Environmental factor modification
Among the most important modifiable external environmental factors is lighting. Bright lights, windows and overhead fluorescent lights often contribute to discomfort glare. These bright light sources need to be controlled with proper blinds, filters or adjustment of the room arrangement so that an acceptable level of lighting is obtained to minimize visual fatigue. Different age group may require different light intensity to work with, workers over 50 years of age tends to require twice the light levels of young adults to perform the same task.14
Imbalanced of light between the computer screen and the surrounding is another important factor to be considered. For example a dark background screens often require lower lights level so when other source of documents are also viewed at the same time additional reading lamp may be needed to prevent ocular strain. Use of screen filters can reduce glare and reflection of the computer screen, but it should be used as a supplement and not a replacement for poor lighting of the room.10 Screen brightness and contrast should be adjusted to provide balance with room lighting and maximum visibility. Musculoskeletal problems related to head and eye postures can often be prevented by proper workstation adjustment. Computer users often assume uncomfortable position in order to have a good view of the screen without realizing that the posture may lead to muscular and ocular stress after long duration of work. Proper distance from the screen, proper adjustment of the image size and proper height of the seat are all important factors to be considered. It is recommended that the eyes should be about 35-40 inches from the screen and that the screen should be placed 10-20 degrees below or that the middle of the screen 5-6 inches below eye level. Improved physical ergonomics of the computer workstation has been proven to reduce ocular discomfort and improve performance.6,15