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.