1. 1 ارگونومی بصری کامپیوتر آیدین تاج زاده نمین 81189803 حمیدرضا حافظ نیا 81190003 اردیبهشت 1385

2. 2 How do you setup a Computer WorkStation? Do you buy monitor risers? Do you buy monitor risers? Will even lower monitor positions cause neck strain? Will even lower monitor positions cause neck strain? Should you invest in indirect lighting? Should you invest in indirect lighting? How about viewing distance? 16”, 25” or even farther? How about viewing distance? 16”, 25” or even farther? Does screen color make a difference? Does screen color make a difference? Is there any evidence that ergonomic workstations improve work performance? Is there any evidence that ergonomic workstations improve work performance?

3. 3 The Most Common Refractive Errors Hyperopia Hyperopia Myopia Myopia Presbyopia Presbyopia Eye Strain : Eye Strain : Burning Burning Tightness Tightness Sharp pains Sharp pains Watering Watering Blurring Blurring Double Vision Double Vision Headache Headache

4. 4 Hyperopia

5. 5 Myopia

6. 6 Presbyopia

7. 7 A Dozen Things You Should Know about Eyestrain 1- Definition: If you have any eye discomfort caused by viewing something, you can call it eyestrain. 2- In Visual Display Terminal (VDT) workstations, the principal factors affecting the ability to see well are:  Glare the luminance (brightness) difference between what is being looked at and its immediate environmentthe luminance (brightness) difference between what is being looked at and its immediate environment The amount of LightThe amount of Light The distance between eye, screen and documentThe distance between eye, screen and document The readability of screen and documentsThe readability of screen and documents The worker’s vision and his/her corrective lensesThe worker’s vision and his/her corrective lenses

8. 8 A Dozen Things You Should Know about Eyestrain 3. Watch out for direct glare. 4. Reflected glare, such as on computer screens, sometimes causes eyestrain. 5. The most overlooked cause of eyestrain in offices is contrast --- usually, a dark screen surrounded by a bright background such as a window or a lit wall. 6. The amount of needed light depends on your age, the quality of the print you're reading, and other factors. 7. Eyes are strained more by close viewing than by distant viewing. 8. If you gaze at something too long, your eyes can tire.(20/20 Rule.) 9. If two objects are only a couple of inches different in their distance from the eyes, the eyes actually do NOT have to refocus to look from one to another. 10. Computer work cause nearsightedness. 11. Sometimes eyestrain is just a case of dry eyes. 12. People who need bifocals should consider other options besides bifocals.

9. 9 Visual Factors Visual Acuity Visual Acuity Binocular Vision Binocular Vision Accommodation Accommodation Oculomotor Skills Oculomotor Skills Hyperphoria Hyperphoria Dry Eyes Dry Eyes

10. 10 Definitions Visual acuity Visual acuity Brightness & Contrast Brightness & Contrast Display Quality Display Quality Refresh Rate Refresh Rate Resolution Resolution Dot Pitch Dot Pitch

11. 11 Resolution

12. 12 Refresh Rate

13. 13 Guidelines: Screen Colors  Screen colors: dark letters on a light background.  With the monitor off, look at your reflection in the screen. Now turn the monitor on and select a Windows- type background, (black letters on a white background). Notice that you cannot see your reflection as well.  Negative screen contrast (black letters/white background) can reduce reflected images.

14. 14 Guidelines: Screen Colors Research Research Bauer and Cavonius (1980) found a lower error rate, with dark letters on a white background. Snyder and his colleagues (1990) also compared black and white backgrounds. Eight out of ten subjects increased their performance by using dark letters on a light background. The improvements ranged from a low of 2.0% to a high of 31.6%. The tasks were visual search and reliable. Bauer and Cavonius (1980) found a lower error rate, with dark letters on a white background. Snyder and his colleagues (1990) also compared black and white backgrounds. Eight out of ten subjects increased their performance by using dark letters on a light background. The improvements ranged from a low of 2.0% to a high of 31.6%. The tasks were visual search and reliable.

15. 15 Guidelines: Vertical Monitor Location  Locate the entire viewing area of the monitor between 15° and 50° below horizontal eye level.

16. 16 Guidelines: Vertical Monitor Location To see the effect of gaze angle on accommodation you can this exercise 1. hold a business card at arm's length and at eye level. 2. Slowly bring it towards you until the letters start to blur. 3. Without moving your head, slowly lower the card in an arc, keeping it the same distance from your eyes 4. You will see the letters come into focus. Your eyes have improved their ability to accommodate simply by lowering their gaze angle

17. 17 Guidelines: Vertical Monitor Location The old guidelines that recommended that the monitor be placed at eye level were based in part on the belief that the resting position of the eyes is 15° below the horizontal. The old guidelines that recommended that the monitor be placed at eye level were based in part on the belief that the resting position of the eyes is 15° below the horizontal. New evidence shows that, while the eyes might be most comfortable with a 15° gaze angle when looking at distant objects, for close objects they prefer a much more downward gaze angle.optimum position for the most important visual display is 20 - 50° below the horizontal line of sight. (according to the International Standards Organization-ISO) New evidence shows that, while the eyes might be most comfortable with a 15° gaze angle when looking at distant objects, for close objects they prefer a much more downward gaze angle.optimum position for the most important visual display is 20 - 50° below the horizontal line of sight. (according to the International Standards Organization-ISO)

18. 18 Guidelines: Vertical Monitor Location

19. 19 Guidelines: Vertical Monitor Location Many computer users experience dry eyes. It has been found that lower monitor placement exposes less of the eyeball to the atmosphere and reduces the rate of tear evaporation. This keeps the eyes more moist and reduces the risk of Dry Eye Syndrome. Many computer users experience dry eyes. It has been found that lower monitor placement exposes less of the eyeball to the atmosphere and reduces the rate of tear evaporation. This keeps the eyes more moist and reduces the risk of Dry Eye Syndrome.

20. 20 Guidelines: Vertical Monitor Location Neck Posture Neck Posture  Neck extension and forward head posture, while acceptable for the visual system, have been associated with both discomfort and disease.  With a low monitor position you can hold your head erect and look downward. When that posture becomes tiring, a low monitor will allow you to alternate among a wide range of flexed neck postures that allow good visual performance and will not increase postural discomfort.  Ergonomic guidelines recommend arms, torso, thighs and legs at 90° angles and the head perfectly erect,the feet are "flat on the floor." This is the "correct posture”.

21. 21 Guidelines: Vertical Monitor Location Neck Posture (Cont’d) Neck Posture (Cont’d) Two recent studies have compared monitor locations with the center of the screen at 15° and 40° below horizontal. 1. The first one the recommended limit for mean muscle activity is 10-14% maximum voluntary contraction (MVC) (MVC is the maximum muscle effort that can be voluntary exerted by the subject.) Although the 40° placement had higher readings than the 15° placement, all were much lower than the recommended limit. The highest was 6.8%. The activity averaged an extremely low 2.2% MVC for the 15° and 2.0% MVC for the 40° conditions.

22. 22 Guidelines: Vertical Monitor Location 2. The second compared monitor positions with the center of the monitor at eye level, and 17.5° and 35° below eye level. All of the conditions resulted in mean EMG levels of below 4% MVC, well below the recommended limit of 10-14%. They found a 10% improvement in productivity when the center of the monitor was changed from eye level to 35° below eye level. Performance was measured as the number of bibliographic references the subjects were able to format in the allowed time.

23. 23 Guidelines: Vertical Monitor Location

24. 24 Guidelines: Placement The screen should be at least 18 to 24 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. The screen should be at least 18 to 24 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. 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 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. Your documents should be positioned close to the monitor, either close to the side or directly in front between the keyboard and the screen.

25. 25 Guidelines: Brightness & Contarst 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. 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.

26. 26 Guidelines: Quality Display The clarity of your screen depends upon refresh rate, resolution and dot pitch. 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.. Your refresh rate should be at least 70 Hz (hertz) or higher. Refresh rate refers to how often your monitor redraws the screen. Slow rates can cause a noticeable 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. 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.) 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.)

27. 27 Guidelines: Luminance The Illuminating Engineering Society of North America (IES), in its Recommended Practice for Lighting Offices Containing Computer Visual Display Terminals states that the average luminance produced by direct lighting luminaires should never exceed the following values: The Illuminating Engineering Society of North America (IES), in its Recommended Practice for Lighting Offices Containing Computer Visual Display Terminals states that the average luminance produced by direct lighting luminaires should never exceed the following values: 850 cd/m2 at 65° 850 cd/m2 at 65° 350 cd/m2 at 75° 350 cd/m2 at 75° 175 cd/m2 at 85° 175 cd/m2 at 85° These recommendations cannot be properly evaluated. for example, the ceiling luminance was 350 cd/m2 then the fixture would be invisible in any screen at 75 because it has no contrast with the ceiling. At 85°, it would have a contrast against the ceiling of 33 percent. However, the contrast of the reflection on a bright background display of 100 cd/m2 would be only 5.8 percent. These recommendations cannot be properly evaluated. for example, the ceiling luminance was 350 cd/m2 then the fixture would be invisible in any screen at 75 because it has no contrast with the ceiling. At 85°, it would have a contrast against the ceiling of 33 percent. However, the contrast of the reflection on a bright background display of 100 cd/m2 would be only 5.8 percent.

28. 28 Guidelines: Luminance It is suggested that the ratio of the ceiling luminance directly above the normally the brightest area to the ceiling illuminance between luminaires should never exceed 10:1 and, preferably, this luminance ratio should be limited to 4:1. The maximum luminance on the ceiling should not exceed 850 cd/m 2 for any area. Using the contrast equation presented in the sidebar, the 850 cd/m 2 maximum luminance, the preferred luminance ratio of 4:1, and assuming an 8 percent reflection from the screen, the contrast of the luminous ceiling reflected in a bright-background VDT display of 100 cd/m 2 will be 18 percent – well in excess of the contrast threshold criteria of 2 and 5 percent. It is suggested that the ratio of the ceiling luminance directly above the normally the brightest area to the ceiling illuminance between luminaires should never exceed 10:1 and, preferably, this luminance ratio should be limited to 4:1. The maximum luminance on the ceiling should not exceed 850 cd/m 2 for any area. Using the contrast equation presented in the sidebar, the 850 cd/m 2 maximum luminance, the preferred luminance ratio of 4:1, and assuming an 8 percent reflection from the screen, the contrast of the luminous ceiling reflected in a bright-background VDT display of 100 cd/m 2 will be 18 percent – well in excess of the contrast threshold criteria of 2 and 5 percent.

29. 29 Thanks For Listening… Any Questions So far?!!!