevent it. "It's a night and day difference in the children's floor,"
    he says. The results appeared in the Journal of Clinical Laser
    Medicine and Surgery in December last year. The Food and Drug
    Administration has now approved further trials in hospitals, which
    will use LEDs donated by NASA.

    What is not yet clear is exactly how the light stimulates healing. But
    Britton Chance of the University of Pennsylvania has shown that about
    50 per cent of the near-infrared light is absorbed by mitochondrial
    proteins called chromophores. Whelan and his colleagues think the
    light boosts the activity of a chromophore called cytochrome c
    oxidase, a key component of the energy-generating machinery.


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