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Youngsub Eom, Mingyu Kim, Hwa Lee, Young-Woo Suh, Jong Suk Song, Hyo Myung Kim; Use of the Ratio of Posterior to Anterior Corneal Radii of Curvature to Improve the Accuracy of Intraocular Lens Power Calculation: Eom’s Adjustment Method. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2719. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The accuracy of intraocular lens (IOL) power calculation using posterior corneal measurements was not improved in normal eyes when corneal power measurements from a Scheimpflug camera were directly applied to the IOL power calculation. We tested the hypothesis that if the conventional keratometry (K) can be adjusted according to the ratio of posterior to anterior corneal radii of curvature without changes to the mean value of the entire dataset, the adjusted corneal power could reduce the refractive prediction error created by the conventional K in IOL power calculation.
This retrospective study included 123 eyes from 123 patients who underwent uncomplicated phacoemulsification with implantation of a Tecnis ZCB00 (Abbott Medical Optics Inc.) IOL. The fictitious refractive index of the cornea for a Scheimpflug camera was calculated and adjusted anterior corneal radius and predicted posterior corneal radius were calculated from conventional K using the ratio of posterior to anterior corneal radii of curvature and fictitious refractive index of the cornea. Then, adjusted corneal power was calculated from obtained anterior and posterior corneal radii using a thick lens formula. The median absolute error (MedAE) based on the adjusted corneal power was compared with that based on the conventional K in the Haigis formula.
The mean ratio of posterior to anterior corneal radii of curvature was 0.813, and the fictitious refractive index of the cornea for the Scheimpflug camera was 1.3277. The mean adjusted corneal power was 44.22 ± 1.57 D, and the mean difference between the adjusted corneal power and conventional K was 0.00 ± 0.21 D. The difference between the adjusted corneal power and conventional K was significantly correlated with the ratio of posterior to anterior corneal radii of curvature (R2 = 0.997, P < 0.001). The MedAE (interquartile range) based on the adjusted corneal power (0.29 [0.14-0.50] D) was significantly smaller than that based on the conventional K (0.33 [0.16-0.58] D; P = 0.010).
IOL power calculation using adjusted corneal power according to the ratio of posterior to anterior corneal radii of curvature provided more accurate refractive outcomes than the calculation using conventional K.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
The keratometry-adjusted intraocular lens power calculator developed for this study.
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