Background: It has been hypothesized that the circadian pacemaker is phase delayed in seasonal affective disorder, (SAD) winter type, and that the phase advance resulting from morning ocular light accounts for the efficacy of light therapy. Extraocular light has been reported to produce phase-shifts of the human circadian pacemaker. This allows a double-blind, placebo-controlled study of light therapy in SAD.
Methods: Twenty-nine SAD patients participated. Clinical state was measured on days 1, 8, and 15 of the protocol. From days 4 through 8, 15 patients (4 M, 11 F) received extraocular light by fiberoptic illumination, and 14 (4 M, 10 F) placebo (no light) in the popliteal fossae, from 8 AM to 11 AM. In the evenings of days 3 and 8, the salivary dim light melatonin onset (DLMO) was assessed. Patients completed daily self-ratings on mood, alertness, and sleep.
Results: Both conditions showed a progressive improvement of clinical state over time. Between conditions, no significant differences were observed in clinical scores, the self-ratings on mood and alertness, and in timing of the DLMO before and directly after treatment.
Conclusions: The response to extraocular light therapy in SAD patients did not exceed its placebo effect. Extraocular light did not induce a phase shift of the circadian pacemaker.