The selection of intraocular lens power by calculation and by reference to the refraction--a clinical study.

Two hundred eyes each received a Rayner Binkhorst pupil-supported intraocular lens (IOL) after cataract extraction. One hundred received a standard power +19 D IOL and one hundred received an IOL of power calculated for emmetropia by the formula of R. D. Binkhorst using biometric data. Calculation reduced the incidence of postoperative refractive error greater than the +/- 2 D range from 20 per cent to 1 per cent virtually eliminating significant postoperative refractive error. Consideration of the preoperative refractions and the calculated IOL powers showed that there is no constant or reliable relationship. Twenty nine 'emmetropic' eyes were shown not to be 'normal' eyes but eyes with a wide range of axial lengths whose different optical components summated to give emmetropia. In the selection of IOL power, reference must be made to biometric data to allow for these optical components and for this reason IOL power cannot be determined from the preoperative refraction of the eye. The case for control of postoperative refraction by calculation of IOL power is a strong one and there appears little justification for the use of standard power IOLs with unpredictable refraction results.