Astigmatic Refraction Using Peaks of the Interferogram Fourier Transform for a Talbot Moiré Interferometer

PURPOSE: To calculate the spectacle correction from a Talbot Moire wavefront sensor using the location of peaks in the Fourier transform of the interferogram image. METHODS: A relationship was developed between the spectacle correction for an ocular wavefront and the location of Fourier transform peaks in the aberrated interferogram. These spectral peaks were located to sub-pixel accuracy using a two-dimensional polynomial fit. A Talbot Moire wavefront system was developed to collect examination images from an astigmatic model eye and human eyes. The authors' Fourier transform calculation procedure was applied to captured interferogram and results were tabulated. RESULTS: Five examinations were made of the astigmatic model eye. The mean sphere and cylinder were -4.26 D (SD = 0.004) and -2.90 D (SD = 0.008), respectively. The axis for all measurements was 92 degrees. These values were consistent with the model eye design parameters. The patient was a 46-year-old man with best spectacle-corrected visual acuity of 20/20. Ten examinations were made of the patient's eye. The mean sphere and cylinder were -0.09 D (SD = 0.11) and -1.45 D (SD = 0.14), respectively. The mean axis was 69.1 degrees (SD = 1.29 degrees). The calculation time was 46 ms per image running on a 3.6-GHz PC using 512x512 fast Fourier transforms. This processing time is fast enough for real-time acquisition and display of a patient's refractive state. CONCLUSIONS: The Fourier transform calculations provided a fast and simple method of determining the spectacle correction in an aberrated ocular wavefront imaged by a Talbot Moire wavefront sensor.