The use of light therapy in psychiatry

In the past 15 years, light therapy has emerged as an effective treatment for a variety of psychiatric conditions. The discovery that nocturnal melatonin secretion was suppressed by exposure to environmental light raised the possibility that other hypothalamically-mediated physiological effects might be modified by such exposure. Patients with seasonal affective disorder (SAD), a condition of recurrent depressions in fall and winter alternating with nondepressed periods in spring and summer, turned out to be particularly responsive to light therapy. Following the initial description of SAD in the mid-1980s, many controlled studies of light therapy have shown it to have an antidepressant effect in SAD, which appears to be mediated via the eyes rather than the skin, and to be dependent on both the intensity and duration of exposure, but relatively independent of the time of day when treatments are administered. Light therapy has also been used in other disorders of mood and appetite regulation with some promise but less well established efficacy. Certain non-seasonally depressed patients may respond to light therapy, as may patients with late luteal dysphoria and bulimia. One controlled study found that light treatment augmented the effects of fluoxetine in non-seasonally depressed patients who had not responded to the medication. Light therapy has also been used successfully to shift rhythms in conditions of stable circadian dysregulation, such as delayed or advanced sleep phase syndrome, or temporary circadian disturbances such as are found with jet lag and shift work. The potential mechanisms for these therapeutic effects will be discussed.