Light Therapy Diagnostic Indications and Contraindications
The chief indication for light therapy is seasonal affective disorder (SAD) (Rosenthal et al. 1984) or, as classified in DSM-IV (American Psychiatric Association 1994), any form of recurrent mood disorder to which the specifier “with seasonal pattern” applies (
As can be seen in
Table 44-2, SAD is the only condition for which the indication for light therapy rests on a large body of scientific evidence. The use of light therapy for the other conditions listed in the table rests on a less secure scientific foundation. Subsyndromal SAD, also known as the “winter blues,” has been found to respond to light therapy in one controlled study (Kasper et al. 1989)—a predictable finding given the resemblance of this condition to its more severe syndromal counterpart.
The value of light therapy for nonseasonal depression has been less clearly established. Researchers have found modest but statistically significant antidepressant effects of light therapy in nonseasonally depressed inpatients in a few controlled studies (Kripke et al. 1986). A number of open trials and case reports of light therapy alone or in combination with other antidepressant treatments have supported this view, but a definitive controlled multicenter trial is required to confirm these reports. Some studies of light therapy in nonseasonal depression have not yielded positive results. Methodologically, the question of light therapy for patients with nonseasonal depression is complicated by the observation that many of these patients experience chronic depression or dysthymic disorder with seasonal exacerbations or they have a seasonal component to their depressive recurrences. Clinical impressions suggest that light therapy is probably useful with many such persons.
The status of light therapy for premenstrual dysphoric disorder (late luteal phase dysphoric disorder) is similar to that for nonseasonal depression, with the current knowledge base consisting of a few controlled studies, which yielded equivocal results, and positive clinical anecdotal impressions. With premenstrual dysphoric disorder, as with nonseasonal depression, debate centers not on the beneficial effects of light therapy, which have been observed in both of these conditions, but on whether or not such improvement is purely a function of the placebo effect.
The capacity of light to shift circadian rhythms in humans is very well accepted, presumably because of the extensive literature on similar effects in animals. There is general agreement that such phase-shifting properties might be helpful to persons with circadian rhythm disturbances, and debate centers around the details of how such phase shifts can best be accomplished. Patients with delayed sleep phase syndrome, a condition in which there is an inability to fall asleep and to wake up at conventional times, have been shown to be helped by exposure to bright light in the morning and light restriction in the evening (Rosenthal et al. 1990). Likewise, it has been suggested that patients with advanced sleep phase disorder, a condition that tends to afflict older persons, may be assisted by exposure to bright light in the evening hours (Lack and Wright 1993), a treatment that is also reported to be generally beneficial for insomnia in elderly patients (Campbell et al. 1993).
The effects of light exposure or restriction on human circadian rhythms can be predicted to some degree by the so-called phase-response curve (PRC), which is a graphic representation of the relationship between these parameters. Such curves appear to be a universal property of biological organisms (Winfree 1987) and apply to humans as well (Czeisler et al. 1990; Minors et al. 1991). The human PRC predicts that in most persons living according to a conventional sleep-wake schedule, light exposure at the beginning of the subjective night will shift rhythms later, whereas light exposure at the end of the subjective night will shift rhythms earlier. Light exposure in the middle of the day would be predicted to have minimal effects on circadian rhythms and corresponds to a portion of the PRC known as the dead zone. Although it is relatively easy to predict when to administer light to patients with stable disorders of circadian rhythms, as in the case of patients with delayed or advanced sleep phase syndrome, it is more difficult to do so when circadian rhythms are in flux, such as during travel across several time zones that results in jet lag, or when working on rotating shifts. Guidelines as to how light exposure (and light restriction) may be used to combat the symptoms of lethargy, fatigue, insomnia, and cognitive disturbances that may accompany such circadian rhythm disturbances go beyond the scope of this present chapter but can be located elsewhere (Eastman 1992; Oren et al. 1993).
Contraindications to Light Therapy
There are no absolute contraindications to light therapy, although there are some circumstances in which caution is required. These include when the patient 1) has a condition that might render his or her eyes more vulnerable to phototoxicity, 2) has a tendency toward mania, 3) has a photosensitive skin condition, or 4) is taking a photosensitizing medication or herb (such as St. John’s wort or a psoralen).
Although there have been no documented cases in which light therapy, when properly administered and supervised, has caused damage to the eyes, the potential for such damage has been raised as a theoretical possibility (M. Terman et al. 1990). The likelihood of light-induced damage to the retina might be increased in patients with retinal diseases such as macular degeneration or retinitis pigmentosa. Patients with retinal abnormalities should not be given light therapy without careful prior evaluation and ongoing supervision by an ophthalmologist. The degree to which patients with normal eyes should have their eyes regularly monitored during the course of light therapy has been debated, with some advocating more stringent monitoring and others advocating less stringent monitoring (Waxler et al. 1992). Concomitant use of certain antidepressants or other medications that may enhance phototoxicity has been cited by some investigators as a reason for additional caution and more frequent monitoring (M. Terman et al. 1990), although no increased prevalence of eye damage has been reported in persons on these medications, despite regular exposure to bright sunlight. In addition, there is no evidence of any increased prevalence of eye problems in patients who have been receiving light therapy for several years, a proportion of whom have been taking concomitant medications (Schwartz et al. 1996).
Although light therapy can occasionally induce hypomania or, very rarely, mania, a history of mania is not in itself an absolute contraindication to treatment. The likelihood of hypomanic symptoms can be greatly decreased by warning the patient about the possibility of such symptoms ahead of time, being vigilant of the patient’s clinical condition, and titrating the dosage of light treatment so as to minimize or counteract the development of such symptoms. Persons with a history of mania warrant increased vigilance in this regard.
Physicians should be alert to prescribe light boxes that screen out most if not all ultraviolet (UV) rays (Oren et al. 1990). UV light, which may cause facial erythema similar to that seen with suntanning, may in some cases get through to the user. This type of effect may cause problems for patients with systemic lupus erythematosus (SLE) or others with photosensitive skin. Nevertheless, with the help of a sun-blocking cream, a few patients with SLE have been effectively treated with light therapy without induction of facial erythema (Moul 1992). This would suggest that SLE is not necessarily a contraindication to the use of light therapy. Neither is a history of skin cancer a contraindication, although when such a history is present, as with SLE and other photosensitive skin conditions, every attempt should be made to screen out UV radiation. Precautions include the use of specially coated fluorescent bulbs, the use of special UV filters on the inside of the diffusing screen, and the use of commercial sunscreen ointments (which absorb about 95% of incoming ultraviolet B light). The value of sun-blocking ointments has been called into question, however, by a recent study that found that the use of such ointments was of no value in preventing UV-induced melanomas in mice, despite the capacity of these ointments to inhibit the development of erythema (Wolf et al. 1994). The relevance of this study to the use of light therapy in persons who have previously had skin cancer is unclear at this time, but those with such vulnerability should be counseled to be attentive to any skin changes in light-exposed areas and to report such changes promptly to their doctor. The risk for these patients must surely be far less, however, than the risk posed by having the skin exposed to unfiltered sunlight, which contains levels of UV light far higher than those emitted by a light box.
Revision date: July 5, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.