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J. C. Merriam, L. Zheng; Optimization of the IOL Constant for the Acrysof SN60WF IOL. Invest. Ophthalmol. Vis. Sci. 2008;49(13):399.
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© ARVO (1962-2015); The Authors (2016-present)
The estimation of refractive error after small incision cataract surgery (CE) with an intraocular lens (IOL) depends on accurate biometry, placement of the IOL within the capsule, an astigmatically neutral incision, and optimization of the IOL constant. Biometry with partial coherence interferometry (Zeiss IOLMaster) is rapid and precise, and the instrument software permits the clinician to optimize the lens constant for 5 IOL calculation formulas. We have reviewed 200 cases of CE with the Acrysof SN60WF IOL (Alcon Laboratories) to determine if the IOL constant varies with axial length.
All procedures were performed by a single surgeon, with a temporal 2.6 mm clear cornea incision. Manifest refraction was determined at least 4 weeks after surgery. The database included keratometry and axial length determined by the IOLMaster, IOL power, date of procedure, and date of last refraction. The IOL constants were optimized for 6 axial length groups: <22 mm, 22 - 22.99 mm, 23 - 23.99 mm, 24 - 24.99 mm, 25-25.99 mm, and greater than 26 mm. The relation of the optimized IOL constant to axial length was analyzed in Origin 6.1 (OriginLab Corp) with the polynomial fitting tool.
The IOL constant varies with axial length. For the SRK/T formula change in the A constant with axial length may be described by a linear equation. A polynomial with two variables describes change in the A constant for the SRK II formula, SF for the Holladay formula, pACD for the Hoffer Q formula, and a0 for the Haigis formula.
For the Alcon Acrysof SN60WF IOL, the constants used to predict postoperative refraction vary with axial length. Optimization of the IOL constant is essential to predict the postoperative refraction.
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