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Abstract
Abstract
IOL Calculation after Corneo-Refractive Surgery
Haigis W.1, Langenbucher A.2, Seitz B.2
1Dept. Ophthalmology, Wuerzburg University; 2Dept. of Ophthalmology, University of Erlangen-Nuremberg
Purpose: IOL calculation after corneo-refractive surgery is a challenge becoming more and more important in the future. When current analytical IOL formulas are applied, difficulties arise especially due to the failure of classical keratometry. Instead, alternative methods were proposed (topography, contact lens method, refractive history method, regression procedures) the results of which, however, are partially not correctly interpreted. A systematic overview of the difficulties of current power formulas and possible solutions for eyes after corneo-refractive surgery does not exist and is attempted in this study.
Method: Currently used IOL formulas (Haigis, HoffferQ, Holladay, SRK/T, SRK II) were analyzed mathematically especially regarding variables which are influenced or altered by corneo-refractive surgery.
Results: Naturally, corneal power is the variable which is most affected. Not only is this parameter defined differently in different IOL formulas, but secondary variables derived from it are additionally used in some algorithms to serve as predictors for IOL position. For this purpose, clearly, only values prior to refractive surgery may be used. Further differences lie in the measurement values for corneal power expected by different formulas which can be equivalent or vertex powers.
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