Accuracy of toric intraocular lens formulas with measured posterior corneal astigmatism of different orientations

Stephen Stewart*, Tun Kuan Yeo, Salissou Moutari, Richard McNeely, Jonathan E Moore

*Corresponding author for this work

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Abstract

Purpose
To assess whether the use of measured posterior corneal astigmatism (PCA) values improves the prediction accuracy of toric intraocular lens power formulas, compared to predicted PCA values, when the orientation of the steep axis of PCA is non-vertical.
Design
Retrospective observational cohort study
Methods
418 eyes of 344 patients were included in the study. Prediction errors (PE) for postoperative refractive astigmatism at 4 weeks postoperatively were determined using vector analysis and compared for the following toric intraocular lens power formulas: Barrett Toric with predicted posterior corneal astigmatism (PPCA); Barrett Toric with measured posterior corneal astigmatism (MPCA); EVO Toric PPCA; EVO Toric MPCA; Holladay I with Abulafia-Koch regression. Subgroup analysis compared PEs for eyes with a vertically orientated steep axis of PCA (60-120o) to eyes with a non-vertically orientated steep axis of PCA.
Setting
Cathedral Eye Clinic, Belfast, United Kingdom and Tan Tock Seng Hospital, Singapoore.
Results
Standard keratometry was with-the-rule in 48% of eyes, while the steep PCA axis was vertically orientated in 91% of eyes. For all eyes, EVO PPCA had a smaller mean absolute error than Barrett-MPCA, Barrett-PPCA and Abulafia-Koch (p < 0.01 for all). EVO-PPCA had the highest percentage of eyes within 0.50D of predicted postoperative astigmatism for eyes with vertical PCA (61%), while EVO-MPCA had the highest percentage for eyes with non-vertical PCA (54%). EVO-MPCA had the smallest centroid error for all eyes, and the subgroups (p < 0.01 for all). Eyes with non-vertical PCA had a lower percentage within 0.50D than eyes with vertical PCA when using PPCA (43% vs 61%, p = 0.034), but there was no significant difference between these groups when MPCA is used for eyes with non-vertical PCA (54% vs 61%, p = 0.40).
Conclusions
hen the steep axis of posterior corneal astigmatism is not vertically orientated, the use of measured posterior keratometry values improves prediction accuracy.
Original languageEnglish
JournalAmerican Journal of Ophthalmology
Early online date04 May 2024
DOIs
Publication statusEarly online date - 04 May 2024

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