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Estimation of effective lens position using a method independent of preoperative keratometry readings
Ian Dooley1, Sofia Charalampidou, John Nolan
1Department of Ophthalmology, Waterford Regional Hospital, Institute of Eye Surgery, Dublin, Ireland. iandooley@eustace.net
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.