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According to a survey by a contact lens manufacturer, office workers spend around 6.5 hours a day sitting in front of a computer screen. This, not counting the additional time spent on the smartphone, tablet and any other screen consulted in the context of private life! Laboratory research has suggested that excessive exposure to blue light can damage certain sensitive cells in the retina. As a result, many manufacturers now market blue light filters. However, one study has questioned the actual effectiveness of these devices on eye fatigue.
Why is using a computer more eye strain than reading printed documents? Mainly because we tend to blink less when we are in front of a screen. Also, we generally don’t get the ideal position, both in terms of distance and viewing angle, which can lead to additional stress. This is why, in addition to headaches, spending too much time in front of a screen sometimes has long-lasting effects on vision.
Respondents complain of difficulty seeing (and sometimes need to enlarge text) and loss of focus flexibility, the eye’s ability to “adapt” to distance. Eye dryness and pain are other symptoms reported by nearly half of the survey participants. All of these symptoms are now grouped together under the name of “digital eye strain” or “computer vision syndrome,” disorders that are supposed to be relieved by anti-blue light filters attached to eyeglasses and optical lenses.
Wavelengths capable of reaching the retina
“When you look at a screen, you are so involved that you forget to blink. The blink rate ranges from 15 times per minute to five to seven times per minute, ”says Dr. Matthew Gardiner, an ophthalmologist at Massachusetts Eye and Ear Infirmary. Blink helps restore the tear film that protects the surface of the eye. Without it, vision becomes blurry and uncomfortable. Fortunately, this dry eye, which can be very painful, can be easily and quickly relieved with a few drops of saline solution.
But overuse of screens has other more worrisome effects. Studies have suggested that the blue light generated by screens can affect the function of photoreceptors and the retinal pigment epithelium, inducing photochemical damage and cell death due to apoptosis. Indeed, these short wavelengths, 400 to 450 nanometers, therefore high energy, are capable of crossing the cornea and lens to the retina. This can accelerate the onset and development of conditions such as age-related macular degeneration (AMD).
Most digital equipment on the market today presents minimal risks because they are designed to emit only a small amount of blue light (or at least an amount that does not directly threaten eye health). However, no studies have evaluated the impact of prolonged exposure to this light.
To reduce the symptoms of digital eye fatigue and decrease the risk of retinal damage, many manufacturers offer blue light filters (ALBs). A 2019 study published in the journal Optometry and Vision Science aimed to examine the effect of such a filter on visual fatigue during a sustained near vision task.
The team led by Dr. Mark Rosenfield, a professor at the State University of New York School of Optometry, asked 23 young people with normal vision to read content on a tablet-like screen. The latter was covered with an ALB filter or a neutral density filter that produced an equal screen luminance. The accommodation response, the pupil diameter and the space between the eyelids were measured at 0, 9, 19 and 29 minutes after the start of the reading task. Participants were also asked to complete a questionnaire to quantify the symptoms of visual fatigue.
No significant effect on eyestrain
The ALB filter blocked 99% of the wavelengths between 400 and 500 nm. The mean total symptom scores reported with the ALB and neutral filters were 42.83 and 42.61, respectively. Regarding the accommodation of the eye and the spacing of the eyelids, no significant difference was observed between the two types of filters. Therefore, the ALB filter was not shown to be more effective than the neutral filter.
Since few of the available ALB devices can block nearly 100% of this light, the team repeated the experience with commercially available spectacle lenses, which typically only block about 20-25% of the blue. This second study was conducted double-blind, without the subjects knowing whether they were looking through an ALB filter or not. But the researchers got the same results: Blue-blocking filters did not produce significant changes in symptoms of digital eyestrain. After an interview, Dr. Rosenfield has stated that the use of these filters is to be seen in revenge and is pertinent to avoid that the lumiere bleue n’interfère with the cycle circadien de l’organisme, notamment lorsque l’on consult are smartphone late dans the night.
While the effectiveness of ALB filters is therefore questionable, eye fatigue and dryness are still very real. Therefore, the American Academy of Ophthalmology offers some simple tips for limiting symptoms, starting with recommendations related to the workstation: the screen should be at arm’s length, about two feet away, and should be adjusted so that the gaze is tilted slightly downward. In addition, care must be taken to adjust the ambient lighting so that there is not too much difference in brightness between the screen and the work area (if the screen is too bright, the eyes tire more quickly).
Then specialists advise taking regular visual breaks, adhering to the following rule: every 20 minutes, look at an object in the distance for 20 seconds, which will give your eyes a small moment of relaxation. It is also advisable to have artificial tears or physiological saline on hand to help lubricate the eyes when they become too dry, especially in winter when the heaters dry the room even more. Finally, an annual eye exam by a specialist is strongly recommended to check eye health and detect any pathology.
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