The accuracy of intraocular lens (IOL) power calculation was evaluated in a multicenter study of 822 IOL implantations using the Binkhorst II, Sanders/Retzlaff/Kraff (SRK I, SRK II, SRK/T), Holladay, and Olsen formulas. All but the first of these were optimized in retrospect with calculation of the SRK A-constant, the Holladay surgeon factor, and the Olsen pseudophakic anterior chamber depth (ACD) for each lens style. The ACD prediction of the Olsen formula was based on a previously described regression formula incorporating preoperative ACD, corneal height, axial length, and lens thickness. Among the optical IOL power calculation formulas, the highest IOL power prediction error was found with Binkhorst's and the lowest with Olsen's, which was more accurate than the SRK/T and the Holladay formulas (P < .05). The SRK/T formula was significantly more accurate than the original SRK regression formulas (P < .001). When analyzed for axial length dependence, all formulas showed the least error in the normal range. Error of the Olsen formula was lower than that of the others in the axial length interval 20 mm to 26 mm. No differences in accuracy were found between the optical IOL calculation formulas in eyes with an axial length above 26 mm (P < .05). The accuracy of IOL power calculation can be improved with optical formulas using newer-generation ACD-prediction algorithms.

The accuracy of two newer generation theoretical intraocular lens (IOL) power calculation formulas and of the empirical SRK I and II formulas was evaluated in a series of 500 IOL implantations including a series of unusually long and short eyes. The prediction error of the theoretical formulas was found to be largely unaffected by the variation in axial length and corneal power, while the prediction of the SRK I formula was less accurate in the short and long eyes. The prediction of the SRK II formula was more accurate than the SRK I in that no systematic offset error with axial length could be demonstrated. However, because of a relatively larger scatter in the long eyes and a significant bias with the corneal power, the absolute error of the SRK II formula was higher than that of the theoretical formulas in the long eyes. The higher accuracy of the newer generation theoretical formulas was attributed to their improved prediction of the pseudophakic anterior chamber depth.

The postoperative intraocular lens (IOL) chamber depth was predicted using a multiple linear regression analysis of the postoperative chamber depth as a function of the corneal height, the preoperative chamber depth, and the axial length in 279 patients with a posterior chamber lens implant. Based on a linear regression formula incorporating these preoperatively defined parameters, the postoperative IOL chamber depth could be predicted with a correlation coefficient of 0.71 and an error of +/- 0.30 mm (SD). It is concluded that an individual prediction of the IOL chamber depth will improve the accuracy in IOL calculation.

The predictability of a theoretical, computerized (PC-assisted) intraocular lens (IOL) power calculation method and of the Sanders-Retzlaff-Kraff [SRK] I and II methods was evaluated from preoperative and postoperative biometry in 202 cataractous patients who had extracapsular cataract extraction (ECCE). The theoretical method resulted in the lowest range and standard deviation of the error, and the highest correlation coefficient between the observed and the predicted refraction (P less than .05). The superiority of the theoretical approach was most clearly demonstrated when the postoperative measurements were used in the predictions (P less than .001). This demonstrated the potential accuracy of the formula used and the importance of incorporating methods to predict the IOL position after surgery. If the prediction of the IOL chamber depth was properly corrected for the axial length dependence, a high prediction accuracy could be obtained in short as well as in long eyes.

The mechanical quality of the diathermic capsulotomy edge is significantly less than that of the capsulorhexis edge, which indicates that the diathermic capsulotomy edge would withstand less surgical manipulation.