Nw2011 Computer Vision Syndrome

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Nw2011 Computer Vision Syndrome

  1. 1. Nawat Watanachai Chiangmai University Hospital 2011
  2. 2. Computer  What is computer
  3. 3. Computer  ‘difference machine’  1938
  4. 4. Guys who brought computer to us all  1981
  5. 5. Guys who brought computer to us all ช่าย... เราทำาสำาเร็จแล้ วอ่ะจ๊อบ คอมพิวเตอร์ทก ุ ครัวเรือน  today และเราว่า แมคกำาลังจะ ขายดีกว่าวิน โด้ฟร่ะบิลล์
  6. 6. Computers are everywhere
  7. 7. Why do ‘some’ computer users develop CVS?  Hardware : computer screen, room  User : human eye  computer tasks : The ways we use computer ปวดตา คร้าฟ บร๊ะเจ้า...ช้าน ปวดหัว... ปวดตา คร้า
  8. 8. 5 types of vision-related components
  9. 9. 1. Computer screen  Viewing a computer screen is much more visually demanding than viewing a paper  Computer screen  self illuminated, not reflection  Brightness : to bright/ unsteady   visual fatique (Anshel, 2005)
  10. 10. 1. Computer screen  High contrast, brightness  character blur  Swithching between light and dark background  fatique of the iris muscle  Recommended  Dark characters against light background display
  11. 11. 1. Computer screen  Angle of viewing  dry eyes and neck pain (Anshel 2005)  Distance between eyes and screen  Not easily adjusted,compared to books
  12. 12. 1. Computer screen  Visual effects of display characteristics  A. Display quality  B. Lighting and glare  C. Refresh rates  D. Radiation
  13. 13. 1.Computer screen A. Display quality  ‘poor display quality probably contributes to the annoyance and discomfort sometimes reported by workers. Visual performance is affected by a number of display parameters, such as character size, structure, and style; and by image contrast and stability’  The US national research council committee on vision, 1983.
  14. 14. 1. Computer screen A. Display quality  Resolution, Pixel-base dots  Pixels : Dim on the outer edge  Less resolution  More blurred image  hard to focus (Miyao 1989)  High contrast  visual strain (Anshel 2005)
  15. 15. 1. Computer screen A. display quality  Pixels : Ziefle, Hum Factors 1998  Viewing document, Compare 62 dpi VS 98 dpi  Search reaction time and fixation durations were increase significantly with 62 dpi
  16. 16. 1. Computer screen B. lighting and glare  surrounding sources of light  Computer screen  (overhead fluorescent, desk lamp, large windows)  Reflection : image behind the computer  Glare : wash out screen character images
  17. 17. 1. Computer screen B. Lighting and Glare  Glare increases the amount of time required to read relatively easy passages. (Garcia, Hum Factors 1985)  Surrounding luminance  reduce the accommodation amplitude. (Wolska, Int J Occup Saf 1999)   annoyance and visual fatique  NOT chronic visual disorder
  18. 18. 1. Computer screen C. refresh rates  Refresh rate (Hz)  Critical fusion frequency = 30-50 Hz  Extremely low rate of ‘flicker’ (8-14Hz) can induce epileptic seizure  Percieved flickers  annoyance, fatique, headache  Recommended frequency = at least 75 Hz  synchronous ERG response
  19. 19. 1. Computer screen C. Refresh rate  Refresh screen  (Blehm 2005, Jaschinski 1996, Kennedy 1991)  Need >75Hz  Should be >300Hz  LCD VS CRT
  20. 20. 1. Computer screen D. radiation  Ionizing radiation   cellular change   tissue damage  VDT  NOT emit alpha, beta, gamma, x ray  NO study shows any hazard
  21. 21. iPad  9.7-inch (diagonal) LED-backlit glossy widescreen Multi-Touch display with IPS technology  132 dots per inch (dpi)  Refresh rate at 200 Hz
  22. 22. iphone  Retina display  3.5-inch (diagonal) widescreen Multi-Touch     display 960-by-640-pixel resolution at 326 dpi Refresh rate at 200 Hz 800:1 contrast ratio (typical) 500 cd/m2 max brightness (typical)
  23. 23. Samsung Galaxy Tab10.1  WSVGA(1,024 x 600)  7.0"  124 dpi  Refresh rate 180 Hz
  24. 24. 2. Computer room  ‘lighting condition’ is the most important part  Ideal computer environment  40-50Fc of ambient light  Non-computerized office 100 Fc  sun in an average outdoor setting 8,000-12,000 Fc  Indoor direct light at noon :1500 Fc  To bright  visual discomfort
  25. 25. 2. Computer room  Equilized brightness  Source of light (overhead flu, windows, desk lamps)  To close   reflection and glare  back and forth focusing   reduce visibility of the screen   discomfort  Other factors : bright-white clothing, light- color desk surface, highly polished furnitures, large mirrors
  26. 26. 2. Computer room  Types of lighting  Natural light  Filament lamps (+)  Luminescent lamps (-)  Sodium lamp (+++)  most conductive to visual capacity  (Blehm 2005)  Mercury-arc lamps (+)
  27. 27. 2. Computer room  Non-light factors (Sheedy 1997)  Air flow (-)  Temperature (-)  Humidity (+)
  28. 28. 3. Human eyes  Eyes are relaxed and comfortable viewing object at a long distance (>6m)  but need a lot more muscles viewing near object (<30cm).  we need tears covering our eye surface  Preserve moisture and O2 supply  Keep the eye surface smooth and comfortable
  29. 29. 3. Human eyes  Blinking : clean off and refresh tearfilm  Blink rate (Freudenthaler 2003, Kadner 2004)  Normal : 15-16 blinks/min  Computer use : 5-6 blinks/min  Viewing angle  Lower in reading books : less exposure  Higher in computer works : more exposure
  30. 30. 3. Human eyes  Eyes need to adjust in order to see objects from different distances  Computer screen < paper on the table  Focus–refocus–refocus-refocus…. -L-’  Headache and blurred vision
  31. 31. 4. Computer users  Computer users wearing corrective lens early and more severe CVS  CL wearers  Youngers  myopia?  253 kids, 6-10YO (Hoenig 2002)  Elders (surface abn, tear abn)
  32. 32. 5. Computer tasks  Tasks : studying, browsing, shopping, communication, business  Eg.  Data entry workers : paper > screen  Graphic artists : screen > paper  Gamers : screen  It will be more CVS with  More time on the screen  Reading small fonts on the screen  Action games

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