Health

How Blue Light Damages Cells In Your Eyes

How Blue Light Damages Cells In Your Eyes

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During daylight, blue wavelengths of light can be beneficial, playing an important role in setting circadian rhythms, boosting attention and mood. But we didn’t evolve to be exposed to it as much as we are. In addition to the ample blue light in sunlight, most of the light we are exposed to via digital devices is also blue. For example, the most common type of LED used in electronic devices is a white-light LED, which actually has a peak emission in the blue wavelength range (400 – 490 nm). Moreover, the eye’s cornea and lens are unable to block or reflect blue light.

Increasing evidence suggests that blue light has a dark side. At night, it can suppress the secretion of melatonin and wreak havoc on our circadian rhythms, and recent studies have shown that extended exposure to blue light can damage the retina, though exactly how it does this has not been clear.

Now, new research from the University of Toledo demonstrates that when blue light hits a molecule called retinal, it triggers a cascade of chemical reactions that are toxic to cells in the retina of the eye.

It’s a bit paradoxical, because we actually need retinal, which is a form of vitamin A, in order to see in the first place.

Confocal microscope image of rod and cone photoreceptors in a human retina. Fluorescent probes have been used to identify rod photoreceptors (green) and cone photoreceptors and horizontal cells (red)Dr. Robert Fariss, National Eye Institute, NIH; Creative Commons 2.0

There are two types of ‘photoreceptor’ cells in the retina responsible for detecting light: rods and cones. Rods make up the majority, and they rely on a protein called rhodopsin in order to detect light.

The molecule retinal, which is able to absorb light, sits in its own specialized spot within the rhodopsin protein. When photons of light hit retinal, it changes shape ever so slightly. It’s like a small twist, really, but because there’s not much room, it nudges part of rhodopsin out of the way. This slight physical readjustment sets of a progression of chemical changes that ultimately results in signals being sent along the optical nerve in the brain.

Ball and stick model of retinal. Carbon (black), oxygen (red), hydrogen (white)Jynto via Wikimedia Commons; Creative Commons 1.0

The rhodopsin protein binds retinal near its centerS. Jähnichen via Wikimedia Commons

"You need a continuous supply of retinal molecules if you want to see," says Ajith Karunarathne of the University of Toledo, who led the current study. "Photoreceptors are useless without retinal, which is produced in the eye."

However, Karunarathne and his colleagues discovered that when photoreceptor rod cells were exposed to blue light in the presence of retinal, this triggers a distortion in an important protein in the cell membrane. This was followed by an increase in both oxidative damage and calcium levels in the cells.

"It’s toxic," says Kasun Ratnayake, a PhD student who was also involved in the study. "If you shine blue light on retinal, the retinal kills photoreceptor cells as the signaling molecule on the membrane dissolves."

"Photoreceptor cells do not regenerate in the eye," he adds. "When they’re dead, they’re dead for good."

If retinal was absent when the photoreceptor cells were exposed to blue light, then no toxicity was observed. Moreover, retinal-associated toxicity did not occur when the researchers used other wavelengths of light, such as red, yellow or green.

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Given all the blue light we’re exposed to, Karunarathne wanted to know why our vision doesn’t degrade more rapidly than it does.

He and his colleagues found that when an anti-oxidant molecule called alpha-tocopherol is present, which is a form of vitamin E, it reduces the damage caused by blue light and retinal, and prevents cells from dying. 

Unfortunately, as we age, vitamin E levels dwindle, and we lose this protection. Progressive destruction of light-detecting cells in the eyes due to prolonged exposure to blue light can therefore lead to age-related macular degeneration, which is a leading cause of blindness. 

"Every year more than two million new cases of age-related macular degeneration are reported in the United States," says Karunarathne. 

"It’s no secret that blue light harms our vision by damaging the eye’s retina. Our experiments explain how this happens, and we hope this leads to therapies that slow macular degeneration, such as a new kind of eye drop," he adds.

"By learning more about the mechanisms of blindness in search of a method to intercept toxic reactions caused by the combination of retinal and blue light, we hope to find a way to protect the vision of children growing up in a high-tech world."

Original Research:

Ratnayake, K et al (2018) Blue light excited retinal intercepts cellular signalling. Scientific Reports 8:10207 DOI:10.1038/s41598-018-28254-8

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During daylight, blue wavelengths of light can be beneficial, playing an important role in setting circadian rhythms, boosting attention and mood. But we didn’t evolve to be exposed to it as much as we are. In addition to the ample blue light in sunlight, most of the light we are exposed to via digital devices is also blue. For example, the most common type of LED used in electronic devices is a white-light LED, which actually has a peak emission in the blue wavelength range (400 – 490 nm). Moreover, the eye’s cornea and lens are unable to block or reflect blue light.

Increasing evidence suggests that blue light has a dark side. At night, it can suppress the secretion of melatonin and wreak havoc on our circadian rhythms, and recent studies have shown that extended exposure to blue light can damage the retina, though exactly how it does this has not been clear.

Now, new research from the University of Toledo demonstrates that when blue light hits a molecule called retinal, it triggers a cascade of chemical reactions that are toxic to cells in the retina of the eye.

It’s a bit paradoxical, because we actually need retinal, which is a form of vitamin A, in order to see in the first place.

Confocal microscope image of rod and cone photoreceptors in a human retina. Fluorescent probes have been used to identify rod photoreceptors (green) and cone photoreceptors and horizontal cells (red)Dr. Robert Fariss, National Eye Institute, NIH; Creative Commons 2.0

There are two types of ‘photoreceptor’ cells in the retina responsible for detecting light: rods and cones. Rods make up the majority, and they rely on a protein called rhodopsin in order to detect light.

The molecule retinal, which is able to absorb light, sits in its own specialized spot within the rhodopsin protein. When photons of light hit retinal, it changes shape ever so slightly. It’s like a small twist, really, but because there’s not much room, it nudges part of rhodopsin out of the way. This slight physical readjustment sets of a progression of chemical changes that ultimately results in signals being sent along the optical nerve in the brain.

Ball and stick model of retinal. Carbon (black), oxygen (red), hydrogen (white)Jynto via Wikimedia Commons; Creative Commons 1.0

The rhodopsin protein binds retinal near its centerS. Jähnichen via Wikimedia Commons

“You need a continuous supply of retinal molecules if you want to see,” says Ajith Karunarathne of the University of Toledo, who led the current study. “Photoreceptors are useless without retinal, which is produced in the eye.”

However, Karunarathne and his colleagues discovered that when photoreceptor rod cells were exposed to blue light in the presence of retinal, this triggers a distortion in an important protein in the cell membrane. This was followed by an increase in both oxidative damage and calcium levels in the cells.

“It’s toxic,” says Kasun Ratnayake, a PhD student who was also involved in the study. “If you shine blue light on retinal, the retinal kills photoreceptor cells as the signaling molecule on the membrane dissolves.”

“Photoreceptor cells do not regenerate in the eye,” he adds. “When they’re dead, they’re dead for good.”

If retinal was absent when the photoreceptor cells were exposed to blue light, then no toxicity was observed. Moreover, retinal-associated toxicity did not occur when the researchers used other wavelengths of light, such as red, yellow or green.

Given all the blue light we’re exposed to, Karunarathne wanted to know why our vision doesn’t degrade more rapidly than it does.

He and his colleagues found that when an anti-oxidant molecule called alpha-tocopherol is present, which is a form of vitamin E, it reduces the damage caused by blue light and retinal, and prevents cells from dying. 

Unfortunately, as we age, vitamin E levels dwindle, and we lose this protection. Progressive destruction of light-detecting cells in the eyes due to prolonged exposure to blue light can therefore lead to age-related macular degeneration, which is a leading cause of blindness. 

“Every year more than two million new cases of age-related macular degeneration are reported in the United States,” says Karunarathne. 

“It’s no secret that blue light harms our vision by damaging the eye’s retina. Our experiments explain how this happens, and we hope this leads to therapies that slow macular degeneration, such as a new kind of eye drop,” he adds.

“By learning more about the mechanisms of blindness in search of a method to intercept toxic reactions caused by the combination of retinal and blue light, we hope to find a way to protect the vision of children growing up in a high-tech world.”

Original Research:

Ratnayake, K et al (2018) Blue light excited retinal intercepts cellular signalling. Scientific Reports 8:10207 DOI:10.1038/s41598-018-28254-8