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Asia-Pacific Journal of Ophthalmology... 2019Dry eyes is one of the most common complications after laser vision correction. Small incision lenticule extraction (SMILE) is a flapless procedure with a smaller... (Review)
Review
Dry eyes is one of the most common complications after laser vision correction. Small incision lenticule extraction (SMILE) is a flapless procedure with a smaller corneal incision, less corneal nerves are transected during, making it theoretically less prone to dry eyes. Both SMILE and femtosecond-laser-assisted in situ keratomileusis (FS-LASIK) induce a transient worsening in dry eye parameters, but there is evidence showing that SMILE holds promises to have fewer negative impacts on the ocular surface parameters and allow an earlier recovery. SMILE-treated eyes may also have shown less corneal denervation and better corneal sensitivity compared with FS-LASIK eyes. This review summarizes the mechanisms of dry eyes after laser vision correction, the short-term (≤6 months) and long-term (>6 months) results in changes to dry eyes signs and symptoms, and corneal sensitivity of SMILE, as compared with FS-LASIK. Limitation of the studies and reasons accounting for their discrepancies will be discussed. Future randomized controlled trials with standardized postoperative regime are needed for better evaluation of dry eyes after SMILE.
Topics: Corneal Stroma; Dry Eye Syndromes; Humans; Keratomileusis, Laser In Situ; Lasers, Excimer; Myopia; Postoperative Complications; Visual Acuity
PubMed: 31490199
DOI: 10.1097/01.APO.0000580136.80338.d0 -
Experimental Eye Research Sep 2020No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma.... (Review)
Review
No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.
Topics: Animals; Collagen; Corneal Stroma; Extracellular Matrix; Extracellular Matrix Proteins; Humans
PubMed: 32663498
DOI: 10.1016/j.exer.2020.108137 -
Asia-Pacific Journal of Ophthalmology... 2019Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high... (Review)
Review
Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high efficacy and safety profile and also carries potential advantages over laser in situ keratomileusis such as a better corneal biomechanical stability, reduction in dry eyes rate, and the avoidance of flap complications. However, there have been concerns regarding the precision of astigmatism correction that undercorrection has been reported to be apparent. Various factors that affect astigmatism correction have been identified in the literature. The purpose of this review is to discuss the factors that affect astigmatism correction in SMILE and several techniques to improve the refractive outcomes.
Topics: Astigmatism; Corneal Stroma; Corneal Topography; Humans; Keratomileusis, Laser In Situ; Lasers, Excimer; Visual Acuity
PubMed: 31490198
DOI: 10.1097/01.APO.0000580140.74826.f5 -
Experimental Eye Research Jan 2021The unwounded, normal corneal stroma is a relatively simple, avascular tissue populated with quiescent keratocytes, along with corneal nerves and a few resident...
The unwounded, normal corneal stroma is a relatively simple, avascular tissue populated with quiescent keratocytes, along with corneal nerves and a few resident dendritic and monocyte/macrophage cells. In the past, the resting keratocytes were thought of as a homogenous cellular population, but recent work has shown local variations in vimentin and nestin expression, and responsiveness to transforming growth factor (TGF)-β1. Studies have also supported there being "stromal stem cells" in localized areas. After corneal wounding, depending on the site and severity of injury, profound changes in stromal cellularity occur. Anterior or posterior injuries to the epithelium or endothelium, respectively, trigger apoptosis of adjacent keratocytes. Many contiguous keratocytes transition to keratocan-negative corneal fibroblasts that are proliferative and produce limited amounts of disorganized extracellular matrix components. Simultaneously, large numbers of bone marrow-derived cells, including monocytes, neutrophils, fibrocytes and lymphocytes, invade the stroma from the limbal blood vessels. Ongoing adequate levels of TGFβ1, TGFβ2 and platelet-derived growth factor (PDGF) from epithelium, tears, endothelium and aqueous humor that penetrate defective or absent epithelial barrier function (EBF) and epithelial basement membrane (EBM) and/or Descemet's basement membrane (DBM) drive corneal fibroblasts and fibrocytes to differentiate into alpha-smooth muscle actin (SMA)-positive myofibroblasts. If the EBF, EBM and/or DBM are repaired or replaced in a timely manner, typically measured in weeks, then corneal fibroblast and fibrocyte progeny, deprived of requisite levels of TGFβ1 and TGFβ2, undergo apoptosis or revert to their precursor cell-types. If the EBF, EBM and/or DBM are not repaired or replaced, stromal levels of TGFβ1 and TGFβ2 remain elevated, and mature myofibroblasts are generated from corneal fibroblasts and fibrocyte precursors that produce prodigious amounts of disordered extracellular matrix materials associated with scarring fibrosis. This fibrotic stromal matrix persists, at least until the EBF, EBM and/or DBM are regenerated or replaced, and keratocytes remove and reorganize the affected stromal matrix.
Topics: Basement Membrane; Biomarkers; Bone Marrow Cells; Corneal Injuries; Corneal Keratocytes; Corneal Stroma; Humans
PubMed: 33068626
DOI: 10.1016/j.exer.2020.108303 -
Current Eye Research Mar 2020The corneal stroma comprises 90% of the corneal thickness and is critical for the cornea's transparency and refractive function necessary for vision. When the corneal... (Review)
Review
The corneal stroma comprises 90% of the corneal thickness and is critical for the cornea's transparency and refractive function necessary for vision. When the corneal stroma is altered by disease, injury, or scarring, however, an irreversible loss of transparency can occur. Corneal stromal pathology is the cause of millions of cases of blindness globally, and although corneal transplantation is the standard therapy, a severe global deficit of donor corneal tissue and eye banking infrastructure exists, and is unable to meet the overwhelming need. An alternative approach is to harness the endogenous regenerative ability of the corneal stroma, which exhibits self-renewal of the collagenous extracellular matrix under appropriate conditions. To mimic endogenous stromal regeneration, however, is a challenge. Unlike the corneal epithelium and endothelium, the corneal stroma is an exquisitely organized extracellular matrix containing stromal cells, proteoglycans and corneal nerves that is difficult to recapitulate in vitro. Nevertheless, much progress has recently been made in developing stromal equivalents, and in this review the most recent approaches to stromal regeneration therapy are described and discussed. Novel approaches for stromal regeneration include human or animal corneal and/or non-corneal tissue that is acellular or is decellularized and/or re-cellularized, acellular bioengineered stromal scaffolds, tissue adhesives, 3D bioprinting and stromal stem cell therapy. This review highlights the techniques and advances that have achieved first clinical use or are close to translation for eventual therapeutic application in repairing and regenerating the corneal stroma, while the potential of these novel therapies for achieving effective stromal regeneration is discussed.
Topics: Animals; Corneal Diseases; Corneal Stroma; Corneal Transplantation; Humans; Regeneration; Stem Cell Transplantation; Tissue Engineering
PubMed: 31537127
DOI: 10.1080/02713683.2019.1663874 -
Investigative Ophthalmology & Visual... May 2024The purpose of this study was to assess the impact of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on corneal stroma characteristics, ocular...
PURPOSE
The purpose of this study was to assess the impact of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on corneal stroma characteristics, ocular manifestations, and post-recovery refractive surgery outcomes after varying recovery durations.
METHODS
Fresh corneal lenticules from patients with post-coronavirus disease 2019 (COVID-19; recovered within 135 days) and healthy controls (HCs) after small incision lenticule extraction (SMILE) surgery were obtained for experimental validation of SARS-CoV-2 susceptibility, morphological changes, and immune response of the corneal stroma. Corneal optical density (CD) was measured using the Pentacam HR. Corneal epithelium thickness (ET) and endothelium parameters were evaluated by wide-field optical coherence tomography (OCT) and non-contact specular microscopy (SP-1P), respectively. All the patients were assessed after SMILE surgery until 3 month of follow-up.
RESULTS
The cornea was susceptible to SARS-CoV-2 with the presence of SARS-CoV-2 receptors (CD147 and ACE2) and spike protein remnants (4 out of 58) in post-recovery corneal lenticules. Moreover, SARS-CoV-2 infection triggered immune responses in the corneal stroma, with elevated IL-6 levels observed between 45 and 75 days post-recovery, which were then lower at around day 105. Concurrently, corneal mid-stromal nerve length and branching were initially higher in the 60D to 75D group and returned to control levels by day 135. A similar trend was observed in CD within zones 0 to 2 and 2 to 6 and in the hexagonal cells (HEX) ratio in endothelial cells, whereas ET remained consistent. Notably, these changes did not affect the efficacy, safety, or predictability of post-recovery SMILE surgery.
CONCLUSIONS
SARS-CoV-2 induces temporal alterations in corneal stromal morphology and function post-recovery. These findings provided a theoretical basis for corneal health and refractive surgery management in the post-COVID-19 milieu.
Topics: Humans; COVID-19; Corneal Stroma; Male; Female; Adult; SARS-CoV-2; Tomography, Optical Coherence; Corneal Surgery, Laser; Middle Aged
PubMed: 38713483
DOI: 10.1167/iovs.65.5.14 -
Experimental Eye Research Nov 2020Bio-engineering technologies are currently used to produce biomimetic artificial corneas that should present structural, chemical, optical, and biomechanical properties... (Review)
Review
Bio-engineering technologies are currently used to produce biomimetic artificial corneas that should present structural, chemical, optical, and biomechanical properties close to the native tissue. These properties are mainly supported by the corneal stroma which accounts for 90% of corneal thickness and is mainly made of collagen type I. The stromal collagen fibrils are arranged in lamellae that have a plywood-like organization. The fibril diameter is between 25 and 35 nm and the interfibrillar space about 57 nm. The number of lamellae in the central stroma is estimated to be 300. In the anterior part, their size is 10-40 μm. They appear to be larger in the posterior part of the stroma with a size of 60-120 μm. Their thicknesses also vary from 0.2 to 2.5 μm. During development, the acellular corneal stroma, which features a complex pattern of organization, serves as a scaffold for mesenchymal cells that invade and further produce the cellular stroma. Several pathways including Bmp4, Wnt/β-catenin, Notch, retinoic acid, and TGF-β, in addition to EFTFs including the mastering gene Pax-6, are involved in corneal development. Besides, retinoic acid and TGF- β seem to have a crucial role in the neural crest cell migration in the stroma. Several technologies can be used to produce artificial stroma. Taking advantage of the liquid-crystal properties of acid-soluble collagen, it is possible to produce transparent stroma-like matrices with native-like collagen I fibrils and plywood-like organization, where epithelial cells can adhere and proliferate. Other approaches include the use of recombinant collagen, cross-linkers, vitrification, plastically compressed collagen or magnetically aligned collagen, providing interesting optical and mechanical properties. These technologies can be classified according to collagen type and origin, presence of telopeptides and native-like fibrils, structure, and transparency. Collagen matrices feature transparency >80% for the appropriate 500-μm thickness. Non-collagenous matrices made of biopolymers including gelatin, silk, or fish scale have been developed which feature interesting properties but are less biomimetic. These bioengineered matrices still need to be colonized by stromal cells to fully reproduce the native stroma.
Topics: Animals; Bioengineering; Collagen; Corneal Stroma; Drug Implants; Humans; Mesenchymal Stem Cells; Recombinant Proteins
PubMed: 32971095
DOI: 10.1016/j.exer.2020.108256 -
Experimental Eye Research Apr 2015The generation of cellular forces and the application of these physical forces to the ECM play a central role in mediating matrix patterning and remodeling during... (Review)
Review
The generation of cellular forces and the application of these physical forces to the ECM play a central role in mediating matrix patterning and remodeling during fundamental processes such as developmental morphogenesis and wound healing. In addition to growth factors and other biochemical factors that can modulate the keratocyte mechanical phenotype, another key player in the regulation of cell-induced ECM patterning is the mechanical state of the ECM itself. In this review we provide an overview of the biochemical and biophysical factors regulating the mechanical interactions between corneal keratocytes and the stromal ECM at the cellular level. We first provide an overview of how Rho GTPases regulate the sub-cellular pattern of force generation by corneal keratocytes, and the impact these forces have on the surrounding ECM. We next review how feedback from local matrix structural and mechanical properties can modulate keratocyte phenotype and mechanical activity. Throughout this review, we provide examples of how these biophysical interactions may contribute to clinical outcomes, with a focus on corneal wound healing.
Topics: Biomechanical Phenomena; Cell Communication; Corneal Keratocytes; Corneal Stroma; Extracellular Matrix; Humans; Microscopy, Confocal
PubMed: 25819454
DOI: 10.1016/j.exer.2014.09.003 -
The Ocular Surface Apr 2019Autophagy is a well-conserved self-eating mechanism of cell survival during periods of nutrient deprivation, stress and injury. Autophagy is implicated in many... (Review)
Review
Autophagy is a well-conserved self-eating mechanism of cell survival during periods of nutrient deprivation, stress and injury. Autophagy is implicated in many pathophysiological conditions across all organ systems. The cornea is an avascular transparent tissue that is prone to damage by trauma, injury and infection. Following insult, the cornea undergoes a complex wound healing process, which is regulated by multiple factors including autophagy. The involvement of autophagy in keratoconus and HSV-1 infection has been demonstrated, underlining the importance of this mechanism in corneal disorders. However, the role of autophagy in corneal wound repair, fibrosis and angiogenesis is still unclear. Recently, we characterized the expression of autophagy-related genes in cornea and are studying their role in the modulation of corneal conditions including fibrosis and dystrophies. Preliminary results presented within this review article support further investigation of the dynamic modulation of autophagy-related genes in corneal health and disease. This article provides an overview of how autophagy modulates corneal function.
Topics: Animals; Autophagy; Cell Survival; Corneal Diseases; Corneal Stroma; Humans; Wound Healing
PubMed: 30690084
DOI: 10.1016/j.jtos.2019.01.008 -
Experimental Eye Research Apr 2015The transparent cornea is the major refractive element of the eye. A finely controlled assembly of the stromal extracellular matrix is critical to corneal function, as... (Review)
Review
The transparent cornea is the major refractive element of the eye. A finely controlled assembly of the stromal extracellular matrix is critical to corneal function, as well as in establishing the appropriate mechanical stability required to maintain corneal shape and curvature. In the stroma, homogeneous, small diameter collagen fibrils, regularly packed with a highly ordered hierarchical organization, are essential for function. This review focuses on corneal stroma assembly and the regulation of collagen fibrillogenesis. Corneal collagen fibrillogenesis involves multiple molecules interacting in sequential steps, as well as interactions between keratocytes and stroma matrix components. The stroma has the highest collagen V:I ratio in the body. Collagen V regulates the nucleation of protofibril assembly, thus controlling the number of fibrils and assembly of smaller diameter fibrils in the stroma. The corneal stroma is also enriched in small leucine-rich proteoglycans (SLRPs) that cooperate in a temporal and spatial manner to regulate linear and lateral collagen fibril growth. In addition, the fibril-associated collagens (FACITs) such as collagen XII and collagen XIV have roles in the regulation of fibril packing and inter-lamellar interactions. A communicating keratocyte network contributes to the overall and long-range regulation of stromal extracellular matrix assembly, by creating micro-domains where the sequential steps in stromal matrix assembly are controlled. Keratocytes control the synthesis of extracellular matrix components, which interact with the keratocytes dynamically to coordinate the regulatory steps into a cohesive process. Mutations or deficiencies in stromal regulatory molecules result in altered interactions and deficiencies in both transparency and refraction, leading to corneal stroma pathobiology such as stromal dystrophies, cornea plana and keratoconus.
Topics: Chondroitin Sulfate Proteoglycans; Collagen; Corneal Stroma; Extracellular Matrix; Humans
PubMed: 25819456
DOI: 10.1016/j.exer.2014.08.001