Melatonin suppression by illumination of upper and lower visual fields.

As a guide to optimizing the geometry of bright light treatment, 12 healthy subjects were studied three times in the laboratory from 11 p.m. to 2 a.m. On three evenings, in counterbalanced orders, subjects received 500 lux in the upper visual field, 500 lux in the lower visual field, or 5 lux while watching television. In the upper visual field, 500 lux significantly suppressed melatonin, as compared to 500 lux in the lower visual field or to 5 lux. In the lower visual field, 500 lux produced intermediate suppression of borderline significance. The results suggest that bright light treatment of depression or circadian phase disorders might be most effective when applied in the upper visual field.