[Significance of optic formula selection for postoperative refraction after cataract operation]

Prediction of postoperative patient refraction is of paramount importance in modern cataract surgery. The choice of the IOL calculation formula plays a major role here. The influence of popular calculation formulas is evaluated in a prospective study.

We performed cataract surgery on 539 eyes with PC-IOL implantation in the capsular bag. The IOL power was computed using 10 different calculation formulas with the help of a personal computer. Patient refraction was examined two days and six months after surgery.

The mean difference between desired and obtained refraction was -0.11 +/- 0.88 dpt 83% of all patients were in a +/- 1 D interval of desired refraction with a median visual acuity of 20/25. The formula used contributes a major part to the precision of calculation despite all problems due to errors of measurement. The theoretical formulas with variable "pseudophacic anterior chamber depth" are superior to the older ones. Standard deviation of the worst formula tested is 25% higher than that of the best one. With the best formula tested there would have been a good result (error < or = 1 D) in 82% of the cases, with the worst one in only 72%.

The use of older formulas like SRK and Binkhorst should be discontinued and only the newer theoretical formulas (e.g. SRK/T, Holladay, Haigis etc.) be used. This is especially true for short and long eyes. For owners of a personal computer calculation and optimization of those more complex formulas should not be a problem.