Determining global shape parameters of a cornea using a two-fold fitting from measurement data to an aspheric toric surface model

A method of determining global shape parameters of a corneal surface, the method comprising:

• determining a height map of the corneal surface by:
• i. Illuminating a cornea of an eye using a stimulator source comprising a plurality of point sources;
• ii. capturing a reflected image of the plurality of point sources and determining a position of reflections of the respective plurality of point sources from the captured reflected image and
• iii. deriving the height map of the corneal surface based on a position of the plurality of point sources and the position of the reflections of the respective plurality of point sources, by performing a surface fitting using a set of global functions;
• fitting the height map as derived to a toric aspheric model to obtain a global fitting of the corneal surface to the toric aspheric model and;
• using the global fitting to determine one or more parameters related to an astigmatism of the cornea.