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When it comes to protecting our eyes, scientific insight makes all the difference. That’s why we asked Dipl.-Ing. Dr. Helmut Walter for his expert assessment. As a professor at the Higher Technical Institute in Waidhofen, he spent many years researching the effects of light on human health in the institute’s laboratory for biomedical technology – with a particular focus on photobiology.
In his summary, Dr. Walter explains why blue light is stressful, especially for the sensitive tissue in the eye. He summarizes which light sources can be problematic – and how you can protect yourself. To make the content more accessible, we’ve broken it down into easy-to-read sections. If you’d like to dive deeper, you can expand the original scientific text by Dr. Walter under each section. His full statement, along with all referenced sources, is available at the bottom of the article as the final fold-out text.
Blue light is a natural component of daylight, but it is also found in many artificial light sources. The blue part of the spectrum ranges from approximately 400 to 480 nanometers and is particularly rich in energy. This is precisely what makes it biologically effective, but also potentially dangerous. In photobiology, this is referred to as high-energy visible light (HEVL).
Unlike gentle, long-wavelength light, blue light carries a high amount of energy deep into the eye. There, it affects cells that are highly sensitive to radiation – particularly in the retina, the area responsible for our sharpest vision. If the exposure is too intense or prolonged, this can lead to lasting damage.
Light, as the visible range of electromagnetic radiation extends from 380 nm in the more energetic blue-violet wavelength range to 780 nm in the less energetic red or near infrared range. All other colors fall between these ranges.
Clinical and laboratory studies show that blue light (400 – 480 nm) damages the retina, especially the pigment epithelium.
Our eyes are high-performance organs that rely on smooth cellular function. Excessive blue light can seriously disrupt these processes – especially in the mitochondria, the so-called “powerhouses” of our cells. If these are damaged, it can ultimately lead to cell death and long-term harm to visual function.
Blue light can trigger oxidative stress in the delicate tissue of the retina and studies suggest that it increases the risk of various eye diseases. Research shows: The greater the exposure to blue light, the greater the risk of permanent damage.
Clinical and laboratory studies show that blue light (400 – 480 nm) damages the retina, especially the pigment epithelium. The absorption of this radiation by flavins and cytochromes in the protein complexes of the respiratory chain in the mitochondria (energy power plants) of the cells leads to a reduction in energy production or ATP deficiency. At the same time, more free oxygen radicals are formed (oxidative stress!), which destroy the mitochondria and trigger cell death. On the one hand, this leads to the dreaded macular degeneration (macula or yellow spot is the place of sharpest vision in the retina) and even to total loss of vision [1] and, on the other hand, if the retinal ganglion cells are mainly affected, to an increase in intraocular pressure (glaucoma), which damages the optic nerve and also threatens blindness [2].
Underlying Mechanisms
The retinal pigment epithelium is protected against oxidative attacks by melanin, which binds redox-active metals; it has an antioxidative and photoprotective effect. With increasing age, the proportion of melanin decreases due to photooxidative processes and the content of melanolipofuscin increases. For blue light, lipofuscin acts as a photosensitizer and thus its action is photooxidative or phototoxic and additionally increases oxidative stress [3]. This destroys the membranes of the lysosomes and releases their contents (lysosomal enzymes) into the cytosol, where they trigger a strong inflammatory response through activation of the NLRP3 inflammasome [4].
The mitochondria in the inner segments of the photoreceptors (rods for brightness and cones for color perception) are not the sole source of free oxygen radicals. Cora Röhlecke and Prof. Richard Funk from the Institute of Anatomy of the TU Dresden discovered that the outer segments of the photoreceptors generate large amounts of oxygen radicals under the action of blue light – much more than the mitochondria. Another important result of their work was the confirmation of the mitochondrial-like activity of the outer segments [5]. Compared to other tissues, the retina is particularly susceptible to oxygen radical formation due to the very high oxygen content of the choroid and its extremely high metabolic rate!
[1] Kasun Ratnayake et al.,
“Blue light excited retinal intercepts cellular signaling”, Scientific Reports (2018) 8:10207, DOI:10.1038/s41598-018-28254-8
[2] Neville N. Osborne et al.,
„Visual light effects on mitochondria: The potential implications in relation to glaucoma”, Mitichondrion 36 (2017) 29-35
[3] Sally M. Yacout et al.,
“Characterization of Retinal Pigment Epithelial Melanin and Degraded Synthetic Melanin Using Mass Spectrometry and In Vitro Biochemical Diagnostics”, Photochemistry and Photobiology, 2019, 95: 183-191
[4] Carolina Brandstetter et al.,
“Inflammasome priming increases retinal pigment epithelial cell susceptibility to lipofuscin phototoxicity by changing the cell death mechanism from apoptosis to pyroptosis”, Journal of Photochemistry and Photobiology, B: Biology, 161 (2016) 177-183
[5] Cora Roehlecke et al,
“Stress reaction in outer segments of photoreceptors after blue light irradiation”, PLoS ONE 8(9). E71570
Compared to other tissues, the retina is particularly susceptible to oxygen radical formation due to the very high oxygen content of the choroid and its extremely high metabolic rate!
While blue light impairs cell function, photobiological research in the red range shows the opposite: light with a longer wavelength (630 to 800 nm) can even stimulate energy production in the cells. This has a supportive effect – and promotes natural repair mechanisms in the eye.
That’s why the right proportions are important. A balanced light spectrum with a sufficient amount of red is well tolerated. It only becomes problematic if this part is missing – as is the case with many artificial light sources.
The effect of light in the red long-wave range from 630 to 800 nm is quite different: stimulation of the respiratory chain and increased ATP formation occur here. Again, free oxygen radicals are produced, but only in a very small extent necessary for the maintenance of important signaling pathways. At the same time, repair processes are set in motion which repair damage from blue radiation [6].
[6] Boris T. Ivandic et al.,
“Low-Level Laser Therapy improves Vision in Patients with Age-Related Macular Degeneration”, Photomedicine and Laser Surgery”, Vol. 26, no. 3, 2008
Not all light is the same. While traditional light bulbs or daylight provide a continuous spectrum with many red components, the situation is different with modern light sources. LEDs and energy-saving lamps often produce isolated, particularly intense light peaks – especially in the blue range.
These engineered light mixtures are much more difficult for the eye to process. Especially when they are permanently used – such as when working at a computer screen. In this case, the balancing red component that provides balance in natural light is completely absent.
Incandescent Light
For light sources that are thermal radiators, that is, when a “black body” (tungsten incandescent filament in incandescent and halogen lamps) is brought to high temperature, a radiation occurs, which emits much red and infrared light and only contains very little blue. Most importantly, this creates a continuous spectrum, i.e. It contains all !! wavelength components, not just individual (discrete) spectral lines. With such light sources and the solar radiation, except for the midday light in summer, there is no danger to the eye and no protective glasses are required. Photobiologically, any small damage caused by the negligible blue components is immediately repaired by the disproportionate red components or does not occur at all. The body protects itself against the high luminance (glare) of the sun or halogen lamps by closing the eyes. Possible overdoses can be detected by the accompanying heat.
Gas discharge lamps and LED light
The situation is quite different for gas discharge lamps, which include the fluorescent tubes or energy-saving lamps, and the light-emitting diodes (LED). In each case, a very narrow spectral line of very high intensity is generated (for fluorescent lamps it is a UV-line with 254 nm and for the “white” LED a blue line with about 450 nm) which is then converted by phosphors into visible radiation. For fluorescent lamps, this can be up to 8 phosphors to get as close as possible to a continuous spectrum, this technology is called an 8-band lamp. For most white LEDs used so far, only one phosphor layer is used, which converts blue into yellow light. A lot of blue and a moderate amount of yellow light is produced by the well-known “cold” LED light.
In the meantime, the industry is trying to produce a sunlight-like “white” light under the heading HCL (Human Centric Lighting), either by producing strong violet radiation that is converted into blue, green, and red with one phosphor each, or through the use of discrete blue, green and red LEDs in a common housing. No matter which technology is used here, these light sources do not currently approach the quality of the light from temperature radiators, in which the intensity of the spectral lines increases with increasing wavelength.
Today, targeted protection from blue light is more important than ever – especially in the workplace or in our everyday lives with digital devices. Special eyewear filters can reliably block out the problematic wavelength range and relieve the eye without distorting perception too much.
The decisive factor here is quality. Only tested glasses that effectively cover the photobiologically relevant range between 400 and 500 nm offer reliable protection. Good models also improve contrast vision and depth of field – a real advantage for long periods of screen time.
Most “blue light protection glasses” available on the market offer no more than blue light reduction. The PRiSMA BlulightProtect models provide the comprehensive protection in the entire blue light range mentioned by Dr. Walter.
Protection against disproportionate blue content
This means that due to the widespread use of fluorescent lamps and LEDs (for example as backlight for PC and TV flat screens), the disproportionate amount of blue in the emission spectrum has to be filtered out by amber protection lenses in order to protect the health of the eyes [7]. Such lenses must be of high quality and above all it has to be tested that they reliably filter out the wavelength range of 400-500 nm and comply with the required specifications. Here, the company “INOVATIVE EYEWEAR” offers a wide range of CE-specified glasses of the PRiSMA® brand, with the possibility to choose the filtering strength and the resulting remianing color perception. There are even certified safety glasses for night driving. In addition, such glasses allow better recognition of contours and contrasts and increase the depth of field. Another good reference for this company is the long-term cooperation with Dr. med. Alexander Wunsch [8], a designated expert on eye health.
[7] Kaho Hiromoto et al.,
“Colored lenses suppress blue light-emitting diode light-induced damage in photoreceptor-derived cells”, Journal of Biomedical Optics 21 (3) 035004 March 2016
[8] A. Wunsch, “Licht ist Leben- aber falsches Licht kann krank machen!”, AUGENBLICK Ausgabe 12, Mai 2012
The natural lens of the eye turns yellow with age and increasingly protects the retina from blue radiation.
With increasing age, the natural lens of the eye turns yellow – and thus assumes an important protective function. The yellowish pigment filters blue components out of the light and thereby reduces the strain on the retina. For this reason, a slightly tinted artificial lens is often used in cataract operations today – with good reason.
Nature’s plans can therefore also be implemented technically. Those who take the strain off their eyes early on can benefit in the long term.
The usefulness of the deployment of such protective glasses can be seen in the fact that nature provides the same protection for the eye: the natural eye lens yellows in the course of life and increasingly protects the retina from blue radiation. This is an enormously important finding for cataract operations, where yellow-tinted artificial lenses are now used, after it had been found that when using un-tinted lenses, the patients quickly developed a macular degeneration after successful surgery.
Anyone who spends hours looking at a screen knows the problem: eyes become dry, start to burn or water. This is because you blink less often when concentrating on your work – and the lubrication of the eye surface decreases.
If light with a high blue content is added to this, irritation is pre-programmed. This is because dry eyes are more susceptible to damage caused by light stress. This is another reason why it is so important to consciously organize screen work – with breaks, good air and the right light protection.
Multiple stressors when workong on a screen
Blue light does not only damage the retina but also the cornea, the conjunctiva and the eye lens as the foremost barrier of the eye. It is particularly interesting that the drier the eye, the stronger the damage is [9]. This shows the multiple damage the eyes can take during screen work: By the rigid view to the screen, the blinking frequency is reduced, the surface of the eye is then no longer sufficiently supplied with liquid, especially at low humidity levels and incorrectly set screen height, and a condition known as state ” Office Eye” or “Sicca syndrome” occurs, which increases the is damage caused by the high blue light content of the screen.
[9] Veronika Marek et al.,
„Blue light phototoxity toward human corneal and conjunctival epithelial cells in basal and hyperosmolar conditions“, Free Radical Biology and Medicine 126 (2018) 27-40
Blue light is a strong signal for the body – especially if it comes at the wrong time. In the evening, it inhibits the production of melatonin, the hormone that makes us tired. It is precisely this effect of light that is a frequent subject of research in photobiology. Light can throw our internal clock out of sync; the result is often problems falling asleep and restless sleep.
But that’s not all: melatonin is also important for neutralizing oxidative damage in the brain. So if you constantly get too much light in the evening, you not only weaken your sleep, but also the protection of important nerve cells.
Impaired hormonal balance
For the sake of completeness, it should be mentioned here that blue light massively interferes with the hormonal balance: too much blue light in the evening prevents the production of the sleep hormone melatonin and disturbs endogenous circadian rhythms. Thus, on the one hand, it disturbs the night’s sleep, which is urgently needed for the regeneration of the body, and on the other hand the brain is missing the melatonin requires for the neutralization of free oxygen radicals and for neurological tumor prophylaxis.
Benefits of blue light protection in a work environment
People who have not slept properly are far less efficient at the workplace, resulting in a significantly reduced productivity, which makes it strongly advisable for employers to provide their employees with such eyewear.
Especially in children, where the eye lens is still colorless and transparent, blue light is transmitted unfiltered and places a heavy burden on the macula.
Children see the world with clear eyes – in the truest sense of the word. Their eye lenses are still completely transparent and allow blue light and even UV light to pass through unfiltered to the sensitive retina. This makes children’s eyes particularly susceptible to light stress.
Protection is particularly important in the first decade of life: many of the light-induced deposits that can later cause problems develop during this phase. Starting early with suitable protective measures lays the foundation for healthy eyes in the long term.
Starting early for optimum protection
An important point in eye protection is that it is started in good time, i.e. in childhood, since eye diseases develop very slowly, and when they are noticed, it is usually already too late. Especially in children, where the eye lens is still colorless and transparent, blue light is transmitted unfiltered and places a heavy burden on the macula.
In addition, there is another anomaly that occurs only in children: Usually, UV radiation is absorbed in the front of the eye (cornea, conjunctiva, lens), which, among other things, explains the formation of lens opacity or of cataract. Only visible radiation, including blue light, can penetrate to the retina. In the first decade of life, however, there is a transmission window in the anterior eye part at 320 nm, which leads to the strong production of lipofuscin when the child’s eye is exposed to this UV radiation. Studies have shown that about 30-40% of the lipofuscin burden of a 90-year life span arises in this first decade. In the second decade, this window closes again, but the risk of macular damage by blue light is permanently increased due to the photo-oxidative effect of lipofuscin described above [10]!
Again, it is advantageous to use protection glasses by PRiSMA®, because these are also certified for UV protection.
[10] Elizabeth R. Gaillard et al.,
“Transmission of Light to the young Primate Retina: Possible Implications for the Formation of Lipofuscin”, Photochemistry and Photobiology, 2011, 87: 18-21
Our eyes do amazing things every day – and are often exposed to enormous strain. Artificial light, digital devices, long periods of screen time: All of this has an impact on the health of the retina and the entire organism. Photobiology systematically researches these effects and can identify clear correlations.
Targeted protection from blue light can help to prevent illness, improve sleep and preserve vision for a long time. The earlier you start, the better. And: even in adulthood, every step towards eye health is worthwhile.
Protection from blue light based on photobiological research
Basic research results
Light, as the visible range of electromagnetic radiation extends from 380 nm in the more energetic blue-violet wavelength range to 780 nm in the less energetic red or near infrared range. All other colors fall between these ranges.
Clinical and laboratory studies show that blue light (400 – 480 nm) damages the retina, especially the pigment epithelium. The absorption of this radiation by flavins and cytochromes in the protein complexes of the respiratory chain in the mitochondria (energy power plants) of the cells leads to a reduction in energy production or ATP deficiency. At the same time, more free oxygen radicals are formed (oxidative stress!), which destroy the mitochondria and trigger cell death. On the one hand, this leads to the dreaded macular degeneration (macula or yellow spot is the place of sharpest vision in the retina) and even to total loss of vision [1] and, on the other hand, if the retinal ganglion cells are mainly affected, to an increase in intraocular pressure (glaucoma), which damages the optic nerve and also threatens blindness [2].
Underlying Mechanisms
The retinal pigment epithelium is protected against oxidative attacks by melanin, which binds redox-active metals; it has an antioxidative and photoprotective effect. With increasing age, the proportion of melanin decreases due to photooxidative processes and the content of melanolipofuscin increases. For blue light, lipofuscin acts as a photosensitizer and thus its action is photooxidative or phototoxic and additionally increases oxidative stress [3]. This destroys the membranes of the lysosomes and releases their contents (lysosomal enzymes) into the cytosol, where they trigger a strong inflammatory response through activation of the NLRP3 inflammasome [4].
The mitochondria in the inner segments of the photoreceptors (rods for brightness and cones for color perception) are not the sole source of free oxygen radicals. Cora Röhlecke and Prof. Richard Funk from the Institute of Anatomy of the TU Dresden discovered that the outer segments of the photoreceptors generate large amounts of oxygen radicals under the action of blue light – much more than the mitochondria. Another important result of their work was the confirmation of the mitochondrial-like activity of the outer segments [5]. Compared to other tissues, the retina is particularly susceptible to oxygen radical formation due to the very high oxygen content of the choroid and its extremely high metabolic rate!
For comparison: the effect of red light
The effect of light in the red long-wave range from 630 to 800 nm is quite different: stimulation of the respiratory chain and increased ATP formation occur here. Again, free oxygen radicals are produced, but only in a very small extent necessary for the maintenance of important signaling pathways. At the same time, repair processes are set in motion which repair damage from blue radiation [6].
What does this mean for eye protection?
Incandescent Light
For light sources that are thermal radiators, that is, when a “black body” (tungsten incandescent filament in incandescent and halogen lamps) is brought to high temperature, a radiation occurs, which emits much red and infrared light and only contains very little blue. Most importantly, this creates a continuous spectrum, i.e. It contains all !! wavelength components, not just individual (discrete) spectral lines. With such light sources and the solar radiation, except for the midday light in summer, there is no danger to the eye and no protective glasses are required. Photobiologically, any small damage caused by the negligible blue components is immediately repaired by the disproportionate red components or does not occur at all. The body protects itself against the high luminance (glare) of the sun or halogen lamps by closing the eyes. Possible overdoses can be detected by the accompanying heat.
Gas discharge lamps and LED light
Ganz anders liegt die Situation bei Gasentladungslampen, zu denen die „Leuchtstoffröhren bzw. Energiesparlampen“ zählen, und bei den Leuchtdioden (LED). Hier wird jeweils eine sehr schmale Spektrallinie sehr hoher Intensität erzeugt (bei Leuchtstofflampen die UV-Linie mit 254 nm und bei der „weißen“ LED die blaue Linie mit etwa 450 nm) die dann durch Leuchtstoffe (Phosphore) in sichtbare Strahlung umgewandelt wird. Bei Leuchtstofflampen können das bis zu 8 Leuchtstoffe sein, um einem kontinuierlichen Spektrum so nahe wie möglich zu kommen, man spricht dann von 8-Banden-Lampen. Bei den meisten bisher eingesetzten weißen LED wird nur eine Phosphorschicht eingestzt, die blaues in gelbes Licht umwandelt. Viel blaues und mäßig viel gelbes Licht gibt das allseits bekannte „kalte“ LED-Licht.
In the meantime, the industry is trying to produce a sunlight-like “white” light under the heading HCL (Human Centric Lighting), either by producing strong violet radiation that is converted into blue, green, and red with one phosphor each, or through the use of discrete blue, green and red LEDs in a common housing. No matter which technology is used here, these light sources do not currently approach the quality of the light from temperature radiators, in which the intensity of the spectral lines increases with increasing wavelength.
Protection against disproportionate blue content
This means that due to the widespread use of fluorescent lamps and LEDs (for example as backlight for PC and TV flat screens), the disproportionate amount of blue in the emission spectrum has to be filtered out by amber protection lenses in order to protect the health of the eyes [7]. Such lenses must be of high quality and above all it has to be tested that they reliably filter out the wavelength range of 400-500 nm and comply with the required specifications. Here, the company “INNOVATIVE EYEWEAR” offers a wide range of CE-specified glasses of the PRiSMA® brand, with the possibility to choose the filtering strength and the resulting remianing color perception. There are even certified safety glasses for night driving. In addition, such glasses allow better recognition of contours and contrasts and increase the depth of field. Another good reference for this company is the long-term cooperation with Dr. med. Alexander Wunsch [8], a designated expert on eye health.
Nature as a model
The usefulness of the deployment of such protective glasses can be seen in the fact that nature provides the same protection for the eye: the natural eye lens yellows in the course of life and increasingly protects the retina from blue radiation. This is an enormously important finding for cataract operations, where yellow-tinted artificial lenses are now used, after it had been found that when using un-tinted lenses, the patients quickly developed a macular degeneration after successful surgery.
Multiple stressors when working on a screen
Blue light does not only damage the retina but also the cornea, the conjunctiva and the eye lens as the foremost barrier of the eye. It is particularly interesting that the drier the eye, the stronger the damage is [9]. This shows the multiple damage the eyes can take during screen work: By the rigid view to the screen, the blinking frequency is reduced, the surface of the eye is then no longer sufficiently supplied with liquid, especially at low humidity levels and incorrectly set screen height, and a condition known as state ” Office Eye” or “Sicca syndrome” occurs, which increases the is damage caused by the high blue light content of the screen.
Impaired hormonal balance
For the sake of completeness, it should be mentioned here that blue light massively interferes with the hormonal balance: too much blue light in the evening prevents the production of the sleep hormone melatonin and disturbs endogenous circadian rhythms. Thus, on the one hand, it disturbs the night’s sleep, which is urgently needed for the regeneration of the body, and on the other hand the brain is missing the melatonin requires for the neutralization of free oxygen radicals and for neurological tumor prophylaxis.
Benefits of blue light protection in a work environment
People who have not slept properly are far less efficient at the workplace, resulting in a significantly reduced productivity, which makes it strongly advisable for employers to provide their employees with such eyewear.
Starting early for optimum protection
An important point in eye protection is that it is started in good time, i.e. in childhood, since eye diseases develop very slowly, and when they are noticed, it is usually already too late. Especially in children, where the eye lens is still colorless and transparent, blue light is transmitted unfiltered and places a heavy burden on the macula.
In addition, there is another anomaly that occurs only in children: Usually, UV radiation is absorbed in the front of the eye (cornea, conjunctiva, lens), which, among other things, explains the formation of lens opacity or of cataract. Only visible radiation, including blue light, can penetrate to the retina. In the first decade of life, however, there is a transmission window in the anterior eye part at 320 nm, which leads to the strong production of lipofuscin when the child’s eye is exposed to this UV radiation. Studies have shown that about 30-40% of the lipofuscin burden of a 90-year life span arises in this first decade. In the second decade, this window closes again, but the risk of macular damage by blue light is permanently increased due to the photo-oxidative effect of lipofuscin described above [10]!
Again, it is advantageous to use protection glasses by PRiSMA®, because these are also certified for UV protection.
Summary
By consistently wearing protective glasses that filter out all spectral lines below 500 nm, the effect of blue light on the following diseases can be prevented
Dipl.-Ing. Dr. Helmut Walter
Professor at the Higher Technical Teaching and Research Institute Waidhofen
Research Laboratory for Biomedical Technology
Ferdinand Andristr. 2/3
A-3340 WAIDHOFEN
References:
[1] Kasun Ratnayake et al., “Blue light excited retinal intercepts cellular signaling”, Scientific Reports (2018) 8:10207, DOI:10.1038/s41598-018-28254-8
[2] Neville N. Osborne et al., „Visual light effects on mitochondria: The potential implications in relation to glaucoma”, Mitichondrion 36 (2017) 29-35
[3] Sally M. Yacout et al., “Characterization of Retinal Pigment Epithelial Melanin and Degraded Synthetic Melanin Using Mass Spectrometry and In Vitro Biochemical Diagnostics”, Photochemistry and Photobiology, 2019, 95: 183-191
[4] Carolina Brandstetter et al., “Inflammasome priming increases retinal pigment epithelial cell susceptibility to lipofuscin phototoxicity by changing the cell death mechanism from apoptosis to pyroptosis”, Journal of Photochemistry and Photobiology, B: Biology, 161 (2016) 177-183
[5] Cora Roehlecke et al, “Stress reaction in outer segments of photoreceptors after blue light irradiation”, PLoS ONE 8(9). E71570
[6] Boris T. Ivandic et al., “Low-Level Laser Therapy improves Vision in Patients with Age-Related Macular Degeneration”, Photomedicine and Laser Surgery”, Vol. 26, no. 3, 2008
[7] Kaho Hiromoto et al., “Colored lenses suppress blue light-emitting diode light-induced damage in photoreceptor-derived cells”, Journal of Biomedical Optics 21 (3) 035004 March 2016
[8] A. Wunsch, “Licht ist Leben- aber falsches Licht kann krank machen!”, AUGENBLICK Ausgabe 12, Mai 2012
[9] Veronika Marek et al., „Blue light phototoxity toward human corneal and conjunctival epithelial cells in basal and hyperosmolar conditions“, Free Radical Biology and Medicine 126 (2018) 27-40
[10] Elizabeth R. Gaillard et al., “Transmission of Light to the young Primate Retina: Possible Implications for the Formation of Lipofuscin”, Photochemistry and Photobiology, 2011, 87: 18-21
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