[Intraocular lens planning. Geometric-optical and Sanders-Retzlaff-Kraff I and II formulas]

In the literature, curves based on the geometrical-optical (theoretical) formula and on regression formulas are established to show the superiority of a certain formula type in respect to the other formula type. Such curves are not based on the data of an individual eye needing an IOL implant, they are (more or less) mean value curves for a certain corneal curvatures and for a certain assumed postoperative position of an IOL. Due to the fact that Sanders, Retzlaff and Kraff suppose a normal corneal curvature, her curve for the theoretical formula gives in short eyes unrealistic and much too high values. A "more realistic" curve for the theoretical formula would be situated in the region of the so called "second generation formulas". All these mean value curves are unable to demonstrate the precision of IOL power formulas for the individual case. For the individual case refractive balances allow precise statements concerning the formulas and the measuring accuracy of the used a-scan. Refractive balances are the comparison of all preoperative data of an eye with all postoperative data including postoperative ultrasound measurings of the pseudophakic eye. Our results of 197 IOL implantations with refractive balances show the clinical precision of the theoretical formula. This is still valid in cases having unusual optical data, for example having short or long eye axes, having unusual corneal curvature or unusual IOL main plain position.