[Accuracy limits in IOL calculation: current status]

Overview over the single independent error contributions of IOL power calculation and their currently achievable lower limits.

Analysis of the reasons of avoidable and unavoidable single errors which contribute to the overall error: measuring errors of axial length and corneal radii; errors due to neglecting of relevant influences such as pupil width, asphericity of cornea and IOL and IOL geometry; calculation errors from inadequate calculation methods; estimation errors of postoperative IOL position; IOL manufacturing errors. The said error contributions are to be compared with the reproducibility error of the refraction. All calculations use a numerical raytracing based on the geometric-optical IOL manufacturing data.

Axial eye length with an error of approximately 0.2 D is no longer the dominating error if the measurements are performed by interferometry, the same is true for corneal readii in normal eyes. The latter, however, causes the dominant error in eyes after corneal refractive surgery ( approximately 1.5 D) if measured only by keratometry. This error can be avoided if a topographic measurement is included into the raytracing, and in some cases also the measurement of posterior corneal surface has to be included. Currently the dominant unavoidable error contribution results from the uncertainty of postoperative IOL position ( approximately 0.35 D).

Some errors of classical IOL formulae can be avoided by raytracing. But if the total error threshold shall be below the error of refraction, the prediction accuracy of postoperative IOL position must be improved.