The Corneal Basement Membranes and Stromal Fibrosis

Drug-free hyaluronic acid-microneedle with unexpected inhibition activity on benzalkonium chloride-induced corneal inflammation and stromal scarring

Topical instilling of commercial artificial tears (cAT, containing 0.1 % hyaluronic acid) is widely employed to alleviate clinical manifestations of mild dry eye disease (DED) by preventing the pathological change of corneal epithelium. However, it showed limited therapy effectiveness on heavy DED which has further involved corneal stroma, due to its low stroma-available for hyaluronic acid (HA) resulting from the barrier of corneal epithelium. The present study developed a new microneedle-dosage form of cAT (cAT-MN). This cAT-MN can overstride the corneal epithelium and act as a long-lasting protective agent. Compared to cAT dosing (4 times/day), cAT-MN with one treatment exerted significantly higher therapeutic effects on curbing benzalkonium chloride (BAC)-induced corneal stroma scaring as well as alleviating the DED symptoms in the first 5-day BAC exposure; whereas, showed limited effects in a 10-day BAC exposure. To expand the therapy effects, MNs containing various amounts of HA were prepared. Thereinto, HA(6 %)-MN recovered corneal damage to healthy levels, which could be attributed to adding stroma-available for HA both by increasing the amounts of HA-delivery and enhancing HA-permeation. This study explores a new drug-free microneedle-dosage form of cAT to cure corneal stroma disorders which has expanded its indication, promising a wide clinical use in ophthalmology.

Long-term alterations of collagen reconstruction and basement membrane regeneration after corneal full-thickness penetrating injury in rabbits

PURPOSE

To investigate the long-term alterations of collagen reconstruction and basement membrane (BM) regeneration after corneal full-thickness penetrating injury in rabbits.

METHODS

The corneal full-thickness penetrating injury model was established in the left eye of New Zealand White rabbits using a 2.0 mm trephine. All corneas were evaluated using slit-lamp photography, hematoxylin and eosin staining, immunofluorescent staining for collagen types I and III (Col I, III), and transmission electron microscopy for collagen fibers and basement membrane.

RESULTS

Between 3 days and 3 weeks, Col I and III expression were documented, exhibiting a largely disorganized distribution throughout the stromal thickness. At 3 weeks, the epithelial basement membrane (EBM) partially regenerated. From 3 weeks to 2 months, Col III was undetectable in the anterior stroma but present in the posterior stroma; Col I was disorganized in the posterior stroma. At 2 months, Descemet's membrane (DM) exhibited incomplete regeneration. From 3 to 4 months, Col I was disorganized in only a small part of the posterior stroma; Col III persisted in the posterior stroma; the EBM fully regenerated while DM exhibited incomplete regeneration.

CONCLUSIONS

Following full-thickness corneal injury, persistent fibrosis within the posterior stroma appears to be primarily responsible for the persistence of corneal scarring. Notably, regeneration of the EBM coincides with remodeling of the anterior stroma, whereas incomplete regeneration of DM is associated with posterior stromal fibrosis.

Changes in posterior corneal elevation and associated factors following small incision lenticule extraction in patients with high myopia and thin cornea: a prospective randomized clinical study

To investigate the safety and efficacy of SMILE in patients with high myopia and analyzed the factors influencing corneal posterior elevation variation (PCE). This was a prospective, comparative, randomized, clinical study. Patients with a corneal thickness < 530 μm at the thinnest point of the right eye with a spherical equivalent (SE) ≤-3.00D (group A: ≤-3.00D, >-6.00D; group B: ≤-6.00D, >-10.00D) who underwent SMILE surgery between January 1, 2020, and May 31, 2021 were randomly selected. We compared the difference in postoperative vertex PCE between the two groups and assessed the correlation between PCE variation (△PCE) and corneal biomechanical parameters. The preoperative SE was - 4.74 ± 0.63D and - 7.38 ± 1.22D in groups A (41 eyes) and B (37 eyes), respectively. PCE was 0.61 ± 2.07 and 0.16 ± 2.19 μm, and △PCE was - 0.93 ± 1.13 and - 1.43 ± 1.07 μm in groups A and B, respectively, showing significant differences (P < 0.05). △A2L and △A2V (r=-0.41, -0.36; P = 0.02, 0.04) were correlated with △PCE. Stepwise regression analysis showed that △A2L was the predictor variable of △PCE (AIC = 0.8, P = 0.02). SMILE surgery is safe and effective for correcting high myopia with a thin cornea. A2L may affect the variation of vertex PCE following SMILE surgery. The higher reduction in A2L indicates less PCE backward displacement.

Trauma-induced corneal epithelial defects may lead to persistent epithelial defects exacerbated by prolonged use of bandage lenses

ObjectiveTo investigate the causes of corneal epithelial defects (CEDs) due to mechanical trauma and analyze the risk factors for progression to persistent epithelial defects (PEDs).MethodA retrospective analyze 241 patients (241 eyes) with CEDs caused by mechanical ocular trauma. All patients received initial treatment as outpatients at our hospital. Data collected included patients' basic information, injury causes, use of adjunctive treatments, improvement in symptoms and adverse reactions before and after treatment. Logistic regression analysis was used to explore the relationship between the causes of injury, the use of adjunctive treatments, and the occurrence of persistent corneal epithelial defects.ResultsThe study involved 241 patients: 164 males (68.1%) and 77 females (31.9%), averaging 38.06 ± 17.88 years old. The most common age groups were 31-40 years (24.1%), 41-50 years (19.9%), and 51-60 years (18.2%). The top five causes of injury were finger pokes (20.4%), impacts from plastic objects (14.6%), branch strikes (13.3%), paper cuts (8.8%), and metal scratches (8.3%). 164 patients used recombinant human growth factor (rhEGF) eye drops with an average healing time of 3.2 ± 1.3 days, while 77 did not use these drops, averaging 7.4 ± 2.2 days. Continuous use of bandage lenses was a risk factor for persistent epithelial defects (P < 0.001).ConclusionTreatment of CEDs caused by mechanical trauma should focus on managing ocular surface inflammation. The use of rhEGF eye drops can be an effective supplement treatment for CEDs. However, caution is needed regarding the use of bandage lenses.

Tissue engineered corneal endothelium transplantation in an ex vivo human cornea organ culture model

Transplantation of corneal tissue is the standard treatment for irreversible corneal endothelium decompensation by replacing the malfunctioning corneal endothelial cells and Descemet's membrane. However, this surgery depends on limited donor tissue supply. Thus, developing suitable alternatives for donor grafting material through a tissue engineering approach is needed to enable the transplantation of cultured endothelial cells to restore normal endothelial function. Here, we proposed using a plastic compressed collagen 3D matrix called Real Architecture For 3D Tissues (RAFT) as a scaffold for cell culture. The porcine cornea endothelial cells (PCECs) were seeded on RAFT to construct a tissue-engineered corneal endothelium. Then, the porcine cell-seeded-RAFT graft was transplanted onto a human cornea and maintained in an ex vivo organ culture model. The results showed that PCECs formed a high-density monolayer on RAFT expressing endothelial cell markers, ZO-1, Na/K ATPase and N-cadherin. More importantly, the cell-seeded RAFT transplantation successfully restored corneal endothelium function, drawing the thickness of endothelium-wounded cornea back to normal in two weeks of the ex vivo human cornea organ culture.

Lamellar keratoplasty using acellular porcine corneal stroma for the treatment of corneal ulcers

Objective

The study aimed to investigate the efficacy and safety of acellular porcine corneal stroma (APCS) for lamellar keratoplasty in the treatment of corneal ulcers.

Methods

A total of 14 patients (14 eyes) diagnosed with corneal ulcers who underwent lamellar keratoplasty using acellular porcine corneal stroma at the Second Affiliated Hospital of Nanchang University between June 2016 and May 2017 were recruited and followed up for at least 12 months. Postoperative visual acuity, epithelial recovery, graft transparency, the recurrence rate of corneal ulcers, the rate of graft rejection, corneal neovascularization, graft infection, secondary glaucoma, and graft melting were examined and analyzed.

Results

All 14 patients (100%) who underwent lamellar keratoplasty using acellular porcine corneal stroma successfully preserved the structure of their eyeballs. The visual acuity improved in 11 patients (78.5%). Graft rejection occurred in one patient (7.1%), while two patients (14.3%) developed recurrent corneal ulcers. Corneal vessel ingrowth was observed in seven patients (50%), and one patient (7.1%) developed pseudopterygium. The average time for complete epithelial recovery was 3-7 days.

Conclusion

Lamellar keratoplasty using acellular porcine corneal stroma is an effective surgical alternative for the treatment of corneal ulcers.

Establishment of an Ex Vivo Human Corneal Endothelium Wound Model

Purpose

A human model able to simulate the manifestation of corneal endothelium decompensation could be advantageous for wound healing and future cell therapy assessment. The study aimed to establish an ex vivo human cornea endothelium wound model where endothelium function can be evaluated by measuring corneal thickness changes.

Methods

The human cornea was maintained in an artificial anterior chamber, with a continuous culture medium infusion system designed to sustain corneal endothelium and epithelium simultaneously. The corneal thickness was used to assess corneal endothelial cell function. Immunostaining was used to evaluate cell viability and endothelial cell marker expression, ZO-1 and Na/K ATPase.

Results

Human corneas with intact corneal endothelium were maintained in the ex vivo model for 28 days, showing normal corneal thickness with a clear and transparent appearance. Corneal endothelial cells were alive and expressed ZO-1 and Na/K ATPase at the end of the organ culture. The endothelium wounded corneas showed persistent corneal edema with an increase in corneal thickness at 654.6 ± 31.7 µm. Staining results showed that no cells migrated to cover the wound and no expression of ZO-1 and Na/K ATPase on the posterior surface of the cornea was found.

Conclusions

This study provided a novel method to establish an ex vivo human cornea organ culture model, where corneal endothelium function can be evaluated by accessing the corneal thickness.

Translational Relevance

The ex vivo model established in this study can provide an alternative to the animal model in studying corneal endothelium decompensation.

Role of epigenetics in corneal health and disease

Epigenetics plays a vital role in corneal health and diseases. Epigenetic changes regulate the expression of genes by altering the accessibility of chromatin via histone modifications, DNA methylation and miRNAs without altering DNA sequence. Ocular trauma and infections are common causes of corneal damage, vision impairment, and mono/bilateral blindness worldwide. Mounting literature shows that epigenetic modifications can modulate corneal clarity, function, and pathogenesis including inflammation, wound healing, fibrosis, and neovascularization. Additionally, epigenetic modifications can be targeted to reverse corneal pathologies and develop interventional therapies. However, current understanding on how epigenetic modifications lead to corneal abnormalities and diseases is limited. This review provides in-depth knowledge and mechanistic understanding of epigenetics alterations in corneal pathogenesis, and information on potential epigenetic targets for treatment of corneal diseases.

Biologically inspired bioactive hydrogels for scarless corneal repair

Corneal injury-induced fibrosis occurs because of corneal epithelial basement membrane (EBM) injury and defective regeneration. Corneal fibrosis inhibition and transparency restoration depend on reestablished EBM, where the collagen network provides structural stability and heparan sulfate binds corneal epithelium-derived cytokines to regulate homeostasis. Inspired by this, bioactive hydrogels (Hep@Gel) composed of collagen-derived gelatins and highly anionic heparin were constructed for scarless corneal repair. Hep@Gel resembled the barrier function of the EBM regarding surface-confined binding, long-time sequestration, and progressive degradation of IL-1, TGF-β, and PDGF-BB, which robustly inhibited the apoptosis and myofibroblast transition of keratocytes. Animal models of rabbits and nonhuman primates confirmed that Hep@Gel effectively limited the influx of inflammatory and fibrotic cytokines from the epithelium into the stroma to down-regulate the wound healing cascade, contributing to better vision quality with 73% reduced fibrosis. Hep@Gel offers a solution for preventing corneal injury-induced scarring and substituting for lamellar keratoplasty to remove scarring.

Characterization of the Ocular Phenotype in a Col4a3 Knockout Mouse Model of Alport Syndrome

Purpose

Alport syndrome (AS) is a genetic condition caused by a dysfunctional collagen (IV) α3α4α5 heterotrimer, leading to basement membrane instability and, ultimately, abnormalities in the kidney, inner ear, and eyes. This study aimed to characterize ocular pathology of AS by focusing on inflammatory and fibrotic markers.

Methods

Col4a3tm1Dec knockout (KO) mice eyes were evaluated for the localization of collagen (IV) α3 and collagen (IV) α4, then stained for transforming growth factor-β1 (TGF-β1), TGF-β2, connective tissue growth factor (CTGF), and β-catenin. mRNA levels of the profibrotic genes S100a4, Acta2, Col1a1, Snai1, Snai2, and Twist1 were assessed using real-time reverse transcription quantitative PCR (RT-qPCR).

Results

Collagen (IV) α3 and collagen (IV) α4 were co-expressed in Descemet's and Bruch's membrane but not in the retina, lens, or other corneal substructures. Immunofluorescence quantitation revealed upregulation of TGF-β1 in the anterior lens and TGF-β2 in the retina of KO eyes. Conversely, CTGF and β-catenin were shown to be elevated in the corneal epithelium but not the retina or lens. RT-qPCR showed an increase in the transcription of Acta2, Col1a1, and Snai2 in the retinas and Snai2 in anterior segments of KO mice.

Conclusions

Col4a3 KO mice exhibited a differential inflammatory and profibrotic response in the cornea, retina, and lens, which may play a role in the ocular pathology of AS.

TGF-β1-mediated upregulation of LMCD1 drives corneal myofibroblast differentiation and corneal fibrosis

Transforming growth factor β1 (TGF-β1) drives corneal fibroblasts to differentiate into corneal myofibroblasts and plays a key role in corneal fibrosis. However, the role of LIM and cysteine-rich domains-1 (LMCD1) in TGF-β1-induced corneal myofibroblast differentiation and corneal fibrosis remains elusive. Thus, this study aimed to investigate the expression, regulatory mechanism, and role of LMCD1 in TGF-β1-induced corneal myofibroblast differentiation and corneal fibrosis. The expression of LMCD1 in TGF-β1-stimulated corneal fibroblasts was found to be upregulated through mRNA sequencing, quantitative PCR (qPCR), and Western blotting. Moreover, LMCD1 was identified to be upregulated in a mouse model of corneal fibrosis via qPCR and Western blotting. Additionally, our results demonstrated that the increase in LMCD1 expression induced by TGF-β1 in corneal fibroblasts was primarily regulated by the SMAD3 signaling pathway. Furthermore, LMCD1 knockdown significantly inhibited TGF-β1-induced corneal fibroblast-to-myofibroblast differentiation and simultaneously activated SMAD3, JNK, and p38 by promoting TGF-β1 transcription. These findings collectively suggest that LMCD1 could upregulate alpha-smooth muscle actin (α-SMA) expression and downregulate TGF-β1 expression in corneal myofibroblast differentiation. Consequently, upregulation of LMCD1 expression could potentially serve as a strategy to mediate the TGF-β1 signaling pathway in corneal myofibroblast differentiation and corneal fibrosis, laying a theoretical reference for corneal fibrosis and contributing to the development of effective therapeutic strategies for corneal fibrosis.

Restoration of corneal epithelial barrier function: A possible target for corneal neovascularization

Corneal neovascularization (CoNV) is the second leading common cause of vision impairment worldwide and is a blinding pathological alteration brought on by ocular trauma, infection, and other factors. There are some limitations in the treatment of CoNV, hence it's critical to look into novel therapeutic targets. The corneal epithelial barrier, which is the initial barrier of the ocular surface, is an important structure that shields the eye from changes in the internal environment or invasion by the external environment. This study sought to collate evidence on the regulation of corneal epithelial barrier injury on the activation of vascular endothelial cells (VECs), basement membrane (BM) degradation, differentiation, migration, and proliferation of VECs, vascular maturation and stability, and other key processes in CoNV, so as to provide a novel concept for CoNV therapy targeting corneal epithelial barrier repair.

A supramolecular hydrogel eye-drop alleviates inflammation via clathrin-mediated endocytosis

The modulation of inflammation is effective to treat many ocular surface diseases. Thus the low bioavailability of common anti-inflammatory eye-drops urges the development of ocular drug delivery systems to extend the ocular retention and enhance the cellular uptake for improving anti-inflammatory effect of eye-drops. Here we covalently conjugate two molecules of clinically anti-inflammatory drug (i.e., dexamethasone) with a small peptide (i.e., Tyr-Glu-Asn-Pro-Thr-Tyr) to generate an anti-inflammatory hydrogel eye-drop. With a self-assembled ability, the designed supramolecular hydrogel achieves gel-sol-gel transition by varying shearing forces which increases the pre-corneal retention of drug. The fluorescent imaging reveals the efficient cellular uptake of designed conjugate via clathrin-mediated endocytosis. A rodent model of endotoxin-induced uveitis verifies that the supramolecular hydrogel eye-drop suppresses inflammation responses without ocular irritation. As a rational approach to design anti-inflammatory drugs as eye-drops, this work overcomes the frequent instillation of clinical eye-drops and further improves the bioavailability of anti-inflammatory drugs, which may provide an effective and household way to fight ocular surface inflammation.

In vitro and ex vivo models of microbial keratitis: Present and future

Microbial keratitis (MK) is an infection of the cornea, caused by bacteria, fungi, parasites, or viruses. MK leads to significant morbidity, being the fifth leading cause of blindness worldwide. There is an urgent requirement to better understand pathogenesis in order to develop novel diagnostic and therapeutic approaches to improve patient outcomes. Many in vitro, ex vivo and in vivo MK models have been developed and implemented to meet this aim. Here, we present current in vitro and ex vivo MK model systems, examining their varied design, outputs, reporting standards, and strengths and limitations. Major limitations include their relative simplicity and the perceived inability to study the immune response in these MK models, an aspect widely accepted to play a significant role in MK pathogenesis. Consequently, there remains a dependence on in vivo models to study this aspect of MK. However, looking to the future, we draw from the broader field of corneal disease modelling, which utilises, for example, three-dimensional co-culture models and dynamic environments observed in bioreactors and organ-on-a-chip scenarios. These remain unexplored in MK research, but incorporation of these approaches will offer further advances in the field of MK corneal modelling, in particular with the focus of incorporation of immune components which we anticipate will better recapitulate pathogenesis and yield novel findings, therefore contributing to the enhancement of MK outcomes.

Influence of Opacity Depth on Big Bubble Formation During Deep Anterior Lamellar Keratoplasty in Corneal Stromal Scars

PURPOSE

To identify the key preoperative predictors of big bubble (BB) formation during deep anterior lamellar keratoplasty in patients with corneal stromal scars (CSS).

METHODS

This retrospective cohort study included consecutive patients with CSS after infective keratitis who underwent BB-deep anterior lamellar keratoplasty between January 2021 and July 2023 at a tertiary referral center. Topographic and tomographic data were collected to compare the rates and types of BB formations. Anterior segment optical coherence tomography (AS-OCT) was employed to assess the maximum depth of opacity by dividing the stroma into 3 zones of equal thickness: anterior (stage A), mid (stage B), and posterior stroma (stage C). Multivariate logistic regression analysis was performed to identify the potential preoperative predictors of bubble formation.

RESULTS

Pneumatic dissection was achieved in 13 of 33 eyes (39.4%), with 11 BB type 1 eyes (33.3%) and 2 BB type 2 eyes (6.1%). According to AS-OCT grading, bubble formation was more frequent with CSS involving more superficial stromal layers ( P <0.032). In the eyes with stage C, bubble formation failed 12 out of 14 times (85.7%, P <0.026). Spearman correlation showed that bubble formation was inversely associated with the AS-OCT grading (rho = -0.443, P = 0.001). After logistic regression analysis, AS-OCT grading was found to be the sole factor that predicted bubble formation (coeff. -1.58, confidence interval 95% -3.03 to -0.12, P = 0.034).

CONCLUSIONS

Depth of opacity in CSS was the key determinant for predicting the success of pneumatic dissection, as advanced AS-OCT stages are strongly associated with BB failure.

Impacts and Correlations on Corneal Biomechanics, Corneal Optical Density and Intraocular Pressure after Cataract Surgery

The study aimed to investigate the extended effects and interrelations of corneal biomechanics, corneal optical density (COD), corneal thickness (CT), and intraocular pressure (IOP) following cataract surgery. Sixteen eyes were analyzed prospectively. The Corneal Visualization Scheimpflug Technology (Corvis ST) device assessed corneal biomechanics, while the Pentacam AxL® (Pentacam) measured COD and CT. Postoperative data were collected around six months after surgery, with a subgroup analysis of data at nine months. The Pearson correlation was used to examine the relationship between surgical-induced changes in corneal biomechanics and COD. At six months, significant postoperative differences were observed in various biomechanical indices, including uncorrected IOP (IOPuct) and biomechanics-corrected IOP (bIOP). However, many indices lost statistical significance by the nine-month mark, suggesting the reversibility of postoperative corneal changes. Postoperative COD increased at the anterior layer of the 2-6 mm annulus and incision site. The changes in COD correlated with certain biomechanical indices, including maximal (Max) deformative amplitude (DA) and stiffness parameter (SP). In conclusion, despite significant immediate postoperative changes, corneal biomechanics, COD, and IOP experienced a gradual recovery process following cataract surgery. Clinicians should maintain vigilance for any unusual changes during the short-term observation period to detect abnormalities early.

Topical Losartan Inhibition of Myofibroblast Generation in Rabbit Corneas With Acute Incisions

PURPOSE

The purpose of this study was to study whether deep central corneal incisions close during topical losartan treatment and the effect of topical losartan on myofibroblast generation after incisions in rabbit corneas.

METHODS

Rabbits (12) had a 0.35-mm deep radial incision from the center of the cornea into the limbus in 1 eye that was approximated with a single 10-0 nylon suture 1 mm inside the limbus. The incision was treated with 50 μL of topical 0.8 mg/mL losartan or 50 μL of balanced salt solution vehicle 6 times per day for 1 month. Standardized slitlamp photographs of the central incisions were analyzed for opacity with ImageJ before euthanasia. Triplex IHC was performed on cryofixed corneas for myofibroblast marker alpha-smooth muscle actin, mesenchymal cell marker vimentin, and basement membrane marker laminin alpha-5. Stromal α-SMA-positive myofibroblasts surrounding the incisions were quantitated with ImageJ.

RESULTS

Topical losartan compared with vehicle did not affect closure of the radial incisions or the opacity that developed surrounding the incisions at 1 month after injury. Topical losartan compared with vehicle did significantly decrease the average density of stromal myofibroblasts surrounding the incisions.

CONCLUSIONS

Topical losartan, a known inhibitor of transforming growth factor beta signaling, did not affect closure of deep corneal incisions. Losartan decreased myofibroblast generation surrounding nearly full-thickness radial corneal incisions compared with vehicle. The opacity at the incisions was not significantly affected by losartan-likely because corneal fibroblasts that develop in the stroma adjacent to the incisions were not changed by the losartan compared with the vehicle.

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Association of Changes in Thickness of Limbal Epithelial and Stroma with Corneal Scars Detected by High-Resolution Anterior Segment Optic Coherence Tomography

AIM

To investigate the corneal central and limbal thickness in cornea scar patients using high-resolution anterior segment optical coherence tomography (AS-OCT) and to determine the changes in the limbal region due to the corneal scar. Also, to evaluate tear film parameters in scar patients.

METHODS

Thirty patients with central corneal scar and 30 control subjects. The control subjects were healthy individuals who came to our clinic for routine ophthalmological examination. They were enrolled in this matched case-control study. Central epithelial thickness (ET), stromal thickness (ST), limbal epithelial thickness (LET), and limbal stromal thickness (LST) were analyzed using high-resolution AS-OCT. For evaluation of the ocular surface, the following techniques were used: tear break-up time (BUT) employing standard sterile strips of fluorescein sodium, Schirmer test-I (SCH), and the Ocular Surface Disease Index (OSDI) Questionnaire.

RESULTS

The mean central ET of the patient group was 51.5 ± 12.4 µm, while the mean central ET of the control group was 59.2 ± 9.0 µm. There was a statistically significant difference between patients and controls (p = 0.008). The mean LST of the patients was 747.9 ± 115.7 µm, and the mean LST of the controls was 726.3 ± 79.7 µm. There was a statistically significant difference between patients and controls according to BUT (p = 0.009) and SCH (p = 0.04). However, there was no significant difference between OSDI results of patients and controls (p = 0.08).

CONCLUSION

Corneal monitoring with high-resolution AS-OCT is a simple, noninvasive, useful technique for corneal scar patients. Cornea scars cause decreased ET. This result could be associated with lower tear film parameters in scar patients. The scar length is associated with higher intraocular pressure (IOP) values. Decreased LET and increased LST were detected in scar patients.

Dimensionality Matters: Exploiting UV-Photopatterned 2D and Two-Photon-Printed 2.5D Contact Guidance Cues to Control Corneal Fibroblast Behavior and Collagen Deposition

In the event of disease or injury, restoration of the native organization of cells and extracellular matrix is crucial for regaining tissue functionality. In the cornea, a highly organized collagenous tissue, keratocytes can align along the anisotropy of the physical microenvironment, providing a blueprint for guiding the organization of the collagenous matrix. Inspired by this physiological process, anisotropic contact guidance cues have been employed to steer the alignment of keratocytes as a first step to engineer in vitro cornea-like tissues. Despite promising results, two major hurdles must still be overcome to advance the field. First, there is an enormous design space to be explored in optimizing cellular contact guidance in three dimensions. Second, the role of contact guidance cues in directing the long-term deposition and organization of extracellular matrix proteins remains unknown. To address these challenges, here we combined two microengineering strategies-UV-based protein patterning (2D) and two-photon polymerization of topographies (2.5D)-to create a library of anisotropic contact guidance cues with systematically varying height (H, 0 µm ≤ H ≤ 20 µm) and width (W, 5 µm ≤ W ≤ 100 µm). With this unique approach, we found that, in the short term (24 h), the orientation and morphology of primary human fibroblastic keratocytes were critically determined not only by the pattern width, but also by the height of the contact guidance cues. Upon extended 7-day cultures, keratocytes were shown to produce a dense, fibrous collagen network along the direction of the contact guidance cues. Moreover, increasing the heights also increased the aligned fraction of deposited collagen and the contact guidance response of cells, all whilst the cells maintained the fibroblastic keratocyte phenotype. Our study thus reveals the importance of dimensionality of the physical microenvironment in steering both cellular organization and the formation of aligned, collagenous tissues.

Clearing the light path: proteoglycans and their important roles in the lens and cornea

Some of the earliest studies of glycans were performed on mammalian corneas and lenses with many of the key concepts we currently recognize as being fundamental to our understanding of basic cell biology arising from these studies. Proteoglycans and their GAG side chains are essential components of the ECM of the lens capsule. They also are present in the anterior corneal epithelial basement membrane and the posterior (Decemet's) basement membrane, and they organize collagen fiber diameters and spacing in the corneal stroma to maintain stromal clarity. Studies using genetically engineered mice and characterization of spontaneously arising mutations in genes controlling proteoglycan synthesis have generated new insight into the roles played by proteoglycans in signal transduction. We now know that proteoglycans and GAGs can regulate cell signaling and the maintenance of avascularity and immune privilege that are hallmarks of these tissues. In addition, proteoglycan-rich matrices provide the pathways for immune cells to populate the surface of the lens as a response to corneal wounding and in a model of Experimental Autoimmune Uveitis. Here we describe what is known about proteoglycans and GAGs in the cornea and lens. This knowledge has begun to provide promising leads into new proteoglycan-based treatments aimed at restoring and maintaining homeostasis in the cornea. Future studies are needed to determine how these new drugs impact the recruitment of immune cells to the lens for functions in restoring/maintaining homeostasis in the eye.

Topical application of calcitonin gene-related peptide as a regenerative, antifibrotic, and immunomodulatory therapy for corneal injury

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide abundantly expressed by corneal nerves. Using a murine model of corneal mechanical injury, we found CGRP levels in the cornea significantly reduced after injury. Topical application of CGRP as an eye drop accelerates corneal epithelial wound closure, reduces corneal opacification, and prevents corneal edema after injury in vivo. CGRP promotes corneal epithelial cell migration, proliferation, and the secretion of laminin. It reduces TGF-β1 signaling and prevents TGF-β1-mediated stromal fibroblast activation and tissue fibrosis. CGRP preserves corneal endothelial cell density, morphology, and pump function, thus reducing corneal edema. Lastly, CGRP reduces neutrophil infiltration, macrophage maturation, and the production of inflammatory cytokines in the cornea. Taken together, our results show that corneal nerve-derived CGRP plays a cytoprotective, pro-regenerative, anti-fibrotic, and anti-inflammatory role in corneal wound healing. In addition, our results highlight the critical role of sensory nerves in ocular surface homeostasis and injury repair.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Pirfenidone: A Promising Drug in Ocular Therapeutics

Pirfenidone, initially indicated for lung fibrosis, has gone beyond its original purpose, and shown promise in eye care. This detailed review tracks its evolution from lung treatment to aiding eye healing as evidenced by published literature. Pirfenidone's multifaceted attributes extend to mitigating corneal fibrosis, inflammation, and trauma. Through rigorous investigations, its efficacy emerges in diabetic retinopathy, macular degeneration, and postoperative glaucoma interventions. As an unheralded protagonist, pirfenidone reshapes ocular care paradigms, inviting renewed research opportunities.

Novel Correlation between TGF-β1/-β3 and Hormone Receptors in the Human Corneal Stroma

This study investigated the interplay between transforming growth factor beta (TGF-β1/T1 and TGF-β3/T3), and sex hormone receptors using our 3D in vitro cornea stroma model. Primary human corneal fibroblasts (HCFs) from healthy donors were plated in transwells at 106 cells/well and cultured for four weeks. HCFs were supplemented with stable vitamin C (VitC) and stimulated with T1 or T3. 3D construct proteins were analyzed for the androgen receptor (AR), progesterone receptor (PR), estrogen receptor alpha (ERα) and beta (ERβ), luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), gonadotropin-releasing hormone receptor (GnRHR), KiSS1-derived peptide receptor (KiSS1R/GPR54), and follicle-stimulating hormone subunit beta (FSH-B). In female constructs, T1 significantly upregulated AR, PR, ERα, FSHR, GnRHR, and KiSS1R. In male constructs, T1 significantly downregulated FSHR and FSH-B and significantly upregulated ERα, ERβ, and GnRHR. T3 caused significant upregulation in expressions PR, ERα, ERβ, LHR, FSHR, and GNRHR in female constructs, and significant downregulation of AR, ERα, and FSHR in male constructs. Semi-quantitative Western blot findings present the interplay between sex hormone receptors and TGF-β isoforms in the corneal stroma, which is influenced by sex as a biological variable (SABV). Additional studies are warranted to fully delineate their interactions and signaling mechanisms.

Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications

The limbus is a transition from the cornea to conjunctiva and sclera. In human eyes, this thin strip has a rich variation of tissue structures and composition, typifying a change from scleral irregularity and opacity to corneal regularity and transparency; a variation from richly vascularized conjunctiva and sclera to avascular cornea; the neural passage and drainage of aqueous humor. The limbal stroma is enriched with circular fibres running parallel to the corneal circumference, giving its unique role in absorbing small pressure changes to maintain corneal curvature and refractivity. It contains specific niches housing different types of stem cells for the corneal epithelium, stromal keratocytes, corneal endothelium, and trabecular meshwork. This truly reflects the important roles of the limbus in ocular physiology, and the limbal functionality is crucial for corneal health and the entire visual system. Since the anterior limbus containing epithelial structures and limbal epithelial stem cells has been extensively reviewed, this article is focused on the posterior limbus. We have discussed the structural organization and cellular components of the region beneath the limbal epithelium, the characteristics of stem cell types: namely corneal stromal stem cells, endothelial progenitors and trabecular meshwork stem cells, and recent advances leading to the emergence of potential cell therapy options to replenish their respective mature cell types and to correct defects causing corneal abnormalities. We have reviewed different clinical disorders associated with defects of the posterior limbus and summarized the available preclinical and clinical evidence about the developing topic of cell-based therapy for corneal disorders.

Topical application of calcitonin gene-related peptide as a regenerative, antifibrotic, and immunomodulatory therapy for corneal injury

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide abundantly expressed by corneal nerves. Using a murine model of corneal mechanical injury, we found CGRP levels in the cornea to be significantly reduced after injury. Topical application of CGRP as an eye drop three times daily accelerates corneal epithelial wound closure, reduces corneal opacification, and prevents corneal edema after injury in vivo. We then used a series of in vitro and in vivo techniques to investigate the mechanisms underlying CGRP's functions. CGRP promotes corneal epithelial cell migration, proliferation, and the secretion of laminin. It reduces TGF-β1 signaling and prevents TGF-β1-mediated stromal fibroblast activation and tissue fibrosis. CGRP reduces corneal endothelial cell apoptosis and death, preserves cell density and morphology, and promotes their pump function, thus reducing edema. Lastly, CGRP reduces neutrophil infiltration, macrophage maturation, and the production of inflammatory cytokines in the cornea. Taken together, our results show that corneal nerve-derived CGRP plays a cyto-protective, pro-regenerative, anti-fibrotic, and anti-inflammatory role in corneal wound healing. Given that current treatment options for corneal injury and opacity are scarce, CGRP has significant therapeutic potential in this area of unmet medical needs. In addition, our results highlight the critical role of sensory nerves in ocular surface homeostasis and injury repair.

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

The corneal fibroblast: The Dr. Jekyll underappreciated overseer of the responses to stromal injury

PURPOSE

To review the functions of corneal fibroblasts in wound healing.

METHODS

Literature review.

RESULTS

Corneal fibroblasts arise in the corneal stroma after anterior, posterior or limbal injuries and are derived from keratocytes. Transforming growth factor (TGF) β1 and TGFβ2, along with platelet-derived growth factor (PDGF), are the major modulators of the keratocyte to corneal fibroblast transition, while fibroblast growth factor (FGF)-2, TGFβ3, and retinoic acid are thought to regulate the transition of corneal fibroblasts back to keratocytes. Adequate and sustained levels of TGFβ1 and/or TGFβ2, primarily from epithelium, tears, aqueous humor, and corneal endothelium, drive the development of corneal fibroblasts into myofibroblasts. Myofibroblasts have been shown in vitro to transition back to corneal fibroblasts, although apoptosis of myofibroblasts has been documented as a major contributor to the resolution of fibrosis in several in situ corneal injury models. Corneal fibroblasts, aside from their role as a major progenitor to myofibroblasts, also perform many critical functions in the injured cornea, including the production of critical basement membrane (BM) components during regeneration of the epithelial BM and Descemet's membrane, production of non-basement membrane-associated stromal collagen type IV to control and downregulate TGFβ effects on stromal cells, release of chemotactic chemokines that attract bone marrow-derived cells to the injured stroma, production of growth factors that modulate regeneration and maturation of the overlying epithelium, and production of collagens and other ECM components that contribute to stromal integrity after injury.

CONCLUSIONS

Corneal fibroblasts are major contributors to and overseers of the corneal response to injuries.

A Biomimetic Peptide-drug Supramolecular Hydrogel as Eyedrops Enables Controlled Release of Ophthalmic Drugs

The rapid clearance of instilled drugs from the ocular surface due to tear flushing and excretion results in low drug bioavailability, necessitating the development of new drug delivery routes. Here, we generated an antibiotic hydrogel eye drop that can extend the pre-corneal retention of a drug after topical instillation to address the risk of side effects (e.g., irritation and inhibition of enzymes), resulting from frequent and high-dosage administrations of antibiotics used to obtain the desired therapeutic drug concentration. The covalent conjugation of small peptides to antibiotics (e.g., chloramphenicol) first endows the self-assembly ability of peptide-drug conjugate to generate supramolecular hydrogels. Moreover, the further addition of calcium ions, which are also widely present in endogenous tears, tunes the elasticity of supramolecular hydrogels, making them ideal for ocular drug delivery. The in vitro assay revealed that the supramolecular hydrogels exhibited potent inhibitory activities against both gram-negative (e.g., Escherichia coli) and gram-positive (e.g., Staphylococcus aureus) bacteria, whereas they were innocuous toward human corneal epithelial cells. Moreover, the in vivo experiment showed that the supramolecular hydrogels remarkably increased pre-corneal retention without ocular irritation, thereby showing appreciable therapeutic efficacy for treating bacterial keratitis. This work, as a biomimetic design of antibiotic eye drops in the ocular microenvironment, addresses the current issues of ocular drug delivery in the clinic and further provides approaches to improve the bioavailability of drugs, which may eventually open new directions to resolve the difficulty of ocular drug delivery. STATEMENT OF SIGNIFICANCE: Herein, we present a biomimetic design for antibiotic hydrogel eye drops mediated by calcium ions (Ca²⁺) in the ocular microenvironment, which can extend the pre-corneal retention of antibiotics after topical instillation. The mediation of Ca²⁺ which is widely present in endogenous tears, tunes the elasticity of hydrogels, making them ideal for ocular drug delivery. Since increasing the ocular retention of antibiotic eye drops enhances its action and reduces its adverse effects, this work may lead to an approach of peptide-drug-based supramolecular hydrogel for ocular drug delivery in clinics to combat ocular bacterial infections.

Dendrimers in Corneal Drug Delivery: Recent Developments and Translational Opportunities

Dendrimers are biocompatible organic nanomaterials with unique physicochemical properties, making them the focus of recent research in drug delivery. The cornea of the human eye presents a challenge for drug transit due to its inherently impenetrable nature, requiring nanocarrier-mediated targeted drug delivery. This review intends to examine recent advancements in the use of dendrimers for corneal drug delivery, including their properties and their potential for treating various ocular diseases. The review will also highlight the benefit of the novel technologies that have been developed and applied in the field, such as corneal targeting, drug release kinetics, treatments for dry eye disease, antibacterial drug delivery, corneal inflammation, and corneal tissue engineering. The review seeks to provide a comprehensive overview of the current state of research in this field, along with the translational developments in the field of dendrimer-based therapeutics and imaging agents and inspire the potential for future developments and translational opportunities in dendrimers based corneal drug delivery.

Basement membrane regeneration and TGF-β1 expression in rabbits with corneal perforating injury

Purpose

To evaluate the relationship between basement membrane (BM) regeneration and the spatiotemporal expression of TGF-β1 during wound healing in rabbits with corneal perforating injury.

Methods

Forty-two rabbits were randomly allocated into 7 experimental groups, with 6 rabbits per group at each time point. The central cornea of the left eye was injured with 2.0 mm trephine to establish the perforating injury model. Six rabbits that received no treatment were used as controls. The cornea was evaluated at 3 days, 1-3 weeks, and 1-3 months after injury with a slit lamp for haze levels. Real-time quantitative polymerase chain reaction (qRT-PCR) was performed to quantify the relative expression of TGF-β1 and α-SMA mRNA. Immunofluorescence (IF) was used to assess TGF-β1 and alpha-smooth actin (α-SMA) expression and localization. BM regeneration was assessed using transmission electron microscopy (TEM).

Results

After injury, dense haze appeared at 1 month and then gradually faded. The relative expression of TGF-β1 mRNA peaked at 1 week and then decreased until 2 months. The relative α-SMA mRNA expression reached its peak at 1 week, then reached a small peak again at 1 month. IF results showed that TGF-β1 was initially detected in the fibrin clot at 3 days and then in the entire repairing stroma at 1 week. TGF-β1 localization gradually diminished from the anterior region to the posterior region at 2 weeks to 1 month, and it was nearly absent at 2 months. The myofibroblast marker α-SMA was observed in the entire healing stroma at 2 weeks. Localization of α-SMA gradually disappeared from the anterior region at 3 weeks to 1 month, remaining only in the posterior region at 2 months and disappearing at 3 months. Defective epithelial basement membrane (EBM) was first detected at 3 weeks after injury, then gradually repaired, and was nearly regenerated at 3 months. A thin and uneven Descemet's membrane (DM) was initially detected at 2 months after injury, then gradually regenerated to some extent, but remained abnormal at 3 months.

Conclusions

In the rabbit corneal perforating injury model, EBM regeneration was observed earlier than DM. At 3 months, complete EBM regeneration was observed, while the regenerated DM was still defective. TGF-β1 was distributed throughout the entire wound area in the early stages and then decreased from the anterior to the posterior region. α-SMA exhibited a similar temporospatial expression to TGF-β1. EBM regeneration may play a key role in low expression of TGF-β1 and α-SMA in the anterior stroma. Meanwhile, incomplete DM regeneration may contribute to the sustained expression of TGF-β1 and α-SMA in the posterior stroma.

Case Report: Corneal Inlay Removal after Myofibroblast Detection under in Vivo Confocal Microscopy

SIGNIFICANCE

Corneal inlays, one of the treatment options for presbyopia, are effective and safe, and various such devices have been developed. However, there have been cases of inlay removal due to complications or patient dissatisfaction.

PURPOSE

The purpose of this study was to report a case of inlay removal due to corneal opacity after inlay implantation and the results of 5 years of follow-up.

CASE REPORT

A 63-year-old man was referred to our hospital with visual disturbance and double vision in his left eye. Two years before presentation at our hospital, he had undergone bilateral laser in situ keratomileusis with corneal inlay implantation in the left eye at another clinic. Slit-lamp examinations showed paracentral corneal opacity. The patient was treated with tranilast eye drops for 18 months, with no progression of symptoms. However, 6 months after stopping the eye drop treatment, the opacity recurred, and vision acuity decreased, along with the formation of myofibroblasts around the inlay, as revealed by in vivo confocal microscopy. Consequently, the inlay was removed at the previous clinic. During the subsequent 5-year follow-up period, ophthalmic examination revealed reduced corneal opacity, although visual acuity did not change; moreover, no myofibroblast was found.

CONCLUSIONS

Corneal inlays can sometimes cause complications. In this case, the patient experienced corneal fibrosis and associated vision loss. In vivo confocal microscopy detected myofibroblasts that cause corneal stromal fibrosis; thus, the removal was decided to avoid fibrosis progression.

Mesenchymal Stem Cell Exosomes as Immunomodulatory Therapy for Corneal Scarring

Corneal scarring is a leading cause of worldwide blindness. Human mesenchymal stem cells (MSC) have been reported to promote corneal wound healing through secreted exosomes. This study investigated the wound healing and immunomodulatory effects of MSC-derived exosomes (MSC-exo) in corneal injury through an established rat model of corneal scarring. After induction of corneal scarring by irregular phototherapeutic keratectomy (irrPTK), MSC exosome preparations (MSC-exo) or PBS vehicle as controls were applied to the injured rat corneas for five days. The animals were assessed for corneal clarity using a validated slit-lamp haze grading score. Stromal haze intensity was quantified using in-vivo confocal microscopy imaging. Corneal vascularization, fibrosis, variations in macrophage phenotypes, and inflammatory cytokines were evaluated using immunohistochemistry techniques and enzyme-linked immunosorbent assays (ELISA) of the excised corneas. Compared to the PBS control group, MSC-exo treatment group had faster epithelial wound closure (0.041), lower corneal haze score (p = 0.002), and reduced haze intensity (p = 0.004) throughout the follow-up period. Attenuation of corneal vascularisation based on CD31 and LYVE-1 staining and reduced fibrosis as measured by fibronectin and collagen 3A1 staining was also observed in the MSC-exo group. MSC-exo treated corneas also displayed a regenerative immune phenotype characterized by a higher infiltration of CD163+, CD206+ M2 macrophages over CD80+, CD86+ M1 macrophages (p = 0.023), reduced levels of pro-inflammatory IL-1β, IL-8, and TNF-α, and increased levels of anti-inflammatory IL-10. In conclusion, topical MSC-exo could alleviate corneal insults by promoting wound closure and reducing scar development, possibly through anti-angiogenesis and immunomodulation towards a regenerative and anti-inflammatory phenotype.

Unravelling the Impact of Cyclic Mechanical Stretch in Keratoconus-A Transcriptomic Profiling Study

Biomechanical and molecular stresses may contribute to the pathogenesis of keratoconus (KC). We aimed to profile the transcriptomic changes in healthy primary human corneal (HCF) and KC-derived cells (HKC) combined with TGFβ1 treatment and cyclic mechanical stretch (CMS), mimicking the pathophysiological condition in KC. HCFs (n = 4) and HKCs (n = 4) were cultured in flexible-bottom collagen-coated 6-well plates treated with 0, 5, and 10 ng/mL of TGFβ1 with or without 15% CMS (1 cycle/s, 24 h) using a computer-controlled Flexcell FX-6000T Tension system. We used stranded total RNA-Seq to profile expression changes in 48 HCF/HKC samples (100 bp PE, 70-90 million reads per sample), followed by bioinformatics analysis using an established pipeline with Partek Flow software. A multi-factor ANOVA model, including KC, TGFβ1 treatment, and CMS, was used to identify differentially expressed genes (DEGs, |fold change| ≥ 1.5, FDR ≤ 0.1, CPM ≥ 10 in ≥1 sample) in HKCs (n = 24) vs. HCFs (n = 24) and those responsive to TGFβ1 and/or CMS. PANTHER classification system and the DAVID bioinformatics resources were used to identify significantly enriched pathways (FDR ≤ 0.05). Using multi-factorial ANOVA analyses, 479 DEGs were identified in HKCs vs. HCFs including TGFβ1 treatment and CMS as cofactors. Among these DEGs, 199 KC-altered genes were responsive to TGFβ1, thirteen were responsive to CMS, and six were responsive to TGFβ1 and CMS. Pathway analyses using PANTHER and DAVID indicated the enrichment of genes involved in numerous KC-relevant functions, including but not limited to degradation of extracellular matrix, inflammatory response, apoptotic processes, WNT signaling, collagen fibril organization, and cytoskeletal structure organization. TGFβ1-responsive KC DEGs were also enriched in these. CMS-responsive KC-altered genes such as OBSCN, CLU, HDAC5, AK4, ITGA10, and F2RL1 were identified. Some KC-altered genes, such as CLU and F2RL1, were identified to be responsive to both TGFβ1 and CMS. For the first time, our multi-factorial RNA-Seq study has identified many KC-relevant genes and pathways in HKCs with TGFβ1 treatment under CMS, suggesting a potential role of TGFβ1 and biomechanical stretch in KC development.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Highly stable fibronectin-mimetic-peptide-based supramolecular hydrogel to accelerate corneal wound healing

Without timely treatment, poor wound healing in corneal injuries can seriously impair vision and lead to blindness. Thus, it is vital to develop a therapeutic strategy to accelerate corneal re-epithelialization. The conjugation of self-assembled motifs with a fibronectin-mimetic peptide sequence (PHSRN) drastically improves the chemical stability of PHSRN against protease hydrolysis and minimally affects its biological activity to promote the migration of corneal epithelial cells. The optimized Nap-FFPHSRN self-assembled into bioactive supramolecular hydrogels increases cell motility by remolding F-actin and boosts the tight junction of the corneal epithelium by increasing the expression of zonula occludens-1 (ZO-1). An in vivo experiment showed that a Nap-FFPHSRN hydrogel provided extended precorneal retention with good ocular tolerance after topical instillation. An animal model of corneal scrape showed that a single daily dose of Nap-FFPHSRN hydrogel had a superior therapeutic effect in facilitating corneal re-epithelialization with complete morphological and architectural recovery. With a rational approach to mimic bioactive proteins, this study presents a new strategy to demonstrate the potential of peptide-based supramolecular hydrogels for use in clinical treatment of corneal injury. STATEMENT OF SIGNIFICANCE: Here we systematically investigate the self-assembly behavior and chemical stability of designed peptide amphiphiles (Nap-FPHRSN, Nap-FFPHSRN and Nap-FFFPHSRN). The introduction of self-assembled motifs (Nap-F, Nap-FF and Nap-FFF) drastically enhances the chemical stability of fibronectin-mimetic peptide (PHSRN). Moreover, topical instillation of Nap-FFPHSRN hydrogel once daily, exhibits a better in vivo effect than PHSRN and the same in vivo effect as fibronectin, both of which are instilled three times daily, for promoting full morphological and architectural recovery after corneal re-epithelialization. As a rational design of conjugating bioactive peptides with self-assembled motifs to mimic bioactive proteins, this work may lead to a new approach that improves the in vivo therapeutic effect for treating corneal injury in clinic settings.

Pre-Clinical Evaluation of Efficacy and Safety of Human Limbus-Derived Stromal/Mesenchymal Stem Cells with and without Alginate Encapsulation for Future Clinical Applications

Corneal opacification or scarring is one of the leading causes of blindness worldwide. Human limbus-derived stromal/mesenchymal stem cells (hLMSCs) have the potential of clearing corneal scarring. In the current preclinical studies, we aimed to determine their ability to heal the scarred corneas, in a murine model of corneal scar, and examined their ocular and systemic toxicity after topical administration to rabbit eyes. The hLMSCs were derived from human donor corneas and were cultivated in a clean room facility in compliance with the current good manufacturing practices (cGMP). Before the administration, the hLMSCs were analyzed for their characteristic properties including immunostaining, and were further subjected to sterility and stability analysis. The corneas (right eye) of C57BL/6 mice (n = 56) were stripped of their central epithelium and superficial anterior stroma using a rotary burr (Alger Brush® II). Few mice were left untreated (n = 8), while few (n = 24) were treated immediately with hLMSCs after debridement (prophylaxis group). The rest (n = 24, scar group) were allowed to develop corneal scarring for 2 weeks and then treated with hLMSCs. In both groups, the treatment modalities included encapsulated (En+) and non-encapsulated (En−) hLMSCs and sham (vehicle) treatment. The follow-up (4 weeks) after the treatment or debridement included clinical photography, fluorescein staining, and optical coherence tomography at regular intervals. All the images and scans were analyzed using ImageJ software to assess the changes in corneal haze, scar area, and the reflectivity ratio of the epithelium to the stroma. The scar area and the scar intensity were found to be decreased in the groups that received hLMSCs. The reflectivity of the stroma was found to be normalized to the baseline levels before the debridement in the eyes that were treated with hLMSCs, relative to the untreated. In the safety study, the central corneas of the left eye of 18 New Zealand rabbits were scraped with a needle and then treated with En+ hLMSCs, En− hLMSCs, and the sham (n = 6 each). Rabbits were then followed up for 4 weeks, during which blood and tear samples were collected at regular intervals. These rabbits were then assessed for changes in the quantities of inflammatory markers (TNF-α, IL-6, and IgE) in the sera and tears, changes in the ocular surface observations such as intraocular pressure (IOP), and the hematological and clinical chemistry parameters. Four weeks later, the rabbits were euthanized and examined histopathologically. No significant changes in conjunctival congestion, corneal clarity, or IOP were noticed during the ophthalmic examination. The level of inflammatory molecules (TNF-α and IL-6 TNF-α) and the hematological parameters were similar in all groups without any significant changes. Histological examination of the internal organs and ocular tissues did not reveal any abnormalities. The results of these studies summarize that the En+ and En− hLMSCs are not harmful to the recipient and potentially restore the transparency of debrided or scarred corneas, indicating that hLMSCs can be assessed for clinical use in humans.

Relationship of Density, Depth, and Surface Irregularity of Superficial Corneal Opacification with Visual Acuity

PURPOSE

To explore the relationship between the density, depth, and surface irregularity of superficial corneal opacities and vision.

METHODS

This prospective imaging study included 19 patients with unilateral superficial corneal opacification due to scarring post-microbial keratitis. Each eye underwent an assessment of uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), contact lens corrected visual acuity (CLCVA), and Scheimpflug and anterior segment optical tomography imaging. Regression analysis was performed to detect the association between density, depth of scarring, and the surface irregularity in terms of higher order aberrations (HOA), and keratometry and UCVA, CLCVA, and the difference between BSCVA and CLCVA.

RESULTS

The mean logMAR UCVA, BSCVA, and CLCVA were 0.76, 0.35, and 0.28, respectively. The corneal scars had a mean thickness of 158.7 ± 61 µ and density of 65.73 ± 24.46 GSU. Bivariate analysis model for UCVA showed an association with Z₄² secondary astigmatism (p = 0.02), Z₄⁴ quadrafoil (p = 0.01), combined coma Z₃ ^± 1(p = 0.03), and combined HOA Z₃-Z₆ (p = 0.045), out of which Z₄⁴ Quadrafoil (p = 0.04) was most significant with multivariate analysis. Bivariate analysis for BCVA-CLVA showed association with Z₃¹ coma horizontal (p = 0.04), Z₃³ oblique trefoil (p = 0.02), Z₄⁰ primary spherical aberration (p = 0.008), and Z₅ ^- 5 (p = 0.007), out of which Z₃¹ horizontal coma (p = 0.04) and Z₄⁰ spherical aberration (p = 0.009) were significant on multivariate analysis. Change in densitometry, corneal thickness, epithelial:stromal reflectivity ratio, scar depth, and keratometry did not show any significant association with UCVA, BSCVA-CLCVA, or CLCVA.

CONCLUSION

In superficial corneal stromal scarring, deranged surface irregularity parameters like higher-order aberrations affect the final visual acuity more than the depth or density of the opacity.

Molecular mechanisms regulating wound repair: Evidence for paracrine signaling from corneal epithelial cells to fibroblasts and immune cells following transient epithelial cell treatment with Mitomycin C

In this paper, we use RNAseq to identify senescence and phagocytosis as key factors to understanding how mitomyin C (MMC) stimulates regenerative wound repair. We use conditioned media (CM) from untreated (CMC) and MMC treated (CMM) human and mouse corneal epithelial cells to show that corneal epithelial cells indirectly exposed to MMC secrete elevated levels of immunomodulatory proteins including IL-1α and TGFβ1 compared to cells exposed to CMC. These factors increase epithelial and macrophage phagocytosis and promote ECM turnover. IL-1α supplementation can increase phagocytosis in control epithelial cells and attenuate TGFβ1 induced αSMA expression by corneal fibroblasts. Yet, we show that epithelial cell CM contains factors besides IL-1α that regulate phagocytosis and αSMA expression by fibroblasts. Exposure to CMM also impacts the activation of bone marrow derived dendritic cells and their ability to present antigen. These in vitro studies show how a brief exposure to MMC induces corneal epithelial cells to release proteins and other factors that function in a paracrine way to enhance debris removal and enlist resident epithelial and immune cells as well as stromal fibroblasts to support regenerative and not fibrotic wound healing.

Extracellular matrix-based sticky sealants for scar-free corneal tissue reconstruction

Regenerative medicine requires both tissue restoration and ease of compliance for clinical application. Considering this, sticky tissue sealants have been shown to have great potentials over surgical suturing and wound treatment. However, tissue sealants currently used pose challenges such as uncontrollable adhesion formation, mechanical mismatch, and lack of tissue restoration. A new sticky sealant based on gelatinized cornea-derived extracellular matrix (GelCodE) with a visible light-activating system is firstly being introduced in this study. De novo tissue regeneration relies on the matrisome in charge of tissue-organization and development within GelCodE while visible light-based photopolymerization with ruthenium/sodium persulfate rapidly induces covalent bonds with the adjacent tissues. The ease of not only in vivo application, biocompatibility, and biointegration, but also exceptional de novo tissue formation is demonstrated in this study. Interestingly, newly regenerated tissues were shown to have normal tissue-like matrices with little scar formation. Hence, this work presents a promising strategy to meet clinical demands for scar-free tissue recovery with superior ease of clinical application.

The Yin and Yang of Mesenchymal Cells in the Corneal Stromal Fibrosis Response to Injury: The Cornea as a Model of Fibrosis in Other Organs

Mesenchymal cells (keratocytes, corneal fibroblasts, and myofibroblasts), as well as mesenchymal progenitor bone marrow-derived fibrocytes, are the major cellular contributors to stromal fibrosis after injury to the cornea. Corneal fibroblasts, in addition to being major progenitors to myofibroblasts, also have anti-fibrotic functions in (1) the production of non-basement membrane collagen type IV that binds activated transforming growth factor (TGF) beta-1 and TGF beta-2 to downregulate TGF beta effects on cells in the injured stroma, (2) the production of chemokines that modulate the entry of bone marrow-derived cells into the stroma, (3) the production of hepatocyte growth factor and keratinocyte growth factor to regulate corneal epithelial healing, (4) the cooperation with the epithelium or corneal endothelium in the regeneration of the epithelial basement membrane and Descemet's membrane, and other functions. Fibrocytes also serve as major progenitors to myofibroblasts in the corneal stroma. Thus, mesenchymal cells and mesenchymal cell progenitors serve Yin and Yang functions to inhibit and promote tissue fibrosis depending on the overall regulatory milieu within the injured stroma.

The Soluble Guanylate Cyclase Stimulator BAY 41-2272 Attenuates Transforming Growth Factor β1-Induced Myofibroblast Differentiation of Human Corneal Keratocytes

Corneal transparency, necessary for vision and depending on the high organization of stromal extracellular matrix, is maintained by keratocytes. Severe or continuous corneal injuries determine exaggerated healing responses resulting in the formation of irreversible fibrotic scars and vision impairment. Soluble guanylate cyclase (sGC) stimulation demonstrated antifibrotic effects in both experimental fibrosis and human lung and skin fibroblasts. Here, we assessed whether sGC stimulation with BAY 41-2272 could attenuate transforming growth factor β1 (TGFβ1)-induced myofibroblast differentiation of human corneal keratocytes. Cells were challenged with TGFβ1, with/without BAY 41-2272 preincubation, and subsequently assessed for viability, proliferation, migration, chemoinvasion, as well for the expression of myofibroblast/fibroblast activation markers and contractile abilities. Treatment with BAY 41-2272 did not affect keratocyte viability, while preincubation of cells with the sGC stimulator was able to inhibit TGFβ1-induced proliferation, wound healing capacity, and invasiveness. BAY 41-2272 was also able to attenuate TGFβ1-induced myofibroblast-like profibrotic phenotype of keratocytes, as demonstrated by the significant decrease in ACTA2, COL1A1, COL1A2, FN1 and PDPN gene expression, as well as in α-smooth muscle actin, α-1 chain of type I collagen, podoplanin, vimentin and N-cadherin protein expression. Finally, BAY 41-2272 significantly counteracted the TGFβ1-induced myofibroblast-like ability of keratocytes to contract collagen gels, reduced phosphorylated Smad3 protein levels, and attenuated gene expression of proinflammatory cytokines. Collectively, our data show for the first time that BAY 41-2272 is effective in counteracting keratocyte-to-myofibroblast transition, thus providing the rationale for the development of sGC stimulators as novel promising modulators of corneal scarring and fibrosis.

Prolactin-Induced Protein facilitates corneal wound healing

The purpose of the study was to investigate the role of Prolactin-Induced Protein (PIP) in corneal wound healing, in vivo and in vitro. In C57BL/6J mice, corneal epithelia was removed using an ocular burr. Phosphate buffered saline (PBS) or PIP (0.5 and 1.0 μg/mL) was applied topically or subconjunctivally injected. PIP accelerated wound closure as early as 24 h. PIP treatment promoted corneal wound healing and epithelial integrity and thickness. Integrin α6, integrin β4, Thrombospondin-1, and TGF-β1 expressions were all downregulated by PIP after wound closure. In vitro, scratch assays were performed using primary human epithelial cells (HCECs) and human corneal fibroblasts (HCFs), stimulated with PIP at various dosages. PIP treatment promoted both HCECs and HCFs migration. PIP upregulated expression of integrin α6, integrin β4, and Thrombospondin-1 in HCECs. Expression of TGF-β1 in HCECs and expression of smooth muscle actin (SMA) and Type III Collagen (Col III) in HCFs were significantly downregulated at 150 ng/mL PIP. PIP exhibits noteworthy anti-fibrotic potentiality. While the mechanism of how PIP is impactful on the corneal wound healing cascade is unknown, our findings are novel and further studies are warranted in order to unravel any therapeutic potential.

Sulfur mustard corneal injury is associated with alterations in the epithelial basement membrane and stromal extracellular matrix

Sulfur mustard (SM; bis(2-chloroethyl) sulfide) is a highly reactive bifunctional alkylating agent synthesized for chemical warfare. The eyes are particularly sensitive to SM where it causes irritation, pain, photophobia, and blepharitis, depending on the dose and duration of exposure. In these studies, we examined the effects of SM vapor on the corneas of New Zealand white male rabbits. Edema and hazing of the cornea, signs of acute injury, were observed within one day of exposure to SM, followed by neovascularization, a sign of chronic or late phase pathology, which persisted for at least 28 days. Significant epithelial-stromal separation ranging from ~8-17% of the epithelial surface was observed. In the stroma, there was a marked increase in CD45+ leukocytes and a decrease of keratocytes, along with areas of disorganization of collagen fibers. SM also disrupted the corneal basement membrane and altered the expression of perlecan, a heparan sulfate proteoglycan, and cellular fibronectin, an extracellular matrix glycoprotein. This was associated with an increase in basement membrane matrix metalloproteinases including ADAM17, which is important in remodeling of the basement membrane during wound healing. Tenascin-C, an extracellular matrix glycoprotein, was also upregulated in the stroma 14-28 d post SM, a finding consistent with its role in organizing structural components of the stroma necessary for corneal transparency. These data demonstrate that SM vapor causes persistent alterations in structural components of the cornea. Further characterization of SM-induced injury in rabbit cornea will be useful for the identification of targets for the development of ocular countermeasures.

Rare giant corneal keloid presenting 26 years after trauma: A case report

BACKGROUND

Corneal keloid is a rare clinical disease with an unknown etiology, which is easily misdiagnosed. Surgery is the most effective treatment but is rarely reported in the literature. Herein, we report the clinical features, histopathology, and surgical outcome of a giant corneal keloid with trophoblastic vessels and discuss the genesis of the mass.

CASE SUMMARY

A 36-year-old young man was admitted to the hospital because of a large mass on the surface of the left cornea. The patient had suffered an injury to his left eye at the age of 6-years-old; however, as the injury did not cause cornea perforation, he did not undergo treatment. Slit lamp exam showed a large, elevated, opaque lesion that covered the entire cornea and protruded from the surface of the eyeball. Anterior segment optical coherence tomography (AS-OCT) revealed a lesion of irregular density involving the anterior stroma. We suspected a secondary corneal fibroproliferative mass based on the clinical history, and slit lamp and AS-OCT findings. The patient subsequently underwent a superficial keratectomy and keratoplasty, and the final diagnosis of corneal keloid was confirmed by intraoperative histopathological examination.

CONCLUSION

Non-penetrating corneal trauma damages corneal epithelium basement membrane, initiating stromal fibrosis and causing corneal keloids. AS-OCT and biopsy confirm diagnosis.

Transcriptomic Profiling of Human Limbus-Derived Stromal/Mesenchymal Stem Cells-Novel Mechanistic Insights into the Pathways Involved in Corneal Wound Healing

Limbus-derived stromal/mesenchymal stem cells (LMSCs) are vital for corneal homeostasis and wound healing. However, despite multiple pre-clinical and clinical studies reporting the potency of LMSCs in avoiding inflammation and scarring during corneal wound healing, the molecular basis for the ability of LMSCs remains unknown. This study aimed to uncover the factors and pathways involved in LMSC-mediated corneal wound healing by employing RNA-Sequencing (RNA-Seq) in human LMSCs for the first time. We characterized the cultured LMSCs at the stages of initiation (LMSC−P0) and pure population (LMSC−P3) and subjected them to RNA-Seq to identify the differentially expressed genes (DEGs) in comparison to native limbus and cornea, and scleral tissues. Of the 28,000 genes detected, 7800 DEGs were subjected to pathway-specific enrichment Gene Ontology (GO) analysis. These DEGs were involved in Wnt, TGF-β signaling pathways, and 16 other biological processes, including apoptosis, cell motility, tissue remodeling, and stem cell maintenance, etc. Two hundred fifty-four genes were related to wound healing pathways. COL5A1 (11.81 ± 0.48) and TIMP1 (20.44 ± 0.94) genes were exclusively up-regulated in LMSC−P3. Our findings provide new insights involved in LMSC-mediated corneal wound healing.

Myofibroblast transdifferentiation of keratocytes results in slower migration and lower sensitivity to mesoscale curvatures

Functional tissue repair after injury or disease is governed by the regenerative or fibrotic response by cells within the tissue. In the case of corneal damage, keratocytes are a key cell type that determine the outcome of the remodeling response by either adapting to a fibroblast or myofibroblast phenotype. Although a growing body of literature indicates that geometrical cues in the environment can influence Myo(fibroblast) phenotype, there is a lack of knowledge on whether and how differentiated keratocyte phenotype is affected by the curved tissue geometry in the cornea. To address this gap, in this study we characterized the phenotype of fibroblastic and transforming growth factor β (TGFβ)-induced myofibroblastic keratocytes and studied their migration behavior on curved culture substrates with varying curvatures. Immunofluorescence staining and quantification of cell morphological parameters showed that, generally, fibroblastic keratocytes were more likely to elongate, whereas myofibroblastic keratocytes expressed more pronounced α smooth muscle actin (α-SMA) and actin stress fibers as well as more mature focal adhesions. Interestingly, keratocyte adhesion on convex structures was weak and unstable, whereas they adhered normally on flat and concave structures. On concave cylinders, fibroblastic keratocytes migrated faster and with higher persistence along the longitudinal direction compared to myofibroblastic keratocytes. Moreover, this behavior became more pronounced on smaller cylinders (i.e., higher curvatures). Taken together, both keratocyte phenotypes can sense and respond to the sign and magnitude of substrate curvatures, however, myofibroblastic keratocytes exhibit weaker curvature sensing and slower migration on curved substrates compared to fibroblastic keratocytes. These findings provide fundamental insights into keratocyte phenotype after injury, but also exemplify the potential of tuning the physical cell environments in tissue engineering settings to steer towards a favorable regeneration response.

Mimicking the Natural Basement Membrane for Advanced Tissue Engineering

Advancements in the field of tissue engineering have led to the elucidation of physical and chemical characteristics of physiological basement membranes (BM) as specialized forms of the extracellular matrix. Efforts to recapitulate the intricate structure and biological composition of the BM have encountered various advancements due to its impact on cell fate, function, and regulation. More attention has been paid to synthesizing biocompatible and biofunctional fibrillar scaffolds that closely mimic the natural BM. Specific modifications in biomimetic BM have paved the way for the development of in vitro models like alveolar-capillary barrier, airway models, skin, blood-brain barrier, kidney barrier, and metastatic models, which can be used for personalized drug screening, understanding physiological and pathological pathways, and tissue implants. In this Review, we focus on the structure, composition, and functions of in vivo BM and the ongoing efforts to mimic it synthetically. Light has been shed on the advantages and limitations of various forms of biomimetic BM scaffolds including porous polymeric membranes, hydrogels, and electrospun membranes This Review further elaborates and justifies the significance of BM mimics in tissue engineering, in particular in the development of in vitro organ model systems.

Topical Losartan and Corticosteroid Additively Inhibit Corneal Stromal Myofibroblast Generation and Scarring Fibrosis After Alkali Burn Injury

Purpose

To evaluate the efficacy of losartan and prednisolone acetate in inhibiting corneal scarring fibrosis after alkali burn injury in rabbits.

Methods

Sixteen New Zealand White rabbits were included. Alkali injuries were produced using 1N sodium hydroxide on a 5-mm diameter Whatman #1 filter paper for 1 minute. Four corneas in each group were treated six times per day for 1 month with 50 µL of (1) 0.8 mg/mL losartan in balanced salt solution (BSS), (2) 1% prednisolone acetate, (3) combined 0.8 mg/mL losartan and 1% prednisolone acetate, or (4) BSS. Area of opacity and total opacity were analyzed in standardized slit-lamp photos with ImageJ. Corneas in both groups were cryofixed in Optimal cutting temperature (OCT) compound at 1 month after surgery, and immunohistochemistry was performed for alpha-smooth muscle actin (α-SMA) and keratocan or transforming growth factor β1 and collagen type IV with ImageJ quantitation.

Results

Combined topical losartan and prednisolone acetate significantly decreased slit-lamp opacity area and intensity, as well as decreased stromal myofibroblast α-SMA area and intensity of staining per section and confined myofibroblasts to only the posterior stroma with repopulation of the anterior and mid-stroma with keratocan-positive keratocytes after 1 month of treatment. Corneal fibroblasts produced collagen type IV not associated with basement membranes, and this production was decreased by topical losartan.

Conclusions

Combined topical losartan and prednisolone acetate decreased myofibroblast-associated fibrosis after corneal alkali burns that produced full-thickness injury, including corneal endothelial damage. Increased dosages and duration of treatment may further decrease scarring fibrosis.

Translational Relevance

Topical losartan and prednisolone acetate decrease myofibroblast-mediated scarring fibrosis after corneal injury.