Infrared pupillometry in the assessment of autonomic function

In order to study normal dynamic pupillary function and to determine reference limits for various pupillary variables, 81 healthy subjects aged between 32 and 60 years were examined using a portable infrared pupillometer. Additionally, 36 patients with type I diabetes mellitus were studied. In healthy subjects, sex had no, or only marginal, effect on the responses. Body mass index or smoking habits had no effect on pupillary dynamics. The relative reflex amplitude (RRA) was independent of age. The time to minimum diameter tmin was dependent on maximum constriction velocity (MCV) (P < 0.001) but not on age, initial diameter or reflex amplitude (RA). The MCV, maximum redilatation velocity (MRV) and time to 75% redilatation (t75%) were strongly dependent on RRA (P < 0.001 for each), but age had no or only a marginal effect. No correlation existed between the results of pupillometry and those of Valsalva or deep breathing tests. The lowest normal value for RRA was 29%. The reference limits for MCV, MRV and t75% were calculated in relation to RRA. The smaller the RRA was, the slower the velocities and the shorter the t75% were. Using these reference limits, 25% of the diabetic patients without cardiac autonomic neuropathy and 50% with definite cardiac autonomic neuropathy had abnormalities in at least one out of four pupillary variables. It is concluded that infrared pupillometry may be a useful additional method for the assessment of autonomic function.