Histologic changes of the iris in the development of angle closure in Chinese eyes

Purpose: To identify the histologic characteristics of the iris in primary angle closure. Methods: Iris specimens were obtained by surgical iridectomy in a series of patients in Zhongshan Ophthalmic Center with newly diagnosed acute angle Closure (AAC, 12 eyes), fellow eyes of AAC subjects (FAAC, 14 eyes), primary angle closure suspect (PACS, 11 eyes), chronic angle closure glaucoma (CACG, 19 eyes), primary open angle glaucoma (POAG, 7 eyes), and 9 age-matched donated eyes as controls without evidence of glaucoma. Patients with secondary causes for angle closure were excluded. The sirius red polarization method was used to quantify the density of collagen and differentiate the type I and type III collagen in the iris stroma. Other structural changes were studied by light and electron microscopy. Results: The density of type I collagen was higher in AAC and FAAC eyes (Wilcoxon test, P < 0.05), lower in all CACG eyes (Wilcoxon test, P < 0.05), and statistically similar in POAG and PACS eyes when compared with normal eyes. Structural damage to the iris stroma was confirmed by light and electron microscopy in AAC, CACG,. and POAG eyes but not in the majority of FAAC and PACS eyes. Conclusions: Eyes that have Suffered ail acute symptomatic episode of angle closure have a higher density of collagen type I fibers, as do the contralateral fellow eyes. Unlike AAC and CACG eyes, contralateral fellow eyes did not have demonstrable structural damage to the iris. These findings suggest that biomechanical properties of the iris may play a role in the development of AAC attacks.