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P. Fournier, P. Harrison, G. Erry, D. Cuevas, C. Torti, L. Diaz-Santana; Real-Time in vivo Measurement of Ocular Aberrations With a Diffraction Grating-Based Curvature Wavefront Sensor. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2771.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate a novel methodology to measure in vivo, real-time ocular aberrations that employs a Diffraction Grating Curvature Wavefront Sensor as a more efficient alternative to the well known Shack-Hartmann sensor.
The Shack-Hartmann (SH) wavefront sensor is the most common sensor available to measure ocular aberrations. Its conceptual simplicity, together with its ease of implementation have put it in this place. However, the SH sensor dynamic range is small, very sensitive to opacities, and to retinal and intraocular scattering. An alternative approach, curvature wavefront sensing (CWS), measures the Laplacian of the wavefront by subtracting two out of focus images of the pupil, one in front, and one behind the pupil, and at the same distance from it. In this scheme, opacities, scattering and speckle have a lesser impact on the wavefront reconstruction. Traditional CWS methods use complicated setups that are difficult to calibrate which reduces their usability in practical situations. We present an approach in which a diffractive element is used to introduce a phase delay in the propagating beam. The use of only one detector and a Green’s function for wavefront reconstruction make this method as quick as SH sensing with the added benefit of lower sensitive to opacities and scattering. Seven eyes from four subjects were successfully measured with the system. Dynamic measurements of accommodation were recorded with targets at 16 and 72 in from the subject’s eye.
The range of measured aberrations in the accommodation experiments were: -1.127 to 0.197D Defocus, 0.265 to 0.781D Astigmatism, 0.187 to 0.388D Coma, 0.120 to 0.199D Trefoil, and -0.128 to 0.243D Spherical. The range of wavefront reconstruction RMS was 0.190 to 0.377D.
A CWS has been implemented which compares both in set-up complexity, computational time for reconstruction and cost to that of a SH. It has the added advantages of an extended dynamic range, compared with the SH and it is, theoretically, less sensitive to scattering and ocular opacities.
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