VISUAL DEMAND WHILE WORKING WITH COMPUTER
There is a difference in visual demand when one is viewing the display on the computer screen compare to reading a printed text. An image which is produced on the screen is made up of thousands of tiny spots or pixels and rasters which collectively form the image. The margin of the image or a word is usually not sharp and this is worsening if the image or word is formed by minimal pixels, or what is known as low resolution. As the resolution goes down the image become poor in quality and the visual demand of a reader has to be increased in order to appreciate well the wording or image. The contrast (intensity of the light) of the word to the background, the glare of the computer screen and the reflection from the glass screen are all important factors determining the amount of visual demand one must put in order to perceive the image well.9,10
Refresh rate refers to the number of times (per minute) the computer screen is repainted to produce an image. When the refresh rate is too slow it causes a flickering screen. Studies have proven that a higher refresh rates is associated with less flickering thus decreases ocular symptoms and more user friendly. Extremely low refresh rates (high flickering) is known to be associated with headache, fatigue, irritability and epileptic seizures.6Many people are worried that the computer screen like most electrical appliances emits radiation. Numerous published studies have shown that there is no evidence to support any direct link between the radiation levels emitted and the worker’s health problems. Similarly there is no evidence that computer radiation contributes to significant cataract formation.6,12,13