Abstract
Clinical assessment of pupil appearance and pupillary light reflex (PLR) may inform us the integrity of the autonomic nervous system (ANS). Current clinical pupil assessment is limited to qualitative examination, and relies on clinical judgment. Infrared (IR) video pupillography combined with image processing software offer the possibility of recording quantitative parameters. In this study we describe an IR video pupillography set-up intended for human and animal testing. As part of the validation, resting pupil diameter was measured in human subjects using the NeurOptics™ (Irvine, CA, USA) pupillometer, to compare against that measured by our IR video pupillography set–up, and PLR was assessed in guinea pigs. The set-up consisted of a smart phone with a light emitting diode (LED) strobe light (0.2 s light ON, 5 s light OFF cycles) as the stimulus and an IR camera to record pupil kinetics. The consensual response was recorded, and the video recording was processed using a custom MATLAB program. The parameters assessed were resting pupil diameter (D1), constriction velocity (CV), percentage constriction ratio, re-dilation velocity (DV) and percentage re-dilation ratio. We report that the IR video pupillography set-up provided comparable results as the NeurOptics™ pupillometer in human subjects, and was able to detect larger resting pupil size in juvenile male guinea pigs compared to juvenile female guinea pigs. At juvenile age, male guinea pigs also had stronger pupil kinetics for both pupil constriction and dilation. Furthermore, our IR video pupillography set-up was able to detect an age-specific increase in pupil diameter (female guinea pigs only) and reduction in CV (male and female guinea pigs) as animals developed from juvenile (3 months) to adult age (7 months). This technique demonstrated accurate and quantitative assessment of pupil parameters, and may provide the foundation for further development of an integrated system useful for clinical applications.
Highlights
The pupillary light reflex (PLR) is a unique physiological mechanism that allows the examination of the function of the autonomic nervous system (ANS) gated by a light stimulus (McLeod and Tuck, 1987; Neuhuber and Schrödl, 2011; Kaiser et al, 2014; McDougal and Gamlin, 2015)
We report that the IR video pupillography set-up provided comparable results as the NeurOpticsTM pupillometer in human subjects, and was able to detect larger resting pupil size in juvenile male guinea pigs compared to juvenile female guinea pigs
Pupil measurements in animals have been described in the literature (Pennesi et al, 1998; Dabisch et al, 2008; Mohan et al, 2013; Ostrin et al, 2014) but the parameters measured were limited to pupil size by the experimental set up or by the method of data analysis
Summary
The pupillary light reflex (PLR) is a unique physiological mechanism that allows the examination of the function of the autonomic nervous system (ANS) gated by a light stimulus (McLeod and Tuck, 1987; Neuhuber and Schrödl, 2011; Kaiser et al, 2014; McDougal and Gamlin, 2015). Other relevant parameters examined include resting pupil size, and the relative afferent pupillary response (Kaiser et al, 2014). These observations are made with the use of a bright pen torch shone into the eyes, rely heavily on the judgment of an experienced clinician, and provide qualitative information only. Available pupillometers are useful clinical tools that measure pupil diameter by first capturing an image of the eye, followed by quantification of the pupil diameter in the static image This type of measurement is a lost opportunity to record the dynamic rate and magnitude of pupil diameter change over time. A more informative and quantitative way of examining the pupils may be achieved by infrared (IR) videography, that allows the pupil constriction velocity (CV), re-dilation velocity (DV), pre and post illumination pupil sizes to be calculated (Miki et al, 2008; Mohan et al, 2013; Kaiser et al, 2014)
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