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

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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