Dynamic pupillometry as an autonomic testing tool

Abstract

To determine normal values for pupillometry indices in healthy control subjects and to examine these indices in patients with autonomic dysfunction and healthy controls. Infrared video pupillometry was used to investigate the pupil response to a brief light flash in 79 healthy controls, 28 patients with normal autonomic function (composite autonomic severity score, CASS<2), and 26 patients with moderate to severe autonomic failure (CASS>4) seen in our autonomic laboratory from January 2008 to June 2011. In six subjects, we examined the effects of varying light stimulus intensity and light stimulus duration. Descriptive analysis, correlation, and ANCOVA adjusted for age were performed. We determined eight indices corresponding to parasympathetic and sympathetic pupil function. Baseline pupil diameter (BPD), maximum constriction velocity (MCV), absolute constriction amplitude (ACA), and maximum dilation velocity (MDV) negatively correlated with age (p<0.01) among controls. MCV and ACA increased with increasing intensity of light stimulus from 3.5 to 112μW. Indices of parasympathetic pupil innervation (MCV and ACA) were lower in the high CASS group compared to others (p<0.0001). Indices of sympathetic pupil function, time to reach 75% of initial resting diameter during pupillary dilation (T¾), and dilation velocity at T¾ (DV¾) did not differ significantly in the three study groups. However, T¾ corrected for the magnitude of pupillary constriction (T¾:ACA) was higher in the high CASS group suggesting sympathetic dysfunction in that group (p=0.0003). Indices of pupillomotor function significantly differ between patients with moderate to severe autonomic failure and healthy controls.