Visual Fatigue

The environmental causes of visual fatigue is divided in to two groups:

(i) those arise out of the visual task itself, and

(ii)    those arise out of the visual environment in which the task is           performed.

5.1 Visual Task

The brain always tries to interpret the visual information sent to it. When this information is of poor quality, the brain attempts to improve it by sending feedback signal to the eye. Strain results when this is an almost continuous process. Examples of poor quality of visual information are:

(i) the size of detail of the task is too small causing problems of focusing and convergence,

(ii) the contrast between parts of the detail is too low,

(iii) the visual task moves,

(iv) the surface texture of the task makes seeing difficult,

(v) the pattern of the task may be disturbing.

5.2 Visual Environment

Examples of working environment causing visual fatigue are:

(i) inadequate illuminance,

(ii) too great a contrast between the task and its background,

(iii) disability and discomfort glare, or veiling reflections from the task,

(iv) flicker from fluorescent lamps, and

(v) psychological factors concerned with the individual's satisfaction with the environment as a          whole, e.g. colour appearance, colour rendering, appearance of environment.