To evaluate structural alterations of iris and pupil diameters (PDs) in patients using systemic α-1-adrenergic receptor antagonists (α-1ARAs), which are associated with intraoperative floppy iris syndrome (IFIS).Eighty-eight eyes of 49 male were evaluated prospectively. Patients were assigned to 2 different groups. Study group included 23 patients taking any systemic α-1ARAs treatment, and control group included 26 patients not taking any systemic α-1ARAs treatment. All patients underwent anterior segment optical coherence tomography to evaluate iris thickness at the dilator muscle region (DMR) and at the sphincter muscle region (SMR). The PD was measured using a computerized infrared pupillometer under scotopic and photopic illumination.The study group included 46 eyes of 23 patients and the control group included 42 eyes of 26 patients. Most treated patients were on tamsulosin (16/23). Mean age was similar in the study and control groups (61.9±7.1 vs. 60.3±8, 2 years, nonsignificant). DMR (506.5±89.4 vs. 503.6±83.5 μm), SMR (507.8±78.1 vs. 522.1±96.4 μm) and the DMR/SMR ratio (1.0±0.15 vs. 0.99±0.23 μm) was similar in the study and control groups and these differences were nonsignificant. Scotopic PDs were also similar in both groups (3.99±1.11 vs. 3.74±1.35, nonsignificant). A significantly reduced photopic PD (2.89±0.55 vs. 3.62±0.64, P<0.001) and an increased scotopic/photopic PD (1.42±0.44 vs. 1.02±0.30, P<0.001) were found in the study group.Evaluating PD alterations might be more useful than evaluating iris structural alterations in predicting IFIS. There is still a need for a reliable method that will determine the possibility of IFIS.