Abstract
The human pupil behavior has gained increased attention due to the discovery of the intrinsically photosensitive retinal ganglion cells and the afferent pupil control path’s role as a biomarker for cognitive processes. Diameter changes in the range of 10–2 mm are of interest, requiring reliable and characterized measurement equipment to accurately detect neurocognitive effects on the pupil. Mostly commercial solutions are used as measurement devices in pupillometry which is associated with high investments. Moreover, commercial systems rely on closed software, restricting conclusions about the used pupil-tracking algorithms. Here, we developed an open-source pupillometry platform consisting of hardware and software competitive with high-end commercial stereo eye-tracking systems. Our goal was to make a professional remote pupil measurement pipeline for laboratory conditions accessible for everyone. This work’s core outcome is an integrated cross-platform (macOS, Windows and Linux) pupillometry software called PupilEXT, featuring a user-friendly graphical interface covering the relevant requirements of professional pupil response research. We offer a selection of six state-of-the-art open-source pupil detection algorithms (Starburst, Swirski, ExCuSe, ElSe, PuRe and PuReST) to perform the pupil measurement. A developed 120-fps pupillometry demo system was able to achieve a calibration accuracy of 0.003 mm and an averaged temporal pupil measurement detection accuracy of 0.0059 mm in stereo mode. The PupilEXT software has extended features in pupil detection, measurement validation, image acquisition, data acquisition, offline pupil measurement, camera calibration, stereo vision, data visualization and system independence, all combined in a single open-source interface, available at https://github.com/openPupil/Open-PupilEXT.
Highlights
The pupil diameter is an essential metric in visual neuroscience, as it has a direct impact on the retinal irradiance, visual acuity and visual performance of the eye (Campbell, 1957; Campbell and Gubisch, 1966; Woodhouse, 1975; Schwiegerling, 2000)
With PupilEXT, we offer a free alternative to commercial solutions and extended features in the topics of pupil detection, measurement resolution, data acquisition, image acquisition, offline measurement, camera calibration, stereo vision, data visualization and system independence, all combined in a single open-source interface
To better estimate how much the pupil diameter deviates depending on the used pupil algorithm, we evaluated the acquired eye images with the top-performing algorithms (ElSe, ExCuSe, PuRe and PuReST) and calculated the steady-state
Summary
The pupil diameter is an essential metric in visual neuroscience, as it has a direct impact on the retinal irradiance, visual acuity and visual performance of the eye (Campbell, 1957; Campbell and Gubisch, 1966; Woodhouse, 1975; Schwiegerling, 2000). The advantage of a NIR-based measurement is that the image quality does not suffer in pupil light response experiments Both the source code of the microcontroller for generating the hardware trigger and the respective NIR circuit board design (Figure 3D) are provided together with the PupilEXT software, allowing to set up the system effortlessly. With PupilEXT, we offer a free alternative to commercial solutions and extended features in the topics of pupil detection, measurement resolution, data acquisition, image acquisition, offline measurement, camera calibration, stereo vision, data visualization and system independence, all combined in a single open-source interface. This function is available for both mono and stereo camera modes
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