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Miranda Bishara, Mujtaba A. Qazi, Li Wang, Ashraf M. Mahmoud, Cynthia J. Roberts, Douglas D. Koch, Jay S. Pepose; Application of Direct Measurement of IOL Position via Tomography for Back-Calculating Corneal and IOL Power Following Myopic LASIK. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5685.
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To utilize post-operative biometric and refractive data, including direct measurement of the IOL position (IOLP) via anterior segment OCT (Visante), to determine the prediction error of IOL power calculation methods and videokeratographic central corneal power measurements.
Post-cataract surgery refractive (refraction, implanted IOL power), biometric (axial length), and anterior segment OCT (IOLP) data were used to back calculate "true" corneal (BCK) power with the double-K Holladay 1 formula. Post-cataract surgery Orbscan raw data, from recorded slits, were processed to recalculate central corneal power, including Total Mean (TMP), Axial and Optical (TOP) Power, using a custom posterior edge-tracing software. Manual keratometry, placido-based (Atlas) topography, and Standard and Reprocessed Orbscan Total corneal power measurements were compared to BCK. IOL powers from the ASCRS post-refractive surgery IOL calculator were compared to the implanted IOL power, applying the post-cataract surgery refraction as the target for back-calculation purposes.
Central 3 mm diameter TMP and TOP had a mean error < 0.25 D compared to BCK (p>0.4). There was a high correlation (Pearson R>0.97) between standard and reprocessed Orbscan total power. Using the ASCRS IOL Calculator, the Modified Masket (error range +2.24 D to -0.56 D), Wang-Koch-Maloney (+1.14 D to -0.84 D), Shammas (+1.41 D to -0.53 D), Haigis-L (+1.57 D to -0.97 D), and Averaged (+1.50 D to -0.25 D) methods provided mean error from the implanted IOL of < 0.50 D.
Strategies to directly measure total central corneal power and incorporate multiple IOL power calculation methods can improve the accuracy of IOL power calculation following myopic keratorefractive surgery.
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