Open the EyeX Settings panel by right-clicking the EyeX icon in the notification area, and select “Settings…” in the context menu. On the Eye Tracker tab in the User Profile area there is a button “Test Eye Tracking”. Click that button to get a live feed of the lightly filtered gaze point data overlayed the points used for calibration. Here you can see how well your eyes are tracked and decide whether you want to recalibrate.
There is no programmatic function for this in EyeX.
Normally you shouldn’t have to recalibrate if you have a good calibration to start with. But maybe you would like to save to different calibration profiles for with or without glasses. Or if you find out that for very specific lighting conditions you could benefit from having a separate calibration profile for that.