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

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.

Ocular features in Alport syndrome: pathogenesis and clinical significance

Alport syndrome is an inherited disease characterized by progressive renal failure, hearing loss, and ocular abnormalities. Mutations in the COL4A5 (X-linked), or COL4A3 and COL4A4 (autosomal recessive) genes result in absence of the collagen IV α3α4α5 network from the basement membranes of the cornea, lens capsule, and retina and are associated with corneal opacities, anterior lenticonus, fleck retinopathy, and temporal retinal thinning. Typically, these features do not affect vision or, in the case of lenticonus, are correctable. In contrast, the rarer ophthalmic complications of posterior polymorphous corneal dystrophy, giant macular hole, and maculopathy all produce visual loss. Many of the ocular features of Alport syndrome are common, easily recognizable, and thus, helpful diagnostically, and in identifying the likelihood of early-onset renal failure. Lenticonus and central fleck retinopathy strongly suggest the diagnosis of Alport syndrome and are associated with renal failure before the age of 30 years, in males with X-linked disease. Sometimes, ophthalmic features suggest the mode of inheritance. A peripheral retinopathy in the mother of a male with hematuria suggests X-linked inheritance, and central retinopathy or lenticonus in a female means that recessive disease is likely. Ocular examination, retinal photography, and optical coherence tomography are widely available, safe, fast, inexpensive, and acceptable to patients. Ocular examination is particularly helpful in the diagnosis of Alport syndrome when genetic testing is not readily available or the results are inconclusive. It also detects complications, such as macular hole, for which new treatments are emerging.

Ocular features in Alport syndrome: pathogenesis and clinical significance

Alport syndrome is an inherited disease characterized by progressive renal failure, hearing loss, and ocular abnormalities. Mutations in the COL4A5 (X-linked), or COL4A3 and COL4A4 (autosomal recessive) genes result in absence of the collagen IV α3α4α5 network from the basement membranes of the cornea, lens capsule, and retina and are associated with corneal opacities, anterior lenticonus, fleck retinopathy, and temporal retinal thinning. Typically, these features do not affect vision or, in the case of lenticonus, are correctable. In contrast, the rarer ophthalmic complications of posterior polymorphous corneal dystrophy, giant macular hole, and maculopathy all produce visual loss. Many of the ocular features of Alport syndrome are common, easily recognizable, and thus, helpful diagnostically, and in identifying the likelihood of early-onset renal failure. Lenticonus and central fleck retinopathy strongly suggest the diagnosis of Alport syndrome and are associated with renal failure before the age of 30 years, in males with X-linked disease. Sometimes, ophthalmic features suggest the mode of inheritance. A peripheral retinopathy in the mother of a male with hematuria suggests X-linked inheritance, and central retinopathy or lenticonus in a female means that recessive disease is likely. Ocular examination, retinal photography, and optical coherence tomography are widely available, safe, fast, inexpensive, and acceptable to patients. Ocular examination is particularly helpful in the diagnosis of Alport syndrome when genetic testing is not readily available or the results are inconclusive. It also detects complications, such as macular hole, for which new treatments are emerging.

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.

Canine Duplication of Descemet's Membrane

The morphology of a duplication phenomenon of the canine Descemet's membrane (DM) is described in relation to signalment, history, and ocular disease status. Sixty-six canine eyes from the Comparative Ocular Pathology Laboratory of Wisconsin archives between 2000 and 2007 were examined. All cases were stained with hematoxylin and eosin and Alcian blue periodic acid-Schiff (PAS), while 14 cases were additionally stained with Masson's trichrome, picrosirius red, cytokeratin AE1/AE3 (CK), vimentin, and α-smooth muscle actin (SMA). Transmission electron microscopy (TEM) examination was performed in 3 corneas and in 1 normal control eye. Alcian blue PAS staining and TEM confirmed the basement membrane nature of the abnormal secondary DM. The thickness of the first DM, referred to as the corneal layer (CL) and the second or anterior chamber layer (ACL), were nearly the same, with no significant difference seen ( P = .93). In 39% (26/66) of the eyes, a fibrous, collagenous matrix component was present between the CL and ACL, which contains vimentin-positive and α-SMA-negative spindle cells (14/14).The corneal endothelial cells in 7/14 eyes stained weakly with CK and strongly in 2 additional eyes. The most frequent histopathologically confirmed, clinical ocular histories were chronic glaucoma in 76% (50/66) of eyes, previous intraocular surgery in 36% (24/66), lens luxation in 21% (4/66), and blunt trauma in 15% (10/66) of the cases. We speculate that activation and migration of endothelial cells, in association with trauma or lens contact, play a role in the pathogenesis of this phenomenon.

Inherited corneal disease: the evolving molecular, genetic and imaging revolution

Advances in molecular genetics and in vivo ocular imaging modalities have enhanced our understanding of the corneal dystrophies. To date at least 11 genes have been identified, in which mutations manifest in corneal disease. In addition there are at least eight other loci identified to which corneal dystrophies have been linked. The information gained from the knowledge of gene function, aberrant protein production, or altered enzyme activity in the cornea, has resulted in greater knowledge of the pathophysiological mechanisms in these disorders. In vivo confocal microscopy has recently enabled microstructural study of dystrophic corneas throughout the disease course, rather than being limited to histopathological analysis of tissue removed at corneal transplantation. This perspective article summarizes the current knowledge, with emphasis on the genes, mutant proteins and resultant mechanisms that lead to manifestations of disease, along with characteristic findings with in vivo confocal microscopy.

In Vivo Confocal Microscopy of Posterior Polymorphous Dystrophy

PURPOSE

This study was designed to delineate the morphologic features of posterior polymorphous dystrophy (PPD) using in vivo confocal microscopy.

METHODS

Six patients with clinically diagnosed PPD were examined by slit-lamp biomicroscopy, Orbscan II slit-scanning elevation topography, and in vivo confocal microscopy.

RESULTS

Endothelial cell densities ranged from 613 to 3,405 cells/mm and endothelial polymegathism was noted in all cases, whereas endothelial pleomorphism was not a prominent feature. Three cases exhibited bright endothelial nuclei. A variety of abnormal curvilinear and vesicular abnormalities were imaged by in vivo confocal microscopy, with lesions ranging between 6 and 159 microm in diameter. Abnormal endothelial cells were visible within some of these lesions. Six cases showed hyperreflectivity at the level of Descemet's membrane around the lesions. Deep stromal keratocytes appeared to aggregate around, or were compressed by, the endothelial lesions in one case.

CONCLUSIONS

We report the largest case series of PPD imaged by in vivo confocal microscopy. The ability of in vivo confocal microscopy to assess the living cornea over time enables monitoring of disease progression and thus the potential to identify and correlate development of, or changes in, microstructural features. As more data become available, these analyses may enable the formulation of prognostic and diagnostic criteria.

Confocal Microscopy of Posterior Polymorphous Endothelial Dystrophy

PURPOSE

To report the in vivo confocal microscopic findings of posterior polymorphous endothelial dystrophy (PPED).

METHODS

Four patients with PPED from 2 unrelated families and 2 asymptomatic children of an index patient were included in this observational case series. The eyes of the 6 subjects were examined by confocal light microscopy.

RESULTS

Confocal microscopy demonstrated craters, streaks, and cracks over the corneal endothelium surface. Pleomorphism and polymegathism were present in eyes with PPED. Guttae and clusters of abnormal endothelial cells were also identified in corneas of these PPED patients. These findings were absent in eyes without clinical manifestations of PPED.

CONCLUSIONS

In vivo confocal microscopy is potentially useful for excluding suspected cases of subclinical PPED. Abnormalities in the Descemet membrane and endothelium were observed.

An immunohistochemical analysis and comparison of posterior polymorphous dystrophy with congenital hereditary endothelial dystrophy

PURPOSE

To evaluate the immunohistochemical profiles of the abnormal endothelial cells of posterior polymorphous dystrophy (PPMD) and congenital hereditary endothelial dystrophy (CHED).

METHODS

Formalin-fixed, paraffin-embedded sections of seven corneas with the diagnosis of PPMD (seven patients), six corneas with the diagnosis of CHED (four patients), and five control corneas were stained with hematoxylin-eosin. Adjacent histologic sections were stained with monoclonal antibodies that react with pancytokeratin, AE1/AE3, cytokeratin (CK) 7, CK 20, CAM 5.2, and epithelial membrane antigen. The immunoreactivity of the corneal endothelium was assessed by light microscopy.

RESULTS

The endothelial cells stained positive for pancytokeratin and CK 7 in seven of seven corneas of patients with PPMD and five of six corneas of patients with CHED; variable positivity was seen to AE1, AE3, and CAM 5.2. The endothelium was uniformly negative to staining by CK 20. The epithelium stained positive with pancytokeratin, AE1, and AE3. All control corneas were negative for pancytokeratin, CK 7, and CK 20.

CONCLUSION

The abnormal endothelium in both PPMD and CHED expresses similar CKs, including CK 7, which is not present in normal endothelium or surface epithelium. This may indicate a shared developmental abnormality in these conditions, as previously suggested by ultrastructural studies and genetic mapping.

Clinical and ultrastructural features of a novel hereditary anterior segment dysgenesis

OBJECTIVE

To describe the clinical, histopathologic, and hereditary features of a novel familial anterior segment dysgenesis.

DESIGN

Prospective, observational case series and interventional case report.

PARTICIPANTS

Ten individuals from three generations of a single family with iris and corneal abnormalities associated with congenital cataracts.

MAIN OUTCOME MEASURES

An ophthalmic evaluation including slit-lamp examination, corneal topography, pachymetry, and specular biomicroscopy of all family members, and histopathologic and ultrastructural evaluation of one excised corneal button.

RESULTS

The proband was an 81-year-old man with bilateral aphakia and diffuse corneal haze, and thinning associated with corneal guttae. His pupils were small, mildly eccentric, and difficult to dilate. Pachymeter readings were 335 microm (right eye) and 330 microm (left eye). Topography confirmed advanced steepening of both corneas. Light microscopic and transmission electron microscopic examinations of the corneal button revealed an attenuated endothelium with prominent intracellular random aggregates of small-diameter filaments staining positively for cytokeratin. Descemet's membrane was thickened and had marked posterior nodularity. Various-sized polymorphic vacuoles containing layered electron-dense material were present within and between collagen lamellae and within keratocytes throughout the stroma and Bowman's membrane. Secondary bullous changes of the epithelium with thickening of the basement membrane were also observed. The family pedigree demonstrated an autosomal dominant inheritance pattern.

CONCLUSIONS

This constellation of autosomal dominantly inherited corneal endothelial and stromal disorder, with congenital cataracts and iris abnormalities, represents a novel anterior segment disorder. Its etiology may involve an abnormal migration of the secondary mesenchyme.

Imaging posterior polymorphous corneal dystrophy by in vivo confocal microscopy

To identify features of posterior polymorphous dystrophy (PPMD) by in vivo confocal microscopy, the corneas of a female patient with PPMD were exam ned using slit-lamp biomicroscopy and slit-scanning in vivo confocal microscopy. Characteristic endothelial vesicular and band lesions were seen clinically and easily identified using in vivo confocal microscopy. However endothelial pleomorphism, an increased density and reflectance of posterior stromal keratocytes, and prominence of corneal nerves were also delineated. In vivo confocal microscopy enhances clinicopathological diagnosis and follow up of corneal dystrophies with subtle clinical presentations, such as PPMD.

Posterior polymorphous dystrophy associated with posterior amyloid degeneration of the cornea

PURPOSE

To describe a case of posterior polymorphous dystrophy associated with posterior amyloid degeneration of the cornea confirmed histopathologically and immunohistochemically.

METHODS

An 80-year-old woman with corneal opacities required penetrating keratoplasty. The keratectomy specimen was evaluated by light microscopy and immunohistochemistry.

RESULTS

Microscopic examination of the keratectomy specimen showed scattered fusiform deposits located in the deep corneal stroma. Congo red stains of the fusiform deposits confirmed the diagnosis of amyloidosis. Immunohistochemical stains for cytokeratin (AE1/AE3) showed that the endothelial cells were immunoreactive, confirming the diagnosis of posterior polymorphous dystrophy.

CONCLUSIONS

To our knowledge, the association between posterior polymorphous dystrophy and posterior amyloid degeneration has not been reported previously.

Alport syndrome. A review of the ocular manifestations

Alport syndrome has a prevalence of 1/5000, and 85% of patients have the X-linked form, where affected males develop renal failure and usually have a high-tone sensorineural deafness by the age of 20. The typical ocular associations are a dot-and-fleck retinopathy which occurs in about 85% of affected adult males, anterior lenticonus which occurs in about 25%, and the rare posterior polymorphous corneal dystrophy. The retinopathy and anterior lenticonus are not usually demonstrated in childhood but worsen with time so that the retinal lesion is often present at the onset of renal failure, and the anterior lenticonus, later. The demonstration of a dot-and-fleck retinopathy in any individual with a family history of Alport syndrome or with end-stage renal disease is diagnostic of Alport syndrome. The presence of anterior lenticonus or posterior polymorphous corneal dystrophy in any individual is highly suggestive of the diagnosis of Alport syndrome. Additional ocular features described in X-linked Alport syndrome include other corneal dystrophies, microcornea, arcus, iris atrophy, cataracts, spontaneous lens rupture, spherophakia, posterior lenticonus, a poor macular reflex, fluorescein angiogram hyperfluorescence, electrooculogram and electroretinogram abnormalities, and retinal pigmentation. All mutations demonstrated to date in X-linked Alport syndrome have affected the COL4A5 gene which encodes the alpha 5 chain of type IV collagen. This protein is probably common to the basement membranes of the glomerulus, cochlea, retina, lens capsule, and cornea. However, the alpha 3(IV) and 4(IV) as well as the alpha 5(IV) collagen chains are usually absent from the affected basement membranes, because the abnormal alpha 5(IV) molecule interferes with the stability of all three. The loss of these collagen molecules from the affected basement membranes results in an abnormal ultrastructural appearance. The ocular and other clinical features of autosomal recessive Alport syndrome are identical to those seen in X-linked disease, while retinopathy and cataracts are the only ocular abnormalities described in the rare autosomal dominant form of Alport syndrome. There are no ocular associations of thin basement membrane disease which is a common disease that probably represents the heterozygous expression of X-linked or autosomal recessive Alport syndrome.

Ocular manifestations of autosomal recessive Alport syndrome

Ocular abnormalities are common in X-linked Alport syndrome, but they have not been studied in patients with the rarer autosomal recessive disease. We have examined the eyes of a family with autosomal recessive Alport syndrome. Four of the eight offspring of a consanguineous marriage had renal failure and deafness by the age of 20 years. The diagnosis of Alport syndrome was confirmed on the ultrastructural demonstration of a lamellated glomerular basement membrane (GBM) in one affected family member. Autosomal recessive inheritance was suggested by the lack of linkage to the COL4A5/COL4A6 locus, and by linkage to the COL4A3/COL4A4 locus. All four affected family members had anterior lenticonus (or had had a lens replacement for this) and the three who were examined had a dot-and-fleck retinopathy. Neither of the two unaffected offspring who were examined nor the father had these abnormalities. The ocular manifestations of autosomal recessive Alport syndrome are probably identical to those for the X-linked form. Although the mutations in these diseases affect genes for different type IV collagen chains, these chains occur together in the basement membranes of the kidney, eye and ear, and abnormalities in any one may result in the same clinical phenotype.