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TAKEO IWAMOTO, A. GERARD DEVOE; Electron Microscopic Studies on Fuchs' Combined Dystrophy I. Posterior Portion of the Cornea. Invest. Ophthalmol. Vis. Sci. 1971;10(1):9-28.
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© ARVO (1962-2015); The Authors (2016-present)
Seven corneal buttons obtained at perforating keratoplasty for typical Fuchs' combined dystrophy were fixed with glutaraldehyde and osmium, and posterior portions of the central corneas were studied with the electron microscope. Descemet's membrane was markedly thickened in six cases and showed various structural alterations. Five different regions could regularly be distinguished in the pathologic Descemet's membrane in all cases. From anterior to posterior they were (1) "anterior banded region" with 1,000 Å-banded pattern, (2) "nonbanded region," without clear banding (these regions are seen in normal corneas); (3) "posterior banded region" filled with 1,000 Å-banded material ("warts" are formed by its partial backward protrusions); (4) "border region" composed of groups of "thin fibrils," "long-spacing bundles" of 1,000 Å periodicity with two types of banded pattern, and "basement membrane-like material"; and (5) "fibrillar region" which consists of "basement membrane-like material" and collagen fibrils. One case had warts located very posteriorly, and another, no clear warts, but both could be interpreted as variations of the above structure. The endothelium was thin, consisting mainly of two types of abnormal cells. Loosening of the functional complexes was common, and partial discontinuity of the endothelial cover was also seen. The Type 1 cell had cytoplasmic filaments, increased rough-surfaced endoplasmic reticulum (RER) and cytoplasmic processes, simulating fibroblasts. The Type 2 cell had elongated RER and lysosomes within a less dense cytoplasm, and was probably a degenerate form of the Type 1 cell. Based on our findings, the following hypothesis is proposed: For unknown reasons, possibly hereditary, the endothelial cell morphology and function become similar to those of fibroblasts and they start producing collagen fibrils and basement membrane-like material, forming the fibrillar region of Descemet's membrane. At the border region, the collagen fibrils disintegrate into thin fibrils and partly further transform into long-spacing bundles. These, together with basement membrane-like material, are finally incorporated into the posterior banded region. Acceleration of this process forms warts. Similar changes can be seen at the extreme periphery of the normal adult cornea as a physiological phenomenon.
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