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E.J. Sarver, W.J. Donnelly, III, R.A. Applegate, J. Schwiegerling; Calculation of Spectacle Correction From the Modulation Transfer Function of Shack–Hartmann Aberrometry Images . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1170.
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© ARVO (1962-2015); The Authors (2016-present)
To calculate the spectacle correction using the modulation transfer function (MTF) of the Shack–Hartmann (SH) aberrometer image.
We developed a relationship between the spectacle correction (sphere/cylinder/axis) for an ocular wavefront and the location of MTF peaks in the aberrated and unaberrated images. A two–dimensional polynomial was fit to the MTF in the neighborhood of the peaks to provide a high resolution estimate of the location of the peaks. Using a COAS (Wavefront Sciences) SH system, we captured several images for: a wavefront generated by a spot located at 1500 mm, a 2.5 D test lens, a plano subject, and a keratoconus subject. We applied our MTF calculation procedure to these test images and tabulated the results. A relation was also derived which relates system parameters to measurement accuracy.
For simplicity, we compared the mean spherical equivalent (SEQ) obtained from the COAS wavefront measurements and the values obtained with our MTF peaks method. The results (see graph) indicate good agreement (R2 = 0.9927) between the two methods. According to the accuracy relation, the difference in the measurements were due to sub–pixel difference in the location of the MTF peaks.
The MTF calculation method provided a simple (no spot centers to find – just two peaks), fast and robust method of determining the spectacle correction in an aberrated ocular wavefront. Using the MTF peaks method, higher accuracy can be achieved for systems which have a micro lens array with a longer focal length.
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