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At least 19 recordsLinked to original sources
PubMed1994

Type V collagen and Bowman's membrane. Quantitation of mRNA in corneal epithelium and stroma.

Bowman's membrane is an acellular matrix of the cornea which lies between the epithelial basal lamina and the corneal stroma. By immunoelectron microscopy, we have determined that types I and V collagen are components of the collagen fibrils in Bowman's membrane of the chick cornea. Although these same components are found in the fibrils of the stroma, the fibrils of Bowman's membrane are smaller in diameter and less uniform than those of the stroma. At early stages of development, the corneal epithelium synthesizes the types I and II collagen of the primary stroma. We therefore asked whether it might also be capable of synthesizing the type V collagen found in Bowman's membrane at later stages of development. Our results, using competitive polymerase chain reaction to quantitate mRNA from avian corneal cells, indicate that the amount of alpha 1(V) collagen mRNA present in epithelia, relative to alpha 2(I) collagen mRNA, is greater than that in stromal fibroblasts. We postulate that this enables the epithelium to synthesize a higher ratio of type V to type I collagen than the stroma and that this proportionally higher amount of type V might account for the ultrastructural appearance of the fibrils in Bowman's membrane.

Amino Acid Sequence↗
PubMed1984

Structure and composition of Bowman's membrane. Study by frozen resin cracking.

Bowman's membrane, seen as a homogeneous layer in light microscopy, is demonstrated by transmission electron microscopy as a layer with fibrils in random distribution, for which reason the term used at present is Bowman's layer. Frozen resin cracking demonstrates that the fibrils of the layer run in certain patterns and lie in 3 or 4 strata in the central areas of the cornea. In the periphery, stratification is scarcely demonstrable. The fibrils consist of collagen inseparable by histochemical methods from the collagen in the stroma, but the diameter is only half or two-thirds of the diameter of the stromal fibrils. The authors discuss the possibility that artifacts are responsible for the findings. However, an explanation of the results may be that Bowman's layer is a condensation of the superficial layers of the stroma resulting from the development of the layer. The fibrils are presumed to break in different ways, but apparently in layers in which the breaking strengths are identical.

Adolescent↗
PubMed2002

Phototherapeutic keratectomy versus diamond burr polishing of Bowman's membrane in the treatment of recurrent corneal erosions associated with anterior basement membrane dystrophy.

PURPOSE: To compare the efficacy of phototherapeutic keratectomy (PTK) to epithelial debridement and polishing of Bowman's membrane using a diamond burr (DB) in the treatment of recurrent corneal erosions associated with anterior basement membrane (ABM) dystrophy. DESIGN: Retrospective nonrandomized comparative trial. METHODS: Medical records of 39 patients (42 eyes) who underwent a PTK or DB procedure for recurrent corneal erosions associated with ABM dystrophy between March 1992 and June 2000 were reviewed. History of injury, prior treatment received, and the corneal slit-lamp findings were noted in all patients. In both procedures, all loose epithelium was completely removed. In PTK patients, 5 microm of Bowman's membrane was ablated with the excimer laser. In patients who underwent DB treatment, a hand-held battery-driven diamond dusted burr was used to gently and uniformly polish Bowman's membrane in the area of the epithelial defect. MAIN OUTCOME MEASURES: Symptomatic improvement, recurrence of painful erosions, development of haze, and change in the visual acuity. Statistical analysis was performed for comparison of data between the two groups. RESULTS: Fifteen eyes of 14 patients underwent PTK, and 27 eyes of 25 patients underwent epithelial debridement and DB treatment. In the PTK group, mild haze was seen in five (35.7%) eyes. Recurrence of painful erosions was seen in four eyes (26.7%). The mean follow-up was 17.6 +/- 5.7 months (range, 0.7-81.9 months). Best-corrected visual acuity was better in five eyes (35.7%) after the procedure and the same in nine eyes (64.3%). In the DB group, mild haze was seen in seven eyes (25.9%). Recurrence of painful erosions was seen in three eyes (11.1%). The mean duration of follow-up was 6.7 months (range, 1-24.2 months). Best-corrected visual acuity was better in 3 eyes (14.3%), the same in 17 eyes (81%), and worse in 1 eye (4.8%) after the procedure. Final visual acuity was not available for one eye in the PTK group and 6 eyes in the DB group. There was no statistically significant difference in haze (Fisher's exact test, P = 0.38), recurrence of erosions (Kaplan-Meier analysis with log rank, P = 0.73), and vision being better or the same (Fisher's exact test, P = 0.6) between the PTK and DB groups. CONCLUSIONS: Both PTK and DB treatment are effective methods of treating recurrent corneal erosions associated with ABM dystrophy. Diamond burr treatment, being a simpler, less expensive office procedure with a tendency toward lesser incidence of haze and recurrence in this study, seems to have advantages over PTK in the treatment of recurrent corneal erosions. Further prospective studies are required to confirm the long-term efficacy of DB treatment in the management of recurrent corneal erosions associated with ABM dystrophy.

Basement Membrane↗
PubMed1988

The ultrastructural organization of the basement membrane of Bowman's capsule in the rat renal corpuscle.

The basement membrane of Bowman's capsule (BCBM) of the rat was studied by means of a modified tissue-preservation technique for transmission electron microscopy, which avoids the usual thorough fixation in OsO4 and applies tannic acid and uranyl acetate for staining (Sakai et al. 1986). At most sites the BCBM is multilayered, consisting of one to seven dense layers separated by electron-lucent layers. The latter, which can be termed laminae rarae, contain fine filaments which connect the dense layers to each other and the innermost dense layer to the basal cell membrane of the parietal epithelium. The laminae densae are basically composed of fine filaments arranged in an anastomosing pattern. Individual filaments ranging from 5 to 15 nm in diameter, combine to form filament bundles up to 100 nm in thickness and 1 to 2 micron in length. Within a dense layer, filaments and filamentous bundles are oriented mainly in the same direction. Often the inner dense layers do not form a continuous sheet, and the filamentous bundles are arranged in anastomosing or spiral patterns to form a ribbon-like structure that we call a "microligament". These microligaments are often embedded in basal furrows of the parietal epithelium and are best developed around the vascular pole. Intracellular actin bundles of the parietal cells are regularly associated with these extracellular ribbon-like structures of the basement membrane. In conclusion, the BCBM has an unusual structure: the laminae densae are characterized by their filamentous nature and are arranged in different patterns, i.e. as a multilayered mat and as microligaments.

Animals↗
PubMed1988

Electrosurgical keratoplasty. Clinicopathologic correlation.

A patient with keratoconus who could not tolerate a contact lens underwent electrosurgical keratoplasty. Postoperatively, the central cornea was markedly flattened, but five weeks later the central steepening had recurred. Six months after the procedure, a penetrating keratoplasty was performed. Pathologic examination of the corneal button revealed an intact epithelium and basement membrane. Bowman's membrane was completely destroyed in the treated areas. Stromal scarring extended to involve the anterior two thirds of the corneal stroma. The collagen in this area was contracted and folded. The keratocytes and stromal collagen of the posterior third of the cornea were normal by light microscopy. Descemet's membrane and the endothelium also were normal. Despite the short-lived flattening of corneal topography, this procedure dramatically altered the stromal collagen in the anterior two thirds of the cornea.

Adult↗
PubMed2002

Cellular incursion into Bowman's membrane in the peripheral cone of the keratoconic cornea.

Analysis of corneal tissue from normal and keratoconic donors has revealed differences which may represent early signs in the pathogenesis of keratoconus. Peripheral areas of keratoconic tissue obtained from transplant surgery were targeted to ascertain cellular disposition and morphological changes which may be masked within the extensive damage of the central keratoconic cone. Peripheral keratoconic corneae exhibited discrete incursion of fine cellular processes into Bowman's membrane. These processes originated from keratocytes and were often observed in conjunction with a defined indentation from the basal epithelium. Comparison of the lysosomal enzymes cathepsin B and G with constitutively expressed cytoplasmic esterase determined that both cathepsins were elevated within keratocytes of keratoconic tissue compared with normal tissue. Some clusters of keratoconic keratocytes had elevated levels of cathepsin exceeding all others. Cathepsin-rich keratocytes localized with morphologically compromised regions of Bowman's membrane. The presence of cell nests deeper within the stroma indicated that the catabolic changes, which are visible within the acellular Bowman's membrane, are probably also occurring deeper within the stroma, but are masked and not readily detectable.

Cathepsin B↗
PubMed1987

[Congenital corneal opacity caused by thickening of Bowman's membrane].

Congenital corneal opacifications are rare, yet their causes are manifold. Only a few cases have been described in which the most striking histopathological feature is a thickening of Bowman's membrane. The authors found an isolated thickening of this membrane in the corneas of a baby who, shortly after birth, presented with corneal opacifications in both eyes. Only a few months after penetrating keratoplasty was performed the condition recurred. Bowman's membrane was found to be thickened in the graft as well.

Child, Preschool↗
PubMed2000

Membranous glomerulopathy with Bowman's capsular and tubular basement membrane deposits.

Bowman's capsular and tubular basement membrane (TBM) deposits are an extremely unusual finding in non-lupus membranous glomerulopathy (MGN). We report three atypical cases of MGN with abundant Bowman's capsular and TBM deposits. In two cases, MGN was idiopathic; in the third case, MGN occurred in the renal allograft in the setting of HCV seropositivity. In addition to the usual glomerular capillary wall deposits, immunofluorescence and electron microscopy revealed extensive immune deposits within Bowman's capsule and TBMs, predominantly at the base of parietal and tubular epithelial cells. These cases suggest a potential pathomechanism of autoantibody to secreted epithelial antigens shared by visceral, parietal, and tubular epithelial cells. In all three cases, indirect immunofluorescence was unable to detect autoantibody to normal renal epithelial or matrix constituents. Furthermore, ELISA was unable to demonstrate circulating antibody to major extracellular matrix components. The implications of these findings for the pathogenesis of MGN are explored.

Adult↗
PubMed1975

Corneal clouding with increased acid mucopolysaccharide accumulation in Bowman's membrane.

Two infants had bilateral congenital corneal clouding and abnormal acid mucopolysaccharide accumulation in a thickened Bowman's membrane. This unusual entity was not associated with acid mucopolysaccharide deposits in the skin and visceral tissues or with increased levels of acid mucopolysaccharide in the urine. The similarity and differences have been compared to the systemic mucopolysaccharidosis and macular corneal dystrophy.

Basement Membrane↗
PubMed1991

[Consequences of different ablation rates in Bowman's membrane and corneal stroma for photorefractive keratectomy].

If photorefractive keratectomy (PRK) is performed with an ArF-excimer-laser, the existence of different ablation rates in Bowman's membrane and corneal stroma is of crucial importance, as ablation rates are considered to be constant in PRK. Consequently, if photoablation cannot be confined to Bowman's layer alone, at least two new surfaces with different refractive powers would result. For the correction of myopia with PRK, different ablation rates would mean that: (1) the central corneal surface with the desired refractive power is smaller than the total ablation zone. The lower the ablation rate in Bowman's layer compared to that of stroma, the smaller the area of desired refraction. (2) the maximum attainable refractive change will also be smaller, the lower ablation rate in Bowman's layer is compared to that of stroma. (3) Enlargement of the central zone of desired refraction is limited by the maximum acceptable ablation depth.

Cornea↗