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W. Chamon; A New Approach to Correct an Inherent Errorin IOL Calculation Formulasfor Eyes Submitted to Keratofractive Procedures . Invest. Ophthalmol. Vis. Sci. 2004;45(13):341.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To mathematically prove an inherent error of IOL calculation formulas in eyes that underwent keratorefractive surgery and to suggest a new approach to correct this error. Methods: Two available IOL calculation formulas were studied and the keratometric input was evaluated. Holladay I® and SRK/T® formulas use only one input for keratometric data. This data is used to provide information on corneal power and on the mathematically estimated anterior chamber depth. On eyes that underwent keratorefractive procedures, keratometry is altered only when referring to the corneal power, while the anterior chamber depth remains the same as preoperative, regardless its refractive change. The new approach separates two keratometric inputs: one for the corneal power (that should be postoperative keratometry) and one for the estimated anterior chamber depth (that should be the preoperative keratometry). Results: Different scenarios have been tested using the new approach and errors of one to two diopters of induced hyperopia were observed when using traditional formulas in eyes that experienced five diopters of keratometric flattening, depending on: preoperative keratometry, postoperative keratometry, axial length and IOL A–constant. Conclusions: All IOL calculation formulas miscalculate the refractive power of implanted IOLs in eyes that underwent keratorefractive surgery. This new approach is able to correct the inherent error of traditional formulas for IOL calculations without empiric nomograms.
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