Purpose To evaluate the incidence and clinical manifestations of intraoperative floppy iris syndrome (IFIS) according to iris alterations in Korean patients taking α1-adrenergic receptor antagonists (α1-ARAs).

Methods This is a prospective observational study. Two surgeons performed cataract surgery in 758 eyes of 596 patients over a period of 12 months. Past medical history was reviewed, especially whether patients had been taking systemic α1-ARAs. Ultrasound biomicroscopy was performed to measure the iris thickness of the dilator muscle region (DMR) at half the distance between the scleral spur and the pupillary margin. Pupil diameter was measured and the occurrence of IFIS was recorded. Measurements of the α1-ARA group were compared with those of a control group matched for age and sex.

Results IFIS occurred only in six eyes of four patients on systemic α1-ARA medications (0.8%). Pupil diameter in the α1-ARA medication group and the control group was not significantly different. The difference in mean DMR thickness in patients taking an α1-ARA and in the control group was also not statistically significant (p=0.641). However, within the α1-ARA population, the DMR thickness of IFIS cases was significantly lower than that of non-IFIS cases (p=0.013)

Conclusions The overall incidence of IFIS was far lower in Korean patients than that reported for western patients. IFIS patients taking α1-ARAs showed significantly greater iris DMR thinning than non-IFIS patients taking α1-ARAs. Our findings indicate that the interaction between α1-ARAs and melanin, which results in iris DMR atrophy and IFIS, is less strong in Korean patients (with dark irises) than western patients.