Single-shot Phase Measuring Deflectometry for Cornea Measurements

Phase measuring deflectometry (PMD) has been applied to measure the topography of specular surfaces. Many successful applications, such as measurement of eyeglasses, windshields or astro-mirrors, have demonstrated that PMD can be an alternative to interferometry for certain problems. We report a new possible application of PMD, namely topography measurements of the human cornea. This would provide a useful tool for ophthalmology. However, due to the uncontrollable movement of the eye and the large curvature of the cornea, there are challenges: the cornea of the eye has to be measured dynamically and with a wide angular dynamic range. Liu[1] introduced a single-shot PMD to measure planar surfaces dynamically. We will demonstrate that this method can be adapted to overcome the mentioned difficulties: the method allows for a very simple fringe generation and, thus, for a geometry that enables high angular dynamics. As single shot PMD requires narrow band signals, we properly pre-distort the fringe patterns. The observed pattern displays nearly constant frequency. Measurement examples will be demonstrated. [1]Liu et al. Adv. Opt. Techn. 2014;3(4):441-445