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PURPOSE To determine the predictors of the postoperative horizontal trabecular iris angle (TIA750) after phakic posterior chamber implantable intraocular lens (IOL) surgery. SETTING Ophthalmology Clinic Vista Sánchez Trancón. DESIGN Retrospective case series. METHODS This study included 330 eyes implanted with spherical/toric Implantable Collamer Lens (ICL). From 230 eyes implanted with 13.2 mm ICL, these were divided in modelling (n=180) and evaluation group (n=50). Two groups implanted with 12.6 and 13.7 mm (n=50 each) were also used as evaluation. Anterior-segment OCT was used preoperatively to perform anterior chamber biometry (angle-to-angle distance (ATA), crystalline lens rise (CLR), anterior chamber depth (ACD), cornea sagittal depth, pupil diameter, nasal/temporal TIA750; postoperatively for measuring the vault, pupil diameter and nasal/temporal TIA750. Corneal curvature and horizontal visible iris diameter were measured using optical tomography. Bivariate correlation analysis was used to determine associations between preoperative and postoperative horizontal TIA750 with anterior chamber biometry, ICL-related parameters and age. Finally, a multivariate linear regression model (MLR) was constructed for predicting the postoperative TIA750. RESULTS Horizontal TIA750 reduced from 42.9±8.0 degrees preoperatively to 24.4±5.6 degrees postoperatively. Postoperative TIA750 was positively correlated with the preoperative TIA750, cornea sagittal depth and ACD, and negatively associated with the vault. The main predictors of the postoperative TIA750 were the preoperative parameters, TIA750, ICLsize - ATA and pupil diameter (adjusted-R2=0.39). The limits of agreement between predicted and real TIA750 were close to ±10 degrees. CONCLUSIONS Implantation of a phakic posterior chamber implantable IOL leads to a reduction in TIA750 and the main factors contributing for this are the preoperative TIA750 aperture and the vault.