“…34,37,43,44 Based on a negative feedback mechanism within the autonomic nervous system and its exclusive innervation, the pupil diameter can be considered as a direct "live" reflection of the functional balance between the sympathetic and parasympathetic nervous system. 37,43,[45][46][47][48] A simultaneous increasing activity of the sympathetic system and decreasing parasympathetic activity will result in a dilation of the pupil. 34,43,49,50 In addition, it has been demonstrated that sympathetic activation through the upper thoracic spine segments can cause pupil dilation.…”