Portable infrared pupillometry using Pupilscan: Relation to somatic and autonomic nerve function in diabetes mellitus

Abstract

The relationship between dynamic pupillary function and peripheral nerve function was studied in 85 randomlyselected diabetic patients and 67 age-matched normals using a portable infrared pupillometer (Pupilscan Version 5). Seven measurements were chosen to represent different components of the pupillary constriction-redilatation curve after a standardized light stimulus. Constriction latency was significantly prolonged in diabetic patients (p = 0.05), as was time to 63% redilatation (p = 0.001). Thermal thresholds at the feet weakly correlated with relative reflex amplitude (warm:r = −0.22,p = 0.05; cool:r = −0.23,p = 0.05), but vibration perception thresholds were more strongly associated with constriction and redilatation velocity (r = −0.42,p = 0.001;r = −0.28,p = 0.03). Among the cardiovascular autonomic function tests, only respiratory R—R variation correlated with constriction velocity (r = 0.47,p < 0.001), and Valsalva ratio with redilatation velocity (r = 0.25,p = 0.04), but postural systolic blood pressure change was also correlated with reflex amplitude and latency time (r = −0.42,p < 0.001;r = 0.41,p = 0.001). There were no significant associations with three measures of sweating function in the feet. Pupil measurements were abnormal in 4–11% of diabetic patients, while other neurological tests were abnormal in 8–35%, consistent with the length-dependence of diabetic neuropathy. Median coefficients of variation were 2.0–7.2% in diabetic patients. Portable pupillometry using this device is currently the simplest method available for measuring a cranial autonomic pathway, though the measurements obtained with it are only weakly associated with the results of other tests of somatic and autonomic function in diabetes, and are unrelated to measurements of distal sudomotor function.