Trillian's Depression Page
Light Therapy
As the cause for Seasonal Affective Disorder (SAD) is lack of bright light,
the treatment is to be in bright light every day by using a light box or a
similar bright light therapy device. (Going to a brightly-lit climate, whether
skiing or somewhere hot, is indeed a cure). The preferred level of light is
about as bright as a spring morning on a clear day and for most people sitting
in front of a light box, allowing the light to reach the eyes, for between
¼ and ¾ hour daily will be sufficient to alleviate the symptoms. The
user does not have to stare at the light, but can watch TV or read or similar,
just allowing the light to reach the eyes.
Is there anything special about the light?
The light must be suitably bright. At least 2500lux (lux is the technical
measure of brightness) is needed, which is 5 times brighter than a well lit
office (a normal living room might be as low as 100lux); brighter lights up to
10,000lux work quicker. Contrary to the old belief the light does not need to
be special daylight, color matching or 'full spectrum' light; simply changing
the lamps in a room to these special types will not produce sufficient light.
Research
Treatment studies of light therapy have shown increasingly rigorous
methodology with larger sample sizes, less diagnostic heterogeneity, longer
treatment periods, and parallel instead of crossover designs. Wavelength of
light used in light therapy was examined in two studies. In one study, the
ultraviolet (UV) spectrum did not add to the therapeutic efficacy of light
therapy [14*].
Because of the potential harmful effects of long-term W exposure, light
therapy devices should have W filters that block wavelengths below 400 nm. In a
comparison light box study, cool-white fluorescent lights were as effective as
full-spectrum fluorescent lights [15], adding evidence to other studies showing
that various light sources (including incandescent lights) are effective for
treating SAD.
Devices other than light boxes were also studied for light therapy. Two
recent studies, with the largest sample sizes in light therapy studies to date,
used a light visor [16*,17*]. In both studies, there was no relationship
between the intensity of light and various measures of response to treatment,
despite the fact that very low intensity light (60 lux) was used. This
contrasts to most light box studies where a dear intensity-response
relationship is found. Several explanations may explain this discrepancy. The
proximity of the visor light source to the eye may increase the amount of light
that reaches the retina, as compared to a light box. Lux, a unit of
illumination, may also not be the best measure of the biologic or therapeutic
effect of light. There is increasing evidence that even low illumination can
affect biologic parameters [18], so that for some patients, light as low as 100
lux may be therapeutically effective. Finally, although the response rate was
high in both studies (over 60% by strictly defined criteria), a non-specific
(placebo) effect of light therapy must also be considered. In this regard, a
light box study by Eastman and associates [19**] using a non-light control
condition (a negative ion generator that, unknown to subjects, was turned off),
found no differences between the control condition and bright light treatment
(7000 lux for 1 hour in the morning). However, the response rate for the bright
light condition (29%) was unusually low compared to other treatment studies.
The selection criteria and unusually sunny weather during the course of their
study may have excluded more light-responsive patients. Thus, the issue of
placebo effects in light therapy remains unresolved.
The Seattle group conducted a series of studies investigating dawn
simulation in SAD [20,21,22*]. Dawn simulation uses a device that gradually
increases illumination exposure, while the patient is sleeping, to simulate a
summer dawn during the winter. Significant improvement occurred using dawn
simulation compared to various control conditions, despite a final illumination
as low as 250 lux.
Two groups studying predictors for light therapy found that hypersomnia and
hyperphagia predicted clinical response [23*,24,25*].
Second Study
Another study, however, reported that only high consumption of sweets in the
latter half of the day predicted response to treatment [26*]. Of interest is
that prospective measures of sleep and eating were used in the latter study,
whereas the other studies used global patient self-report.
Light therapy has been considered a rather benign treatment with few side
effects. A systematic report of side effects to light therapy using a light
visor showed that approximately 20% of patients reported mild side effects,
including headache, eyestrain, and "feeling wired" [27]. A more
controversial topic is the potential for prolonged bright light exposure to
produce harmful effects on the retina. The intensities of light used in light
therapy regimens are not considered harmful to the human retina based on short
term studies, but the retinal effects of long term bright light exposure are
not known. Some investigators have called for routine ophthalmologic evaluation
prior to starting light therapy because of the small, potential risk of
aggravating previously unrecognized retinal conditions (e.g. macular
degeneration) [28*]. Others suggest ophthalmologic screening only in patients
with a history of pre-existing retinal disease, patients taking highly
photosensitizing drugs, and the elderly [29*]. Empiric data are still sparse,
but a recently reported five-year prospective study of patients on chronic
light therapy has not shown any significant clinical or electrophysiologic
changes in the eyes [30].
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