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AFB  ®
Technology News for People Who Are Blind or Visually Impaired
From the American Foundation for the Blind
 September 2000 Issue  Volume 1  Number 5

Survey

CCTV Users Report Symptoms of Computer Vision Syndrome

If you experience symptoms of fatigue when using your closed-circuit television (CCTV), you are one among many. You should know that this fatigue can affect your health and safety and how well you do your job. In our recent survey of CCTV users, 76 percent of the 115 respondents reported serious fatigue symptoms when using their CCTVs, and many experienced the fatigue after fewer than 15 minutes of use.

Tired Eyes: Trouble at Work

Why do CCTV users feel this fatigue? When you think about it, the connection is obvious: Using a CCTV is a visually demanding task, and since users are visually impaired they are going to be especially susceptible to visual fatigue. Ironically, for most visually impaired people, using a CCTV is unavoidable—the vast majority of survey respondents rated their CCTVs as extremely important to them in their jobs. So, it is not surprising that visual fatigue is often implicated in workplace accidents.

Information about CCTV user fatigue in the research literature is nonexistent, but there is a wealth of information about a related subject: fatigue experienced by sighted computer users. Even though a CCTV is not a computer and sighted people are not visually impaired, a comparison can still be quite instructive. After all, both the CCTV monitor and the computer monitor are video display terminals, and both sighted people and visually impaired people rely on the same basic biological equipment to allow them to see.

In our survey, CCTV users reported eye fatigue, neck fatigue, back fatigue, and dizziness, and these same symptoms occur among sighted computer users. The recently coined name for the cluster of symptoms is "computer vision syndrome," or CVS. The main difference in the effects of CVS on visually impaired people and on sighted people is that sighted computer users experienced symptoms after many hours of steady computer use—not after one or two hours and certainly not after 15 minutes, as reported by many of the CCTV users.

CVS among sighted computer users is also commonplace. Estimates vary widely, but in a recent telephone survey of 1,011 video display terminal users, 41 percent reported CVS symptoms.

Symptoms

The symptoms of CVS are visual fatigue and neck, shoulder, and back pain. Visual fatigue refers to the following symptoms:

  1. painful eye irritation accompanied by tearing, reddening, and conjunctivitis
  2. double vision
  3. headaches
  4. blurred near vision and slowness in focusing
  5. light sensitivity.

What To Do

If you suffer from any of these symptoms when using a CCTV or a computer, the first thing to do is see a vision care specialist. There are also some things you should be aware of that can reduce fatigue.

Before computers were commonplace in work settings, lighting was often a problem because there was too little of it. The rule of the day in the computer era should be the following: All important surfaces in the visual field should be of the same order of brightness. The reason for this rule is not just that too much light causes bright screen reflections; it is also the case that every time you look from one light level to another, your eyes require time to adapt. The retina just does not perform well in uneven lighting. Glare is a particular problem because the eyes are drawn to a bright light source and become adapted to the higher illumination level. Then, in returning to the visual task, they are less sensitive and visibility is reduced.

Get the Light Right?

Here are some practical considerations to keep in mind if lighting-related visual fatigue is a problem when using either a CCTV or a computer:

  1. Try turning down the lighting.
  2. Use indirect lighting. Don't use reflective ceiling and wall paint.
  3. Don't use reflective surfaces, such as white desktops.
  4. Use several low-intensity light sources instead of one bright one.
  5. To avoid glare from windows, reorient the workstation to be perpendicular to the window, use window shades, and try tilting the monitor to minimize reflections and glare.
  6. Be aware that white clothing is very reflective and can create an annoying reflection on the screen.
  7. Don't forget to try increasing screen luminance.
  8. Keep the screen clean: dirt, smudges, and fingerprints can cause reflections.

Screen Polarity

Conspicuously absent from the above list of recommendations is screen polarity. It is well known that many CCTV users prefer positive polarity (white letters on a black background). Yet negative polarity (black letters on a white background) is less reflective than positive polarity and closer in brightness level to the surroundings than positive polarity. However, with negative polarity comes increased screen flicker. Even very subtle flicker can cause discomfort. If you are unsure if negative or positive polarity is best for you, the logical thing to do is try them both and see.

Posture and Workstation Design

Improper posture and poor workstation design can cause neck, shoulder, and back pain, and how you position yourself at the computer or CCTV can also cause visual fatigue. A few common-sense principles are always mentioned in the literature. First, maintaining the same body position for long periods of time can lead to musculoskeletal problems, so computer users should take short breaks and walk around or change position. The same can be said for CCTV users. Similarly, staring at the computer or CCTV for long periods of time can cause visual fatigue for the simple reason that it is accompanied by a reduced blink rate.

Seating distance is also important. The recommended distance between the user's eyes and the screen is 20-26 inches, which is more than twice the average distance used by respondents to our survey. The farther back from the screen, the less the need for "convergence" (the coordinated turning of the eyes inward to focus on a near point).

Another disadvantage for those who sit close to a big screen is the excessive realignment and movement of the eyes from one fixed point to another, leading to fatigue.

Looking up at the monitor causes neck strain and reduces blink rate. To set proper monitor height, the user's eyes should be level with the top of the monitor so that when the user is looking at the center of the screen there is a slightly downward gaze. The monitor should have a slightly upward tilt. Setting monitor height is primarily a function of seat height and table height, which implies that both should be height adjustable. This feature is particularly important when using a large monitor or an "in-line" CCTV, in which the monitor is mounted over the camera. Both in-line CCTVs and monitors larger than 17 inches were very popular among the respondents of our survey. Guidelines and standards for computer workstation design that promotes good posture are readily available (see <www.pc.ibm.com/healthycomputing>), but, generally speaking, too few people follow them.

So what is your experience with CCTV fatigue? Send us an E-mail to let us know at: E-mail address is: muslan@afb.net.

Alec F. Peck, Ph.D., is Associate Professor, Teacher Education Department, Lynch School of Education, Boston College. E-mail address is: alec.peck.1@bc.edu; <http://www2.bc.edu/˜peck/>.

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