Hi @pascalius, interesting idea although the consumer range of the Tobii eye trackers are designed to work alongside traditional keyboard and mouse rather than a replacement, for which there is the Tobii dynavox range of trackers.
That being said, if you check out the Tobii Core API reference guide with respect to the Eye Position Data class, herein
we describe the methodology for obtain validity codes for each eye
For example, “HasLeftEyePosition” Gets a value indicating the validity of the left eye position.
Declaration
public bool HasLeftEyePosition { get; }Further details about this method online @ https://tobii.github.io/CoreSDK/api/Tobii.Interaction.EyePositionData.html
Perhaps this is of use to you?