Visual outcome following IOL power calculated by SRK/T and Barrett Universal-II formulae: A prospective comparative study

Abstract

Purpose: To compare the refractive prediction accuracy of the SRK/T and Barrett Universal II intraocular lens (IOL) power-calculation formulas in uncomplicated phacoemulsification cataract surgery. Materials and Methods: This prospective comparative study included 200 eyes of 200 patients undergoing cataract surgery, independently allocated into two groups of 100 eyes each. Preoperative biometric evaluation using the IOLMaster 700 included axial length, keratometry, anterior chamber depth, and lens thickness measurements. IOL power was calculated using the assigned formula (SRK/T or Barrett Universal II) for each respective group, and the calculated IOL power was implanted accordingly. Postoperative refractive outcomes were assessed at six weeks. Prediction error (PE), absolute error (AE), refractive accuracy, pre-specified subgroup analyses based on axial length and keratometry, and biometric correlations were evaluated. Results: Mean prediction error was lower with Barrett Universal II than with SRK/T (0.51 ± 0.29 D vs 0.57 ± 0.44 D), although the difference was not statistically significant (p = 0.198). Mean absolute error was also lower with Barrett Universal II (0.51 ± 0.28 D vs 0.60 ± 0.40 D, p = 0.065). A significantly higher proportion of eyes calculated using Barrett Universal II achieved postoperative refraction within ± 0.75 D (86% vs 62%, p < 0.001) and ± 1.00 D (94% vs 81%, p = 0.005). Barrett Universal II demonstrated lower absolute error in steep corneas, whereas SRK/T showed lower error in long eyes. Conclusion: Both formulas achieved satisfactory postoperative refractive outcomes. Barrett Universal II demonstrated more consistent refractive predictability across varying biometric profiles and achieved a higher proportion of eyes within clinically acceptable refractive error thresholds.