Computerised intraocular lens calculation: clinical results and predictability

The predictability of a theoretical, computer-assisted IOL calculation method and of the Sanders-Retzlaff-Kraff (SRK) method was evaluated from pre- and postoperative biometry in 110 cataractous patients subjected to a routine IOL calculation. With the theoretical method and the preoperative data the refraction was on the average 0.72 D (SD 0.78) more myopic than expected, an error which could be corrected for by (1) substituting the assumed postoperative chamber depth by the actual mean value and (2) adding 0.16 mm to the preoperative axial length. With the postoperative data the error was 0.05 D (SD 0.78) (p greater than 0.05). By the SRK method the refraction was 0.15 D (SD 0.71) and 0.37 D (SD 0.69) more hyperopic than expected with the pre- and the postoperative data respectively. These offset errors could be corrected for in either case by adjusting the assumed A constant in the SRK formula. With appropriate empirical corrections for offset errors the theoretical and the SRK method were similar in accuracy, that is, about 82% of the predictions within +/- 1 D, 99% within +/- 2 D, and 100% within +/- 3 D error. The variation in postoperative refraction after computerised IOL calculation was about one-third of the variation previously seen after implantation of standard power IOL.

Radial keratotomy for pseudophakic myopia

Cataract extraction with implantation of a standard power IOL occasionally gives rise to considerable post-operative myopia. When operation of the second eye is indicated, the question may arise whether the patient should be made strongly myopic in both eyes, be made anisometropic, or have the already implanted IOL exchanged for a weaker one. We report here on 3 patients made isometropic and low-grade myopic after radial keratotomy in the myopic pseudophakic eye followed by cataract extraction and implantation of an IOL of predicted power in the second eye.