Posterior polymorphous dystrophy: a light and electron microscopic study.

Abstract

SUMMARY Microscopic study of a keratoplasty specimen in a case of posterior polymorphous dystrophy demonstrated via serial sections a multilaminar Descemet's membrane with focal fusiform nodular protrusions of connective tissue. The latter are thought to represent the polymorphous lesions of the posterior limiting layers of the cornea seen clinically. Ultrastructurally, fibroblast-like cells lined the posterior surface of the cornea. It is postulated that those reported cases of PPD in which epithelial-like transformation of the endothelial layer has been described may represent more advanced cases, in which corneal oedema is likely to be a prominent feature clinic,ally. An evolving process of metaplasia rather than a static one might explain the variety of altered endothelial cells, fibroblasts, and epithelial cells which have been reported on the posterior cornea in the few PPD keratoplasty specimens studied to date.Posterior polymorphous dystrophy (PPD) is a bilateral, congenital, usually dominantly inherited disorder of the posterior limiting layers of the cornea which is characterised clinically by discrete geographic nodular or vesicular lesions at the level of Descemet's membrane that protrude towards the anterior chamber. As the condition is rare, usually non-progressive, and commonly causes minimal visual impairment, few cases have necessitated keratoplasty. Three light microscopic studies (Morgan and Patterson, 1967;Hanselmayer, 1972a;Malbran, 1972) and 6 ultrastructural studies (Hogan and Bietti, 1969;Boruchoff and Kuwabara, 1971;Hanselmayer, 1972b;Grayson, 1974;Bron and Tripathi, 1974;Rodrigues et al., 1975) of these specimens have resulted in a variety of findings, and the term 'polymorphous' seems as applicable microscopically as it is clinically. A recent study (Rodrigues et al., 1975) suggested that the characteristic ultrastructural finding in PPD is multilayers of epithelial cells on the back of the cornea. We wish to report the morphological findings in a case of PPD that lacked epithelial cells on the posterior cornea, and compare the pathology in this case with that in previously reported cases.

The molecular genetics of the corneal dystrophies - current status

“…Cells on the posterior corneal surface of Descemet's membrane may also have a fibroblast-like appearance (296).…”

“…irregularly thickened, m ultilaminar Descemet's membrane, occasionally contains focal nodular excrescences (296,301). The normal non-banded portion is thinner than normal and a layer posterior to it contains numerous delicate collagen fibrils (10-20 nm in diameter with a normal cross-striational periodicity) as well as long spacing collagen (with a banding of 55-110 nm) interspersed with fine granular homogeneous basement membrane-like material.…”

Novel Corneal Phenotype in a Patient With Alport Syndrome

“…23 In few areas, the endothelium was multilayered, consistent with PPMD, but mature (prominent) desmosomes between the cells and the microvilli on the posterior endothelial surface were absent. 24,25 Genetic sequencing was done to determine the type of ATS that the patient had. No X-linked mutation or polymorphisms that were consistent with ATS were found.…”

Posterior Polymorphous Corneal Dystrophy of Schlichting

“…This means that the endothelium in corneas with posterior polymorphous dystrophy is able to maintain a normal hydrated cornea. This is notable since pathological reports of this condition have shown a severely changed endothelium: a layer 2-3 cells thick of epitheloid cells with microvilli and desmosomes (Boruchoff et al 197 1;Grayson 1974;Tripathi et al 1974;Johnson et al 1978;Witschel et al 1980;Rodrigues et al 1981).…”