Light therapy

Bright light therapy is a common treatment for seasonal affective disorder and for circadian rhythm disorders.

Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light—by a so-called light box. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day. Light therapy directed at the skin is used to treat acne vulgaris and neonatal jaundice. Light therapy which strikes the retina of the eyes is used to treat circadian rhythm disorders such as delayed sleep phase syndrome and can also be used to treat seasonal affective disorder, with some support for its use also with non-seasonal psychiatric disorders.

History

Danish physician Nils Finsen is believed to be the father of modern phototherapy. He developed the first artificial light source for this purpose, and used his invention to treat lupus erythematosus. He received the Nobel Prize in Physiology or Medicine in 1903.

Skin related

Acne vulgaris

Sunlight was long known to improve acne, and this was thought to be due to antibacterial and other effects of the ultraviolet spectrum which cannot be used as a long-term treatment due to the likelihood of skin damage.^[1]

It was found that some of the visible violet light present in sunlight (in the range 405–420 nm) activates a porphyrin (Coproporphyrin III) in Propionibacterium acnes which damages and ultimately kills the bacteria by releasing singlet oxygen. A total of 320 J/cm² of light within this range renders the bacteria non-viable.^[2]

Deep penetrating light therapy for 3 consecutive days has been shown to reduce the bacteria in the pores by 99.9%. Since there are few porphyrins naturally found in the skin, the treatment is believed safe except in patients with porphyria;^[3] although eye protection is used due to light-sensitive chemicals in the retina. The light is usually created by fluorescent lamps, or very bright LEDs.

Overall improvements of on average 76% for 80% of patients occurs over 3 months; most studies show that it performs better than benzoyl peroxide and the treatment is far better tolerated. However, approximately 10% of users see no improvement.^[2]

Psoriasis and eczema

A feature of psoriasis is localized inflammation mediated by the immune system. UV radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis or eczema use UVA (315-400 nm wavelength) or UVB (280-315 nm wavelength) light waves. UVA, combined with a drug taken orally, is known as PUVA treatment. Narrow band UVB is the 310 nm wavelength and is given as a light therapy treatment rather than full spectrum UVB.

Tanning

Tanning is caused by the effects of two different spectrums of ultraviolet radiation: UVA and UVB.

Wound healing

Light therapy has been suggested for use in healing of wounds. Some^[4] say that low-level laser therapy does not appear to be effective, while others^[5] find that it can be effective. LLLT is used clinically in many areas outside the United States including Canada, Europe and Asia.^[4]

Photodynamic therapy

Visible blue light is used with aminolevulinic acid for the treatment of actinic keratosis. This is not a U.S. FDA-approved treatment for acne vulgaris.^[6]

Mood and sleep related

Light boxes

The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders. Hence, for the purpose of manipulating melatonin levels or timing, light boxes providing very specific types of artificial illumination to the retina of the eye are effective.

Light therapy either uses a lightbox which emits up to 10,000 lux of light, much brighter than a customary incandescent lamp, or a lower intensity of specific wavelengths of light from the blue (470 nm) to the green (525 nm) areas of the visible spectrum.^[7] Low dose (350 lux) green light therapy can produce melatonin suppression and phase shifts equivalent to 10,000 lux bright light therapy.^[8][9] It is possible that the cone cells, too, contribute to non-image forming light reception, suggesting that the blue light often used for therapy in depression, shift work and circadian rhythm disorders should be replaced by green or white illumination.^[10]

In treatment, the patient's eyes are to be at a prescribed distance from the light source with the light striking the retina. This does not require looking directly into the light.

Seasonal affective disorder

While full sunlight is preferred for seasonal affective disorder (SAD), light boxes may be effective for the treatment of the condition. The United States Food and Drug Administration has not approved the use of light boxes to treat SAD due to unclear results in clinical trials,^[11] but light therapy is still seen as the main form of treatment for SAD.^[12] Direct sunlight, reflected into the windows of a home or office by a computer-controlled mirror device called a heliostat, has also been used as a type of light therapy for the treatment of SAD.^[13][14]

It is possible that response to light therapy for SAD could be season dependent.^[15]

Non-seasonal depression

Light therapy has also been suggested in the treatment of non-seasonal depression and other psychiatric disturbances, including major depressive disorder, bipolar disorder^[16] and postpartum depression.^[17][18] A meta-analysis by the Cochrane Collaboration concluded that "For patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy".^[19]

Circadian rhythm sleep disorders

Chronic CRSD

In the management of circadian rhythm disorders such as delayed sleep phase syndrome (DSPS), the timing of light exposure is critical. For DSPS, the light must be provided to the retina as soon after spontaneous awakening as possible to achieve the desired effect, as shown by the phase response curve for light in humans. Some users have reported success with lights that turn on shortly before awakening (dawn simulation). Morning use may also be effective for non-24-hour sleep-wake syndrome, while evening use is recommended for advanced sleep phase syndrome.

Situational CRSD

Light therapy has been tested for individuals on shift work,^[20] and for jet lag.^[21]

Neonatal jaundice

A newborn infant undergoing white-light phototherapy to treat neonatal jaundice.

Light therapy is used to treat cases of neonatal jaundice^[22] through the isomerisation of the bilirubin and consequently transformation into compounds that the newborn can excrete via urine and stools. A common treatment of neonatal jaundice is the Bili light.

Parkinson's disease

Bright light therapy may ease Parkinson's disease by reducing patients' tremors.^[23][24]

Safety

Ultraviolet light causes progressive damage to human skin. This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and vitamin C in the skin and free radical generation. Researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration.^[25]

Modern phototherapy lamps used in the treatment of seasonal affective disorder and sleep disorders either filter out or do not emit ultraviolet light and are considered safe and effective for the intended purpose, as long as photosensitizing drugs are not being taken at the same time and in the absence of any existing eye conditions. Light therapy is a mood altering treatment, and just as with drug treatments, there is a possibility of triggering a manic state from a depressive state, causing anxiety and other side effects. While these side-effects are usually controllable, it is recommended that patients undertake light-therapy under the supervision of an experienced clinician, rather than attempting to self-medicate.^[26]

It is reported that bright light therapy may activate the production of reproductive hormones, such as testosterone, luteinizing hormone, follicle-stimulating hormone, and estradiol.^[27][28]

There are few absolute contraindications to light therapy, although there are some circumstances in which caution is required. These include when a patient has a condition that might render his or her eyes more vulnerable to phototoxicity, has a tendency toward mania, has a photosensitive skin condition, or is taking a photosensitizing herb (such as St. John's wort) or medication.^[29] Patients with porphyria should avoid most forms of light therapy. Patients on certain drugs like methotrexate or chloroquine should use caution with light therapy as there is a chance that these drugs could cause porphyria.

Side effects

Side effects of light therapy for sleep phase disorders include jumpiness or jitteriness, headache, and nausea. Some nondepressive physical complaints (such as poor vision and skin rash or irritation) may improve with light therapy.^[30]

See also

• Low level laser therapy
• Deep penetrating light therapy
• Blood irradiation therapy

References