Effect of partially coherent light on the subjective measurement of ocular astigmatism

Abstract

In this paper, we study the effect of meridional accommodation response of the eye, in the measurement of ocular astigmatism, using different targets (single slit, multiple slit and interference fringes) under different illumination conditions (white light, quasimonochromatic light and partially coherent light) in a subjective optometer. We have found that, under natural illumination conditions (incoherent white light), the accommodation of a subject viewing different orientations of a target varies in a manner that compensates for his or her ocular astigmatism. The compensation effect is minimum when interference fringes are used as targets. We also form interference images of different orientations, directly on the retina of the eye, using the meridional refraction properties of the eye and an optical field that has coherence only along specific meridians. Use of interference images formed directly on the retina yields values of cylinder that compares well with objective measurements obtained using an autorefractor.