Eye openness
Several definitions exist regarding eye openness. If wanting to compare data between different studies and eye tracker manufacturers, it is important to understand the different definitions.
How eye openness is defined in Tobii Eye Trackers
Tobii eye trackers supply a raw unprocessed eye openness signal that lets you apply any post-processing or filter to meet a wide spectrum of different use cases.
Eye openness is defined as the diameter in millimeters of the largest sphere that can be fitted between the upper and lower eyelids.
Upper and lower eyelids are defined by the contrast lines between the sclera and the lashes/lid structure.
The eye openness data is provided for the left and the right eye individually. If the eye openness for an eye cannot be estimated, this will be marked invalid.
Both Tobii Pro Spectrum and Tobii Pro Fusion provide eye openness signal for research purposes. The eye openness samples are at the same frequency as the gaze, for example in 600 Hz when the frequency is set to 600 Hz. Note that the Tobii Pro Fusion eye openness signal is only available at 120 Hz or lower frequencies.
The eye openness signal can be used independently of the other signals. The timestamps of the eye openness signal will match those in the gaze stream, as they are based on the same eye images.
To access this signal, you should use Tobii Pro SDK v. 1.10 or newer, and make sure to run a firmware version on your eye tracker that supports this feature.