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Nawat WatanachaiChiangmai University Hospital2011
Computer
What is computer
Computer
‘difference machine’
1938
Guys who brought computer to us all
1981
Guys who brought computer to us all
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Computers are everywhere
Why do ‘some’ computer users develop CVS? Hardware : computer screen, room User : human eye computer tasks : The ways we use
computer
บร�ะเจ�า...ช่�านปวดีหั�ว...
ปวดีตาคร�าฟ
ปวดีตาคร�า
5 types of vision-related components
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)
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
1. Computer screen
Angle of viewing dry eyes and neck pain (Anshel 2005)
Distance between eyes and screen Not easily adjusted,compared to books
1. Computer screen
Visual effects of display characteristics A. Display quality B. Lighting and glare C. Refresh rates D. Radiation
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.
1. Computer screenA. 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)
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
1. Computer screenB. 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
1. Computer screenB. 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
1. Computer screenC. 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
1. Computer screenC. Refresh rate
Refresh screen (Blehm 2005, Jaschinski 1996, Kennedy
1991) Need >75Hz Should be >300Hz
LCD VS CRT
1. Computer screenD. radiation
Ionizing radiation cellular change tissue damage
VDT NOT emit alpha, beta, gamma, x ray NO study shows any hazard
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
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)
Samsung Galaxy Tab10.1
WSVGA(1,024 x 600) 7.0" 124 dpi Refresh rate 180 Hz
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
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
2. Computer room Types of lighting
Natural light Filament lamps (+) Luminescent lamps (-) Sodium lamp (+++)
most conductive to visual capacity (Blehm 2005)
Mercury-arc lamps (+)
2. Computer room
Non-light factors (Sheedy 1997) Air flow (-) Temperature (-) Humidity (+)
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
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
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
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)
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