Estimation of effective lens position using a method independent of preoperative keratometry readings

Purpose: To evaluate the validity of a keratometry (K)-independent method of estimating effective lens position (ELP) before phacoemulsification cataract surgery. Setting: Institute of Eye Surgery, Whitfield Clinic, Waterford, Ireland. Design: Evaluation of diagnostic test or technology. Methods: The anterior chamber diameter and corneal height in eyes scheduled for cataract surgery were measured with a rotating Scheimpflug camera. Corneal height and anterior chamber diameter were used to estimate the ELP in a K-independent method (using the SRK/T [ELP_rs] and Holladay 1 [ELP_rh] formulas). Results: The mean ELP was calculated using the traditional (mean ELP_s 5.59 mm ± 0.52 mm [SD]; mean ELP_h 5.63 ± 0.42 mm) and K-independent (mean ELP_rs 5.55 ± 0.42 mm; mean ELP_rh ± SD 5.60 ± 0.36 mm) methods. Agreement between ELP_s and ELP_rs and between ELP_h and ELP_rh were represented by Bland-Altman plots, with mean differences (± 1.96 SD) of 0.06 ± 0.65 mm (range -0.59 to +0.71 mm; P=.08) in association with ELP_rs and -0.04 ± 0.39 mm (range -0.43 to +0.35 mm; P=.08) in association with ELP_rh. The mean absolute error for ELP_s versus ELP_rs estimation and for ELP_h versus ELP_rh estimation was 0.242 ± 0.222 mm (range 0.001 to 1.272 mm) and 0.152 ± 0.137 mm (range 0.001 to 0.814 mm), respectively. Conclusion: This study confirms that the K-independent ELP estimation method is comparable to traditional K-dependent methods and may be useful in post-refractive surgery patients.