Polar Scanning Algorithm is the an advanced version of the Elliptical Scanning algorithm specified in Espinosa's paper (link). This is not only more robust and handles more distorted ring images well, it is also computationally more efficient.
This algorithm detects the labels of the rings in a placido ring image which can be extremely helpful for corneal topography.
Run the file example.m to see the result of the algorithm. Unfortunately, this has not been compensated for broken rings. The compensated algorithm can be found in the full code folder for the corneal topographer. link
Demo can be found here.