Intraocular lens formula calculation in pediatric eyes: Do we have an answer? A retrospective comparison between Sanders–Retzlaff–Kraff II and Barret's formula

Purpose: The ideal formula for intraocular lens (IOL) power calculation following cataract surgery in pediatric eyes till date has no answer. We compared the predictability of the Sanders–Retzlaff–Kraff (SRK) II and the Barrett Universal (BU) II formula and the effect of axial length, keratometry, and age. Methods: This was a retrospective analysis of children who were under eight years of age and who underwent cataract surgery with IOL implantation under general anesthesia between September 2018 and July 2019. The prediction error of SRK II formula was calculated by subtracting the target refraction and the actual postoperative spherical equivalent. Preoperative biometry values were used to calculate the IOL power using the BU II formula with the same target refraction that was used in SRK II. The predicted spherical equivalent of the BU II formula was then back-calculated using the SRK II formula with the IOL power obtained with the BU II formula. The prediction errors of the two formulae were compared for statistical significance. Results: Seventy-two eyes of 39 patients were included in the study. The mean age at surgery was 3.8 ± 2 years. The mean axial length was 22.1 ± 1.5 mm, and the mean keratometry was 44.7 ± 1.7 D. The group with an axial length >24 mm showed a significant and strong positive correlation (r = 0.93, P = 0) on comparison mean absolute prediction errors using the SRK II formula. There was a strong negative correlation between the mean prediction error in the overall keratometry group using the BU II formula (r = −0.72, P < 0.000). There was no significant correlation between age and refractive accuracy using the two formulae in any of the subgroups of age. Conclusion: There is no perfect answer to an ideal formula for IOL calculation in children. IOL formulae need to be chosen keeping in mind the varying ocular parameters.