Influence of Optional Biometric Variables on Refractive Outcomes Predicted Through the Barrett Universal II Formula
DOI:
https://doi.org/10.48560/rspo.33244Keywords:
Biometry, Cataract, Lens Implantation, Intraocular, Lenses, Intraocular, Outcome Assessment, Health Care, Refractive Errors, Refractive Surgical ProceduresAbstract
INTRODUCTION: Modern intraocular lens (IOL) calculation formulas depend on a set of mandatory biometric parameters – axial length (AL), keratometry, anterior chamber depth (ACD) – as well as optional biometric parameters. The Barrett Universal II (BUII) formula considers two optional parameters - lens thickness (LT) and white-to-white distance (WTW). These parameters may not be measurable using older optical biometry devices, and there is currently a lack of evidence regarding their effect on refractive outcomes. We compared refractive outcomes of uncomplicated cataract surgery with and without the use of optional parameters.METHODS: Retrospective consecutive case study of eyes that underwent uncomplicated cataract surgery with single piece monofocal IOL implantation (Alcon Acrysof SN60AT). We compared the predicted spherical equivalent (SE) for the implanted lens obtained through the BUII formula, with and without optional parameters, to the postoperative SE obtained by subjective refraction performed 6-12 weeks post-operatively. The primary outcome variable was the absolute prediction error (AE) evaluated by the median (MedAE) and interquartile range (IQR). A multivariate logistic regression model for the odds of improving the predictions was fitted with biometric variables.
RESULTS: We included 1346 eyes with mean AL 23.36±1.08 mm (20.87-29.73), ACD 3.32±0.39mm (2.12-4.36), mean anterior keratometry 44.10±1.54D (38.48-49.63), LT 4.59±0.42 mm (3.12-6.00) and WTW 11.85±0.41 mm (10.51-13.36). After optimization, the median AE with optional parameters was significantly lower than without (with optional: MedAE 0.283D, IQR 0.310; without 0.289, IQR 0.326; p=0.005). The postoperative SE prediction changed by more than 0.1D (absolute values) in 26.15% (n=352). In this subset, a more accurate prediction was seen in 44.9% of cases (n=158), notably with lower LT (LT < 4.17 mm, 1SD cutoff, OR 2.00, p=0.014) and more extreme WTW (WTW > 12.67 or < 11.03, 2SD cutoff, OR 3.43, p=0.007).
CONCLUSION: In our sample, the inclusion of optional biometric variables in the Barrett UII formula significantly improved outcomes. A greater benefit was observed for lower-than-average pre-operative LT and extreme pre-operative WTW.
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OTHER CITED MATERIAL
A. Barrett Universal II Formula. Available at: https://calc.apacrs.org/barrett_universal2105
B. Barrett RX Formula Outcome Analysis. Available at: https://calc.apacrs.org/barrett_rx105
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