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R. A. Applegate, D. E. Koenig, J. D. Marsack, E. J. Sarver, L. C. Nguyen; Pupil Center Location Uncertainty Is a Major Source of Instrument Noise in WFE Measurements. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6160.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the impact of pupil center location uncertainty in Shack/Hartmann (S/H) wavefront sensing on the variance in repeated measures of the high order RMS wavefront error (HO WFE).
Dilated WFE for five eyes of five subjects representing a large range of HO WFEs (HO WFE over a 6 mm pupil ranging from 0.26 to 1.57µm) were measured using a custom wavefront sensor (lenslet spacing 400µm). Twelve measurements for each subject were averaged to form the best estimate of the WFE. The impact of the uncertainty in pupil center location on WFE quantification was modeled on the assumption that the pupil center of a 6mm diameter pupil can vary randomly by up to 200 µm in any direction. 1000 new pupil centers were sampled for each subject and used to calculate the amount of variance in the actual eye measurements attributable to uncertainty in the pupil center location.
The percentage of variance accounted for by pupil location uncertainty for each individual results from a complex interaction between magnitude and distribution of the HO-WFE and the magnitude of pupil centering error. Uncertainty in the pupil center location accounts for 31, 15, 37, 53 and 61% of the variance in the repeated measurement of the HO RMS WFE for each of the five subjects, respectively.
Uncertainty in the pupil center location accounts for a significant amount of the variance in repeated wavefront measurements. Methods to minimize measurement noise due to pupil center location uncertainty include: increasing the sampling density of the lenslet array, increasing the sophistication of pupil center finding algorithms, and/or a utilization of a separate pupil camera.
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