In the context of work or leisure, the cathode screen has become essential in our daily lives. The proliferation of computers has led to the widespread use of terminals in the workplace and at home. Yet, they often have a bad reputation, accused of causing visual disturbances, dry eyes or worse.
What are the risks?
During the last thirty years, computer screens have invaded workplaces. According to the World Health Organization (WHO), more than 150 million jobs are currently in use worldwide.
Shortly after their introduction in the workplace, these screens were quickly accused of all the ills: headaches, vertigo, fatigue, cataracts, rashes, problems related to pregnancy … Suspects, the different radiations (luminous, X, electromagnetic, etc.) were, in turn, out of the question.
The X-rays of very low energy produced in the cathode ray tube are stopped by the glass of the screen and do not escape from the screen.
The light rays include ultraviolet (UV), visible radiation and infrared (IR). The IR is dissipated as heat by the terminal. Very small amounts of UV are emitted by the tube but, according to the WHO, they remain well below those passing through a window on a winter day. According to François Cail, a researcher at the “Man at Work” department of the National Research and Safety Institute (INRS) exposure to a month of work in front of a screen is equivalent to one minute in full sun.
Finally, the electronic circuits of VDTs produce electric and electromagnetic fields of low and high frequency. The latter is often at the forefront of the accused.
For about forty years, electromagnetic radiation has been particularly studied. The sources of these emissions are many: power lines, appliances driven by electric motors, telecommunication and broadcasting facilities, mobile phones and computer screens. However, the emission of electromagnetic radiation by the screens remains well below the authorized standards. Expert committees consider them too weak to have an effect on health. In 1997, the National Research Council of the United States concluded that exposure to magnetic fields detected in the domestic environment posed no danger to humans.
In addition, no study has revealed relationships between rashes, for example, or miscarriages and various computer screen emissions.
No effect of electromagnetic fields on the reproductive process has been shown: if there are effects related to this type of work, they would be related to stress.
Similarly, the dermatological problems observed in the Scandinavian countries are more related to environmental factors (excessive drought of the air) and psychological (stress).
No link could be found between cataracts and eye disorders and screen work. “Since 1982, Swedish researchers have estimated that to contract a cataract, it would be necessary to remain in front of a screen for 650 years,” says François Cail. However, according to WHO, the brightness and reflection of screens can cause eyestrain and headaches in extreme situations.
According to the Quebec Association of Optometrists, eye strain is most often favored by a visual impairment: close visual acuity, focusing ability, convergence, ocular movements, tear system, contrast sensitivity … “According to Swiss studies, 20 to 30% of the population suffers from slight non-handicapping visual defects. The screen work is not responsible for these problems but serves as revealing, “says François Cail. Reflections on the screen, insufficient eye-screen distance (less than 50 cm) and poor definition are all aggravating factors. The particularity of the work on screen (axis of the gaze higher) also causes an insufficient blinking of the eyes. This fixity can cause evaporation of lachrymal secretions and therefore dry eye. To avoid these inconveniences, it is advisable to take breaks and it is recommended that the top of the monitor is at eye level.
These disorders are not durable and can be relieved after a little rest and a better ergonomic workstation. Very often, faulty lighting is accused.
So far, it appears that all these fears remain unfounded. Recently, other misdeeds of screen work are highlighted: a proliferation of musculoskeletal disorders (MSDs) to the forearm, wrist, index finger or thumb. In the United States, 22% of these disorders are now due to screen work.