How Closed-Circuit Television Users Develop Computer Vision Syndrome
In the September 2000 issue of AccessWorld, we introduced readers to computer vision syndrome (CVS). This condition can be defined as visual fatigue or neck, shoulder, or back pain that results from using a computer for long periods of time. CVS reflects the impact of using computer monitors for reading and keyboards for input. We surveyed closed-circuit television (CCTV) users and found similar symptoms; like a computer, a CCTV has a monitor for reading, but instead of a keyboard for typing, it has an X-Y table requiring hand and arm movement when the object being viewed is moved under the camera so it can be enlarged. In this report, we look in depth at personal and environmental factors that put one at risk for CVS.
What Is CVS, Anyway?
According to James Sheedy, an authority on CVS at the University of California, Berkeley, School of Optometry, the major cause of CVS is uncorrected refractive errors. Computer users may need to have a separate prescription for computer viewing (at a relatively short distance) than they have for regular viewing at greater distances, and many people who did not obtain separate prescriptions experience fatigue.
Another major consideration is the work environment itself. Modern office buildings typically cool or warm air and recycle it via blowers. Windows usually can't be opened, which leads to air that is often exceptionally dry, which in turn requires frequent eye blinking in order to moisten the eyes. Staring at a computer screen can reduce blink rate just because you are staring. In addition, staring at a screen that is eye level instead of below eye level reduces the blink rate, which in turn leads to more dryness and irritation. Finally, computer monitors both create dusty environments because they generate static electricity, and this dust adds to eye irritation.
As mentioned in our previous article, too much light in the work environment causes glare and screen reflections. Computer screens themselves are sources of illumination, so ambient light levels should probably be reduced when computers are in use.
Finally, prolonged near vision work is naturally associated with certain physical symptoms such as double vision, headache, and blurred vision. These symptoms apparently result from the strain that is placed on the visual system by the need to focus and refine that focus for extended periods of time. When computer users focus on screens in environments that fail to allow for rest or focusing on infinity (such as occasionally looking out through windows), they often suffer from these symptoms.
Eyestrain is not the only component of CVS. Neck, shoulder, and back pain are caused in part by poor posture in viewing the screen, and in part by poor workstation design. We all have favorite chairs and places to work, but they may not be ergonomically sound. Adjusting the height of the chair and the table on which the monitor rests so that you are not looking up but instead are looking ahead or slightly downward can bring relief from symptoms of CVS.
What About CCTVs?
CCTVs are not computers, but they share obvious features—they have screens the same size as computer screens, which are read from close proximity, and they primarily display text. They share many of the same features that can cause CVS. Since these are major issues in the development of CVS, CCTV users are equally susceptible. Furthermore, visual impairment may well exacerbate the symptoms. For example, eye strain caused by focusing on nearby objects will be more pronounced in those people for whom near focus is more difficult in the first place.
AFB's Careers and Technology Information Bank (CTIB) database includes information on the career and technology interests of employed visually impaired people. Using this database, we contacted 115 individuals who use CCTVs as a component of their work. Fifteen-minute interviews were conducted over the telephone with each of these people, and much was learned about their use of CCTVs in their jobs.
Part of this interview focused on problems they might be experiencing when they use CCTVs. We learned that certain users are more likely to develop symptoms of CVS, although, with almost 70 percent of users reporting at least some symptoms, it is almost as interesting to look at who doesn't develop CVS.
Virtually everyone who uses a CCTV reports feeling fatigue in less than an hour, regardless of age or visual status. Almost 60 percent of those who develop symptoms of CVS report fatigue in less than 30 minutes. One respondent said, "My eyes get easily fatigued after 15 minutes." It may not be easy to recover from CVS fatigue, and this may have an important impact on productivity.
Our survey results show that most people really do like their CCTVs. The vast majority (80%) are satisfied or very satisfied with their devices, and a large majority (70%) report that it is easy for them to read standard print with a CCTV. One respondents said that the CCTV "helps me stay employed." Another said, he "couldn't do his job without it." Nevertheless, about 40 percent of CCTV users stop after only 10 minutes or less per sitting. Coupled with the finding that about 75 percent use their CCTVs several times a day, this finding suggests that many people may have been conditioned to avoid fatigue by working on their CCTVs only in short bursts. One respondent commented that the CCTV is "perfect for quick, short reads." Others apparently work through their fatigue and just "live with it" in order to get their job done.
Three major symptoms of CVS were frequently reported by CCTV users: neck strain, back strain, and eye strain. Dizziness was rare, and no other symptoms were reported with any frequency. Overall, neck strain was reported more often by those who used smaller text sizes. The probable reason is that smaller text sizes require more movement of the head across the screen than large text sizes, which require more movement of the X-Y table. This fact is supported by the finding that, in general, larger screen sizes (19 inches or larger) were also associated with more frequent reports of neck strain. Once again, larger screens require more head movement across the screen than do small screens. Also, large monitors are typically higher in the field of view, which may require neck movement at an awkward angle.
Intuitively, one would think that distance from the CCTV screen would also be an important consideration. Sitting close to a monitor should require more head movement, hence more neck strain. However, although we asked about typical viewing distance, we found no such relationship. It may be that viewing angle (looking up rather than straight ahead or down) is more important than simple back-and-forth movement. We will be investigating this issue further in future studies.
Back strain was not commonly reported (only about 25 percent of the users reported experiencing it) but it was also related to text size and screen size. The larger the text displayed by a CCTV, the more likely the user reported back strain. Also, the larger the screen size, the more likely the user reported back strain. Although we have no additional data to support this finding, it may be explained by movement of the X-Y table. Larger text sizes require more movement of the platform, and larger screens may require more awkward movement of the platform. Both of these movements could contribute to back pain.
Eye strain was the most commonly reported symptom. However, it was not systematically related to text size, screen size, or distance from the CCTV screen. Neck, shoulder, and back strain can be explained by musculoskeletal issues, but eye strain in CCTV users is a much more complex problem. How does eye strain brought on by CCTV use interact with conditions such as macular degeneration, retinitis pigmentosa, glaucoma, and diabetic retinopathy, which were common among our sample of CCTV users? It may simply be that these conditions supersede the impacts of text and screen size.
Users of CCTVs appear to be susceptible to many of the same problems reported by computer users who suffer from CVS. Poor ergonomics and close focusing put many CCTV users in awkward postural positions. When eye conditions of people with visual impairment are combined with glare or environmental features that promote eye irritation, people become even more susceptible to fatigue.
We will be conducting further studies of this phenomenon. We invite you, the readers, to tell us about your experiences with CCTVs. We know that CCTV use is important to many people, and we want to identify the factors that make up healthy, comfortable CCTV viewing.
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