The Photomotor Response - Dynamic Quantification by a Portable Pupillometer

Abstract

The pupillary light reflex (PLR) is a key component of the physical examination as it reliably tests the functional integrity of the neuromuscular loop between pupil and midbrain. Unlike the traditional manual testing the PLR with a penlight that frequently leads to incorrect interpretation due to its subjectivity, the specialized “pupillometer” tool allows objective testing and trending of pupillary data. We performed quantitative unilateral pupillometry several times in 53 healthy subjects (aged 21-74) in different background illumination levels using the NeurOptics NPi®-200 pupillometer. A number of key parameters describing the PLR were collected and analysed. We found that the individual PLR was very consistent. In general, constriction velocity (the first part of the PLR when the pupil constricts promptly after the onset of a light stimulus) was brisker than the dilation velocity (the second part of the PLR, when the pupil recovers from the constriction). Most importantly, both velocities depend on the initial pupillary resting size. We proved that pupillary parameters depend on environmental light conditions and age, but not gender, and scrutinized the nature and dynamics of anisocoric pupils. Taking together, pupillometry is becoming an important, non-invasive clinical tool for testing the autonomic nervous system. Here, we describe baseline parameters representing the physiological PLR, confirming and extending previously reported data. We thus provide the clinician important criteria to precisely assess the PLR and hence the autonomic nervous system in different pathological conditions such as diabetes, traumatic brain injury or cardiac and other autonomic neuropathies.