Reading or working in front of a computer screen with bright light in the background is capable of affecting not only our eye muscles, but also our neck muscles, according to research.
Study results
The results of the study at the University College of Southeastern Norway, led by Randi Mork and colleagues, showed that exposure to direct and bright light affects the trapezius muscle, probably due to an interaction between the visual system, the sympathetic nervous system and the head muscle stabilisation system.
The results of this study were published in a prestigious journal in the field (Optometry and Vision Science), and may well help in the proper design and organisation of workplaces (ergonomics).
What causes long hours in front of the computer?;
Previous studies have shown that working in front of a computer screen can cause discomfort in the eyes, neck and shoulders, indicating that there is a correlation between these symptoms.
Comparing the observation of objects that are far away from us with the observation of a computer screen, we understand that in the second case a greater load is created on the muscles in and around our eyes.
Also, being in front of a computer for several hours a day increases eye fatigue, as convergence (the ability of eyes to move together in order to maintain the image we see as a single rather than a double image) and adaptation (the ability of the eye to change its power in order to maintain a clear image and focus at all distances) of the eyes play a constant and primary role in close-up work. Similarly, the muscles of the neck are affected by the stabilisation of the gaze, which implies constant stabilisation of the head. The bright light caused by the computer screen affects the response of the eye adaptation and can lead to increased discomfort in and around the eyes, as well as affecting reading performance.
How does the bright light behind our screen affect us?;
In order to examine how bright light affects the muscles in the neck and shoulder blade area, the researchers asked 15 healthy students with normal vision from the Department of Optometry at the University College of Southeastern Norway to participate in a study. Twelve of the students were women. The average age of the participants was 19-25 years old and they had been using computers for an average of 11 years.
Criteria for participation and exclusion of the study
The study excluded people who had chronic neck problems, dyslexia, other chronic conditions, or were taking medications on a daily basis that could affect blood circulation, or affect the participants’ vision. The average visual acuity of the participants was quite high (about 10/10). The eight students in the study who were contact lens wearers or wore glasses had to wear their corrective lenses throughout the study.
How was the study done?;
The researchers assigned participants to read a text on a screen under two different conditions: 30 minutes in an optimal environment and ergonomic workstation and 30 minutes exposed to bright light behind the screen. The order of conditions was chosen randomly. Between the two conditions there was a 5-minute break for all participants. The researchers asked participants to sit in a normal position and optimized the positions according to international recommendations. To keep the trapezius muscle as relaxed as possible, participants were allowed to rest their forearms on the seat supports. The height of the table was above elbow height when participants were seated.
Participants were asked to read a text in front of a 24-inch liquid crystal display with a resolution of 1920×1200 pixels and an average refresh rate of 69.5Hz. The screen had an anti-reflective coating and was connected to a laptop computer. In order to keep participants focused, the researchers pointed out that they would have to answer certain questions related to text comprehension later on. Between breaks, participants could rest, but not walk, and there was also a closed-circuit monitor inside the room. The computer monitor and bright light source were turned off during the breaks.
The researchers created bright light with two large flat luminaires, placed about 70cm behind the computer screen, to simulate the placement of windows behind the computer screen and ensure symmetrical exposure to the glare in both eyes.
They constructed the luminaires from translucent diffusion material with 60Watt fluorescent lamps. The intensity of the luminaires ranged from 2800-5100 cd/m2, which is similar to the brightness of a window on a cloudy day. During the optimum condition, brightness levels were 155 cd/m2on the monitor's desktop and 46cd/m2on the background. These values coincide with the recommended brightness ratio of 5:3:1 specified for a workplace.
When a participant was under bright light conditions, the brightness was 155cd/m2at the workstation, 590 cd/m2on the computer screen and 4268 cd/m2on the background. This ratio of 1:4:28 is considered excessive background light.
Participants rated their discomfort or discomfort for various anatomical areas on a visual anatomical scale. The researchers respectively used electromyography to objectively measure participants' electrical activity in the trapezius and sphincter muscle. Blood flow in the muscle area and heart rate were also measured.
Symptoms of exposure to bright light in front of a computer: Study results
Regarding the results, initially there was no statistically significant difference between the two reading conditions (bright light and optimal light). However, after 10, 20 and 30 minutes of reading, a higher incidence of eye pain was observed when patients were exposed to bright light (glare) compared to optimal light. This difference was statistically significant (p=0.011). Participants also reported dry eye symptoms, blurred vision, photophobia and headache in the bright light condition, compared to optimal lighting conditions, after 30 minutes of reading. Eye fatigue was more pronounced in the bright light condition, as was neck pain. It was further observed that eye pain, neck pain and general fatigue increased with time in both light conditions.
The researchers detected more muscle activity in the sphincter muscle in the bright light condition, compared to optimal lighting conditions. Blood flow to the trapezius muscle was also higher in the bright light than in the optimal condition. A correlation was found between sphincter muscle activity, trapezius blood flow and neck pain in both lighting conditions to which participants were exposed.
Both psychological stress and exposure to bright light have been shown by previous studies to increase heart rate. However, in this study there was no significant difference in heart rate between the dazzle and optimal lighting conditions.
The researchers conclude that the eyes and the neck are closely linked and this suggests the important role that the neck muscles play in normal visual performance, as well as in stabilising the gaze. In addition, the perception of proprioception (where my body is in relation to space and where my body parts are in relation to each other), which is extracted by cranial muscles, may influence motor activity and may be a possible explanation for how we see.
