Modulation transfer function of the Stokes lens and its computer-controlled application for clinical optometry of astigmatism

Astigmatism is a highly prevalent cylindrical refractive vision defect. The capability of the Stokes lens to compensate for astigmatism of a human eye was examined with a primary interest towards clinical optometry. A prototype of a computer-controlled apparatus, based on the Stokes lens principle, was designed and built with an objective to simplify clinical subjective refraction of astigmatism. Physical properties of the employed optical system were studied using modulation transfer function (MTF) as a metric. It was shown that the apparatus is capable of both compensating an arbitrary astigmatic defect and measuring its optical characteristics. The accuracy of the optometric measurements was evaluated. The proposed apparatus enables a novel method of optometry of astigmatism which relies on a patient’s feedback obtained through intuitive manipulation of a computer human interface device, such as a mouse, in a 2-dimensional X-Y plane, rather than verbal interaction. This two-dimensional input is then translated into a virtual 2-dimensional space of optical power and the orientation angle of the cylinder axis and provides a measurement of astigmatism of the eye.