Cautionary Notes About Bright Light Exposure
Light energy can interact with and damage skin and eye tissues, especially when a photosensitizing molecule – whether from a drug or produced by the body – is bound within those tissues. The highest risk (for damage to the skin, and cornea and lens of the eyes) is from invisible, short-wavelength ultraviolet (UV) light, which has been filtered out of CET’s recommended light therapy system.
Long-term exposure to intense visible light in the blue range adjacent to the UV range may also pose a hazard to retinal photoreceptors and the pigment epithelium, which takes part in the photoreceptor renewal process. Above age 50, there is concern about blue-light exacerbation of age-related macular degeneration. Although some blue is an important component of white light exposure, lamps with relatively less blue (for example, soft-white fluorescents with color temperatures in the range of 3000-4000 Kelvin) should be favored over cool-white, daylight, or “full spectrum” lamps (5000 Kelvin and higher).
Pre-Existing Medical Conditions May Enhance Exposure Risks
There are certain pre-existing medical conditions of eyes and skin (retinal dystrophies, age-related macular degeneration, porphyria, lupus erythematodes, chronic actinic dermatitis and solar urticaria) that also can show photosensitized reactions to intense visible light. In such cases, bright light therapy should be administered only under guidance of an ophthalmologist or dermatologist, as indicated. Ophthalmologists should keep in mind that in some genetic retinal diseases the eyes are especially light sensitive.
Medications & Enhanced Exposure Risks
Certain medications are known to photosensitize skin and/or retinal tissues. Examples in the visible range of light include psychiatric neuroleptic drugs (e.g., phenothiazine), psoralen drugs, antiarrhythmic drugs (e.g., amiodarone), antimalarial and antirheumatic drugs, porphyrin drugs used in photodynamic treatment of skin diseases, and St. John’s Wort (hypericum). Bright light therapy should not be used concurrently with these drugs. Melatonin can be used in conjunction with light therapy at opposite times of day (usually, evening and morning, respectively), but if used concurrently, it can cause photosensitization.
Drugs that photosensitize primarily in the invisible UVA range (just below the blue range) may also have a “tail” of light absorption that extends into the lower visible blue light range, which could cause photosensitization. Examples are tetracycline, diuretic drugs (e.g., hydrochlorothiazide), sulfonamide drugs and tricyclic antidepressants (e.g., imipramine, nortriptyline, desipramine, amitriptyline). If such a reaction is experienced or suspected, bright light therapy should be discontinued unless substitute medication is available, or it can be administered with protective measures under medical supervision.
For the practice of bright light therapy, we must therefore consider the wavelength range of the light (and with that, its energy range) and the absorbing tissues in the eye. For normal healthy eyes, the exposure to bright white light is a physiological situation and does not inflict any overt damage to the skin, visual cells and pigment epithelium. There are, however, certain important caveats:
- Medications that can enter the skin or retina and that absorb light in the visible range. This might cause photosensitization with subsequent absorption of “too many photons,” leading to damage. If you want to use bright light therapy but are questioning your medication, consult an ophthalmologist or dermatologist.
- Certain inherited dystrophies of the retina that alter the visual pigments and can render the retina especially sensitive to visible light. If you suffer from an inherited retinal dystrophy and want to use bright light therapy, consult an ophthalmologist.
- Age–related or other macular degenerations. For age–related macular degeneration, genetic factors increase the risk of disease by about 50%. Patients with such risk factors, or those with several family members suffering macular degeneration, should consult an ophthalmologist before using bright light therapy.
- Young eyes up to an age of about 30–40 years transmit much more light to the retina than older eyes. Thus, young eyes receive generally higher light doses than older ones.
Vincent DeLeo, M.D., St. Luke’s-Roosevelt Medical Center, New York; Charlotte Remé, M.D., University of Zurich, Switzerland.