[Clinical evaluation of modifications of the SRK formula]

It was previously reported that the axial length and the refractive error were analyzed in selecting intraocular lens powers which were calculated by the SRK formula. Moreover, the predicted postoperative refraction was compared with the actual postoperative refraction. Two modifications of the SRK formula were derived from these relationships as follows; Modified SRK formula 1: R = 0.98 (P-I)-0.16L + 4.48, Modified SRK formula 2: R = 0.82 (P-I)-0.21L + 5.39. The modifications of the SRK formula were evaluated in 200 other eyes after posterior chamber lens implantation. As a result, the average refractive error was + 0.397 +/- 0.585D by the standard SRK formula, but it decreased by an average numbers of + 0.037 +/- 0.557D and + 0.047 +/- 0.547D respectively by modified SRK formulae 1 and 2. While the incidence of deviation within +/- 1.0D was 87.0% for the standard SRK formula, it was 94. 5% for both modified SRK formulas. The refractive errors, moreover, were less dependent on the axial length with both modified SRK formulae. The predicted postoperative refraction was more accurate by modified SRK formulae, especially between emmetropia and myopia up to 0.5 diopters.