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Does Dark Mode on Your Devices Reduce Eye Strain?

Posted on March 10th, 2020
Does Dark Mode on Your Devices Reduce Eye Strain?

Dark Mode seems to be a recent trend that’s taken off in 2020. Switching your screens, for example, from displaying a white background with black text to a black background with white text is being promoted by many as a healthier vision choice. Apple and Google operating systems now offer dark mode, also known as “night mode,” in iOS 13 and Android 9 and 10. More and more popular apps are asking users which mode they prefer. But why was dark mode created in the first place? And what do we really know about dark mode and its effect on vision? We explore some of the information out there today.

Screen Time and Your Vision

We do know there can be risks to prolonged screen time. Particularly, there are studies that show blue light emitted from technology can suppress the hormone melatonin, which is important for sleep. In 2012, Harvard Medical School published a health letter that outlined results from a blue light experiment they conducted: 

“While light of any kind can suppress the secretion of melatonin, blue light at night does so more powerfully. Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to exposure to green light of comparable brightness. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours).”

From this Harvard study, it could be true that blue light does effect circadian rhythms and potentially can disrupt sleep. It’s findings like this, which may have instigated the emergence of dark mode into our technologies. While dark mode can reduce blue light, it’s unclear if this feature’s positives outweigh their negatives. Dr. Euna Koo, an ophthalmologist at the Stanford Byers Eye Institute told CNN Business, "I do not think dark mode affects eye health in any way given the data that is out there in the literature. The duration of use is likely much more important than the mode or the intensity of the brightness of the device when it comes to the effect of this dark mode on eye fatigue and potentially eye health."

Dr. Koo makes a valuable observation regarding the duration of screen time, which should be considered regardless of which mode, dark or light, you are switched to. However, it’s also essential to be weary of the possible affects dark mode presents on its own.

Dark Mode and Uncorrected Astigmatism

Uncorrected astigmatism is a common eye defect that occurs when the surface of the cornea, the lens of the eye, becomes imperfect in shape and light is no longer evenly refracted and properly concentrated on the retina.

Basically, uncorrected astigmatism causes distorted vision because of the cornea’s inability to focus light on the retina. What is interesting about uncorrected astigmatism is its possible connection to dark mode. There has been some preliminary research first reported by Gizmodo from the Sensory Perception & Interaction Research Group of The University of British Columbia on the correlation between uncorrected astigmatism and dark displays:

“People with astigmatism (approximately 50% of the population) find it harder to read white text on black than black text on white. Part of this has to do with light levels: with a bright display (white background) the iris closes a bit more, decreasing the effect of the "deformed" lens; with a dark display (black background) the iris opens to receive more light and the deformation of the lens creates a much fuzzier focus at the eye.”

Considering this research, it is possible that dark mode could be more difficult for people with uncorrected astigmatism because of the iris’s opening reaction to dark displays and the fuzzy vision that results. For those reading on dark mode with uncorrected astigmatism, this could potentially cause eyes to fatigue more quickly than if on a regular light display.  

Text and Background Colour on Readability

There may also be a connection between readability and the typical black text on white background (positive polarity) versus white text on black background (negative polarity). Axel Buchner from the Department of Experimental Psychology at the University Düsseldorf, conducted several studies on positive and negative polarity displays. Buchner’s 2007 study examined the effect of background polarity on proofreading performance and found positive polarity displays yielded better performance versus negative polarity. In 2013, Buchner researched the link between pupil size and proofreading on these displays, finding a “positive polarity advantage.” The conclusion was that black text on white background provided higher luminance, decreasing pupil size and yielding a sharper retinal image.

While these studies are not absolute, they do suggest a possible disadvantage to white text on black background and reading on dark mode displays. Dark mode could possibly block out blue light, but the negative polarity on our screens may increase the difficulty of reading and ultimately could lead to more eye strain for some individuals. What we do know is that research continues to explore these features as digital technology evolves.

Safe Ways of Blocking Blue Light

You might be wondering what the best solution for eye protection is when it comes to screen time. If you do not suffer from uncorrected astigmatism, dark mode could be an option for you to block out blue light. However, talk to your optometrist about how to properly adjust your screen usage with uncorrected astigmatism. You may want to discuss with them this issue of light mode vs. dark mode and which would be more suitable for you. FYidoctors offers glasses with a blue light lens coating that can block out blue wavelengths, which could be a potential option to try. Have a conversation with your optometrist about whether this coating is necessary for your eye health. To find out more, visit an FYidoctors location near you to talk to our team of professionals.