Ultrastructural changes in scleral proteoglycans precede destruction of the collagen fibril matrix in necrotizing scleritis

Proteoglycans were localized using cuprolinic blue and visualized by electron microscopy in sclera from the eye of a 58-year-old woman with necrotizing scleritis. Samples of sclera taken from clinically normal anterior and posterior sclera and from sites involved in anterior necrotizing scleritis with ulceration and posterior scleritis showed markedly different patterns of proteoglycan distribution. Proteoglycans appeared as stain-positive filaments associated regularly with the 'd/e' bands of the collagen fibrils in normal anterior sclera, but were absent from intact collagen fibrils in the zone of anterior ulcerative scleritis. In posterior sclera including a site of posterior scleritis, proteoglycans were reduced in number with more heterogeneous associations with collagen fibrils. Depletion of scleral proteoglycans therefore precedes the degradation of scleral collagen in necrotizing scleritis, which may also involve the synthesis of atypical proteoglycan types in pathological sclera.