In psychiatry, it is primarily used in the treatment of Seasonal Affective Disorder (SADS). SADS is a syndrome where the intensity of depressive symptoms, and their frequency, follows a seasonal pattern with onset in autumn/winter and symptoms reducing in spring/summer. This syndrome is sometimes referred to as winter depression. The depressive features comprise depressed mood, social withdrawal and also increased appetite, hypersomnia and weight gain.
How does phototherapy work?
In most medical conditions, phototherapy requires skin-exposure. However, in the treatment of SADS, the eyes are used as the main avenue of entry.
In the treatment of physiological jaundice of the newborn, and sometimes in haemolytic disease of the newborn, the newborn is exposed to intense light in the blue-green part of the visible spectrum. Light of these particular frequencies promotes the conversion of excessive and damaging bilirubin in the newborn's blood to water-soluble and harmless biliverdin. Elevated bilirubin in the newborn can cause serious neurological damage and subsequent complications and disability.
Natural sunlight has a therapeutic effect in psoriasis. Skin exposure to sub-erythematous doses of UVB (ultraviolet light of short wavelength) can be very helpful. Often the skin is bathed in a tar bath that sensitizes the skin to the effects of the UVB before controlled exposure is undertaken.
PUVA is a more robust form of this treatment for some forms of psoriasis. In this case, the patient takes oral psoralens (photosensitizing agents) two hours before exposure to ultraviolet rays of long wavelength (UVA). The course comprises 2-3 treatments per week for about 3 months, followed by maintenance treatment, until no longer necessary.
In the treatment of SADS, a light box containing fluorescent tubes mounted behind a translucent plastic screen is placed at the patient's eye-level. Although the exact mechanism of action is not yet known, it is thought that such light treatment exerts its effects by modulating the levels of melatonin produced in the body. Melatonin, a hormone produced in the brain, has various functions which include the stimulation of skin-pigmentation and effects on brain transmitters which may explain its ability to relieve depressive symptoms. There could also be further effects via the hypothalamus which is a part of the brain with a central role in the control of circadian rhythms and also in the control of certain neurotransmitters, such as serotonin, which is known to be involved in mood regulation. It does appear that a mechanism, mediated through the impact of light on the retinae of the eyes is essential for the antidepressant effect.
Are there any negative side effects?
In general, phototherapy is a well-tolerated, safe procedure. Although mild side effects are common, especially initially, it is rare for the side effects to be severe enough to interrupt or halt a course of treatment.
Mild side effects include eyestrain, headache, insomnia, nausea and fatigue. Irritability can also occur and if this persists or worsens, the duration of treatment may have to be decreased. There have been reports of manic episodes. With properly adjusted and maintained equipment there is no evidence that phototherapy can damage the retina.
