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,] 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 ELPrh +/- SD 5.60 +/- 0.36 mm) methods. Agreement between ELP, and ELP and between ELPh and ELPrh 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, and -0.04 +/- 0.39 mm (range -0.43 to +0.35 mm; P = .08) in association with ELPrh. The mean absolute error for ELP, versus ELP, estimation and for ELPh versus ELPrh 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.