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Journal of Cataract and Refractive... Mar 2011The importance of the cornea to the ocular structure and visual system is often overlooked because of the cornea's unassuming transparent nature. The cornea lacks the... (Review)
Review
The importance of the cornea to the ocular structure and visual system is often overlooked because of the cornea's unassuming transparent nature. The cornea lacks the neurobiological sophistication of the retina and the dynamic movement of the lens; yet, without its clarity, the eye would not be able to perform its necessary functions. The complexity of structure and function necessary to maintain such elegant simplicity is the wonder that draws us to one of the most important components of our visual system.
Topics: Bowman Membrane; Cornea; Corneal Stroma; Descemet Membrane; Endothelium, Corneal; Epithelium, Corneal; Humans; Ophthalmic Nerve; Sympathetic Nervous System
PubMed: 21333881
DOI: 10.1016/j.jcrs.2010.12.037 -
Ophthalmic Research 2021For nearly a century, the definitive treatment of many corneal dystrophies and ectactic disorders was limited to penetrating keratoplasty, but over the past 2 decades, a... (Review)
Review
For nearly a century, the definitive treatment of many corneal dystrophies and ectactic disorders was limited to penetrating keratoplasty, but over the past 2 decades, a surge of surgical innovation has propelled the treatment of many corneal diseases to more targeted approaches with significantly better visual outcomes. Anterior stromal diseases were first changed through endothelial-sparing techniques, such as deep anterior lamellar keratoplasty, but have more recently transitioned to stromal-sparing approaches. Ultraviolet corneal crosslinking strengthens the cornea and halts progression of keratoconus in >90% of cases. Intracorneal ring segment and corneal allogenic ring segment implantation offer methods to flatten ectatic corneas. However, Bowman layer transplantation - inlay and more recently onlay techniques - has shown promise for treating advanced keratoconus and preventing keratoplasty. The advent of endothelial keratoplasty radically changed the treatment of corneal endothelial dysfunction, and Descemet membrane endothelial keratoplasty specifically offers an average postoperative visual acuity of 20/25 (0.8) with only 8.8% of grafts requiring retransplantation in the first 5 years. Here, we review the rapid innovations for surgical treatment of corneal diseases, spanning from endothelial keratoplasty and endothelial regeneration to anterior lamellar keratoplasty and stromal augmentation, highlighting key steps which may be moving us closer to a "postkeratoplasty" world.
Topics: Cornea; Corneal Transplantation; Descemet Membrane; Humans; Keratoconus; Keratoplasty, Penetrating
PubMed: 33761502
DOI: 10.1159/000516093 -
Kidney International Jun 2016Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines... (Review)
Review
Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines the particular vulnerability of the glomerulus. Recent podocyte biology and gene disruption studies in vivo indicate a causal relationship between abnormalities of single podocyte molecules and proteinuria and glomerulosclerosis. Podocytes live under various stresses and pathological stimuli. They adapt to maintain homeostasis, but excessive stress leads to maladaptation with complex biological changes including loss of integrity and dysregulation of cellular metabolism. Podocyte injury causes proteinuria and detachment from the glomerular basement membrane. In addition to "sick" podocytes and their detachment, our understanding of glomerular responses following podocyte loss needs to address the pathways from podocyte injury to sclerosis. Studies have found a variety of glomerular responses to podocyte dysfunction in vivo, such as disruption of podocyte-endothelial cross talk and activation of podocyte-parietal cell interactions, all of which help us to understand the complex scenario of podocyte injury and its consequences. This review focuses on the cellular aspects of podocyte dysfunction and the adaptive or maladaptive glomerular responses to podocyte injury that lead to its major consequence, glomerulosclerosis.
Topics: Apoptosis; Bowman Capsule; Cell Communication; Cell Differentiation; Endothelial Cells; Glomerular Basement Membrane; Glomerulosclerosis, Focal Segmental; Humans; Oxidative Stress; Podocytes; Proteinuria; Sclerosis; Stress, Mechanical
PubMed: 27165817
DOI: 10.1016/j.kint.2016.01.012 -
Saudi Journal of Ophthalmology :... 2023To evaluate a new surgical method for managing nonhealing neurotrophic ulcers using a novel technique of tucking-in Bowman's membrane lenticule in the ulcer defect.
PURPOSE
To evaluate a new surgical method for managing nonhealing neurotrophic ulcers using a novel technique of tucking-in Bowman's membrane lenticule in the ulcer defect.
METHODS
A total of 22 eyes of 22 patients with neurotrophic ulcers of various etiologies and stages were included and underwent a surgical process where a donor Bowman's membrane lenticule was harvested and fashioned according to the lesion and tucked inside the ulcer after making a recess in anterior one-third of stroma all around 360 degrees. The primary outcomes measured were healing (stable epithelialization at 12 months) and best-corrected visual acuity (BCVA) improvement.
RESULTS
Twenty-two eyes of 22 patients with neurotrophic ulcers underwent Bowman's membrane lenticule tuck-in procedure. Complete re-epithelialization was achieved in 21 eyes (95.45%). The average healing time was 2.77 ± 0.79 weeks. The mean corneal thickness improved from 267.36 ± 94.56 mm preoperatively to 435.9 ± 47.71 mm at six months postoperatively. The mean BCVA also improved from 0.05 ± 0.07 preoperatively to 0.24 ± 0.24 postoperatively one year. One patient (4.54%) showed recurrence after one month, and the epithelial defect persisted till the end of the study.
CONCLUSION
Donor Bowman's membrane lenticule tuck-in for neurotrophic ulcers is a safe and highly effective treatment and requires minimal instruments and expertise.
PubMed: 37492212
DOI: 10.4103/sjopt.sjopt_56_22 -
Biomaterials May 2020As the outermost layer of the eye, the cornea is vulnerable to physical and chemical trauma, which can result in loss of transparency and lead to corneal blindness....
As the outermost layer of the eye, the cornea is vulnerable to physical and chemical trauma, which can result in loss of transparency and lead to corneal blindness. Given the global corneal donor shortage, there is an unmet need for biocompatible corneal substitutes that have high transparency, mechanical integrity and regenerative potentials. Herein we engineered a dual-layered collagen vitrigel containing biomimetic synthetic Bowman's membrane (sBM) and stromal layer (sSL). The sBM supported rapid epithelial cell migration, maturation and multilayer formation, and the sSL containing tissue-derived extracellular matrix (ECM) microparticles presented a biomimetic lamellar ultrastructure mimicking the native corneal stroma. The incorporation of tissue-derived microparticles in sSL layer significantly enhanced the mechanical properties and suturability of the implant without compromising the transparency after vitrification. In vivo performance of the vitrigel in a rabbit anterior lamellar keratoplasty model showed full re-epithelialization within 14 days and integration of the vitrigel with the host tissue stroma by day 30. The migrated epithelial cells formed functional multilayer with limbal stem cell marker p63 K14 expressed in the lower layer, epithelial marker K3 and K12 expressed through the layers and tight junction protein ZO-1 expressed by the multilayers. Corneal fibroblasts migrated into the implants to facilitate host/implant integration and corneal stromal regeneration. In summary, these results suggest that the multi-functional layers of this novel collagen vitrigel exhibited significantly improved biological performance as corneal substitute by harnessing a fast re-epithelialization and stromal regeneration potential.
Topics: Animals; Biomimetics; Bowman Membrane; Collagen; Cornea; Corneal Stroma; Corneal Transplantation; Rabbits
PubMed: 32097748
DOI: 10.1016/j.biomaterials.2020.119880 -
Graefe's Archive For Clinical and... Jan 2022This study evaluated the safety and efficacy of Bowman's membrane electrocautery in blind painful eyes with bullous keratopathy not amenable to corneal transplantation.
PURPOSE
This study evaluated the safety and efficacy of Bowman's membrane electrocautery in blind painful eyes with bullous keratopathy not amenable to corneal transplantation.
METHODS
Eleven eyes of 11 subjects with painful bullous keratopathy and poor visual potential who underwent electrocautery of Bowman's membrane at a tertiary referral ophthalmology clinic were reviewed retrospectively. Subject demographics and preoperative and postoperative data were collected, including description of pain, slit lamp biomicroscopy, best corrected visual acuity, topical medication use, and complications. Efficacy of the procedure on pain reduction, bullae resolution, and topical medication use were assessed at post-operative visits. Safety was also evaluated based on any complications.
RESULTS
Bowman's membrane electrocautery effectively resolved bullae in all eyes examined up to 6 months postoperatively; however, 2 eyes had recurrence by 1 year. Mean age at the time of surgery was 69.8 years and mean duration of follow-up was 15.4 months. Pain reduction was achieved in all eyes at 1 month, but 1 subject had pain recurrence by 6 months and another by 1 year. The median number of drops per day decreased from 6 preoperatively to 1.7 at 6 months. Two subjects who had underlying advanced ophthalmic disease had a mild reduction in vision.
CONCLUSION
Bowman's membrane electrocautery is a safe and minimally invasive procedure for the management of painful bullous keratopathy in eyes with low vision potential and not amenable to corneal transplantation. Duration of effect appears to last at least 6 months and up to 3 years post-procedure.
Topics: Bowman Membrane; Corneal Diseases; Corneal Transplantation; Electrocoagulation; Humans; Pain; Retrospective Studies; Visual Acuity
PubMed: 34453605
DOI: 10.1007/s00417-021-05360-4 -
Current Opinion in Ophthalmology Jul 2019Bowman layer transplantation is a novel technique that may stabilize progressive ectatic corneal changes in eyes with keratoconus, which are too steep or too thin for... (Review)
Review
PURPOSE OF REVIEW
Bowman layer transplantation is a novel technique that may stabilize progressive ectatic corneal changes in eyes with keratoconus, which are too steep or too thin for ultraviolet corneal crosslinking or intracorneal ring segments. In this way, patients can maintain stable vision with contact lenses, and avoid or postpone more invasive corneal transplants, such as penetrating keratoplasty or deep anterior lamellar keratoplasty. This review aims to summarize the currently available literature on Bowman layer transplantation.
RECENT FINDINGS
Bowman layer transplantation seems to be a promising, minimally invasive procedure for managing advanced keratoconus with a reported 5-year success rate of 84%. The procedure allows patients to maintain acceptable visual acuity with glasses or contact lens correction. Although graft preparation and surgical technique can be challenging, adaptation of technologies, such as femtosecond laser and intraoperative anterior segment optical coherence tomography, may help overcome these barriers to enable Bowman layer transplantation to become a more widely adopted procedure.
SUMMARY
Bowman layer transplantation may offer an alternative, less invasive treatment option for eyes with advanced, progressive keratoconus.
Topics: Bowman Membrane; Corneal Transplantation; Humans; Keratoconus
PubMed: 31033731
DOI: 10.1097/ICU.0000000000000570 -
Experimental Eye Research Jun 2020Bowman's layer lies immediately posterior to the epithelial basement membrane (EBM) and anterior to the stroma proper in humans, chickens, quail, zebra fish, deer,... (Review)
Review
Bowman's layer lies immediately posterior to the epithelial basement membrane (EBM) and anterior to the stroma proper in humans, chickens, quail, zebra fish, deer, giraffe, antelope, California sea lions, guinea pig and several other species. It is not found in dog, wolf, cat, tiger, lions, rabbit, pigs, cows, goats, or horses. Developmental anomalies of Bowman's layer are rare, but acquired damage to Bowman's layer, or even complete destruction, is frequently seen in advanced bullous keratopathy or Fuchs' endothelial dystrophy. No detrimental effects of removal of Bowman's layer over the central 6-7 mm of central cornea have been noted in millions of patients who've had photorefractive keratectomy (PRK). Recent studies have suggested the randomly-oriented collagen fibrils that make up Bowman's layer do not have a significant barrier function in modulating the passage of moderate- to large-sized proteins. It is hypothesized that Bowman's layer develops in the corneas of those species that have one because of cytokine-mediated interactions occurring between corneal epithelial cells and underlying keratocytes, including negative chemotactic and apoptotic effects on the keratocytes by low levels of cytokines such as interleukin-1α that are gradually released as epithelial cells die and slough during their normal development. A "Bowman's like layer" can generate around stromal epithelial plugs after radial keratotomy, and possibly beneath the central corneal epithelial basement membrane many years after PRK.
Topics: Animals; Basement Membrane; Epithelium, Corneal; Humans; Regeneration
PubMed: 32339517
DOI: 10.1016/j.exer.2020.108033 -
Indian Journal of Ophthalmology Sep 2018Lamellar keratoplasty (LK) has revolutionized corneal graft surgery in several ways. Deep anterior LK (DALK) has eliminated risk of failure due to endothelial rejection.... (Review)
Review
Lamellar keratoplasty (LK) has revolutionized corneal graft surgery in several ways. Deep anterior LK (DALK) has eliminated risk of failure due to endothelial rejection. Endothelial keratoplasty (EK) has almost eliminated induced astigmatism and the "weak" graft-host junction as seen with penetrating keratoplasty (PK) and also reduced the risk of endothelial rejection. LK provided new insights into posterior corneal anatomy that led to better understanding and performance of DALK and to the development of another EK procedure, namely pre-Descemet's EK (PDEK). Surgical procedures for LK were further refined based on the improved understanding and are able to deliver better surgical outcomes in terms of structural integrity and long-term patient satisfaction, reducing the need of further surgeries and minimizing patient discomfort. In most specialist centers, anterior lamellar techniques like DALK and EK techniques like Descemet's stripping EK (DSEK) and Descemet's membrane EK (DMEK) have replaced the full-thickness PK where possible. The introduction of microkeratome, femtosecond laser, and PDEK clamp have made LK techniques easier and more predictable and have led to the innovation of another LK procedure, namely Bowman membrane transplant (BMT). In this article, we discuss the evolution of different surgical techniques, their principles, main outcomes, and limitations. To date, experience with BMT is limited, but DALK has become the gold standard for anterior LK. The EK procedures too have undergone a rapid transition from DSEK to DMEK and PDEK emerging as a viable option. Ultrathin-DSEK may still have a role in modern EK.
Topics: Cornea; Corneal Diseases; Humans; Keratoplasty, Penetrating; Visual Acuity
PubMed: 30127133
DOI: 10.4103/ijo.IJO_95_18 -
Clinical Nephrology Dec 2000Bowman's capsular and tubular basement membrane (TBM) deposits are an extremely unusual finding in non-lupus membranous glomerulopathy (MGN). We report three atypical... (Review)
Review
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.
Topics: Adult; Aged; Basement Membrane; Biopsy; Enzyme-Linked Immunosorbent Assay; Female; Fluorescent Antibody Technique; Glomerulonephritis, Membranous; Humans; Kidney; Kidney Glomerulus; Kidney Tubules; Male; Microscopy, Electron
PubMed: 11140809
DOI: No ID Found