Assessing the efficacy of four methods established by four parameters in ICL size selection and relevant influencing factors: a prospective cohort study

Purpose To compare the efficacy and relevant influencing factors of four ICL size selection methods established by four different parameters. Methods This prospective study included 60 patients (120 eyes) who underwent bilateral ICL implantation. Patients were equally divided into four groups, and each group used the Parkhurst nomogram based on sulcus-to-sulcus (STS), the manufacturer's Online Calculation & Ordering System (OCOS) nomogram based on white-to-white (WTW), the KS formula based on angle-to-angle (ATA) and the NK formula based on anterior chamber width (ACW) to determine the ICL size. Recorded the vault one month after operation and compared the consistency between STS and WTW, ATA and ACW and their effects on the vault of different groups. Results The Parkhurst nomogram, OCOS nomogram, KS formula and NK formula determined 86.7%, 70.0%, 83.3% and 66.7% of properly sized ICL, respectively. STS and ATA were correlated ( P < 0.05). The mean difference between the STS and WTW, ATA and ACW was -0.37 ± 0.62 mm, -0.42 ± 0.53 mm and -0.44 ± 0.52 mm, respectively. The vault in the OCOS group was negatively correlated with △ STS-WTW, and the vault in the NK group was negatively correlated with △ STS-WTW, △ STS-ATA and △ STA-ACW. The vault in the Parkhurst group and KS group was not affected by anterior segment biometry variables. Conclusion ATA can be served as an alternative parameter to STS, and STS-based Parkhurst nomogram and ATA-based KS formula determined the most appropriate ICL size. When using OCOS nomogram and NK formula to select ICL size, postoperative abnormal vault was associated with a larger difference between STS and other anterior segment parameters.