Murray Waldmanin henkilökohtainen tiedote sinisen valon riskeistä
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Subject: Re: Blue light hazards
Date: Sat, 06 Mar 1999 20:19:03 -0600
From: Murray Waldman <mwaldman@escape.ca>
To: Ilkka Pekanheimo <adlux@adlux.fi>
References: 1 , 2 , 3
Dear Ilkka
I would agree the claim that their unit (tässä tarkoitetaan Työpiste-Päivänsädettä) is safe is not accurate; and in fact that it is more likely to cause damage to the eye than many other types of commercial bright light units.
UV light absorbed by the lens and cornea of the eye causes oxidative damage which is cumulative over a lifetime and results in cataracts. The capacity of a person's repair mechanism to prevent permanent damage varies with the person, their age, whether they smoke, whether they are taking some types of medication, and even what they have eaten before exposure. To make the statement that certain levels of UV are safe because they don't exceed a certain threshold developed to provide some guidelines to industry is, to me, misleading.
Besides, cataracts are now removable by laser surgery and today I believe all commercial bright light units screen out UV light, as almost any plastic sheet will basically absorb most of the UV coming from the lamp. So their claim that their unit is better because it has reduced UV output, which they don't say specifically, except in comparison to the two other units in this study, is not solid. In fact the risk to the eye from their lamp with lower UV output, as measured by a meter, may be greater than another depending on the geometry of the presentation of the light to the eye, and the wavelength of the UV light. This is explained in greater detail towards the end of this message.
The real problem is with the visible light that penetrates to the retina (which is why it is called visible - we can detect it). There are two different types of risk from high intensity visible light, acute and long term.
1) Acute retinal damage appears to be caused by light induced oxidation that exceeds the repair mechanism's ability to repair the damage. This is wavelength dependant and the risk diminishes with increasing wavelength with the greatest risk in the blue region, from 400-480 nm. This type of damage can also be caused by lasers or by looking at the sun - often during an eclipse. This results in lesions and scarring in the retina. It can also be caused by bright light therapy units, as described in the reference in our web site, in which case lesions appeared in both retina of a closely monitored individual within 5 days of using a bright light therapy unit. I have recently been contacted by a person using a commercial 10,000 lux unit in the U.S. since 1995, who has developed retinal scarring to such an extent that she is now legally blind. This case is not yet published, as the ophthalmologists were not aware of her use of bright light therapy while her condition developed, until recently. They are currently re-assessing her damage, and I expect will publish her case in the near future.
2) long term retinal damage which is cumulative over time and may be caused by repeated oxidative insult from bright visible light. It may also be caused by light damage to the retinal pigment epithelium which causes a break in the blood-retinal barrier and allows microphage from the body's immune system to invade the retina where they can live up to five years, attacking and destroying photoreceptor cells- which they don't recognize as "self". Over time this can result age related macular degeneration and permanent blindness. The wavelengths to which this damage is most susceptible is around 430-460 nm.
The reason for stating earlier that their units appear to have greater risk than others is because of the small size of the lamp and the lack of a diffuser. Thus the image formed on the retina is very small and bright, and it is the intensity or brightness (number of photons per cm2 ) of the retinal image of the light source that is related to its potential retinal hazard.
Regarding flicker from the fluorescent bulbs, although they give the impression that their lamps don't flicker, all they say is that they have eliminated "fluorescent vibration and flashing" when the light is being turned on. (i.e. they are using a rapid start or instant start bulb). The implication regarding the calm light might be that they are using an electronic ballast to eliminate flicker, but they don't say it.
The most thorough summary regarding the ocular risks of bright light is "Bright Light Therapy for Winter Depression: Potential Ocular Effects and Theoretical Implications" in Photochemistry and Photobiology 1990; 51(6):781-792 by Terman et al. You might also find the paper "Long Term Light-Induced Retinal Degeneration in the Miniature Pig" by Dureau interesting- It can be found at here
Relevant recent papers are:
- "Bright Light Therapy in Focus: Lamp Emission Spectra and Ocular Safety" by Reme et al in Technology and Health Care 1996;4:403-413
- "Light History and Age-Related Changes in Retinal light Damage" by Organisiak at al in Investigative Ophthalmology and Visual science 1998; 39(7):1107-1116
- "Light Damage Revisited: Converging Evidence, Diverging Views?" by Reme et al, in Graefes Archives of Clinical and Experimental Ophthalmology 1996;234:2-11
An expert in this field is Charlotte Reme MD PhD in the department of Ophthalmology at the University of Zurich in Switzerland. I think her E- Mail address is chreme@opth.unizh.ch
Regarding wavelengths that are most damaging to the retina and retinal pigment epithelium "Blue Light Induced Dysfunction of the Blood-Retinal Barrier at the Pigment Epithelium in Albino vs Pigmented Rabbits" by Putting et al Exp Eye Res 1994; 358; 31- 40 lists 439 +/- 6 nm as the most damaging. In an earlier paper "Spectral Sensitivity of the Blood Retinal Barrier at the Retinal Pigment Epithelium for Blue Light" in the 400 to 500 nm Range" in Graefes Archives of Clinical and Experimental Ophthalmology 1993; 231:600-06 he found that the RPE is most sensitive to damage at about 420 nm.
Re humans, in "Blue Light Induced Reactivity of Retinal Age Pigment" in The Journal of Biological Chemistry 1995; 270(32):18825-18830 Rozanowska et al the abstract state "Exposure to the eye to intense light, particularly blue light, can cause irreversible, oxygen-dependent damage to the retina. We have found that illumination of human retinal pigment epithelium cells induces significant uptake of oxygen that is both wavelength and age dependent...and contribute to the development of age-related maculopathy".
In summary retinal damage primarily dependant on the number and energy of photons that impact on a portion of the retina. Blue light under 450 nm is the most hazardous.
The retinal risk from light depends on the brightness the image of the light source on the retina, regardless of whether it provides a reading of 1,000, 10,000, or 50,000 lux on a light meter.
I hope that you find this helpful. If you need further information, please don't hesitate to ask.
Murray Waldman
Sunnex Biotechnologies
mwaldman@sunnexbiotech.com
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