Increased iris stiffness in patients with a history of angle-closure glaucoma: An image-based inverse modeling analysis

PURPOSE. Previous studies have shown that iris mechanical properties may play a role in the pathophysiology of primary angle-closure glaucoma (PACG). Such studies, however, were not conducted in vivo and as such were limited in application and scope, especially for the development of diagnostic methods or new treatment options. The purpose of this study was to quantify in vivo iris mechanical properties both in patients with a history of angle-closure glaucoma and in healthy volunteers. METHODS. We acquired optical coherence tomography scans of anterior segments under standard and dim light conditions. Using a combination of finite element simulation and an inverse fitting algorithm, we quantified the stiffness of the iris. RESULTS. The irides in the eyes of patients with a history of PACG were significantly stiffer when compared with healthy control irides, a result consistent with ex vivo studies. This result was independent of the compressibility assumption (incompressible: 0.97 ± 0.14 vs. 2.72 ± 0.71, P = 0.02; compressible: 0.89 ± 0.13 vs. 2.57 ± 0.69, P = 0.02) when comparing the normalized elastic modulus of the iris between patients with PACG and healthy controls. CONCLUSIONS. Our noninvasive, in vivo quantification is free of numerous ethical issues and potential limitations involved with ex vivo examinations. If further studies confirm that the iris stiffness is an omnipresent PACG risk factor and a mechanistic role between increased iris stiffness and angle-closure glaucoma does exist, treatment methods such as lowering the iris stiffness can be developed.