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The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the surgeon determines the IOL power. In order to determine the power of intraocular lens several values need to be known: * Eye's axial length (AL) * Corneal power (K) * Postoperative IOL position within the eye known as estimated lens position (ELP) * The anterior chamber constant: A-constant or another lens related constant Of these parameters the first two are measured before the implantation, the third parameter, the ELP, need to be estimated mathematically before the implantation and the last parameter is provided by the manufacturer of the intraocular lens. ==Axial Length== The axial length (AL) is the distance between the anterior surface of the cornea and the fovea and usually measured by A-scan ultrasonography or optical coherence biometry. The AL is the most important factor in IOL calculation: A 1-mm error in AL measurement results in a refractive error of approximately 2.88 D or about 3.0-3.5 D error of IOL power in an average eye. A mean shortening of 0.25–0.33mm can translate into an error of IOL power by approximately 1 D〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intraocular lens power calculation」の詳細全文を読む スポンサード リンク
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