Suggested Approach for Pupil Measurement with Prior Information

[cancan101]

I am currently using the MediaPipe model (see paper) to provide keypoints for each iris. This model produces for each eye: the pupil center, 4 points of the outer iris circle, and 16 points of eye contour. However, I want to then measure the diameter of the pupil itself. Given I already have a strong prior for the center of pupil along with the ellipse for the iris, what is the suggested way of leveraging this information when trying to measure the pupil?