In epithelial basal membrane dystrophy of the cornea Bron's dystrophy plays a prominent role (frequently combined with fingerprint dystrophy). It can be visualized only in retroillumination, and is without doubt the most common corneal dystrophy. It should be distinguished from Cogan's microcysts, which were seen in only 11% of the authors patients. The incidence of map dystrophy is about the same, while subepithelial plaques are least frequently observed.
A report on 11 cases of maplike dystrophy of the cornea; it is characterized by the presence of fine whitish intraepithelial lines, which may easily be overlooked during biomicroscopic examination: they are most easily descernable in bright oblique illumination. Similarities with Cogan's, fingerprint, and bleblike dystrophy (Bron) are discussed, and the potential weakness of the corneal epithelium found in these patients is pointed out.
Histologically, pterygium is characterized, apart from the presence of typical collagen fibers, by the appearance of fibres which take up elastic stain but differ from normal elastic tissue, as was confirmed by electron-microscopic investigations. Thus, "elastoid degeneration" of collagen is characterized by the loss of the characteristic periodic fibril structure and by the appearance of coiled and knotty fibres. Collagen types in pterygium were identified biochemically for the first time. The main bulk of collagenous tissue consists of 80-90% Type I collagen, while only 10-20% Type III collagen was detected. Type IV collagen (basal membrane collagen) was present in low amounts. Digestion with elastase resulted in 20% solubilization of pterygium, while bacterial collagenase digested up to 40% of the tissue dry weight.
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