Analysis of moire fringes for application in ophthalmology

TLDR: In this paper, the contrast and the form of the interference fringes are calculated by simple optical filtering of the diffraction spectrum of two similar gratings in contact when illuminated by spatially coherent light (moire technique).

Abstract: The contrast and the form of the interference fringes are calculated which are obtained by simple optical filtering of the diffraction spectrum of two similar gratings in contact when illuminated by spatially coherent light (moire technique). The conditions to be fulfilled by the gratings in order to produce fringes of high contrast and simple form, that is, with only one maximum and one minimum per period, are indicated. Such properties of the fringes are required when retinal visual acuity is to be measured by an apparatus proposed by Lotmar using the method of Le Grand. The proposed computation method as well as the results could be useful for applications as for example in metrology. The computed results are confirmed by experimental findings on a variety of gratings.