In order to gain a better understanding of the visual capabilities of the visually impaired and in order to learn to use them optimally in the rehabilitation, it is essential to have adequate (preferably quantitative) information about the residual visual functions of the visually impaired individual.

Special attention is given to the extra information that is provided by the results of measurement of the contrast sensitivity, especially in combination with the results of other measurements, such as the visual field, the amount of intra-ocular straylight and the visual acuity.

The value of the contrast sensitivity function will be discussed, as a predictor for the extent of dysfunctioning in visual activities of everyday life. As far as this is concerned a comparison is made between the value of the visual acuity and the contrast sensitivity as a measure of the extent of vision and visual dysfunctioning.