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A J Quantock

Publications and source records attributed to A J Quantock.

At least 37 records · Page 2Linked to original sources
PubMed1998

Histopathology of recurrent gelatinous drop-like corneal dystrophy.

PURPOSE: To elucidate more fully the histopathology of gelatinous drop-like corneal dystrophy in a case that recurred and was operated on 7 years after the original surgery. METHODS: Transmission electron microscopy, including the use of cuprolinic blue to image sulfated proteoglycans, and horseradish peroxidase as a marker for in vitro epithelial permeability. RESULTS: Our patient's epithelium was often abnormally thick, and many intercellular spaces were present at all levels, although cell-cell contact via desmosomes was also evident. Horseradish peroxidase, when used as an in vitro tracer, was able to penetrate the most superficial tight junctions of the corneal epithelium. Basal epithelial cells were not columnar, and numerous spike-like projections protruded into the underlying amyloid/collagenous tissue from the basal epithelium. Beneath this, duplication of a discontinuous epithelial basement membrane was noted. In this region, collagen often coexisted with amyloid, the deposition of which was extensive. As in some other corneal pathologies, long-spacing collagen was detected. The association of small proteoglycans with collagen was unremarkable, although some abnormally large, sulfated proteoglycan filaments were interspersed with the amyloid and underlying stroma. CONCLUSION: Recurrent gelatinous drop-like corneal dystrophy shares several histopathologic features with its primary counterpart, although some features, such as the presence of abnormally large, sulfated proteoglycans and long-spacing collagen, the permeability of the epithelial tight junctions, and the duplication of the epithelial basement membrane, have not been reported previously.

Amyloid↗
PubMed1998

An ultrastructural investigation into proteoglycan distribution in human corneas.

PURPOSE: We report an investigation into the distribution of proteoglycans (PGs) in normal, organ-cultured and dextran-treated human corneas. METHODS: Immunogold labeling was carried out at the electron microscope level to localize keratan sulphate (KS), chondroitin sulphate (CS), and heparan sulphate (HS) PGs. RESULTS: High levels of labeling for CS was found in the epithelium, endothelium, and keratocytes, with light labelling present in the basement membranes and the corneal stroma. Labeling for HS was present in the epithelium, endothelium, and keratocytes, with intense labeling present at the endothelium/Descemet's membrane interface and the epithelium/Bowman's layer interface. Large filaments were also observed in these regions in cuprolinic blue-stained specimens. Keratan sulphate was present at high levels in the stroma and the basement membranes with low levels present within the keratocytes, epithelium, and endothelium. The pattern of KS labeling along the collagen fibrils in the stroma sometimes showed evidence of periodicity. Organ-cultured corneas had extensive collagen-free "lakes," the interior of which immunolabeled positively for KS and showed staining with cuprolinic blue. The lakes were greatly reduced in the dextran-treated samples. CONCLUSION: This investigation determined the ultrastructural distribution of KS, CS, and HS PGs in human cornea and showed that organ culture is associated with a change in distribution of stromal PGs.

Chondroitin Sulfates↗
PubMed1997

Macular corneal dystrophy type II: multiple studies on a cornea with low levels of sulphated keratan sulphate.

We investigated an individual macular corneal dystrophy (MCD) type II cornea from a 42-year-old woman with markedly reduced antigenic keratan sulphate levels. A characteristic 4.6 A X-ray reflection was evident, and the mid-stroma contained 30% less sulphur than normal. Close packing of collagen was restricted to the superficial stroma. Abnormally large proteoglycan filaments were noted throughout the extracellular matrix and Descemet's membrane's posterior non-banded zone, but not its anterior banded zone. Small, collagen-associated stromal proteoglycans were susceptible to digestion with chondroitinase ABC, but not keratanase I or N-glycanase. On occasion, collagen fibrils ranged in size from 20 nm to 58 nm, with preferential diameters of 34 nm and 42 nm. Corneal guttae were evident, as were numerous endothelial inclusions, most probably due to intracellular fibrillogranular vacuoles similar to those found in the stroma. The endothelium expressed reduced anti-keratan sulphate labelling.

Adult↗
PubMed1997

Isolation and chromosomal localization of a cornea-specific human keratin 12 gene and detection of four mutations in Meesmann corneal epithelial dystrophy.

Keratin 12 (K12) is an intermediate-filament protein expressed specifically in corneal epithelium. Recently, we isolated K12 cDNA from a human corneal epithelial cDNA library and determined its full sequence. Herein, we present the exon-intron boundary structure and chromosomal localization of human K12. In addition, we report four K12 mutations in Meesmann corneal epithelial dystrophy (MCD), an autosomal dominant disorder characterized by intraepithelial microcysts and corneal epithelial fragility in which mutations in keratin 3 (K3) and K12 have recently been implicated. In the human K12 gene, we identified seven introns, defining eight individual exons that cover the coding sequence. Together the exons and introns span approximately 6 kb of genomic DNA. Using FISH, we found that the K12 gene mapped to 17q12, where a type I keratin cluster exists. In this study, four new K12 mutations (Arg135Gly, Arg135Ile, Tyr429Asp, and Leu140Arg) were identified in three unrelated MCD pedigrees and in one individual with MCD. All mutations were either in the highly conserved alpha-helix-initiation motif of rod domain 1A or in the alpha-helix-termination motif of rod domain 2B. These sites are essential for keratin filament assembly, suggesting that the mutations described above may be causative for MCD. Of particular interest, one of these mutations (Tyr429Asp), detected in both affected individuals in one of our pedigrees, is the first mutation to be identified within the alpha-helix-termination motif in type I keratin.

Base Sequence↗
PubMed1997

Proteoglycans contain a 4.6-A repeat in corneas with macular dystrophy: II. Histochemical evidence.

PURPOSE: Synchrotron x-ray diffraction experiments indicate that corneas with macular corneal dystrophy (MCD) contain unusual 4.6-A periodic repeats thought to reside in proteoglycans or glycosaminoglycans. Recently the 4.6-A x-ray reflection was found to be significantly diminished after incubation of MCD specimens in buffer containing chondroitinase ABC or N-glycanase. We examined the sulfated proteoglycans in these glycosidase-digested MCD corneas. METHODS: Transmission electron microscopy was used in conjunction with cuprolinic blue-staining for sulfated proteoglycans. RESULTS: Incubation of an MCD specimen in enzyme buffer left both small and large proteoglycan filaments in the stromal matrix, whereas incubation in the presence of chondroitinase ABC removed these molecules from the tissue. Incubation in buffer containing N-glycanase, on the other hand, removed the large proteoglycan filaments from the MCD stroma but left unaffected the small collagen-associated proteoglycans. CONCLUSION: These results are consistent with the interpretation that 4.6-A periodic repeats in MCD corneas reside in large sulfated proteoglycan filaments (or aggregates thereof) that may contain chondroitin/dermatan sulfate and keratan sulfate or keratan components.

Chondroitin↗
PubMed1996

Proteoglycans contain a 4.6 A repeat in muscular dystrophy corneas: x-ray diffraction evidence.

Synchrotron x-ray diffraction patterns from macular corneal dystrophy (MCD) corneas contain an unusual reflection that arises because of an undefined ultrastructure with a periodic repeat in the region of 4.6 A. In this study, we compared with wide-angle x-ray diffraction patterns obtained from four normal human corneas and four MCD corneas. Moreover, portions of two of the MCD corneas were pretreated with a specific glycosidase to shed light on the origin of the 4.6 A reflection. None of the normal corneas produced an x-ray reflection in the region of 4.6 A, whereas all four of the MCD corneas did (MCD type I at 4.65 A and 4.63 A, MCD type II at 4.63 A and 4.67 A). This reflection was diminished after incubation of the MCD tissues with either chondroitinase ABC or N-glycanase. The findings indicate that glycosaminoglycans or proteoglycans contribute to the unusual MCD x-ray reflection and hence most likely contain a periodic 4.6 A ultrastructure. Furthermore, the results imply that periodic 4.6 A MCD ultrastructures reside in either intact, unsulfated lumican molecules and regions of the CS/DS-containing molecules or in a region of a hybrid macromolecular aggregate formed by the interaction of the two molecules.

Adult↗
PubMed1996

Characterization of a central corneal cloudiness sharing features of posterior crocodile shagreen and central cloud dystrophy of François.

A 56-year-old black woman with full-thickness mosaic pattern central corneal cloudiness, similar in appearance to central cloudy dystrophy and posterior crocodile shagreen, underwent corneal transplantation. Atypical features included decreased vision, photophobia, and epithelial involvement, with occasional foreign body sensation. Numerous 0.5-2.0-micron-diameter lacunae were present in the corneal stroma and Bowman's layer, and a saw-toothed lamellar pattern was often evident in the corneal stroma. Soybean agglutinin (SBA), a lectin that binds N-acetyl-galactosamine residues, bound diffusely to stromal foci exhibiting similar size and distribution to the lacunae observed by electron microscopy. An absence of histochemically detectable lipid associated with these lacunae suggests that SBA reacted with glycoconjugates other than glycolipids. Biochemical analyses revealed similar contents of keratan sulfate, chondroitin/dermatan sulfate, and collagen as in normal controls, suggesting that the SBA binding moieties are associated with a glycoprotein or proteoglycan that is structurally or compositionally different from those found in normal cornea. This patient may represent an extreme variant of Vogt's or François central corneal clouding or a previously undescribed corneal dystrophy.

Corneal Dystrophies, Hereditary↗
PubMed1996

Cell surface-associated keratan sulfate on normal and migrating corneal endothelium.

PURPOSE: To investigate cell surface-associated keratan sulfate on the corneal endothelium. METHODS: Immunolabeling techniques were used at the light, scanning, and transmission electron microscopic level to localize keratan sulfate on the corneal endothelium. The investigation included human, bovine, and rabbit corneal endothelia. A quantitative study of the relationship between cell size and keratan sulfate levels was conducted on normal bovine corneal endothelium. Changes in the distribution of keratan sulfate and chondroitin sulfate on endothelial cell surfaces were investigated on organ cultured bovine corneas during endothelial wound healing. Changes in the levels of keratan sulfate during endothelial wound healing were investigated in organ cultured human corneas and in vivo in rabbit corneas. Inhibition-enzyme-linked immunosorbent assay also was used to detect keratan sulfate in the aqueous humor. RESULTS: A variegated distribution of keratan sulfate was revealed on normal human, bovine, and rabbit corneal endothelia. Some cells had high levels of keratan sulfate on their surfaces whereas others, sometimes immediately adjacent, had little or none. Wound healing experiments resulted in changes of keratan sulfate levels on the migrating endothelial cells in bovine, human, and rabbit. In wounded organ cultured bovine corneas, there was a decrease in keratan sulfate levels and an increase in chondroitin sulfate levels on migrating endothelial cells. Keratan sulfate was detected in bovine aqueous humor. CONCLUSIONS: The pattern of occurrence of keratan sulfate and chondroitin sulfate on the corneal endothelial cells in normal and wounded cornea suggests that these glycosaminoglycans have differing roles in endothelial adhesion and migration.

Aged↗
PubMed1995

Stromal healing following explantation of an ICR (intrastromal corneal ring) from a nonfunctional human eye.

We examined the cornea of the nonfunctional left eye of a 46-year-old man, which was enucleated 8 months following explantation of an ICR (Intrastromal Corneal Ring). Corneal haze was confined to the midstroma, in the region of the tissue from which the ICR had been removed. Stromal tissue in this area was subtly compressed and irregular. Electron microscopy in conjunction with cuprolinic blue staining demonstrated an unremarkable proteoglycan population and several areas of slight collagen disruption at midstromal depth at the site of the previously implanted ICR. We conclude that disruptions of the corneal stroma that remain 8 months following explantation of an ICR are minimal.

Blindness↗
PubMed1994

A combined incision technique of radial keratotomy. A comparison to centripetal and centrifugal incision techniques in human donor eyes.

PURPOSE: To evaluate and compare the extent of corneal flattening and the anatomy of the incision grooves produced by centrifugal, centripetal, and combined incisions in a human donor eye model. METHODS: Twenty-seven eyes, divided into three groups of nine, received eight-incision radial keratotomy using the centrifugal, centripetal, or combined incision technique. Corneal curvature was evaluated using a topography system, and the anatomy of the incision was assessed by light microscopy and scanning electron microscopy. RESULTS: The average central corneal flattening at the 3-mm clear zone was 4.16 +/- 1.47 diopters (D) for centrifugal incisions; 7.71 +/- 2.77 D for centripetal incisions; and 9.26 +/- 1.75 D for combined incisions. The difference in corneal flattening between eyes that received centrifugal versus either centripetal or combined incisions was significant (P < 0.01), whereas the difference between combined and centripetal incisions was not significant (P = 0.174). Anatomic differences were observed within the incision grooves produced by the three techniques. CONCLUSION: The authors describe a novel combined incision technique of radial keratotomy that provides the potential safety of a centrifugal incision with the effect of a centripetal incision.

Aged↗
PubMed1994

Remodelling of the corneal stroma after lamellar keratoplasty. A synchrotron x-ray diffraction study.

Patients healing from lamellar keratorefractive surgeries invariably experience postoperative corneal haze. In our lamellar keratoplasty (LKP) rabbit model, visual recovery is concomitant with the invasion of the grafted tissue by viable keratocytes from adjacent host tissue, and the return of corneal clarity is attributed to the remodelling of the stromal tissue by these keratocytes. We used synchrotron x-ray diffraction techniques to elucidate the ultrastructure of the stromal collagen fibrils in rabbit corneas at various time points in the 3 months after LKP surgery. Lenticules were frozen in 50% of the cases. The average spacing of the collagen molecules, which constitute the stromal fibrils, remains unchanged by LKP in both frozen (1.69-1.73 nm) and nonfrozen (1.58-1.75 nm) cases. In the nonfrozen case, the collagen fibril diameters are initially slightly larger than normal (38.3-41.9 nm) but have receded by 2 months postoperatively [similar to the frozen cases (37.7-41.9 nm)]. The post-LKP spacing of the collagen fibrils in the nonfrozen corneas is unremarkable (56.2-69.2 nm). In contrast, the increased collagen interfibrillar spacing in the frozen case is considerable (56.7 to > 94.6 nm) and variable up to 21 days postoperatively. Because the changes in interfibrillar spacing did not always mirror pachymetry changes in the frozen cases, we suspect occasional graft malapposition or the formation of intrastromal, fluid-filled, collagen-free "lakes."

Animals↗
PubMed1993

Corneal iron lines associated with the intrastromal corneal ring.

Corneal epithelial iron lines commonly occur, and their shape is characteristically influenced by the underlying corneal surface topography. We studied a pattern of iron deposition, observed after implantation of the Intrastromal Corneal Ring (KeraVision, Inc., Santa Clara, California). In five of ten patients undergoing placement of the Intrastromal Corneal Ring, an arcuate pattern of epithelial iron deposition was observed eight to 12 months postoperatively. There was no significant clinical or topographic difference over time among the corneas of patients who developed an iron line vs those who did not. Of the five patients with an arcuate epithelial iron line, three underwent explantation of their Intrastromal Corneal Ring at 12 months according to the study protocol. Iron deposition either reverted to a Hudson-Stähli pattern or disappeared in each of these three patients.

Adult↗
PubMed1993

Synchrotron X-ray diffraction in atypical macular dystrophy.

This report documents the first case of X-ray diffraction techniques aiding the diagnosis of a corneal dystrophy with a clinically ambiguous presentation. Post-operatively, a high-angle synchrotron X-ray diffraction pattern was obtained from an in vitro portion of a pathological cornea. This pattern displayed two X-ray reflections which we recently demonstrated to be unique to the high-angle X-ray diffraction patterns of both type I and type II macular dystrophy corneas; on the basis of this evidence we were able to offer a post-operative diagnosis of macular corneal dystrophy. An electron microscopical evaluation of the cornea revealed stromal lacunae at all levels and an extensive layer of vacuoles, predominantly between Bowman's layer and the anterior stroma. These vacuoles were often associated with large proteoglycan filaments, as identified by Cuprolinic blue staining. Abnormally large collagen fibrils were documented, for the first time, in a macular dystrophy cornea; they existed in localised regions, frequently adjacent to the vacuoles and abnormal proteoglycans, and could well have implications for corneal transparency. We propose that the dystrophy is an atypical variant of macular corneal dystrophy which is encompassed by the heterogeneous nature of the condition.

Aged↗
PubMed1993

Scheie's syndrome: the architecture of corneal collagen and distribution of corneal proteoglycans.

Processes that modulate the regular architecture and, hence, transparency of the cornea are poorly understood, although proteoglycans are thought to be involved. Scheie's syndrome displays corneal opacification and systemic accumulation of glycosaminoglycans. The manifestations of these two occurrences were examined in relation to the corneal stroma. Collagen architecture was investigated by transmission electron microscopy and synchroton x-ray diffraction. Cuprolinic blue staining located sulfated glycosaminoglycan deposits that disrupted the extracellular matrix. Unlike normal cornea, which contained collagen fibrils of remarkably uniform diameter (26.0 +/- 2.4 nm), there was a large range of fibril sizes in the Scheie's syndrome stroma (19.9 to 52.0 nm). Moreover, the distribution of fibril diameters appeared bimodal. X-ray diffraction confirmed the discovery of abnormally large stromal collagen. The results suggest a link in Scheie's syndrome between proteoglycan content/distribution and stromal disruption, and between stromal disruption and corneal opacification.

Collagen↗
PubMed1992

Analysis of high-angle synchrotron x-ray diffraction patterns obtained from macular dystrophy corneas.

Six macular dystrophy corneas from six individuals were investigated by synchrotron x-ray diffraction. Immunochemical evidence demonstrated that five of the patients had type I macular corneal dystrophy and that one had type II. Analysis of the high-angle x-ray diffraction patterns showed that the intermolecular spacing of macular dystrophy corneal collagen increases with hydration from the dry state in a fashion similar to the intermolecular spacing of normal human corneal collagen. The high-angle x-ray diffraction pattern from all six corneas contained two "extra reflections" not obtained from other human corneas, normal or pathologic. The reflections, which arise from 4.61 and 9.62 A periodic structures, are independent of the type of macular dystrophy. Furthermore, their position is independent of corneal hydration. We propose that a glycosaminoglycan structure is the origin of the unique extra reflections.

Collagen↗
PubMed1991

Alteration of the stromal architecture and depletion of keratan sulphate proteoglycans in oedematous human corneas: histological, immunochemical and X-ray diffraction evidence.

The structure and content of the extracellular stromal matrix of several oedematous human corneas was investigated using electron microscopy, X-ray diffraction and biochemical techniques. Electron microscopy revealed the presence of wavy lamellae and various sized collagen-free 'lakes' within the stroma of the oedematous corneas, with their posterior sections containing by far the largest 'lakes'. The existence of 'lakes' was supported by the equatorial X-ray diffraction evidence. Staining the oedematous corneas with Cuprolinic blue prior to electron microscopical and meridional X-ray diffraction studies demonstrated a loss of stromal proteoglycans normally associated with collagen. Immunochemical evidence demonstrated reduced levels of antigenic keratan sulphate in the oedematous corneas while biochemical techniques revealed constant chondroitin sulphate levels in the same corneas.

Chondroitin Sulfate Proteoglycans↗
PubMed1991

Synchrotron x-ray diffraction studies of the cornea, with implications for stromal hydration.

The intermolecular and interfibrillar spacings of collagen in bovine corneal stroma have been measured as a function of tissue hydration. Data were recorded from low- and high-angle x-ray diffraction patterns obtained using a high intensity synchrotron source. The most frequently occurring interfibrillar spacing varied from 34 nm in dry corneas to 76 nm at H = 5 (the hydration, H, is defined as the ratio of the weight of water to the dry weight). The most frequently occurring intermolecular Bragg spacing increased from 1.15 nm (dry) to approximately 1.60 nm at normal hydration (H approximately 3.2) and continued to increase only slowly above normal hydration. Most of the increase in the intermolecular spacing occurred between H = O and H = 1. Over this hydration range the interfibrillar and intermolecular spacings moved in tandem, which suggests that the initial water goes equally within and between the fibrils. Above H = 1 water goes preferentially between the fibrils. The results suggest that, even at normal hydration, water does not fill the interfibrillar space uniformly, and a proportion is located in another space or compartment. In dried-then-rehydrated corneas, a larger proportion of the water goes into this other compartment. In both cases, it is possible to postulate a second set or population of fibrils that are more widely and irregularly separated and therefore do not contribute significantly to the diffraction pattern.

Animals↗