Entwicklung eines minimal-invasiven Magnetsystems zur hochqualitativen drahtlosen Aufzeichnung von Augenbewegungen bei nicht-menschlichen Primaten
Zusammenfassung der Projektergebnisse
Non-human primates represent a very important animal model for research on the visual and oculomotor systems, and this is due to a multitude of reasons. This importance requires precise measurements of eye position, especially since visual perception is known to be a highly active process. The most popular current method for tracking eye movements in nonhuman primates is to use the non-invasive video-based eye tracker, of which many commercial and custom systems exist. However, besides the high costs associated with these non-invasive systems (whether in terms of money for purchasing commercial systems or in terms of time and effort for developing custom ones), video-based eye trackers leave plenty to be desired in terms of signal-to-noise ratio, accuracy, and resolution to measure the tiniest of eye movements. At the other end of the spectrum, implantable scleral search coils, developed approximately 50 years ago, provide impeccable eye tracking performance but at the cost of highly invasive implants that are prone to a variety of problems. Here, we developed and tested a high-quality magnetic eye tracking system that provides very high performance on par with that of scleral search coils, but while at the same time being wireless and minimally-invasive. The technique requires a one-time sub-conjunctival implantation of tiny magnets around the eye orbit (adaptations to human applications can involve wearing soft contact lenses with the magnets already embedded within these lenses). As the eye rotates, the magnetic field around it is modulated because the implanted magnets rotate with it. Thus, a wireless magnetic field sensor placed near the eye detects changes in eye position via altered magnetic fields. We tested this system on multiple macaque monkey eyes, and we solved several challenges related to magnet size, implant procedure, sensor electronics, and signal calibration. Simultaneous measurements with video-based eye tracking revealed massive improvements in signal quality relative to videobased eye trackers, allowing the detection of the tinies possible microsaccades and ocular position drifts during gaze fixation. Moreover, comparisons to previous scleral search coil measurements in the same animals revealed eye tracking performance as good as, if not slightly better than, that obtained with scleral search coils. The system is also very cost-effective, with magnetic field sensors being cheap to purchase from any electronic components supplier. Currently, we are working to improve on what we have learned so far during this project, and we particularly aim to test the long-term stability of the magnet implants in the eyes. If we can demonstrate that the implants can stay stable in the eye for an expected experimental lifetime of an animal in a project, and if we can develop even better calibration procedures than what we have achieved so far, we should be able to publish the technique and extend its use in the field.
Projektbezogene Publikationen (Auswahl)
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A minimally-invasive magnetic system for high-quality wireless eye movement tracking in non-human primates. Oculomotor Meeting of München, Zürich, and Tübingen, München (Feb. 2023)
Hafed et al.
