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International Journal of Molecular... Jul 2022The cornea is an avascular, innervated, and transparent tissue composed of five layers: the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It...
The cornea is an avascular, innervated, and transparent tissue composed of five layers: the epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. It is located in the outermost fraction of the eyeball and is responsible for the refraction of two-thirds of light and protection from external mechanical damage. Although several studies have been done on the cornea on the macroscopic scale, there is a lack of studies on the micro-nanoscopic scale, especially an analysis evaluating the cornea layer by layer. In this study, atomic force microscopy (AFM) was employed to assess four layers that form the cornea, analyzing: adhesion, stiffness, and roughness. The results showed microvilli in the epithelial and endothelial layers, pores in the basement membrane, and collagen fibers in the Stroma. These data increase the knowledge about the human cornea layers' ultrastructures and adds new information about its biophysical properties.
Topics: Biomechanical Phenomena; Cornea; Endothelium; Epithelium; Humans; Microscopy, Atomic Force
PubMed: 35887181
DOI: 10.3390/ijms23147833 -
Translational Vision Science &... Aug 2022The purpose of this study was to assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain...
PURPOSE
The purpose of this study was to assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain (LF-SD) optical coherence tomography (OCT) for the measurement of Bowman's and epithelial thickness, and to provide a reference range of these values for healthy corneas.
METHODS
Volunteers with no history and evidence of corneal disease were included in this study. An in vivo graph search image segmentation of the central cornea was obtained at the normal interface vector orientation. The Mirau-UHR-LF-SD-OCT system used has an axial resolution down to 2.4 µm in air (1.7 µm in tissue), with an A-scan speed of 204.8 kHz and a signal to noise ratio (sensitivity) of 69 (83) dB.
RESULTS
Nine volunteers were included, one of whom wore contact lenses. The repeatability of mean Bowman's and epithelial thicknesses were 0.3 and 1.0 µm, respectively. The measured 95% population range for healthy in vivo thickness was 13.7 to 19.6 µm for the Bowman's layer, and 41.9 to 61.8 µm for the epithelial layer.
CONCLUSIONS
The measured thicknesses of Bowman's layer and the corneal epithelium using the Mirau-UHR-LF-SD-OCT were both accurate, with the range for healthy in vivo thicknesses matching prior confocal and OCT systems of varying axial resolutions, and repeatable, equaling the best value prior reported.
TRANSLATIONAL RELEVANCE
T1. Development of a commercially viable clinical UHR OCT technology, enabling accurate measurement and interpretation of Bowman's and epithelial layer thickness in clinical practice.
Topics: Bowman Membrane; Contact Lenses; Cornea; Epithelium, Corneal; Humans; Tomography, Optical Coherence
PubMed: 35930278
DOI: 10.1167/tvst.11.8.6 -
Clinical Kidney Journal Mar 2021Foods prone to deteriorate renal function are rich in fat and in phosphorus (P), but the interaction between these two factors is not well studied.
BACKGROUND
Foods prone to deteriorate renal function are rich in fat and in phosphorus (P), but the interaction between these two factors is not well studied.
METHOD
Detailed structural and ultrastructural histopathological studies were performed on the kidneys of rats fed different amounts of fat and P: low (4%) fat (LF) and normal (0.6%) P (NP), LF and high (1.2%) P (HP), high (35%) fat (HF) and NP, HF and HP, and HF with low (0.2%) P (LP) for 28 weeks.
RESULTS
Glomeruli of the HF groups showed segmental areas of retraction, sclerosis and thickening of the Bowman's capsule and basal membranes, which were more accentuated in the HF-HP group. Ultrastructural lesions in the glomeruli also were prominent in rats fed HF, particularly in the HF-HP group, and included thickening of the capillary membrane, endothelial damage, mesangial matrix hypercellularity and podocyte effacement. P restriction reduced the severity of endothelial damage, mesangial matrix hypercellularity, thickening of capillary basement membrane and podocyte effacement. The kidneys of rats fed HP showed significant tubular atrophy and dilatation, focal tubular hyperplasia, thickening of the tubular basal membrane, interstitial edema, inflammation and calcification. All groups fed HF also showed tubular lesions that were more prominent in the HF-HP group. P restriction had a beneficial effect on inflammation and calcification.
CONCLUSIONS
Intake of both HF and HP damages the kidneys and their noxious effects are additive. HF intake was preferentially associated with glomerular lesions, while lesions related to HP intake were located mainly in the tubuli and in the interstitium.
PubMed: 33777367
DOI: 10.1093/ckj/sfaa009 -
Eye (London, England) Feb 2017This review is in two sections. The first section summarises 35 conditions, both common and infrequent, causing cicatrising conjunctivitis. Guidelines for making a... (Review)
Review
This review is in two sections. The first section summarises 35 conditions, both common and infrequent, causing cicatrising conjunctivitis. Guidelines for making a diagnosis are given together with the use of diagnostic tests, including direct and indirect immunofluorescence, and their interpretation. The second section evaluates our knowledge of ocular mucous membrane pemphigoid, which is the commonest cause of cicatrizing conjunctivitis in most developed countries. The clinical characteristics, demographics, and clinical signs of the disease are described. This is followed by a review and re-evaluation of the pathogenesis of conjunctival inflammation in mucous membrane pemphigoid (MMP), resulting in a revised hypothesis of the autoimmune mechanisms causing inflammation in ocular MMP. The relationship between inflammation and scarring in MMP conjunctiva is described. Recent research, describing the role of aldehyde dehydrogenase (ALDH) and retinoic acid (RA) in both the initiation and perpetuation of profibrotic activity in MMP conjunctival fibroblasts is summarised and the potential for antifibrotic therapy, using ALDH inhibition, is discussed. The importance of the management of the ocular surface in MMP is briefly summarised. This is followed with the rationale for the use of systemic immunomodulatory therapy, currently the standard of care for patients with active ocular MMP. The evidence for the use of these drugs is summarised and guidelines given for their use. Finally, the areas for research and innovation in the next decade are reviewed including the need for better diagnostics, markers of disease activity, and the potential for biological and topical therapies for both inflammation and scarring.
Topics: Aldehyde Dehydrogenase 1 Family; Autoantibodies; Autoimmune Diseases; Cicatrix; Conjunctivitis; Fibroblasts; Fluorescent Antibody Technique, Indirect; Humans; Immunosuppressive Agents; Inflammation; Isoenzymes; Pemphigoid, Benign Mucous Membrane; Retinal Dehydrogenase; Tretinoin
PubMed: 28106896
DOI: 10.1038/eye.2016.284 -
Journal of Clinical Medicine Sep 2021We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges....
We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges. Seventy-four corneal sample donors were included in the study. Firstly, the corneal transmittance was measured using a spectrophotometer. Then, all samples were fixed for histopathological analysis, which allowed us to measure the thickness of each corneal layer. Finally, the absorption coefficients of the corneal layers were computed by a linear model reproducing total transmittance. The results show that corneal transmission was almost in unity at the visible and IR ranges but not at the UV range, in which the layer with higher transmission is Descemet's membrane, whereas the stroma showed the lowest transmittance. Regarding the absorption coefficient, the most absorptive tissue was Bowman's layer, followed by the endothelium. Variations on transmittance due to changes in the stroma, Bowman's layer, or Descemet layer were simulated, and important transmission increases were found due to stroma and Bowman changes. To conclude, we have developed a method to measure the transmittance and thickness for each corneal layer. All corneal layers absorb UV light to a greater or lesser extent. The absorption coefficient is higher for Bowman's layer, while the stroma is the layer with the lowest transmittance due to its thickness. Variations in stroma thickness or changes in the corneal tissue of Bowman's layer or the endothelium layer due to some pathologies or surgeries could affect, to a greater or lesser degree, the total transmission of the cornea. Thus, obtaining accurate absorption coefficients for different layers would help us to predict and compensate these changes.
PubMed: 34640506
DOI: 10.3390/jcm10194490 -
The British Journal of Ophthalmology Feb 2003To describe the optics of in vivo confocal microscopy, its advantages over previous methods, and to summarise the literature that arose from its use for the observation... (Review)
Review
AIMS
To describe the optics of in vivo confocal microscopy, its advantages over previous methods, and to summarise the literature that arose from its use for the observation of the human cornea. A critical review of the clinical usefulness of this new technology for the corneal examination is undertaken.
METHODS
Confocal microscopes obtain increased resolution by limiting the illumination and observation systems to a single point. Rapid scanning is used to reconstruct a full field of view and allows for "real time" viewing.
RESULTS
Coronal sections of the in situ epithelium, Bowman's membrane, stroma, and endothelium can be visualised at a resolution of 1-2 micro m. A backscattered light intensity curve allows objective measurements of sublayer thickness and corneal haze to be taken. In vivo confocal microscopy is therefore particularly useful in the areas of infective keratitis, corneal dystrophies, refractive surgery, and contact lens wear, where it aids in differential diagnosis and detection of subtle short and long term changes. Real time endothelial cell assessment can also be performed.
CONCLUSION
Because of their ability to visualise living tissue at cellular levels, confocal microscopes have proved useful additions to the current clinical tools.
Topics: Cell Count; Contact Lenses; Cornea; Corneal Diseases; Corneal Dystrophies, Hereditary; Diagnosis, Differential; Humans; Keratitis; Keratomileusis, Laser In Situ; Microscopy, Confocal; Optics and Photonics; Refractive Surgical Procedures; Reproducibility of Results
PubMed: 12543757
DOI: 10.1136/bjo.87.2.225 -
American Journal of Physiology. Renal... Oct 2001Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular... (Review)
Review
Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.
Topics: Animals; Capillary Permeability; Humans; Kidney Glomerulus; Models, Biological; Ultrafiltration
PubMed: 11553505
DOI: 10.1152/ajprenal.2001.281.4.F579 -
Disease Models & Mechanisms Feb 2016Collagen IV is a major component of basement membranes, and mutations in COL4A1, which encodes collagen IV alpha chain 1, cause a multisystemic disease encompassing...
Collagen IV is a major component of basement membranes, and mutations in COL4A1, which encodes collagen IV alpha chain 1, cause a multisystemic disease encompassing cerebrovascular, eye and kidney defects. However, COL4A1 renal disease remains poorly characterized and its pathomolecular mechanisms are unknown. We show that Col4a1 mutations in mice cause hypotension and renal disease, including proteinuria and defects in Bowman's capsule and the glomerular basement membrane, indicating a role for Col4a1 in glomerular filtration. Impaired sodium reabsorption in the loop of Henle and distal nephron despite elevated aldosterone levels indicates that tubular defects contribute to the hypotension, highlighting a novel role for the basement membrane in vascular homeostasis by modulation of the tubular response to aldosterone. Col4a1 mutations also cause diabetes insipidus, whereby the tubular defects lead to polyuria associated with medullary atrophy and a subsequent reduction in the ability to upregulate aquaporin 2 and concentrate urine. Moreover, haematuria, haemorrhage and vascular basement membrane defects confirm an important vascular component. Interestingly, although structural and compositional basement membrane defects occurred in the glomerulus and Bowman's capsule, no tubular basement membrane defects were detected. By contrast, medullary atrophy was associated with chronic ER stress, providing evidence for cell-type-dependent molecular mechanisms of Col4a1 mutations. These data show that both basement membrane defects and ER stress contribute to Col4a1 renal disease, which has important implications for the development of treatment strategies for collagenopathies.
Topics: Animals; Basement Membrane; Collagen Type IV; Endoplasmic Reticulum Stress; Humans; Kidney Glomerulus; Kidney Tubules; Mice; Mutation
PubMed: 26839400
DOI: 10.1242/dmm.021741 -
PloS One 2023The steep cornea in keratoconus can greatly impair eyesight. The etiology of keratoconus remains unclear but early injury that weakens the corneal stromal architecture...
BACKGROUND
The steep cornea in keratoconus can greatly impair eyesight. The etiology of keratoconus remains unclear but early injury that weakens the corneal stromal architecture has been implicated. To explore keratoconus mechanics, we conducted two numerical simulation studies.
METHODS
A finite-element model describing the five corneal layers and the heterogeneous mechanical behaviors of the ground substance and lamellar collagen-fiber architecture in the anterior and posterior stroma was developed using the Holzapfel-Gasser-Ogden constitutive model. The geometry was from a healthy subject. Its stroma was divided into anterior, middle, and posterior layers to assess the effect of changing regional mechanical parameters on corneal displacement and maximum principal stress under intraocular pressure. Specifically, the effect of softening an inferocentral corneal button, the collagen-based tissues throughout the whole cornea, or specific stromal layers in the button was examined. The effect of simply disorganizing the orthogonally-oriented posterior stromal fibers in the button was also assessed. The healthy cornea was also subjected to eye rubbing-like loading to identify the corneal layer(s) that experienced the most tensional stress.
RESULTS
Conical deformation and corneal thinning emerged when the corneal button or the mid-posterior stroma of the button underwent gradual softening or when the collagen fibers in the mid-posterior stroma of the button were dispersed. Softening the anterior layers of the button or the whole cornea did not evoke conical deformation. Button softening greatly increased and disrupted the stress on Bowman's membrane while mid-posterior stromal softening increased stress in the anterior layers. Eye rubbing profoundly stressed the deep posterior stroma while other layers were negligibly affected.
DISCUSSION
These observations suggest that keratoconus could be initiated, at least partly, by mechanical instability/damage in the mid-posterior stroma that then imposes stress on the anterior layers. This may explain why subclinical keratoconus is marked by posterior but not anterior elevation on videokeratoscopy.
Topics: Humans; Keratoconus; Biomechanical Phenomena; Cornea; Corneal Stroma; Collagen
PubMed: 36730305
DOI: 10.1371/journal.pone.0278455 -
American Journal of Physiology. Renal... Nov 2021Following our previous reports on mesangial sclerosis and vascular proliferation in diabetic nephropathy (DN) (Kriz W, Löwen J, Federico G, van den Born J, Gröne E,...
Following our previous reports on mesangial sclerosis and vascular proliferation in diabetic nephropathy (DN) (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. 312: F1101-F1111, 2017; Löwen J, Gröne E, Gröne HJ, Kriz W. 317: F399-F410, 2019), we now describe the advanced stages of DN terminating in glomerular obsolescence and tubulointerstitial fibrosis based on a total of 918 biopsies. The structural aberrations emerged from two defects: ) increased synthesis of glomerular basement membrane (GBM) components by podocytes and endothelial cells leading to an accumulation of GBM material in the mesangium and ) a defect of glomerular vessels consisting of increased leakiness and an increased propensity to proliferate. Both defects may lead to glomerular degeneration. The progressing compaction of accumulated worn-out GBM material together with the retraction of podocytes out of the tuft and the collapse and hyalinosis of capillaries results in a shrunken tuft that fuses with Bowman's capsule (BC) to glomerular sclerosis. The most frequent pathway to glomerular decay starts with local tuft expansions that result in contacts of structurally intact podocytes to the parietal epithelium initiating the formation of tuft adhesions, which include the penetration of glomerular capillaries into BC. Exudation of plasma from such capillaries into the space between the parietal epithelium and its basement membrane causes the formation of insudative fluid accumulations within BC spreading around the glomerular circumference and, via the glomerulotubular junction, onto the tubule. Degeneration of the corresponding tubule develops secondarily to the glomerular damage, either due to cessation of filtration in cases of global sclerosis or due to encroachment of the insudative spaces. The degenerating tubules induce the proliferation of myofibroblasts resulting in interstitial fibrosis. Based on analysis of 918 human biopsies, essential derangement in diabetic nephropathy consists of accumulation of worn-out glomerular basement membrane in the mesangium that may advance to global sclerosis. The most frequent pathway to nephron dropout starts with the penetration of glomerular capillaries into Bowman's capsule (BC), delivering an exudate into BC that spreads around the entire glomerular circumference and via the glomerulotubular junction onto the tubule, resulting in glomerular sclerosis and chronic tubulointerstitial damage.
Topics: Biopsy; Bowman Capsule; Capillaries; Capillary Permeability; Diabetic Nephropathies; Disease Progression; Endothelial Cells; Fibrosis; Glomerular Basement Membrane; Glomerulonephritis; Humans; Microscopy, Electron, Transmission; Neovascularization, Pathologic; Nephrons; Podocytes
PubMed: 34541901
DOI: 10.1152/ajprenal.00669.2020