Abstract

DO.03.05

Accuracy limits in IOL calculation: current status

Preußner P.-R.
University Eye Hospital Mainz

Axial eye length measurements are no longer the source of the dominating error in IOL calculation, provided, the instruments are calibrated correctly. With such a calibration in one patient collective, the mean prediction error of two other collectives of altogether more than 1500 eyes in two different hospitals is only ≈0.1D, with 12 investigated IOL models. The mean reproducibility error of axial eye length measurement pre- versus postoperative is only 0.15D. More relevant are the influence of the pupil width causing a focus shift due to spherical aberration as well as the influence of changing IOL design within the same IOL model. Both of these effects can be addressed only by raytracing based on the manufacturer's original IOL data, not by closed formulae (≈0.3D). Currently, the dominating error in normal eyes is the uncertainty of postoperative IOL position (≈0.35D), in eyes after corneal refractive surgery or perforating keratoplasty it is the corneal radius (1.5D). The latter, however, can be determined from topography with much higher accuracy inside the raytracing. Only in a few cases corneal thickness or posterior shape are needed in addition. Manufacturing errors are not negligible. They often cause non-stochastical but systematical bias, depending on the single IOL charge (≈0.3D).

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