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Eye Strain

Visual discomfort is a frequent complaint of computer workers. Eyestrain and headaches blurred vision are the most common problems reported. Other problems include double vision, burning and dry eyes, eye fatigue, light sensitivity, and after-images.

Neck shoulder and back pain can also be related to viewing the computer keyboard and/or screen. The American Optometric Association has designated this complex of problems as computer vision syndrome (CVS).

 

Lighting and vision are inter-dependent. Workplace lighting and visual ability both play a significant role in work posture. Workers alter postures to relieve stress on the eyes. Complaints of neck, shoulder and back pain can frequently be alleviated if visual ergonomics are addressed. For more information on workplace lighting, see “Preventing Visual Discomfort” article.


Vision and Eye Problems:

Difficulties with focusing and eye alignment can result in eyestrain, neck pain and headaches during computer work. To avoid problems, have your vision checked by an eye doctor aware of problems that can interview with computer vision. Make sure you measure the distance you sit from your computer before seeing a doctor. He will need this information to evaluate your need for computer glasses.

Your doctor should check for the following:

  • Visual acuity - the ability to see clearly and efficiently at various distances.
  • Binocular vision - ability to coordinate eyes by integrate the image recorded by each eye into a single vision.
  • Accommodation - the ability of the eyes to shift focus between varying distances. This skill becomes more difficult over the age of 40 due to reduced lens flexibility.
  • Oculomotor skills - the ability of the eye muscles to position the eyes correctly to locate and scan text.
  • Hyperphoria - tendency of each eye to see objects at different levels. Presence of this disorder results in a tendency to tilt the head to line up things visually, resulting in neck strain.
  • Dry eyes – some individuals do not produce enough tear flow to the eyes because of tear duct problems.

Use of Corrective Lenses for Reading or General Activities:

  • Contact lenses - Individuals who wear contact lenses blink less than people who have normal vision or wear glasses. Contact wearers must be educated to blink often and use artificial tears to reduce eye irritation. If your eyes are worse using artificial tears, contact your eye doctor to determine if you have a sensitivity or allergy to the product you use.
  • Use of glasses designed for reading - Regular glasses are not always suited for computer work. Most monitors are positioned in the intermediate visual zone, rather than in the near or far zones. Reading glasses correct for the near zone, and bifocals correct for only the near and far zones. Trifocals and progressive lenses have only a small portion of the lens corrected for the intermediate zone. This portion is generally not large enough for comfortable computer work.
  • Awkward postures - Use of inappropriate glasses can result in blurred vision. Attempts to compensate for blurred vision can encourage awkward postures such as leaning forward. Bifocal users often tilt their necks and heads up to see through the bottom of their glasses. Both of these actions can result in neck aches and backaches.

Monitor Issues:

The type and location of the monitor you use plays a significant role in visual comfort.
Remember that the location of the visual target plays a major role in determining sitting posture. Visual requirements result in the user positioning the body so that the face is parallel to the viewing surface. This principle should be remembered when determining placement of a monitor.


Visual acuity determines the optimal viewing distance to the monitor. Although ANSI and Canadian standards require a minimum viewing distance of 12 inches, research studies have shown a preferred viewing distance of 30 to 40 inches from the screen.


Standards also require that the user’s viewing area should be located between 0 and 60 degrees below the horizontal plane. Recent studies have demonstrated that it is easier to look downward rather than horizontally or upward. Lower targets may be more comfortable for users, especially when preferred viewing distances are considered. These findings suggest that VDT monitors should possibly be located lower and further away from the user than previously thought to offer greatest visual comfort.


Lowering the monitor without angling it up toward the user’s face encourages a forward-thrust head posture. Awkward shoulder, arm, wrist postures results from this compensation. Concern has resulted about the effect of this forward head position and tilted neck. Make sure you adjust the tilt of the monitor to match the height for optimal sitting posture.

For Proper Monitor Placement – Follow these guidelines:

  • The screen should be at least 20 to 26 inches distance. Adjust this distance for your visual acuity needs and comfort. The farther away the better in most cases. Distances of 30-40 inches are frequently preferred.
  • You should be able to view the screen with a slight downward gaze without tilting your head up or down. The top of the screen should be about at mid-forehead level. If you have a screen larger than 17”, the top of the screen may need to be a little higher.
  • Your face should be parallel to the screen. Setting the tilt will help to adjust the height. Be sure to test for excessive glare when tilting the screen. If you can see your image in the screen, reflections and glare will strain your eyes while working.
  • Your documents should be positioned close to the monitor, either close to the side or directly in front between the keyboard and the screen.

Brightness and Contrast – The monitor’s brightness should match the room brightness. Begin making adjustments by reducing glare from sources in the room such as windows and overhead lights. Use light switches, blinds, curtains, filters or remove bulbs as necessary. Then adjust the brightness control on the monitor somewhere close to the monitor’s mid-range if possible. After adjusting the brightness, set the contrast to a comfortable level. Usually, the higher the contrast the better.

Display Quality – The clarity of your screen depends upon refresh rate, resolution and dot pitch.

  • Refresh rate refers to how often your monitor redraws the screen. Slow rates can cause a noticeable flicker. People vary in their sensitivity to flicker. Your refresh rate should be at least 70 Hz (hertz) or higher.
  • Resolution refers to the monitor’s pixel density and determines the level of detail. The higher the resolution, the better the detail. 800 x 600 is recommended. Make sure you don’t sacrifice the refresh rate for resolution. They are related to each other and should both be high for good quality.
  • Dot pitch determines sharpness of the display. The lower the dot pitch number, the sharper the image. Select a monitor with a dot pitch or .28 mm (millimeters) or lower. (If your dot pitch is listed as horizontal or stripe pitch, divide it by 0.866 to determine the equivalent regular dot pitch.)

Check your refresh rate and resolution for adjustment if necessary. They can be adjusted using the Settings tab in the Display properties dialog box in Windows.
Dot pitch is not adjustable.


Computer Glasses

Computer glasses correct your vision in the intermediate zone, the distance you normally sit from your computer screen. If you also require correction in the near and/or far zones, you will need to consider multiple focusing options.

  • Lens design - There are several types of computer lenses available. They range from occupational progressive lenses and trifocals with larger than normal intermediate zones, to single-vision (intermediate) lenses. Specially designed bifocals or computer prescriptions that clip-on to your regular eyeglasses are also available. Your eye doctor can help you decide which lens design you need.
  • Tints and coatings - Computer lenses can be tinted to help with reducing eyestrain from excessive glare from windows or fluorescent overhead lights. Antireflective coating or ultraviolet coatings and amber tints can all help relieve eyestrain.