AIM: To compare the dynamic changes of anterior segment parameters especially iris morphology induced by pharmacologic mydriasis between angle closure suspects and normal controls. METHODS: The study group comprised 19 eyes of 19 angle closure suspects and 19 eyes of 19 age- and sexmatched normal open-angle eyes. Pentacam and optical coherence tomography measurements before and 30min after instillation of compound tropicamide eye drop were performed and compared. Biometric evaluations of iris tomography and anterior chamber angle were estimated by a customized image-processing software. RESULTS: Baseline axial length, iris cross sectional area and volume did not differ significantly between angle closure suspects and normal controls. Angle closure suspects had smaller pupil size, narrower anterior segment dimension and axial length, thinner iris with greater curve in comparison with normal controls. Pharmacologic mydriasis led to significant increments in iris thickness at 750 mu m, anterior chamber depth and volume, whereas significant decrements in iris curve, cross sectional area and volume in both groups. Angle opening distance at 500 mu M was increased significantly in normal controls (from 0.465 +/- 0.115 mm to 0.539 +/- 0.167 mm, P=0.009), but not in angle closure suspects (from 0.125 0.100 mm to 0.145 +/- 0.131 mm, P=0.326). Iris volume change per millimeter of pupil dilation (Delta IV/Delta PD) decreased significantly less in angle closure suspects than normal controls (-2.47 +/- 1.33 mm(2) vs -3.63 +/- 1.58 mm(2), P=0.019). Linear regression analysis showed that the change of angle opening distance at 500 mu M was associated most with the change of central anterior chamber depth (beta= 0.841, P=0.002) and Delta IV/Delta PD (beta=0.028, P=0.002), followed by gender (beta=0. 062, P=0.032). CONCLUSION: Smaller iris volume decrement per millimeter of pupil dilation is related significantly with the less anterior angle opening in angle closure suspects after pharmacologic mydriasis. Dynamic iris change may be as a prospective indicator of iris compressibility and angle closure glaucoma.