Corneal wound healing in an osteopontin-deficient mouse

PURPOSE: To investigate the effects of loss of osteopontin (OPN) in the healing of the injured cornea in mice. Cell culture study was also conducted to clarify the effects of OPN in fibroblast behaviors. METHODS: Ocular fibroblasts from wild-type (WT) and OPN-null (KO) mice were used to study the role of OPN on cell behavior. The effect of the lack of OPN on corneal wound healing was evaluated in mice. RESULTS: In cell culture, OPN is involved in cell adhesion and in the migration of ocular fibroblasts. Adhesion of the corneal epithelial cell line was not affected by exogenous OPN. OPN was upregulated in a healing, injured mouse cornea. Loss of OPN did not affect epithelial healing after simple epithelial debridement. Healing of an incision injury in cornea was delayed, with less appearance of myofibroblasts and transforming growth factor beta1 expression in a KO mouse than in a WT mouse. The absence of OPN promoted tissue destruction after an alkali burn, resulting in a higher incidence of corneal perforation in KO mice than in WT mice. CONCLUSIONS: OPN modulates wound healing-related fibroblast behavior and is required to restore the physiological structure of the cornea after wound healing.     

Corneal wound healing

PURPOSE: To examine the latest theories in understanding wound healing, primarily as it pertains to refractive surgery but also, briefly, incisional surgery and nonsurgical corneal conditions (iatrogenic injury and noninfectious corneal ulcers). RECENT FINDINGS: Corneal wound healing involves transformation of fibroblasts; intercellular signaling-for example between epithelial and stromal cells-from cytokines, neuropeptides, growth factors, and chemokines; action of matrix metalloproteinases; and protection of tissue from free radical damage. There may be a common wound healing pathway after different types of surgery and injury to the cornea-for example, the wound healing cascades after laser in situ keratomileusis and photorefractive keratectomy may be similar, and yet the effects on the cornea differ because of the extent of disruption to the basement membrane-but the outcomes may depend on small differences in the cascade. SUMMARY: Interest in the study of corneal wound healing has increased with the proliferation of keratorefractive surgery. Important contributions come from intercellular signaling, fibroblast transformation, remodeling of the extracellular matrix, and free radical scavengers. Despite these advances, a formalized, unified vision of the wound healing cascade remains elusive.     

Corneal epithelial wound healing

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. The renewal process also maintains the smooth optical surface of the cornea. This rate of renewal is closely maintained by an integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. Attempts to understand this complex cascade make it evident that the appropriate integration and coordination of corneal epithelial renewal depends on the actions of a myriad of cytokines. We have attempted in this review to collate the receptor and cell signaling events and cytokine studies that are responsible for mediating corneal wound healing.     

Corneal alkali wound healing in the monkey

Healing of a corneal alkali wound was followed in the monkey eye (Macaca fascicularis) for 4 months. A corneal alkali wound was inflicted in one eye in each of 30 monkeys under general anesthesia. A round filter paper, 5.5 mm in diameter, soaked in 1 N NaOH was put centrally on the cornea for 60 seconds. The alkali wounded all layers in the cornea underlying the filter paper, including the endothelium. Epithelial and endothelial healing was assessed morphometrically from photographs and micrographs, respectively. Stromal healing was documented using quantitative microradiography. During the observation period the wounds regained complete transparency. The epithelium showed few complications after primary healing during the first three days. The stroma regained normal thickness and dry mass content within one week. The endothelium resurfaced within one week and then remained intact. The role of the endothelial healing behaviour for the wound healing process is emphasized.     

Corneal wound healing after excimer laser keratectomy

Excimer laser keratectomy is widely used to correct refractive errors. Several complications of excimer laser keratectomy are reported including corneal infection, regression, corneal haze formation, glare and halo. Most of the complications are closely related to the corneal stromal wound healing process. In order to perform the excimer laser keratectomy with minimum complications, we should understand the mechanism of the corneal stroma wound healing process. In addition, such knowledge will help us to regulate the corneal stromal wound healing process in the future. In the present article, we discuss the molecular mechanism of the corneal stromal wound healing process after excimer laser keratectomy and its regulation by anti-inflammatory agents.     

Corneal epithelial wound healing in partial limbal deficiency.

Previous studies have shown that the corneal epithelial stem cells are located at the limbal basal layer. The limbal stem cells are regarded as the ultimate source for corneal epithelial cell proliferation and differentiation. This paper examines epithelial wound healing in rabbit corneas with partial limbal deficiency (PLD), which was created by the surgical removal of two-thirds of the limbal zone (superior and inferior). Four to eight months after PLD creation, all corneas appeared normal, without vascularization. The residual stem cell capacity then was challenged by two sizes of corneal epithelial debridement created with combined n-heptanol and mechanical scraping. In the first group, two consecutive 6-mm defects were created 1 month apart. After the first wounding, three of eight PLD corneas had delayed wound healing and two of the three had vascularization, as compared to controls (n = 7). After the second wounding, both controls (n = 7) and the remaining PLD (n = 5) corneas showed similar rapid healing. In the second group, a large defect of up to 1 mm within the limbus was created. Healing was completed in 25-40 days in PLD (n = 6) corneas, a more marked delay compared to the 10-12 days for controls (n = 6) (P = 0.001). In addition, all PLD corneas showed increased vascularization and had epithelium of the conjunctival phenotype, verified by the immunofluorescent staining positive to AM-3 monoclonal antibody but negative to AE-5 monoclonal antibody. Thus, a deficiency of limbal stem cells contributes to the triad of conjunctival epithelial ingrowth, corneal vascularization, and delayed healing with recurrent erosion. In PLD, corneal epithelium is still compromised, particularly when a large epithelial cell mass is removed.     

LASIK术后角膜的创伤愈合反应

准分子激光原位角膜磨镶术（LASIK）是目前应用最广,最具发展前途的角膜屈光手术.术后角膜愈合反应机制十分复杂,受到多种因素共同作用.术后角膜愈合反应是影响手术稳定性及预测性的重要原因之一.本文就LASIK术后角膜的愈合反应机制进行综述,并探讨皮质类固醇在LASIK术后角膜愈合反应中的可能作用.     

Corneal wound healing: II. The process

Corneal wound repair is a complex dynamic process in which cells, extracellular matrix, tears, and growth factors interact to bring about the restoration of the integrity of the tissues while maintaining clarity and hydration. This article reviews major recent findings that might affect innovations in therapeutic applications.     

Corneal wound healing: I. The players

With the advent of molecular biology and its precise sophisticated techniques, it has been possible to immunolabel and otherwise identify the presence and distribution of many of the compounds that participate in wound healing and to gain some understanding of their interaction. Many are currently being tested for their possible pharmacologic application. This article identifies the compounds and cellular activities that are part of wound healing in order to facilitate an understanding of this complex process in the cornea.     

Corneal wound healing relevance to wavefront guided laser treatments

Corneal wound healing makes important contributions to the outcomes of both traditional excimer laser ablation procedures and custom corneal ablations and contributes to the poor predictability of keratorefractive surgery in some patients. In addition, wound healing makes important contributions to some complications of PRK, LASEK or LASIK,including haze and diffuse lamellar keratitis. Detailed characterization of the wound healing cascade that occurs following refractive procedures is fundamental to pharmacological and molecular approaches for controlling or normalizing the response to surgery,thereby reducing biological diversity in variables such as epithelial hyperplasia and stromal remodeling that often tend to mask attempts at custom ablation.     

Corneal epithelial wound healing in the absence of limbal epithelium.

Corneal epithelial stem cells are thought to be at the limbus. The limbal epithelium was surgically removed in 12 New Zealand white rabbits. After 6 months, four showed mild vascularization. To challenge the remaining proliferative reserve, two consecutive 7.5-mm epithelial woundings were created 3 weeks apart in 11 limbal-deficient corneas and 11 controls. After the first wounding, five of the limbal-deficient corneas showed delayed healing, and seven became moderately vascularized; the controls healed normally. After the second wounding, eight experimental corneas showed intense vascularization; the controls did not. Recurrent erosions with delays in healing were noted in nine experimental animals but not in controls. Flat-mount preparation and impression cytology revealed centripetal migration of conjunctival epithelium with goblet cells onto the experimental corneas. These results indicate that only limited proliferative capacity of corneal epithelium remains in the absence of limbus. The constellation of delayed healing with recurrent erosion, corneal vascularization, and conjunctival epithelial ingrowth can be considered possible signs of limbal stem cell dysfunction.     

Corneal stromal wound healing: Major regulators and therapeutic targets

Corneal stromal wound healing is a complex event that occurs to restore the transparency of an injured cornea. It involves immediate apoptosis of keratocytes followed by their activation, proliferation, migration, and trans-differentiation to myofibroblasts. Myofibroblasts contract to close the wound and secrete extracellular matrix and proteinases to remodel it. Released proteinases may degenerate the basement membrane allowing an influx of cytokines from overlying epithelium. Immune cells infiltrate the wound to clear cellular debris and prevent infections. Gradually basement membrane regenerates, myofibroblasts and immune cells disappear, abnormal matrix is resorbed, and transparency of the cornea is restored. Often this cascade deregulates and corneal opacity results. Factors that prevent corneal opacity after an injury have always intrigued the researchers. They hold clinical relevance as they can guide the outcomes of corneal surgeries. Studies in the past have shed light on the role of various factors in stromal healing. TGFβ (transforming growth factor-beta) signaling is the central player guiding stromal responses. Other major regulators include myofibroblasts, basement membrane, collagen fibrils, small leucine-rich proteoglycans, biophysical cues, proteins derived from extracellular matrix, and membrane channels. The knowledge about their roles helped to develop novel therapies to prevent corneal opacity. This article reviews the role of major regulators that determine the outcome of stromal healing. It also discusses emerging therapies that modulate the role of these regulators to prevent stromal opacity.     

Epi-LASIK手术后角膜伤口愈合反应及相关机制

Epi-LASIK是目前最受关注的准分子激光角膜表层切削术.近年的研究发现,术后角膜愈合反应是在神经体液调节下,多种细胞及细胞因子相互影响、相互作用的复杂过程;是影响术后早期炎症刺激和远期疗效的关键因素.上皮瓣在愈合过程中的作用也是目前研究的热点.本文就Epi-LASIK术后角膜伤口愈合反应相关分子生物学机制及其愈合特点进行综述.