If you suffer from computer vision syndrome (CVS) in one of its manifestations (symptoms) you want to find out what are the different causes for it so you can start looking for solutions. You can find some of the causes many places, but very few (if any) sources also list some of the less well known causes like font rendering, lack of IR-A light, and flicker.
Disclaimer: I am NOT a vision scientist nor a physician but a more computer glare and light-sensitive person, hence my interest in what causes computer vision syndrome.
Intense use of the eyes is the generic cause of eye strain – or asthenopia – in a person with normal vision. Activities likely to cause eye strain are extended periods of driving, reading, writing, sewing, … Of course the use of digital screens is similar to all these, but in addition, what causes computer vision syndrome (CVS) may be a constellation of many other issues that are unique to digital screens. Secretaries, accountants, bookkeepers, draftsmen, are some obvious jobs with a greater risk of eye strain [Is all Asthenopia the Same? (2003)]. But as we are becoming increasingly digitized (at work and otherwise) the experience of computer vision syndrome is starting to affect more and more people.
Eye strain may be further intensified when using the eyes intensely under certain adverse conditions such as straining to see in sub-optimal lighting conditions or exposure to glare (contrast in brightness). Both of these quite common in digital screen-based activities.
Add possible unfavorable characteristics of one’s visual system (for example greater sensitivity to light, glare, or blue light) and sooner or later the result will be computer vision syndrome or even chronic eye strain.
Inadequate prescription is a major cause of CVS [Computer vision syndrome: A review (2014)], but it is not specific to digital screens and therefore not listed below among the CVS causes below.
What else causes computer vision syndrome
In terms of human evolution digital screens are a very recent phenomenon. Yet they differ in many ways from natural light human eyes had been used to view:
– fonts displayed by screens tend to be fuzzy: CVS may also result from trying to continuously focus the un-focusable
– computer screens are prone to glare and reflections; in nature, only water and snow might compare – both are hard on the eyes, but luckily not very common settings for most of us
– computer screens are sources of light; our eyes evolved viewing reflections of light, not its sources
– computer screens don’t emit near-infrared (IR-A) light (nor do other energy saving light sources, prevalent in many work environments), yet – based on the evidence of its benefits elsewhere in our body [Is It Time to Consider Photobiomodulation As a Drug Equivalent? (2013), The Nuts and Bolts of Low-level Laser (Light) Therapy (2012)] – near-infrared light is hypothesized to facilitate important, regenerative processes in our eyes as well
– most computer screens flicker, particularly at lower brightness levels – natural light sources don’t
– faint ghost images on the back of your computer glasses lenses, on your screen or screen protector
– finally, they emit High Energy Visible (HEV) or blue light with higher intensity compared to longer wavelengths. Said differently, the composition of light – spectral power distribution (SPD) – emitted by screens is substantially different from the spectral characteristics of natural light sources.
Moreover, blue light intensity in light reflected from objects we view in nature is further attenuated: very few surfaces are naturally white or blue, meaning that they absorb blue light while reflecting other, longer wavelengths.
Researchers estimate that 5% to 12% of the population suffers from severe visual stress, and imply that high blue light is to be blamed for the majority of the cases [Levels of visual stress in proficient readers: Effects of spectral filtering of fluorescent lighting on reading discomfort; 2015].
Other possible CVS causes
Our vision is a very complex phenomenon that has to do with our eyes, but also to a large extent with our brain. And there, many inexplicable things happen. For example, there are people who suffer from different types of visual stress from other wavelengths. If you find that what causes your computer vision syndrome is not listed above, you should also consider investigating Irlen syndrome.
Because in some cases blue light is preferred to other wavelengths for greater visual comfort (watch this 8 min video about Irlen syndrome).
If you think some possible causes might be missing from the list above, please let me know in the comments or write to me.