International Health News

Light therapy involving knee not effective

BOSTON, MASSACHUSETTS. In January 1998 researchers at Cornell University reported a major discovery that could be of significant benefit to patients with seasonal affective disorder (SAD). Exposing the eyes (retina) of such patients to bright light can reset the internal circadian clock and thereby reduce SAD symptoms. The Cornell researchers found that shining a bright light (13,000 lux) on the back of the knee was effective in resetting the circadian clock. They speculated that if light was directed at the back of the knees rather than into the eyes then light therapy could presumably be performed during the night or early morning without actually waking the patient.

Now researchers at the Harvard Medical School report that they have been unable to repeat the findings observed by the Cornell researchers. Their experiment included 22 patients who were exposed to either no light or to light specifically directed at the retina or at the knee. Shining light directly at the retina (13,000 lux for three hours) resulted in a significantly delayed melatonin phase and acutely suppressed melatonin when compared with controls. No such effect was observed when shining the light at the back of the knee. The Harvard researchers conclude that the idea that light signals are carried from the back of the knee to the human brain via the circulatory system "is not supported by our data."
Wright, Kenneth P. and Czeisler, Charles A. Absence of circadian phase resetting response to bright light behind the knees. Science, Vol. 297, July 26, 2002, p. 571

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