neurosciencenews.com/eye-trauma-mark-16659/

A study carried out jointly between Cardiff and Swansea University has found that people who have suffered PTSD show different pupil dilation and constriction patterns.

The study looked both at constriction in response to light changes, but also enhanced pupil dilation in response to both exciting-positive and traumatic-negative imagery, and perceiving both as equally negative.

This points to an increase in arousal which is apparent by watching a person’s pupils, and indicates that therapists should be mindful that clients could potentially interpret positive arousing stimuli as a threat.