Impact of blue vs red light on retinal response of patients with seasonal affective disorder and healthy controls.

OBJECTIVES: Seasonal affective disorder (SAD) is characterized by a mood lowering in autumn and/or winter followed by spontaneous remission in spring or summer. Bright light (BL) is recognized as the treatment of choice for individuals affected with this disease. It was speculated that BL acts on photosensitive retinal ganglion cells, particularly sensitive to blue light, which led to the emergence of apparatus enriched with blue light. However, blue light is more at risk to cause retinal damage. In addition, we reported using electroretinography (ERG) that a 60 min exposure of BL could reduce rod sensitivity. The goal of the present study was to verify if this decreased in sensitivity could be a consequence of the blue light portion present in the white light therapy lamps. We also wanted to assess the effect of monochromatic blue light vs red light in both healthy controls and patients with SAD.

METHOD: 10 healthy subjects and 10 patients with SAD were exposed in a random order for 60 min to two different light colors (red or blue) separated by an interval of at least 1 day. Cone and rod ERG luminance-response function was assessed after light exposure.

RESULTS: A two-way ANOVA indicates that blue light decreases the maximal ERG response (Vmax) in both groups in photopic (p<0.05) and scotopic conditions (p<0.01).

CONCLUSION: The main finding of this experiment is that blue light reduces photoreceptor responses after only a single administration. This brings important concerns with regard to blue-enriched light therapy lamps used to treat SAD symptoms and other disorders.