A method and apparatus for measuring refractive properties of a refractive optical system by fitting measurement data points to a derived function are disclosed. In a preferred embodiment relating to an automatic objective optometer, each data point represents a peak signal amplitude extracted from a scan of a plurality of pixels on an area detector array receiving light from the illuminated refractive optical system at a particular optometer position. The derived function describes a relationship between the peak pixel signal and optometer position based on changing focusing conditions of light at the detector array, which correspond to focusing conditions at an image plane of the refractive optical system under a confocal arrangement. A first derived function is applied for fast and slow sphere optometer sweeps through broad and refined ranges and includes a pair of poles at first and second astigmatic focal points to give the magnitude of sphere and cylinder powers of the eye, and a second derived function is applied for a cylinder sweep varying the axis of a non-zero cylinder component introduced to the illuminating light and includes a single pole for giving the cylinder axis.
Automatic optometer evaluation method using data over a wide range focusing positions