Phototherapy introduced in 1984 by Rosenthal as a treatment for SAD (
Seasonal Affective Disorder) is the first therapeutic answer to season-related psychopathology. Findings in chronobiology have largely contributed to pathophysiological theories of disorders in the internal circadian system. Actual researches on the etiology of SAD covers fields as
retinal deficiency (i.e. disorder of photoreceptors), phase disturbance of the internal circadian rhythms given by internal oscillators and neuroendocrinologically drived disorders, supposing that
melatonin is the main mediator of human circadian systems in the CNS. Disorders of the
neurotransmitters are an other explored cue. Recent longitudinal studies show a prevalence of seasonal depressive symptoms in general population up to 10%. In populations treated for depression the prevalence of SAD is up to 20%. The SAD sex-ratio (women/men) of 3/1 is found repeatedly. Above 55 years SAD get rare. Effectiveness of
phototherapy is showed in nearly all controlled studies. Bright light for patients with mild SAD appears to be most effective as is also the authors clinical impression through the practice of
phototherapy in Geneva since 1991. A true placebo for bright light is still to be found according to enable evaluation of potentially important impact that unspecific therapeutic factors may trigger in
phototherapy. Actually possible new indications for
phototherapy are being explored: bright light for non seasonal depression has been tested with features with SAD; effectiveness in
bulimia has been suggested and recently
sleep disorders in psychogeriatric patients have been improved. Non seasonal circadian disorders such as
jet lag might be sensitive to light.