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D. A. Berntsen, D. O. Mutti, K. Zadnik; Evaluating the Influence of Oval Pupils on the Fitting of Zernike Polynomials. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3319. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Because most aberrometry software only fits circles with diameter equal to the minor axis of an oval pupil, additional processing is needed to utilize all data from peripheral measurements. We evaluate the effect on the central Zernike polynomial fit of including missing data and data outside the circular diameter of the oval pupil minor axis.
A peripheral measurement 30º temporal on the retina from the line of sight was made on the dilated right eye of thirty subjects using the Complete Ophthalmic Analysis System (COAS; AMO WaveFront Sciences). Subjects ranged in age from 23 to 45 years (mean ± SD = 31 ± 6.7 years), and central spherical equivalent refractive error ranged from +0.63 to -8.41 D (mean ± SD = -2.63 D ± 2.05 D). A 6-mm analysis diameter within the minor axis of the oval pupil was used to analyze the data with the COAS software. Complete Light Analysis System (CLAS-2D; AMO WaveFront Sciences) software was then used to draw an analysis circle with diameter equal to the major axis of the oval pupil, which includes missing data outside the oval pupil. Using methods described by Schwiegerling (2002), CLAS-2D Zernike coefficients through 6th order were scaled down to a 6-mm pupil diameter and compared to 6-mm COAS Zernike results. Paired t-tests were used to compare the 6-mm Zernike coefficients and RMS errors calculated by these two methods.
The mean differences and 95% limits of agreement (LoA) are shown in Table 1 for total RMS (2nd to 6th order), higher-order RMS (3rd to 6th order), Z(3,1), Z(3,-1), and Z(4,0). Although three of the differences calculated were significantly different than zero, the mean differences are not clinically meaningful. For a 6-mm pupil, the largest significant mean difference and LoA (for total RMS error) were equivalent to 0.03 D and ±0.11 D of spherical defocus, respectively.
Drawing an analysis circle equal to the major axis of an oval pupil, which includes missing data and data outside the diameter of the minor axis of the oval, does not have any substantial influence on the wavefront fit within the minor axis diameter. Additional work is necessary to validate the wavefront fit outside the smaller diameter.
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