Apparatus and method for operating a real time large diopter range sequential wavefront sensor
An apparatus including a position sensing detector and a processing system, with the processing system configured to determine axis of astigmatism and cylinder and sphere diopter values of a subject eye.
1. An apparatus comprising:
a position sensing detector configured to output a sequence of position sensing signals, with each position sensing signal indicating deflection of a centroid of a wavefront sample from a reference point on the detector, with the wavefront sample being a sample of an annular ring shaped wavefront portion of an incident wavefront returned from a subject eye; and
a processing system coupled to the position sensing detector to receive the sequence of position sensing signals, with the processing system configured to calculate a sequence of deflection coordinates indicating the deflection of each centroid, to calculate a center point of the sequence of centroid deflection coordinates, to associate the sequence of deflection coordinates to an ellipse centered at a center point, with the sequence of centroid deflection coordinates fitted to the ellipse expressed in U, V Cartesian coordinates, with the ellipse having a major axis of amplitude=a and a minor axis of amplitude=b, with the center of the ellipse located at U=0, V=0, and each centroid deflection having coordinates U(t)=a·cos(t), V(t)=b·sin(t) where t=time dependent phase of receipt of a set of sequentially received centroid deflection coordinates and where the ellipse is a circle if the amplitudes of the major and minor axes are equal, to determine the axis of astigmatism based on angular orientation of the major and minor axes and to determine relative magnitude of divergence and convergence based on relative magnitudes of a and b.
2. The apparatus of claim 1 with the processing system further configured to locate the origin of the U, V Cartesian coordinate system to the intersection of the major and minor axes of the ellipse.
3. The apparatus of claim 1 with the processing system further configured to rotate the U, V Cartesian coordinate system so that the major and minor axes are coincident with the U, V coordinate system axes.
4. The apparatus of claim 1 with the processing system further configured to determine orientation of convergent and divergent portions of the sampled wavefront based on whether the amplitudes of the major and minor axes have positive or negative values.
5. The apparatus of claim 4 with the processing system further configured to calculate cylinder diopter values based on the amplitudes of the major and minor axes.
6. The apparatus of claim 5 with the processing system further configured to output display data qualitatively depicting eye refractive errors in terms of sphere and cylinder diopter values and cylinder axis orientation.