The cellular and molecular biology of the iris, an overlooked tissue: the iris and pseudoexfoliation glaucoma

Located between the cornea and the lens, the Iris is fully immersed in aqueous humor. During exfoliation syndrome, a disorder of the elastic fibers, an abnormal fibrillar material (XFM) is deposited on the anterior lens capsule underneath the pigment epithelium of the Iris. Release of this material to the aqueous humor reaches the trabecular meshwork where its presence is associated with elevated intraocular pressure. Ultrastructural studies suggest that the XFM material is produced by the lens capsule, lens epithelial and iris pigment epithelial cells (IPE). The involvement of the IPE in pseudoexfoliation glaucoma has not been extensively addressed. Immunohistochemistry studies have shown higher levels of LOXL1 and clusterin in the IPE extracellular space of specimens from exfoliation patients. But studies using IPE cells to understand the formation of the XFM in vitro and/or in vivo are scarce. A focus on the Iris and its IPE cells would be key for the elucidation of XFM and the understanding of the development of pseudoexfoliation glaucoma.