Pseudoexfoliation (PEX) syndrome has recently been acknowledged as a
generalized disorder of the extracellular matrix characterized by the
production and progressive accumulation of an abnormal fibrillar extracellular
material in many intra- and extraocular tissues. Its ocular manifestations
affect all structures of the anterior segment and lead to a wide spectrum of
spontaneous and intraoperative ocular complications, such as lens dislocation,
zonular ruptures, blood-aqueous barrier breakdown, melanin dispersion,
formation of posterior synechiae, corneal endothelial decompensation, and
open-angle as well as angle-closure glaucomas. Secondary open-angle glaucoma
may develop in patients with PEX syndrome due to active and local production of
PEX material by trabecular cells, the progressive accumulation of the material
in the juxtacanalicular tissue, and subsequent degenerative structural changes.
The characteristic fibrillar PEX material is composed of microfibrillar
subunits surrounded by an amorphous matrix. The material has a complex
glycoprotein/proteoglycan structure composed of a protein core surrounded by
glycoconjugates, e.g. glycosaminoglycans. The material appears to be
multifocally produced by various cell types, e.g. the nonpigmented ciliary
epithelium, the iris pigment epithelium, the preequatorial lens epithelium,
corneal endothelium, trabecular cells, vascular endothelia and smooth muscle
cells of the iris. Immunohistochemical evidence of elastic fiber epitopes in
PEX material as well as molecular biologic data showing overexpression of
elastic fiber components have led to the current pathogenetic concept which
explains PEX syndrome as a type of elastosis affecting especially elastic
microfibrils. Significantly increased aqueous humor levels of TGF-ß1 in PEX
patients suggest a role for this growth factor in the abnormal matrix
formation.