Abstract
Purpose: Achieving the desired post-operative refraction in cataract surgery requires accurate calculations for intraocular lens (IOL) power. Latest-generation formulae use anterior-chamber depth (ACD)—the distance from the corneal apex to the anterior surface of the lens—as one of the parameters to predict the post-operative IOL position within the eye, termed the effective lens position (ELP). Significant discrepancies between predicted and actual ELP result in refractive surprise. This study aims to improve the predictability of ELP. We hypothesise that predictions based on the distance from the corneal apex to the mid-sagittal plane of the cataractous lens would more accurately reflect the position of the principal plane of the non-angulated IOL within the capsular bag. Accordingly, we propose that predictions derived from ACD + ½LT (length thickness) would be superior to those from ACD alone.
 Design: Retrospective cohort study, comparing ELP predictions derived from ACD to aproposed prediction parameter.
 Method: This retrospective study includes data from 162 consecutive cataract surgery cases, with posterior-chamber IOL (AlconSN60WF) implantation. Pre- and postoperative biometric measurements were made using the IOLMaster700 (ZEISS, Jena, Germany). The accuracy and reliability of ELP predictions derived from ACD and ACD + ½LT were compared using software-aided analyses.
 Results: An overall reduction in average ELP prediction error (PEELP) was achieved using the proposed parameter (root-mean-square-error [RMSE] = 0.50 mm), compared to ACD (RMSE = 1.57 mm). The mean percentage PEELP, comparing between eyes of different axial lengths, was 9.88% ± 3.48% and −34.9% ± 4.79% for predictions derived from ACD + ½LT and ACD, respectively. A 44.10% ± 5.22% mean of differences was observed (p < 0.001).
 Conclusion: ACD + ½LT predicts ELP with greater accuracy and reliability than ACD alone; its use in IOL power calculation formulae may improve refractive outcomes.
Highlights
In cataract surgery, achieving the desired post-operative refraction depends on selecting the appropriate intraocular lens (IOL) power
Many formulae have been developed to predict the optical properties of the pseudophakic eye, yet accurately and reliably predicting effective lens position (ELP) remains a challenge in modern IOL power calculations.[1]
Our results demonstrate that PEELP observed with the use of anterior-chamber depth (ACD) + 1⁄2LT occurs in a single direction, as do predictions made using ACD
Summary
In cataract surgery, achieving the desired post-operative refraction depends on selecting the appropriate intraocular lens (IOL) power. In IOL power calculation formulae, corneal curvature, axial length (AL) and the post-operative position of the IOL implant within the eye, referred to as the effective lens position (ELP), play an important part in the prediction of the refractive outcome. Many formulae have been developed to predict the optical properties of the pseudophakic eye, yet accurately and reliably predicting ELP remains a challenge in modern IOL power calculations.[1] As such, improving the predictability of ELP should minimise refractive surprise and thereby improve refractive outcomes. In IOL power calculations, it has been shown that inaccuracy in predictions of post-operative ELP represent one of the greatest sources of total refractive prediction error.[1] Many modern IOL power calculation formulae, including Holladay II, Olsen, Barrett Universal II and Haigis, use anterior-chamber depth (ACD) as one of the parameters to predict post-operative ELP
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