Apparatus and method for operating a real time large diopter range sequential wavefront sensor
An wavefront sensor uses a calibration wave generator to calculate correction factors to be applied to ratiometric combinations of position sensor output signals to determine real centroid deflection values.
1. A wavefront sensor comprising:
a light source configured to output a light beam to illuminate a subject eye;
a position sensitive detector having a plurality of detector elements configured to output a plurality of output signals indicating signal strength of incident light on each detector element;
a beam deflecting element configured to intercept a wavefront beam returned from a subject eye when the subject eye is illuminated by the light source and configured to direct a portion of the wavefront beam from the subject eye through an aperture toward the detector, where the portion of the wavefront beam directed through the aperture forms a spot on the detector, where an amplitude of deflection of a centroid of the spot from a reference point on the detector is approximately indicated by a ratiometric combination of the output signal strengths, and where the amplitude of the deflection indicates the degree of tilt or convergence or divergence of the portion of the wavefront from a plane wave;
a reference wavefront generator configured generate a calibration wavefront equivalent to a wavefront beam returned from the subject eye and having a specified degree of convergence or divergence from a plane wave, where the deflection of the centroid of the calibration wavefront on the position sensing detector is a real centroid deflection for the specified convergence or divergence; and
a processing unit, coupled to the light source, the beam deflecting element, and the position sensitive detector, configured to control the beam deflecting element to deflect the wavefront beam to direct portions of an annular ring portion of the calibration wavefront on the position sensitive detector referenced to a reference point and further configured to compare the real centroid deflection at the specified degree of convergence or divergence from a plane wave to the approximate deflection indicated by the ratiometric combination of output signal strengths in order to calculate correction terms to be applied to the ratiometric combination when calculating deflections of a wavefront beam returned from the subject eye.
2. The wavefront sensor of claim 1 with the processing unit further configured to apply the correction terms to the ratiometric combination of output signal strengths output by the position sensing detector indicating approximate centroid deflections of convergence or divergence to obtain real centroid deflections to accurately indicate convergence or divergence.
3. The wavefront sensor of claim 1 where the reference wavefront generator is a calibration target configured to be position to intercept the light beam and generate the calibration wavefront.
4. The wavefront sensor of claim 1 with the processing unit further configured to perform a partial calibration each time the wavefront sensor is powered up.
5. The wavefront sensor of claim 1 with the processing unit further configured to process the real centroid deflection to determine misalignment of the light beam or of optical elements.