Predicting Actual Lens Position to Generate a Novel Intraocular Lens Power Calculation Formula for Marfan Syndrome

Purpose: To develop a novel intraocular lens (IOL) power calculation formula by predicting the actual lens position (ALP) in patients with Marfan syndrome who have ectopia lentis undergoing IOL implantation. Methods: Patients with Marfan syndrome undergoing in-the-bag IOL implantation or scleral-fixated IOL (SF-IOL) implantation were prospectively recruited. ALP was calculated by adding anterior chamber depth to half of the IOL thickness, measured using the IOLMaster 700 (Carl Zeiss Meditec). A generalized linear model was developed to predict the ALP and integrated into effective lens position (ELP) predictions. A supplementary strategy was adjusting axial length (AL). The proposed formulas were evaluated by refraction prediction error (PE) and its absolute value (AE) and compared with both classic and state-of-the-art formulas. Results: A total of 408 patients (408 eyes) were divided into a training set and a validation set. ALP was significantly correlated with ELP, but the discrepancy increased with longer AL. A significant anterior shift of ALP was observed in the SF-IOL procedure compared to in-the-bag IOL implantation. The ALP prediction model, stratified by AL and surgical procedure, was constructed in the training set. In the validation set, the ALP-based formula demonstrated the highest proportion of AE within 1.00 diopter (D) (83.78% for AL ≤ 24 mm; 92.50% for AL > 24 mm) and significantly reduced extreme PE compared to other formulas. For SF-IOL implantation, the AL-adjusted formula was the most accurate. An online calculator was developed to facilitate its application. Conclusions: The proposed formulas demonstrated superior accuracy for IOL power calculation in patients with Marfan syndrome compared to existing formulas.