"Dark
Therapy", in which complete darkness is used as a mood stabilizer in
bipolar disorder, roughly the converse of
light therapy for depression, has support in several preliminary studies. Although data are limited, darkness itself appears to organize and stabilize circadian rhythms. Yet insuring complete darkness from 6 p.m. to 8 a.m. the following morning, as used in several studies thus far, is highly impractical and not accepted by patients. However, recent data on the physiology of human circadian rhythm suggests that "virtual darkness" may be achievable by blocking blue wavelengths of light. A recently discovered retinal photoreceptor, whose fibers connect only to the biological clock region of the hypothalamus, has been shown to respond only to a narrow band of wavelengths around 450 nm.
Amber-tinted
safety glasses, which block transmission of these wavelengths, have already been shown to preserve normal nocturnal
melatonin levels in a light environment which otherwise completely suppresses
melatonin production. Therefore it may be possible to influence human circadian rhythms by using these
lenses at night to blunt the impact of electrical light, particularly the blue light of ubiquitous television screens, by creating a "virtual darkness". One way to investigate this would be to provide the
lenses to patients with severe sleep disturbance of probable circadian origin. A preliminary case series herein demonstrates that some patients with
bipolar disorder experience reduced sleep-onset latency with this approach, suggesting a circadian effect. If
amber lenses can effectively simulate darkness, a broad range of conditions might respond to this inexpensive therapeutic tool: common forms of
insomnia;
sleep deprivation in nursing mothers; circadian rhythm disruption in shift workers; and perhaps even rapid cycling
bipolar disorder, a difficult- to -treat variation of a common illness.