Predicting Iridocorneal Angle Reduction After Evo Icl Implantation: A New Sizing Approach

To analyze the reduction of the iridocorneal angle following implantable collamer lens (ICL) implantation in the horizontal meridian. Additionally, to evaluate the relationship between ICL sizing, intraocular anatomical measurements, and iridocorneal angle reduction. The study also aims to optimize a sizing nomogram by incorporating sulcus-to-sulcus (STS) measurement and crystalline lens rise (CLR), ensuring controlled horizontal compression of the EVO ICL while minimizing angle narrowing.

Retrospective study conducted in one single clinical site, including myopic and myopic-astigmatic patients implanted with EVO ICLs.

Anterior segment optical coherence tomography (AS-OCT, CASIA2, Topcon, Japan) was performed preoperatively and at 1 month postoperatively. The angle open distance at 500 microns (AOD500) and trabecular-iris angle at 500 microns (TIA500) were measured. Additional evaluations included ultrasound biomicroscopy (UBM, Quantel Medical), optical biometry (IOLMaster 700, Zeiss, Germany), and corneal topography (Pentacam, Oculus). Postoperative refractive and visual outcomes were assessed. A predictive model for postoperative angle narrowing was developed using quadratic regression analysis. 

A total of 153 eyes were analyzed. At 1 month, the nasal AOD500 decreased by -0.33±0.22 mm (-39.65±14.01%), and the temporal AOD500 by -0.39±0.24 mm (-43.54±14.01%). The nasal TIA500 was reduced by -16.41±8.13º (-31.18±12.11%), and the temporal TIA500 by -17.87±8.43º (-33.83±12.76%). A strong correlation was found between ICL compression and CLR, with lower CLR values associated with lower compression. The predictive model for TIA500N was: Diff TIA500N = -40.183 + (0.913 ACD x ICL Size) + (-0.001 (ACD x TIA500N)²), R²=0.474.

Greater anterior chamber depth (ACD) and larger ICL size lead to greater postoperative iridocorneal angle reduction. The effect of preoperative TIA500N on angle narrowing follows a quadratic trend, with narrower preoperative angles experiencing the most significant reduction. This model can aid in optimizing ICL selection by suggesting smaller lenses for eyes with deep ACD and wide angles to prevent excessive closure. Patients at risk of significant angle reduction should be closely monitored for postoperative complications.