The SRKII formula in the calculation of intraocular lens power.

This study compares the predictive accuracy of the SRKII formula for groups with average axial length and long eyes. 344 eyes which underwent cataract extraction with implantation of a posterior-chamber intraocular lens were included in the survey; 246 eyes had an average axial length (22.0-24.49 mm), and 98 eyes had an axial length of more than 24.50 mm. Mean absolute errors were 0.26+/-0.68 dpt in the first group and 1.16+/-1.78 dpt in the second group. 94.3% of the average eyes were within 1.0 dpt of the expected refraction, 98.8% within 2.0 dpt, whereas in the long-eye group 58.2% were within 1.0 dpt and 84.7% within 2.0 dpt. The results show that the SRKII formula performed credibly in average-length eyes; in the long eyes the ratio of large refractive deviations was greater than that of the other group.