This document discusses factors that can contribute to computer vision syndrome (CVS) for computer users. It outlines 5 main types of vision-related components: 1) computer screens which can cause eye strain due to brightness, resolution, refresh rates and other factors, 2) computer rooms where improper lighting and glare can impact vision, 3) the human eye which has to work harder to focus on nearby screens, 4) computer users who may be more prone to CVS like those wearing corrective lenses, and 5) computer tasks like long periods of small font reading or gaming which increase visual demands. Addressing issues with screens, lighting, tasks and user factors can help reduce risks of developing CVS.

1. Nawat Watanachai
Chiangmai University Hospital
2011

2. Computer
 What is computer

3. Computer
 ‘difference machine’
 1938

4. Guys who brought computer to us all
 1981

5. Guys who brought computer to us
all
ช่าย...
เราทำาสำาเร็จแล้
วอ่ะจ๊อบ
คอมพิวเตอร์ทก
ุ
ครัวเรือน
 today
และเราว่า
แมคกำาลังจะ
ขายดีกว่าวิน
โด้ฟร่ะบิลล์

6. Computers are everywhere

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. 5 types of
vision-related components

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. 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. 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. 1. Computer screen
 Visual effects of display characteristics
 A. Display quality
 B. Lighting and glare
 C. Refresh rates
 D. Radiation

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. 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. 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. 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. 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. 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. 1. Computer screen
C. Refresh rate
 Refresh screen
 (Blehm 2005, Jaschinski 1996, Kennedy 1991)
 Need >75Hz
 Should be >300Hz
 LCD VS CRT

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. 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. 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. Samsung Galaxy Tab10.1
 WSVGA(1,024 x 600)
 7.0"
 124 dpi
 Refresh rate 180 Hz

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. 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. 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. 2. Computer room
 Non-light factors (Sheedy 1997)
 Air flow (-)
 Temperature (-)
 Humidity (+)

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. 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. 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. 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. 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