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Abstract
Bright light treatment has become an important method of treating depression and circadian rhythm sleep disorders. The efficacy of bright light treatment may be dependent upon the position of the light-source, as it determines the relative illumination in each portion of the visual field. This study compared illumination of upper and middle visual fields to determine whether melatonin suppression is different or equivalent. Thirteen older volunteers received three illumination conditions in counterbalanced orders: 1000 lux in the upper visual field, 1000 lux in the middle visual field, or dim diffuse illumination <5 lux. A four-choice reaction time task was performed during tests to ensure eye direction and illumination of the intended portion of the visual field. Illumination in the upper and middle visual fields significantly suppressed melatonin compared to <5 lux (p<0.001). Melatonin suppression was not significantly different with upper or middle field illumination. These results indicate that bright light treatments placed above the eye level might be as effective as those requiring patients to look directly at the light source. Clinical comparative testing would be valuable. In addition, this study demonstrates that significant suppression of melatonin may be achieved through the use of bright light in healthy older volunteers.