Concentration and molecular weight dependency of rabbit corneal epithelial wound healing on hyaluronan.

Hyaluronan (hyaluronic acid) is a high molecular weight viscoelastic polymer which has been postulated to enhance wound healing. We investigated the dose and molecular weight (9 x 10(4)-280 x 10(4) dependent effects of hyaluronan on the rate of migration of rabbit corneal epithelium in organ culture and on wound closure in vivo after debridement with n-heptanol. When corneal blocks were cultured with hyaluronan for 20 hours, distances of epithelial migration significantly increased over exposed stroma in proportion to hyaluronan concentration. However, there was no difference in the stimulatory action of hyaluronan on epithelial migration when corneal blocks were cultured at 1 mg/ml of hyaluronan irrespective of changes in the molecular weight range between 9 x 10(4) and 280 x 10(4). Glycosaminoglycans other than hyaluronan (chondroitin, chondroitin sulfate, keratan sulfate and heparan sulfate) failed to increase the epithelial migration. When hyaluronan eye drops were instilled after corneal epithelial removal with n-heptanol, hyaluronan stimulated wound closure in a dose-dependent manner, but its stimulatory efficacy was not dependent on molecular weight.     

Hyaluronan-induced stimulation of corneal wound healing is a pure pharmacological effect.

The aim of this study was to evaluate whether corneal reparative activity of hyaluronan is a concentration-dependent phenomenon. Corneal blocks from rabbit eyes were cultured for 20 hours with hyaluronan in different concentrations and molecular weight ranges. In another experiment, the corneal epithelium was denuded and hyaluronan was administered as eye drops. Distances of epithelial migration increased over exposed stroma proportionally to concentration, when hyaluronan was added with a molecular weight of 800-1,400 kD. Maximum effect was observed with 0.2% hyaluronan concentration. No difference was seen when corneal blocks were cultured with hyaluronan 0.2% in different molecular weight ranges (800-1,400, 1,400-2,000, and 2,000-2,600 kD). When hyaluronan (molecular weight, 800-1,400 kD) eye drops were administered after corneal epithelial denudation in rabbits, it was found to have faster wound reparation. This effect was concentration-dependent. The 2 highest concentrations (0.2% and 0.4%) were not different for the time needed to complete wound healing. In conclusion, hyaluronan-induced stimulation of corneal wound healing fulfills standards for being considered as a pharmacological effect.     

The contribution of blood flow by the anterior ciliary arteries to the anterior segment in the primate eye

The rate and mode of corneal wound healing in severely diabetic rats were studied by light microscopy and scanning electron microscopy. Diabetes mellitus was induced in 52 rats by alloxan injection, and 52 nondiabetic rats were used as controls. After 3 weeks, a nonpenetrating razor-blade wound was made in the central cornea of both eyes in 48 diabetic and 48 normal rats. The incision passed through the epithelium and into the stroma. The effects of diabetes on the unwounded cornea were observed by comparison with corneas from eight unwounded rats (four diabetic and four normal). Whole corneas from wounded diabetic and normal rats were studied at 0, 1, 3, 6, 12 and 24 hr and at 2–7 days after wounding. The rate and mode of healing were not found to differ between diabetics and normals. The surfaces of corneal wounds in both groups appeared to be completely healed and indistinguishable from the surrounding unwounded epithelium after 24 hr. The epithelial cells involved in the initial healing process were derived primarily from the layer of wing cells which progressed across the wound close to the connective-tissue base. Only in the final stages of healing, after the wound had been filled by the deeper epithelial cells, did superficial epithelial cells migrate. There appeared to be more exfoliating superficial epithelial cells over the entire cornea in diabetic rats than in normals. Because the healing of central corneal incisions occurs initially and primarily by sliding of the deeper epithelial cells, and because the diabetic condition appears to be associated with increased exfoliation of surface cells, the healing of central incisions may be less affected by diabetes than the healing of defects of the whole corneal surface, where the superficial epithelial cells have been reported to be the main migratory cells in the initial healing process and where healing in diabetics is delayed.     

Restoration of corneal epithelial barrier function and wound healing by substance P and IGF-1 in rats with capsaicin-induced neurotrophic keratopathy

PURPOSE: To investigate the effects of topical application of the combination of substance P (SP) and insulin-like growth factor (IGF)-1 on corneal epithelial barrier function and epithelial wound closure in rats with capsaicin-induced neurotrophic keratopathy. METHODS: Neonatal rats were injected subcutaneously with a single dose of capsaicin to induce neurotrophic keratopathy. Corneal epithelial barrier function was evaluated with an anterior fluorophotometer. Tear fluid secretion was measured by the Schirmer test. Corneal epithelial wound healing was determined by measurement of the size of the epithelial defect after debridement of the entire epithelium. The combination of SP (1 mM) and IGF-1 (1 micro g/mL) in phosphate-buffered saline was administered in eye drops six times daily. RESULTS: Corneal epithelial barrier function was impaired and corneal epithelial wound healing was delayed in rats injected with capsaicin. The application of eye drops containing the combination of SP and IGF-1 to capsaicin-injected rats resulted in a significant improvement in corneal epithelial barrier function compared with that apparent in capsaicin-injected animals that received eye drops containing vehicle alone. Such treatment with SP and IGF-1 also significantly increased the rate of corneal epithelial wound closure in capsaicin-injected animals. CONCLUSIONS: Topical application of the combination of SP and IGF-1 improved both corneal epithelial barrier function and epithelial wound healing in an animal model of neurotrophic keratopathy.     

Delayed wound closure and phenotypic changes in corneal epithelium of the spontaneously diabetic Goto-Kakizaki rat

PURPOSE: To characterize wound closure and phenotypic changes in the corneal epithelium of the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes. METHODS: Corneal wound healing was monitored by fluorescein staining after epithelial debridement. Tear secretion was measured with the Schirmer test, and corneal sensation was evaluated with an esthesiometer in 13- to 15-week-old GK and Wistar (control) rats. The distributions of cytokeratin 12 (K12), K14, and connexin43 in the corneal epithelium were examined by immunohistofluorescence analysis. The proliferation capacity of epithelial cells in the intact cornea and during wound healing was evaluated by immunostaining for Ki-67. RESULTS: Tear secretion, corneal sensation, and corneal epithelial wound closure rate were all decreased in GK rats compared with those in Wistar rats. Whereas connexin43, K14, and Ki-67 were all restricted to the single layer of basal cells in the corneal epithelium of Wistar rats, they were detected in the two layers of cells closest to the basement membrane in that of GK rats. The frequency of Ki-67-positive cells in the intact corneal epithelium was greater in GK rats than in Wistar rats, and it was increased to a greater extent in the peripheral cornea of GK rats than in that of Wistar rats during wound healing. CONCLUSIONS: Spontaneously diabetic GK rats manifest characteristics similar to those of diabetic keratopathy in humans, including delayed wound closure, and they exhibit phenotypic changes in corneal epithelial cells.     

Abnormal deposition of laminin and type IV collagen at corneal epithelial basement membrane during wound healing in diabetic rats

PURPOSE: To understand the pathophysiology of the corneal basement membrane in diabetes, we compared the localization of laminin and type IV collagen in the epithelial basement membrane during corneal epithelial wound healing in diabetic and nondiabetic rats. METHODS: Streptozotocin was used to induce diabetes in half the rats. Two weeks later, the whole corneal epithelium was debrided. Diabetic and healthy rats (3-5 per group) were sacrificed before debridement and 1, 3, and 7 days and 1 month afterwards. The localization of laminin and type IV collagen was observed in cryosections by epifluorescence microscopy. RESULTS: In unwounded corneas of both diabetic and normal rats, laminin and type IV collagen were localized in the corneal epithelial basement. The intensity of fluorescence, however, was clearly stronger in the diabetic rats. In normal rats, wounding initially removed laminin and type IV collagen, but during healing these two proteins reappeared beneath the resurfacing corneal epithelium. Although similar results were observed in diabetic rats, the expression of laminin and type IV collagen was delayed, and their deposition was fragmented and irregular. CONCLUSIONS: These results suggest that delayed corneal epithelial wound healing in diabetes might involve delayed reappearance and abnormal reformation of epithelial basement membrane proteins.     

Hyaluronan stimulates corneal epithelial migration.

Hyaluronan (hyaluronic acid), well-known for its viscoelastic properties, is also recognized as a biological signal to cells. Using organ cultures of the rabbit cornea, we investigated the effects of hyaluronan on the migration of corneal epithelium. The addition of hyaluronan to the culture medium increased the length of the path of the corneal epithelial layer in a dose-dependent fashion. Other glycosaminoglycans (chondroitin, chondroitin sulphate, keratan sulphate and heparan sulphate) were also tried, but only hyaluronan exhibited a stimulatory effect on corneal epithelial migration. The effects of hyaluronan and fibronectin or epidermal growth factor (EGF) were additive; the addition of antisera against fibronectin or against EGF did not alter the stimulatory effect of hyaluronan. These results demonstrate that hyaluronan stimulates corneal epithelial migration by mechanism(s) different from those of fibronectin and EGF.     

Impaired epithelial wound healing and EGFR signaling pathways in the corneas of diabetic rats

PURPOSE. The purpose of the study was to investigate the effects of hyperglycemia on EGFR (epidermal growth factor receptor)-mediated wound response and signal transduction in the corneal epithelium of rats with type I diabetes mellitus (DM). METHODS. Corneal epithelia were removed from streptozotocin (STZ)- and weight-matched normal rats. Wound healing was monitored by fluorescein staining at 24 or 48 hours after epithelial debridement. Phosphorylation of EGFR, AKT, ERK, and BAD was determined by Western blot analysis. The distribution of phospho-AKT and proliferating cell nuclear antigen (PCNA) in rat corneas was examined by immunohistochemistry. Cell death was evaluated by TUNEL staining. RESULTS. A significant delay in corneal epithelial wound healing was observed 48 hours after wounding in the diabetic rats compared with the weight-matched control rats. In the DM rat corneas, epithelial cells demonstrated diminished responses to wounding, as assessed by the phosphorylation of EGFR and its downstream signaling molecules, AKT and ERK. Furthermore, although the distribution pattern of phospho-AKT suggested a role for AKT in epithelial migration and proliferation in the normoglycemic rat corneas, it was abrogated in the healing epithelia of the DM rats. Consistent with impaired AKT activity, the number of PCNA-stained cells was also greatly reduced in the healing corneas of the diabetic rats. Finally, decreases in pBAD (Ser(136) and Ser(112)) and increases in TUNEL-positive cells were observed in both the uninjured and healing corneal epithelia of the DM rats, but not of the control rats. CONCLUSIONS. In the corneas of SZT rats, EGFR-PI3K-AKT and ERK, as well as their downstream BAD signaling pathways in migratory epithelium, were altered, resulting in increased apoptosis, decreased cell proliferation, and delayed wound closure.     

Application of homologous fibronectin to persistent human corneal epithelial defects

Six eyes with persistent corneal epithelial defects of various etiologies were treated in a randomized, prospective, double-masked study to evaluate the effect of fibronectin on corneal epithelial wound healing. Study eyes received homologous human fibronectin (300 micrograms/ml), mixed with gentamicin and artificial tears, 4 times a day. Control eyes received the mixture of gentamicin and artificial tears. If no healing occurred after 2 weeks, the drug was unmasked and where control drops had been given, the mixture containing fibronectin was administered in open-label fashion. All 4 eyes in diabetic patients had successful epithelial healing when treated with the fibronectin solution. The 2 remaining corneas, which had defects secondary to a thermal injury and a presumed infectious etiology, did not heal with fibronectin.     

Effects of substance P and IGF-1 in corneal epithelial barrier function and wound healing in a rat model of neurotrophic keratopathy

PURPOSE: To establish a rat model of neurotrophic keratopathy and to examine the effects of the combination of substance P (SP) and insulin-like growth factor (IGF)-1 on corneal epithelial barrier function and wound healing in this model. METHODS: Corneal denervation was achieved by thermocoagulation of the ophthalmic branch of the trigeminal nerve. A modified Schirmer test was performed without topical anesthesia. Corneal epithelial barrier function was assessed by measurement of fluorescein permeability with an anterior fluorophotometer. Epithelial wound healing was evaluated by measurement of the area of the defect at various times after removal of the entire epithelium. Eye drops containing both 1 mM SP and IGF-1 (1 micro g/mL) were administered six times daily. RESULTS: The Schirmer test result in eyes subjected to trigeminal denervation was lower than that in control eyes. The fluorescein permeability of the corneal epithelium of denervated eyes was increased relative to that of control eyes. Furthermore, trigeminal denervation induced a delay in corneal epithelial wound healing. Application of eye drops containing SP and IGF-1 to denervated corneas restored the fluorescein permeability of the corneal epithelium to control levels and abolished the delay in epithelial wound healing. CONCLUSIONS: A rat model of neurotrophic keratopathy, characterized by reduced tear secretion, loss of corneal sensation, impaired epithelial barrier function, and delayed epithelial wound healing, was established by trigeminal denervation. Treatment with both SP and IGF-1 improved corneal epithelial barrier function and stimulated corneal epithelial wound healing in this model.     

Wound healing following anterior keratectomy and lamellar keratoplasty in the pig

PURPOSE: To examine corneal wound healing in an animal model of two types of mechanical lamellar keratectomy. METHODS: One eye from each of 28 pigs was studied. Using a motorized keratome, corneas were subjected to an anterior lamellar keratectomy with removal of anterior stroma and epithelium, or to automated lamellar keratoplasty (ALK) with reapposition of a corneal flap. The exposed stromal surfaces were labeled intraoperatively with a fluorescent dye (DTAF) to assess deposition of stromal components during subsequent wound healing. Examination before surgery and enucleation included measurement of corneal curvature and intraocular pressure, and assessment of corneal haze. Eyes were prepared for histological examination, fluorescence microscopy, and for fibronectin immunohistochemistry. RESULTS: Both keratectomy procedures produced flattening of corneas by up to 3.80 diopters, 28 days after surgery. Corneal haze was more pronounced in eyes from which epithelium was removed (anterior lamellar keratectomy group). The increased haze in this group was associated histologically with appearance of many reactive keratocytes and inflammatory cells, deposition of new stromal material, and more widespread appearance of fibronectin immunoreactivity. In the lamellar keratoplasty group, only the edges of the corneal wound showed significant reactivity, and included keratocyte activation and epithelial ingrowth. CONCLUSIONS: The pig provides a useful model for studies of refractive surgical techniques using procedures and instruments designed for use in humans. Mechanized keratectomy procedures that minimize disruption of the epithelium and Bowman's layer produce a less reactive corneal wound than procedures in which an expanse of epithelium and anterior stroma are removed.     

Biosynthetic responses of the rabbit cornea to a keratectomy wound

Following a corneal wound involving removal of the epithelium and basement membrane, the epithelium must migrate across bare stroma. To examine the effect of the removal of the basement membrane on epithelial migration and on protein and glycoprotein synthesis in both the epithelium and stroma, we performed superficial keratectomies on rabbits and allowed the corneas to heal in organ culture. We then analyzed the following parameters: (1) rate of epithelial wound closure; (2) proteins synthesized during epithelial wound closure in both the epithelium and stroma using SDS-PAGE; and (3) presence of fibronectin in the epithelium and stroma using immunodot blots and immunofluorescence. We found that: (1) a 7 mm keratectomy wound heals in 66 hr with a maximal rate of epithelial migration of 0.83 mm2/hr; (2) four proteins, 400+K, 220K, 70K, and 58K, are present in the epithelium migrating to close the wound that are not seen in the control epithelium; (3) a 220K band is seen in the wounded stroma but not in control stroma; and (4) fibronectin represents 2% of the total protein in the stroma 66 hr post-keratectomy but less than 0.02% in wounded epithelium, unwounded epithelium, and unwounded stroma.     

Distribution of fibronectin in human and rabbit corneas

In order to study the possible role of fibronectin (FN) in corneal wound healing and the relationship between FN and sensory innervation, FN was demonstrated immunohistochemically in both normal and sensorily denervated rabbit corneas and in normal or tissue-cultured human corneas. The distribution of FN was the same in the groups examined: a thin subepithelial band of FN-like immunoreactivity was seen at the level of epithelial basement membrane and at the stromal side of Descemet's membrane. Epithelial abrasions were also performed in both normal and denervated rabbit corneas. The results were compared with those obtained from organ-cultured human corneas. Following abrasion of the corneal epithelium, FN was detected in the anterior margin of the denuded stroma 18 hr after the operation in the areas where the epithelium had not healed, but not 49 hr after. Sensory denervation did not affect the distribution of FN in normal, denervated or healing rabbit cornea. It is concluded that FN is probably not controlled by sensory innervation.     

The effect of chronic corneal epithelial debridement on epithelial and stromal morphology in dogs

PURPOSE: To determine the effect of chronic corneal epithelial debridement on epithelial and stromal morphology and extracellular matrix components, and to compare those changes to those in spontaneous chronic corneal epithelial defects (SCCED) in dogs. METHODS: Axial corneal epithelial wounds, 10 mm in diameter, were created weekly for 8 weeks in five normal adult laboratory beagles. Slit lamp biomicroscopy and corneal pachymetry were performed weekly before wounding. Three days after the last debridement the dogs were killed humanely, and corneas were processed for light and electron microscopy and immunohistochemistry for collagen IV, collagen VII, fibronectin, and laminin. RESULTS: No significant changes in corneal thickness were found. All samples demonstrated epithelial dysmaturation adjacent to the wound edge, and, in four of five, a narrow zone of nonadherent epithelium formed adjacent to the exposed stroma. All samples had a stromal acellular zone in the area of the defect and continuing for a short distance under the adjacent attached epithelium. Experimentally wounded dogs did not form the superficial hyaline acellular lamina found in 92% of dogs with SCCED. Laminin, collagen IV, and fibronectin were present on the stromal surface in all samples, and collagen VII was present in four of five samples. Transmission electron microscopy (TEM) demonstrated the presence of basement membrane on the surface of the exposed stroma. CONCLUSIONS: Epithelial changes are similar between experimentally wounded dogs and dogs with SCCED. The stromal acellular zone that forms in experimentally wounded dogs is distinct from the hyaline lamina observed in dogs with SCCED. The difference in the acellular stromal layers between chronically wounded dogs and dogs with SCCED may be of relevance to our understanding of the pathophysiology of persistent epithelial defects.     

The Therapeutic Roles of Recombinant Hsp90α on Cornea Epithelial Injury

PurposeThe purpose of this study was to explore the therapeutic role of heat shock protein 90 (Hsp90) in wound healing of injury cornea epithelium.MethodsThe right eye of C57BL/6N male mice were performed the debridement wounds in the center of the cornea using an algerbrush II blade. The injured area was determined by staining the cornea with fluorescein sodium and measured with image-J. Immunoblotting, ELISA and immunochemistry were used for determining protein expression. The quantitation PCR was performed to measure mRNA expression.ResultsHsp90α is upregulated at both the mRNA and protein levels, and is secreted extracellularly into the corneal stroma and tear film during the healing process after corneal injury in mice. This upregulation is associated with activation of HSF1. Administration of recombinant exogenous Hsp90α (eHsp90α) speeds up wound healing of injured corneal epithelium. The eHsp90α binds to low-density lipoprotein (LDL)-related protein-1 (LRP-1) on the corneal epithelial cells and increases phosphorylation of AKT at S473, which is associated with proliferation and migration corneal epithelial cells in vitro or vivo. Inhibition of AKT by its inhibitor LY294002 abolishes eHsp90α-induced migration and proliferation of corneal epithelial cells.ConclusionsHsp90α is upregulated and secreted after corneal injury and acts to promote the healing process. Recombinant Hsp90α may be a promising therapeutic drug candidate for corneal injury.     

Opioid growth factor modulation of corneal epithelium: uppers and downers

PURPOSE: This paper presents a concise review of the role of the intrinsic opioid growth regulation system (IOGRS) in homeostasis and wound repair of the corneal epithelium. METHODS: The article is a summary of published research on the topic. RESULTS: The native opioid peptide, [Met(5)]-enkephalin, also termed opioid growth factor (OGF), has been demonstrated to be present in a wide variety of classes of the phylum. Chordata, and acts as an autocrine/paracrine produced, tonically active, receptor specific, negative growth modulating factor in homeostatic (uninjured) corneal epithelium in humans and non-primates. Similarly, OGF acts to down-regulate epithelial cell division and migration of corneal epithelium in the closing of corneal epithelial abrasions. Such repair can be up-regulated (hastened) in non-diabetic animals by treatment with exogenous administration of the potent opioid antagonist, naltrexone (NTX). The system also is functional in diabetic animals and can be manipulated to restore epithelial wound healing rates to normal. CONCLUSIONS: The IOGRS plays a vital role in supporting corneal epithelial homeostasis, and in modulating closure of epithelial wounds. The system should provide opportunities for novel therapies especially for corneal epithelial wound healing disorders.     

Promotion of corneal epithelial wound healing in vitro and in vivo by annexin A5

PURPOSE: To investigate the effect of annexin A5, a calcium-dependent phospholipid-binding protein, on corneal epithelial wound healing. METHODS: The effect of annexin A5 on migration of rabbit corneal epithelial (RCE) cells in vitro was examined in scrape-wounded cell monolayers. The effect of annexin A5 on the release of urokinase-type plasminogen activator (uPA) from cultured RCE cells was determined by zymography, fluorogenic assay of PA activity, and enzyme-linked immunosorbent assay. The proliferation of RCE cells was assessed by measurement of [3H]thymidine incorporation. The effect of annexin A5 on corneal wound closure in rabbits was investigated after removal of the corneal epithelium, either by exposure to iodine vapor or surgically. Eye drops containing annexin A5 were instilled into one eye and vehicle into the other. The area of the epithelial defect was measured at various times after wounding, and the healing rate was calculated by linear regression analysis. RESULTS: Annexin A5 significantly promoted the migration of RCE cells in a wounded monolayer. However, annexin A5 had no effect on RCE cell proliferation. Annexin A5 also increased the release of uPA both from wounded RCE cell monolayers and from nonwounded semiconfluent RCE cells. In both models of corneal wound closure, the healing rate was significantly increased by instillation of eye drops containing annexin A5 compared with that apparent in the eyes that received vehicle. CONCLUSIONS: Annexin A5 promoted corneal epithelial wound healing both in vitro and in vivo. Upregulation of uPA release from corneal epithelial cells may contribute to this effect of annexin A5.     

Corneal complications in streptozocin-induced type I diabetic rats

PURPOSE. This study seeks to characterize corneal functions and complications in a streptozocin (STZ)-induced rat model of type I diabetes mellitus (DM) and to understand the pathogenesis of diabetic keratopathy. METHODS. DM was induced via STZ injection in Sprague-Dawley rats. Body weight, length, and corneal size were measured and compared with the age-matched normal controls. Corneal morphology and histology were evaluated with slit lamp, digital confocal microscopy and hematoxylin and eosin staining. Tear secretion was measured with cotton threads, and corneal sensitivity was determined with an esthesiometer. Protein expression and distribution were assessed with Western blotting and immunohistochemistry. Wound healing was determined using an in vivo corneal epithelial debridement model. RESULTS. Compared with the normal control rats, STZ rats had reduced body weight, and body length, but minimally affected corneal size. No significant changes in ocular surface regularity, corneal thickness, and morphology were noted in diabetic corneas. STZ rats showed stronger Rose Bengal staining, decreased tear secretion, slightly attenuated sensitivity, less innervation, delayed epithelial wound healing, and impaired epidermal growth factor receptor signaling in their corneas. While the expression of adherens junction protein β-catenin, and tight junction proteins occludin and ZO-1 was unchanged, the formation of these junctions after wound closure was delayed. CONCLUSIONS. Pathogenesis of diabetic keratopathy involves multiple tissues and/or cell types and several events including reduced tear secretion, impaired innervation, weakened cell junction, and altered wound responses. These insights may prove useful for the clinical translation of evolving strategies for the management and treatment of diabetic corneal complications.     

Gross factors in treatment of nonhealing corneal ulcers and recurrent erosions

Epidermal growth factor (EGF) is known to promote corneal epithelial wound healing in experimental scrape and keratectomy models. We studied its efficacy in treating alkali-burned epithelial ulceration. EGF induced hyperplasia and cell proliferation to resurface the denuded and denatured corneal stroma, but it did not prevent recurrent erosions. A combination of EGF with fibronectin (Fn) was noted to enhance epithelial defect closure after alkali burns of the cornea and was seen to prevent recurrent erosions. Histopathologic examination of these corneas revealed marked leukocytic infiltration of the alkali-burned corneal stroma. To find ways to retard this inflammatory response, we studied the role of topical steroids and their efficacy when used with EGF, Fn, and laminin (Ln) in the management of alkali-burned corneas. Use of steroids decreased the incidence of recurrent erosions and corneal perforations. Histologically, steroids markedly decreased the leukocytic infiltration of stromal tissue, thereby retarding the collagenolysis. Topical steroids used with EGF and fibronectin were seen to promote epithelial wound closure and to prevent recurrent erosions in alkali-burned corneas. Combinations of EGF, fibronectin, and steroids may have a place in the treatment of clinical corneal alkali burns.