Psychological impact on the motor function of pupil

Psychological processes have an impact on the size of the pupil. The muscle which expands the pupil (musculus dilatator pupillae) is joint indirectly over the sympathetic nervous system with the limbic system. It is involved in the genesis of emotions, in learning processes and in saving of what has been learned in the long-term memory. When being highly active, pupils enlarge ("shock-widened eyes"/once again literal interpretation). However, in case of excessive demand the muscle flags and the pupil scales down. As willful control of the pupil movement is normally not possible, the pupils size can be an indicator for the mental load which weights on someone.
Pupilometrics
Method for measurement of pupil diameter. One technique uses an infrared camera which phtographs the pupil. The designation of the pupil width is later one carried out computer-controlled.