Calibration-free retinal-anterior eye-tracker for high-speed, high-accuracy, and high-precision eye movement estimation during fixations, saccades, and smooth pursuit

Eye-tracking is increasingly prevalent across various aspects of our lives. It is currently used for research, education, diagnostics, and entertainment, for example, in virtual reality goggles. However, widely used video-based eye-trackers require subject-dependent calibration, which makes them unsuitable for examining individuals with unstable fixation, such as patients with neurodegenerative diseases. We present a novel calibration-free retinal-anterior eye tracker that uses retinal images to track changes in eye orientation. On an artificial eye, the eye tracker achieves an accuracy better than 0.6′ (0.01°) and a sample-to-sample precision of 0.09′ (0.0015°) for the reference-frame signal, improving to 0.05′ (0.0008°) after Kalman fusion. Under similar conditions, this precision exceeds that reported for video-based eye trackers. After a one-point trajectory offset correction, the eye tracker enables determination of the absolute gaze direction.The eye-tracker was tested with an artificial eye over a traverse of − 8° to + 8°. In human recordings we typically work within approximately ± 4°, a practical limit based on operating experience rather than on a systematic characterization. The eye-tracker is capable of measuring saccadic velocities of up to 300 °/s, incorporates an integrated display for dynamic stimulus presentation, and requires only a simple chin- and forehead rest for subject stabilization. The potential of this eye-tracker is demonstrated in healthy subjects and in participants who are unable to undergo a conventional calibration procedure. Additionally, the device is equipped with a synchronized video-based eye-tracker, making it a powerful research platform for developing eye-tracking technologies.