Why is glaucoma associated with exfoliation syndrome?

Abstract

Exfoliation syndrome (XFS) is an age-related, generalized disorder of the extracellular matrix characterized by production and progressive accumulation of a fibrillar material in tissues throughout the anterior segment and also in connective tissue portions of various visceral organs. Mature exfoliation fibrils are composed of 8-10 nm microfibrils resembling elastic microfibrils. The exact chemical composition of exfoliation material (XFM) remains unknown. It appears to consist of a complex glycoprotein/ proteoglycan structure composed of a protein core surrounded by abundant glycoconjugates. The protein components include both non-collagenous basement membrane components and epitopes of the elastic fiber system, particularly components of elastic microfibrils. Overall, XFS is the most common identifiable cause of glaucoma, accounting for the majority of cases in some countries, and causing both open-angle glaucoma and angle-closure glaucoma. Iridolenticular friction leads to loss of XFM from the anterior lens surface and disruption of the iris pigment epithelium, resulting in pigment deposition in the trabecular meshwork, which also produces XFM locally. The primary cause of chronic pressure elevation appears to be the active involvement of trabecular cells and Schlemm's canal cells in particular, in the generalized pathologic matrix process with subsequent degenerative changes of Schlemm's canal and adjacent tissues. Narrow angles and angle-closure are common in XFS. Pupillary block may be caused by a combination of posterior synechiae, increased iris thickness or rigidity, or anterior lens movement secondary to zonular weakness or dialysis. Enlargement of the lens due to cataract formation and relative pupillary constriction are additional factors.