On the ultrastructure and the formation of pseudo-exfoliation material.

Pseudo-exfoliation (PE) excrescences on the anterior lens surface were studied by electron microscopy. In some cases the superficial layer of the excrescences consisted of a meshwork of fibrils and filamentous subfibrillar units. It could be clearly seen that the fibrils were formed by lateral aggregation of filamentous units. Both the filaments and the fibrils had crossbands regularly spaced at 17 nm. In some fibrils, every third crossband was fainter than their neighbouring crossbands. Thereby a secondary periodicity appeared, the new period consisting of three crossbands in the order dense-faint-dense. The length of this period was 17 x 3 = 51 nm, i.e. the same as the distance between the crossbands of conventional PE fibrils. All transitional forms between the fibrils with 17 nm periodicity and the conventional PE fibrils were found, and there was a gradual transition between the material described and conventional PE material. It is suggested that the material on the surface of the PE excrescences represent newly formed PE material. This may be formed by condensation and linear polymerization of two kinds of units, corresponding to the dense and the faint crossbands.