Predictability of Contemporary Regression and Theoretical Formulae in Intra-Ocular Lens Power Calculation in Small Incision Cataract Surgery

Abstract

BACKGROUND Present era of refractive cataract surgery mandates the requirement of accurate intra-ocular lens (IOL) power calculation. Attainment of this objective underscores the need for accurate biometric data and suitable formulae for precise IOL power calculation. Applicability of contemporary theoretical and regression formulae for different sets of eyes remains an area of interest. MATERIALS AND METHODS A retrospective analysis was done on 304 eyes (301 patients) that underwent uneventful cataract surgery at our hospital, after due approval of Institutional Ethical Committee. Accurate biometric data; axial length (AL), corneal curvature (K value) & anterior chamber depth (ACD) were ensured. IOL power for implantation was predicted by six contemporary formulae (Sanders-Retzlaff-Kraff (SRK-I), SRK-II, SRK/T, Binkhorst, Holladay 1 & Hoffer Q), employing incorporated software of the Nidek US4000 device. This was compared with the ideal expected power determined by the post-operative spherical equivalent of refractive status at 6 weeks. Refractive status variations from the predicted value for each set of formulae were statistically compiled & analysed employing one way ANOVA on SPSS software. RESULTS Mean age of patients was 59.68 ± 10.3 years (range 40-90 years), mean axial length was 22.72 ± 0.92 (range 19.34-25.19) mm, mean keratometric value was 44.87 ± 1.78 (range 39.13-50.13) diopters and mean ACD was 2.93 ± 0.41 (range 1.81-5.36) mm. Myopic shift in predicted values was noted for each set of formulae except SRK-1. Mean refractive variations were 0.