BackgroundsTo investigate the changes of anterior eye segment with implantable collamer lens (ICL) under mesopic and photopic conditions.MethodForty-seven eyes of myopic patients who underwent ICL V4c implantation were included. Three months after surgery, the pupil diameter (PD), dynamic vault, ACD (distance from the posterior corneal surface to the anterior lens surface), ACD-ICL (distance from the posterior corneal surface to the anterior ICL surface), and anterior chamber angle parameters were measured using the anterior segment optical coherence tomography (AS-OCT, Carl Zeiss AG, Germany) under completely mesopic (0 lx) and photopic (5290 lx) lighting conditions.ResultsCompared with mesopic conditions, a significant decreased vault was detected in photopic conditions (486.7 ± 186.1 μm versus 643.5 ± 191.2 μm,p< 0.001), while the ACD-ICL increased significantly (2.54 ± 0.24 mm versus 2.37 ± 0.23 mm,p< 0.001). The pupil was smaller in photopic condition (2.66 ± 0.23 mm versus 5.62 ± 0.55 mm,p< 0.001). ACD didn’t change(3.32 ± 0.24 mm versus 3.31 ± 0.22 mm,p= 0.079). The change of the vault was positively related to the changes of the PD (r2= 0.301,p= 0.04). There were no statistical difference between the change of vault and the change of ACD-ICL (158.0 ± 58.1 μm versus 165.9 ± 65.3 μm,p= 0.320).ConclusionWhen exposed to high intensity light after ICL surgery, the pupil constricted, vault decreased, ACA widened and ACD-ICL increased. All these changes were caused by the change of iris not the crystalline lens.