Posterior polymorphous dystrophy of the cornea: cell culture studies

Characteristics of corneal dystrophies: a review from clinical, histological and genetic perspectives

Corneal dystrophy is a common type of hereditary corneal diseases. It includes many types, which have varied pathology, histology and clinical manifestations. Recently, the examination techniques of ophthalmology and gene sequencing advance greatly, which do benefit to our understanding of these diseases. However, many aspects remain still unknown. And due to the poor knowledge of these diseases, the results of the treatments are not satisfoctory. The purpose of this review was to summarize the clinical, histological and genetic characteristics of different types of corneal dystrophies.

In vivo confocal microscopic findings in posterior polymorphous corneal dystrophy

PURPOSE

To describe the corneal findings in posterior polymorphous corneal dystrophy (PPCD) as imaged with laser scanning in vivo confocal microscopy (IVCM).

METHODS

IVCM images of 7 subjects with PPCD who had typical slit-lamp biomicroscopic findings of endothelial vesicular, band, and/or placoid lesions were evaluated.

RESULTS

Five women and 2 men aged 7 to 64 years were included in this study. Laser scanning IVCM (Heidelberg Retina Tomograph II, Rostock Cornea Module) revealed hyporeflective, round, vesicular lesions with diameters ranging between 20 and 200 µm in 3 subjects, combined vesicular and curvilinear hyperreflective band-like lesions in 3 subjects, and combined vesicular and placoid hyperreflective lesions in 1 subject at the level of Descemet membrane (DM), endothelial cell layer, and posterior stroma adjacent to DM. One subject had coassociated epithelial basement membrane dystrophy. Additional findings included posterior stromal keratocytes with elongated spindle-like nucleus, giant and nucleated endothelial cells, endothelial deposits, and guttae-like dark spots. The mean endothelial cell density was 1485.7 ± 486.3 cells per square millimeter (range, 990-2365 cells/mm). The mean central corneal thickness was 585.3 ± 37.17 μm (range, 534-643 μm).

CONCLUSIONS

Laser scanning IVCM is able to highlight the characteristic microstructural alterations at the level of endothelium and DM in the setting of PPCD and may have diagnostic utility in equivocal cases with borderline biomicroscopic findings. The possible association of PPCD with epithelial basement membrane dystrophy warrants further investigation.

Recurrence of posterior polymorphous corneal dystrophy is caused by the overgrowth of the original diseased host endothelium

Posterior polymorphous corneal dystrophy (PPCD) is a rare, bilateral autosomal dominant disorder affecting primarily the corneal endothelium and descemet membrane (DM). The aim of this study was to establish the origin of abnormal endothelium in a patient with PPCD exhibiting cornea graft failure after keratoplasty surgery. A sex-mismatched graft obtained from a patient with PPCD who underwent repeat penetrating keratoplasty and the patient's original cornea were investigated. Combined fluorescent immunohistochemistry for cytokeratin (CK) 19 (a marker of aberrant PPCD endothelium) with fluorescence in situ hybridization (FISH) of the sex chromosomes were used in order to characterize the cells on the posterior graft surface. The pathological endothelium of the failed PPCD cornea revealed strong positivity for CK19 using fluorescent immunohistochemistry. In all the CK19-positive cells, both X and Y chromosomes were simultaneously detected using FISH. The results clearly showed the original cells of the patient (XY), within 3.5 years, almost totally overgrown the posterior corneal surface of the graft (XX). Moreover, an abnormal posterior collagenous layer populated by fibroblast-like cells was observed between DM and the endothelium in the failed graft, but its exact origin could not be established due to the low number of cells. Simultaneous detection of CK19 using fluorescent immunohistochemistry together with the detection of gonosomes using FISH was performed for the first time in the cornea and allowed us to prove that the recurrence of PPCD was caused by pathological abnormal proliferation and migration of recipient cells into donor graft.

Immunohistochemical characterization of cytokeratins in the abnormal corneal endothelium of posterior polymorphous corneal dystrophy patients

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting Descemet's membrane and the endothelium. The aim of the present study was to determine the spectrum of cytokeratin (CK) expression in cells on the posterior surface of the cornea in PPCD patients. Ten corneal buttons and one specimen of the trabecular meshwork (TM) from PPCD patients who underwent graft or glaucoma surgery were used, as well as six corneal buttons and two TM specimens obtained from healthy donors as controls. Cryosections were fixed and indirect immunofluorescent staining was performed using antibodies directed against a wide spectrum of cytokeratins (CKs). The number of positive cells and the intensity of the staining were assessed using fluorescent microscopy. All 10 PPCD corneal specimens had areas of endothelium displaying typical endothelial morphology as well as areas consisting of layers two to six cells thick with both flat endothelial-like cells and polygonal cells with round nuclei and a large cytoplasm. Both of these morphologically distinct cell types showed strong immunostaining for CK7, CK19, CK8 and CK18, while weaker positive signals were observed for CK1, CK3/12, CK4, CK5/6, CK10, CK10/13, CK14, CK16 and CK17. PPCD endothelium was completely negative for CK2e, CK9, CK15, and CK20. Focal positivity was detected in PPCD TM for CK4, CK7 and CK19. CK8 and CK18 were the only CKs expressed in control endothelium. PPCD and control epithelium displayed similar staining patterns. The distinct positivity for CK3/12, CK4, CK5/6, CK10/13, CK14, CK16 and CK17 was observed in aberrant PPCD endothelium for the first time. We demonstrate that the abnormal endothelium of PPCD patients expresses a mixture of CKs, with CK7 and CK19 predominating. In terms of CK composition, the aberrant PPCD endothelium shares features of both simple and squamous stratified epithelium with a proliferative capacity. The wide spectrum of CK expression is most probably not indicative of the transformation of endothelial cells to a distinct epithelial phenotype, but more likely reflects the modified differentiation of metaplastic epithelium.

An ultrastructural investigation of an early manifestation of the posterior polymorphous dystrophy of the cornea

BACKGROUND

Posterior polymorphous dystrophy of the cornea is an uncommon, but well-recognized, congenital disease affecting Descemet's membrane and endothelium. Visual impairment usually is minimal and slowly progressive. Edema develops in a small number of patients, necessitating a corneal graft in middle age. An early manifestation of posterior polymorphous dystrophy with corneal edema present at birth or soon thereafter is extremely rare; only a few ultrastructural reports are available.

METHODS

The corneal button of a 5-month-old baby with posterior polymorphous dystrophy was examined by conventional light and electron microscopy.

FINDINGS

The anterior banded zone of Descemet's membrane was thinned (2 microns) in the axial part of the cornea, contained defects in the paraxial part, and was absent at the periphery. Where present, the anterior banded zone was lined posteriorly by a fibrocellular layer (containing fibroblast-like spindle cells and striated collagen fibrils) and a fibrillar layer forming an abnormal posterior collagenous layer. This layer was lined posteriorly by degenerate overlapping endothelial cells, which also were in apposition to the stroma in regions with an absent anterior banded zone. The defects in Descemet's membrane were used by the abnormal keratocytes to migrate between the anterior banded zone and the posterior collagenous layer. At the periphery, a multilayer of spindle cells was present behind the stroma.

CONCLUSIONS

Failure to produce a continuous anterior banded zone indicates an onset of the disease before the twelfth week of gestation. It appears that, in posterior polymorphous dystrophy, there is a mosaic of better preserved and dystrophic endothelial cells and that the presence or absence of the normal components of Descemet's membrane is determined by the proportion of dystrophic cells in the endothelial cell population.

The corneal endothelium

The endothelium is a monolayer of cells on the posterior corneal surface that transports water from the stroma into the anterior chamber. This movement of water counters a natural tendency for the stroma to swell and is necessary to maintain a transparent cornea. Embryologic studies, in particular the demonstration of the derivation of the endothelium from the neural crest, have provided insight into the factors that govern the response of this tissue to disease. In some species the endothelium can regenerate after injury, but in man cellular enlargement is the main mechanism of repair after cell loss. A clinical estimate of endothelial cell density and function is provided by specular microscopy, fluorophotometry and pachymetry. In this paper we review the development, structure and function of the corneal endothelium, and then consider the pathological processes that can affect this tissue.

Localization of keratin in the cells of the cornea in aphakia and normal mouse embryos

Abnormal lens morphogenesis in the aphakia mutant in the mouse often results in a club-shaped elongated 'lens' that remains attached to the surface epithelium by a persistent connecting stalk, which is partially solid and partially cystic. Usually, the cells are continuous with the surface epithelium of the cornea and also with the cuboidal cells lining the corneal inner surface. Immunofluorescence with keratin antiserum not only gave positive reactions with the corneal epithelial cells, but also with many cells of the lens stalk, including its cysts, and with islands of cells on the inside of the cornea. These keratin-containing 'endothelial' cells may be the product of metaplasia of the endothelium into epithelium-like cells. Alternatively, they may also be the result of abnormal migration of epithelial cells into the eye or of abnormal differentiation of neural crest cells.

Morphologic characteristics of posterior polymorphous dystrophy. A study of nine corneas and review of the literature

Based on their own study of nine corneas with clinically documented posterior polymorphous dystrophy and a review of the literature, the authors describe the morphologic features of this entity. Study by phase contrast light microscopy and transmission and scanning electron microscopy found that changes were primarily in the endothelium and consisted of endothelial cell degeneration and loss with focal fibroblastic and epithelial-like cell transformation. Secondary alterations of Descemet's membrane were seen; they consisted of abnormal lamination with deposition of abnormal collagen material, particularly in the posterior collagen layer, and formation of guttate excrescences and pits.

Posterior polymorphous corneal dystrophy of Schlichting. A clinical study on four families

Posterior polymorphous corneal dystrophy of Schlichting was studied in 4 families. Nine persons were found with the typical lesions. Two families suggested a dominant mode of inheritance, in one of these with a penetrance less than 100%. There were 2 sporadic cases. No corneal oedema was present, and the central corneal thickness showed normal values, which means that the corneal endothelium in this dystrophy is able to maintain a normal hydrated cornea.

Clinical specular microscopy of posterior polymorphous endothelial dystrophy

By means of clinical specular microscopy in 27 patients with posterior polymorphous corneal endothelial dystrophy diagnosed by slit lamp examination and 26 relatives with normal findings by slit-lamp and specular microscopic examinations, we identified two clinical and specular microscopic patterns of posterior polymorphous dystrophy. (1) The localized vesicular or band pattern consisted of clear corneas with localized lesions resembling craters that were lined by abnormal cells and surrounded by enlarged, pleomorphic cells. (2) The geographic pattern was associated with Descemet's membrane haze and deep stromal haze, occasional peripheral iridocorneal adhesions, and glaucoma. By specular microscopy, this type had large, well circumscribed areas of abnormal pleomorphic cells with indistinct borders and increased reflective highlights. These areas were surrounded by normal-sized and smaller polygonal cells. The former cells appear to represent epithelial cells and the latter endothelial cells.