Icl Sizing Formula (Nk-V Formula) For Vertical Fixation

Recently, implantable collamer lens (ICL) have been fixated vertically to prevent postoperative rotation. This study aimed to develop and validate an ICL sizing formula for vertical fixation.

Nagoya Eye Clinic, Nagoya, Japan

This study included 98 eyes from 56 patients who underwent vertical fixation ICL surgery.Participants were randomly divided into two groups: a formula development groupand a validation group in a 2:1 ratio. Based on the measured postoperative vault at 3 months, the optimal ICL size to achieve a 0.5 mm vault was calculated using a previously published formula (Nakamura T et al. J Cataract Refract Surg. 2020). A multiple regression analysis was then performed using the optimal ICL size as the dependent variable and horizontal anterior chamber parameters measured by CASIA2 (TOMEY) as independent variables. Finally, the predicted vault obtained using the formula was compared to the measured postoperative vault in the validation group.

The analysis identified angle to angle distance (ATA), crystalline lens rise (CLR), and anterior chamber depth (ACD) as explanatory variables, with standardized coefficients of 0.408, 0.699, and 0.29, respectively. The coefficient of determination was R² = 0.649 (adjusted R² = 0.632). In the validation group, the measured vault was 0.508 ± 0.213 mm, and the predicted vault was 0.513 ± 0.170 mm. The mean error was -0.0053 ± 0.210 mm, and the absolute error was 0.173 ± 0.116 mm. The difference between the measured and predicted vaults was within ±0.25 mm for 75% (24/32) of cases and within ±0.5 mm for 97% (31/32) of cases.

The ICL sizing formula for vertical fixation using CASIA2 was found to be useful for selecting the appropriate ICL size.