Ophthalmic Refractor and Method of Ophthalmic Refractor Signal Analysis

A method for measuring ophthalmic refractive error, the method comprising:

• utilising a relay system to image wavefront of a return light beam from a subject eye onto a Hartmann-Shack sensor system at a location in front of the cornea, so as to provide a non-linear relationship between spherical power and refractive error;
• utilising a computational system to receive from the Hartmann-Shack sensor system a spot distribution and compute a value indicative of the refractive error.

A method of analysing wavefront data generated by a Hartmann-Shack sensor system with a non-linear relationship between spherical power and refractive error, the method comprising, in a computational system:

• performing linear regression on centroid positions of spots defined by the wavefront data in at least two different directions to compute a slope value for each said direction;
• utilising the computed slope values to compute and output a value for at least one of the group comprising M, J0 and J45 vectors for the subject eye.