Computer Vision Syndrome (CVS) is a term used to describe a wide range of visual symptoms experienced by operators of visual display terminals (VDT) . As many as 90% of VDT users report at least one symptom (ocular or non-ocular) , but the cause of these symptoms is often overlooked by employees, ergonomist and occupational health representatives. In this week’s blog post, we would like to look at some causes of these symptoms.
The impact of image quality on oculomotor functions
Understanding the development of CVS begins with attempting to understand how images displayed on a screen are interpreted by our eyes and brain. The accuracy and speed with which the eyes and brain are able to decipher information is dependent on the properties of the image. For example, images that are too small or at too low of a resolution, too bright, too blurry or flicker are difficult to decipher. The oculomotor system makes adjustments in an attempt to improve the viewing/understanding of these difficult to decipher images. However, these adjustments are at the root of developing the symptoms associated with CVS.
The first adjustment is to squint. Squinting improves visual accommodation and vergence, and therefore improves our ability to recognize the small and out of focus objects . However, squinting requires activity of highly-fatigable (fast twitch) ocular musculature, and previous research has noted the association between increased eye muscle activity and sensations of eye-tiredness during a 2-hour computer task .
The second adjustment involves reduced frequency and quality of blinking [1, 3, 4]. Blinking helps to protect the eyes from becoming dry and irritable by spreading moisture and protective oils over the eye surface. But, it also interrupts the flow of information from the screen to the optic nerves. Maintaining the eyes in an open position improves our ability to decipher images. However, increased exposure of the eyes to the air increases moisture evaporation, and temporarily impairs the function of ocular glands that produce tears/moisture and sebaceous oils [5, 6]. The result is eye dryness and irritation that leads to discomfort and difficulty maintaining work performance.
The impact of workstation design on oculomotor functions :
Screen height can also impact on the evaporation of eye moisture. Raised screens require the eyes to look straight ahead or upward; this upward position of the eye increases surface exposure which also increases moisture evaporation [1, 5].
Workstation design can also impact on the amount of glare in the room. Glare refers to the situation where lighting in the room is brighter than the screen, causing light to reflect from the entire screen, or in specific screen locations [1, 7]. Glare increases the difficulty in interpreting images, and forces the oculomotor system make the same squinting and blinking adjustments described above. This outcome is particularly common in environments that are open to too much natural light, or have inappropriate indoor lighting.
The impact of environmental factors on oculomotor functions:
Eye dryness, irritation and impairment of glands can be further exasperated by environmental exposure. For example, dry air, high heating and excessive air movement can increase evaporation of eye moisture . While dust and airborne allergens can lead to increased irritation, and further impairment of ocular gland .
EWI Works Comments:
The research on CVS is very interesting for office workers and ergonomists. Understanding some mechanisms of CVS can help us to develop interventions and management strategies to mitigate the problems. At present, EWI Works is using this information and other available literature, along with ongoing research projects conducted by our group, to compile intervention strategies. Our goal is to develop an effective, evidence-based list of recommendations and strategies that we can bring to our clients.
Please feel free to comment on this blog post and contact us if you would like to include address computer vision syndrome in your workplace.
REFERENCES:1. Blehm, C., et al., Computer Vision Syndrome: A Review. Survey of Ophthalmology, 2005. 50(3): p. 253-262. 2. Segui, M.D., E. Ronda, and P. Wimpenny, Inconsistencies in Guidelines for Visual Health Surveillance of VDT Workers. Journal of Occupational Health, 2012. 54(1): p. 16-24. 3. Thorud, H.-M.S., et al., Eye-Related Pain Induced by Visually Demanding Computer Work. Optometry and Vision Science, 2012. 89(4): p. E452-E464. 4. Wolkoff, P., “Healthy” eye in office-like environments. Environment International, 2008. 34(8): p. 1204-1214. 5. Rosenfield, M., Computer vision syndrome: a review of ocular causes and potential treatments. Ophthalmic and Physiological Optics, 2011. 31(5): p. 502-515. 6. Wolkoff, P., T. Kaercher, and H. Mayer, Problems of the “Outer Eyes” in the Office Environment An Ergophthalmologic Approach. Journal of Occupational and Environmental Medicine, 2012. 54(5): p. 621-631. 7. Rodriguez, R.G. and A. Pattini, Effects of a Large Area Glare Source in Cognitive Efficiency and Effectiveness in Visual Display Terminal Work. Leukos, 2012. 8(4): p. 283-299.