Overview of the Cornea: Structure, Function, and Development

RAD21 deficiency drives corneal to scleral differentiation fate switching via upregulating WNT9B

The cornea and sclera are distinct adjacent tissues, yet their stromal cells originate from common neural crest cells (NCCs). Sclerocornea is a disease characterized by an indistinguishable boundary between the cornea and sclera. Previously, we identified a RAD21 mutation in a sclerocornea pedigree. Here, we investigated the impacts of RAD21 on NCC activities during eye development. RAD21 deficiency caused upregulation of PCDHGC3. Both RAD21 knockdown and PCDHGC3 upregulation disrupted the migration of NCCs. Transcriptome analysis indicated that WNT9B had 190.9-fold higher expression in scleral stroma than in corneal stroma. WNT9B was also significantly upregulated by both RAD21 knockdown and PCDHGC3 overexpression, and knock down of WNT9B rescued the differentiation and migration of NCCs with RAD21 deficiency. Consistently, overexpressing wnt9b in Xenopus tropicalis led to ocular developmental abnormalities. In summary, WNT9B is a determinant factor during NCC differentiation into corneal keratocytes or scleral stromal cells and is affected by RAD21 expression.

Longevity factor FOXO3a: A potential therapeutic target for age-related ocular diseases

The forkhead box protein O3 (FOXO3a) belongs to the subgroup O of the forkhead transcription factor family and plays an important role in regulating the aging process by participating in the regulation of various life processes, including cell cycle arrest, apoptosis, autophagy, oxidative stress, and DNA repair. The eye is an organ that is affected by aging earlier. However, the functional role and potential clinical applications of FOXO3a in age-related eye diseases have not received widespread attention and lacked comprehensive and clear clarification. In this review, we demonstrated the relationship between FOXO3a and visual system health, summarized the functional roles of FOXO3a in various eye diseases, and potential ocular-related therapies and drugs targeting FOXO3a in visual system diseases through a review and summary of relevant literature. This review indicates that FOXO3a is an important factor in maintaining the normal function of various tissues in the eye, and is closely related to the occurrence and development of ophthalmic-related diseases. Based on its vital role in the normal function of the visual system, FOXO3a has potential clinical application value in related ophthalmic diseases. At present, multiple molecules and drugs targeting FOXO3a have been reported to have the potential for the treatment of related ophthalmic diseases, but further clinical trials are needed. In conclusion, this review can facilitate us to grasp the role of FOXO3a in the visual system and provide new views and bases for the treatment strategy research of age-related eye diseases.

Association Between Endothelial Cell Density and Corneal Thickness in Medium, Short, and Long Eyes of Han Chinese Cataract Patients

PURPOSE

To evaluate the association between the endothelial cell density (ECD) and central corneal thickness (CCT) in medium, short, and long eyes of preoperative Han Chinese cataract patients.

DESIGN

Retrospective cross-sectional study.

METHODS

We consecutively enrolled 410 eyes, namely, 50 short eyes (axial length [AL]<22.0 mm), 150 medium eyes (22.0≤AL<24.0 mm), 120 medium-long eyes (24.0≤AL<26.0 mm), and 90 long eyes (AL≥26.0 mm), of 410 adult patients scheduled for cataract surgery. The ECD and CCT were determined preoperatively with a noncontact specular microscope. The association between the CCT and ECD was identified by using a multivariable regression analysis. A thin cornea was defined as having a CCT less than 500 µm.

RESULTS

After adjusting for age, the presence of arterial hypertension, the presence of diabetes mellitus, intraocular pressure, and AL, a positive association between the CCT and ECD was identified in short eyes (linear regression coefficient [B]=3.40; standardized B [β]=0.52; P = .03), medium eyes (B = 2.33; β=0.28; P = .002), medium-long eyes (B = 1.84; β=0.25; P = .02), and long eyes (B = 2.69; β=0.41; P = .04). In the total group, the multivariable logistic analysis showed a significant link between the presence of a thin cornea and a lower ECD (odds ratio [OR]=0.80 per 100 cells/mm2 increase; P = .001).

CONCLUSIONS

For cataract patients of Han ethnicity, a significant association between a thin CCT and a lower ECD was shown across the AL spectrum and was most prominent in short eyes. Eyes with a thin cornea are more likely to have a lower ECD.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Dynamic changes of endothelial and stromal cilia are required for the maintenance of corneal homeostasis

Primary cilia are distributed extensively within the corneal epithelium and endothelium. However, the presence of cilia in the corneal stroma and the dynamic changes and roles of endothelial and stromal cilia in corneal homeostasis remain largely unknown. Here, we present compelling evidence for the presence of primary cilia in the corneal stroma, both in vivo and in vitro. We also demonstrate dynamic changes of both endothelial and stromal cilia during corneal development. In addition, our data show that cryoinjury triggers dramatic cilium formation in the corneal endothelium and stroma. Furthermore, depletion of cilia in mutant mice lacking intraflagellar transport protein 88 compromises the corneal endothelial capacity to establish the effective tissue barrier, leading to an upregulation of α-smooth muscle actin within the corneal stroma in response to cryoinjury. These observations underscore the essential involvement of corneal endothelial and stromal cilia in maintaining corneal homeostasis and provide an innovative strategy for the treatment of corneal injuries and diseases.

Topical Insulin Eye Drops: Stability and Safety of Two Compounded Formulations for Treating Persistent Corneal Epithelial Defects

Compounded insulin eye drops were prepared at 1 IU/mL from commercially available subcutaneous insulin by dilution in saline solution or artificial tears. Physicochemical characterization and in vitro tolerance testing in human and conjunctival cells were followed by a 28-day short-term stability study under various conditions. The formulations were isotonic (280-300 mOsm/L), had a pH close to neutral (7-8), medium surface-tension values (<56 MN/m-1), and low (≈1 mPa·s) and medium (≈5 mPa·s) viscosities (compounded normal saline solution and artificial tear-based preparation, respectively). These values remained stable for 28 days under refrigeration. Microbiological stability was also excellent. Insulin potency remained in the 90-110% range in the compounded formulations containing normal saline solution when stored at 2-8 °C for 28 days, while it decreased in those based on artificial tears. Although both formulations were well tolerated in vitro, the compounded insulin diluted in a normal saline solution exhibited better cell tolerance. Preliminary data in humans showed that insulin in saline solution was an effective and safe treatment for persistent corneal epithelial defects. Compounded insulin eye drops diluted in normal saline solution could, therefore, constitute an emergent therapy for the treatment of persistent corneal epithelial defects.

The role of topical insulin in ocular surface restoration: A review

Corneal epithelial defects are one of the most common ocular disorders. Restoring corneal integrity is crucial to reduce pain and regain function, but in cases of neurotrophic or desensitized corneas, healing can be significantly delayed. Treating neurotrophic corneas is challenging for ophthalmologists, and surgical intervention is often indicated to manage refractory cases that are unresponsive to medical therapy. Over the last decade, as more expensive therapeutics reach the market, topical insulin has returned to the forefront as an affordable option to improve corneal wound healing. There is still a paucity of data on the use and the efficacy of topical insulin, with no consensus regarding its indications, preparation, or posology. Here we review the literature on topical insulin for corneal and ocular surface pathologies, with a focus on the current evidence, its mechanisms of action, and its safety profile. Additionally, we share our experience in the field and provide a potential framework for future research.

SMAD4-Dependent Signaling Pathway Involves in the Pathogenesis of TGFBR2-Related CE-like Phenotype

(1) Background: Our previous data indicated that disturbance of the Transforming Growth Factor beta (TGFB) signaling pathway via its Type-2 Receptor (TGFBR2) can cause a Corneal Ectasia (CE)-like phenotype. The purpose of this study is to elucidate whether the SMAD4-dependent signaling pathway is involved in the TGFBR2-related CE-like pathogenesis. (2) Methods: Smad4 was designed to be conditionally knocked out from keratocytes. Novel triple transgenic mice, KerartTA; Tet-O-Cre; Smad4flox/flox (Smad4kera-cko), were administered with doxycycline (Dox). Optical Coherence Tomography (OCT) was performed to examine Central Corneal Thickness (CCT), Corneal Radius, Anterior Chamber and CE-like phenotype and compared to the littermate Control group (Smad4Ctrl). (3) Results: The OCT revealed normal cornea in the Smad4Ctrl and a CE-like phenotype in the Smad4kera-cko cornea, in which the overall CCT in Smad4kera-cko was thinner than that of Smad4Ctrl at P42 (n = 6, p < 0.0001) and showed no significant difference when compared to that in Tgfbr2kera-cko. Furthermore, the measurements of the Anterior Chamber and Corneal Radius indicated a substantial ectatic cornea in the Smad4kera-cko compared to Smad4Ctrl. The H&E staining of Smad4kera-cko mimics the finding in the Tgfbr2kera-cko. The positive immunostaining of cornea-specific marker K12 indicating the cell fate of cornea epithelium remained unchanged in Smad4kera-cko and the Proliferating Cell Nuclear Antigen (PCNA) immunostaining further indicated an enhanced proliferation in the Smad4kera-cko. Both immunostainings recapitulated the finding in Tgfbr2kera-cko. The Masson's Trichrome staining revealed decreased collagen formation in the corneal stroma from both Smad4kera-cko and Tgfbr2kera-cko. The collagen type 1 (Col1a1) immunostaining further confirmed the reduction in collagen type 1 formation in Smad4kera-cko. (4) Conclusions: The aforementioned phenotypes in the Smad4kera-cko strain indicated that the SMAD4-dependent signaling pathway is involved in the pathogenesis of the CE-like phenotype observed in Tgfbr2kera-cko.

Keratan sulfate, an electrosensory neurosentient bioresponsive cell instructive glycosaminoglycan

The roles of keratan sulfate (KS) as a proton detection glycosaminoglycan in neurosensory processes in the central and peripheral nervous systems is reviewed. The functional properties of the KS-proteoglycans aggrecan, phosphacan, podocalyxcin as components of perineuronal nets in neurosensory processes in neuronal plasticity, cognitive learning and memory are also discussed. KS-glycoconjugate neurosensory gels used in electrolocation in elasmobranch fish species and KS substituted mucin like conjugates in some tissue contexts in mammals need to be considered in sensory signalling. Parallels are drawn between KS's roles in elasmobranch fish neurosensory processes and its roles in mammalian electro mechanical transduction of acoustic liquid displacement signals in the cochlea by the tectorial membrane and stereocilia of sensory inner and outer hair cells into neural signals for sound interpretation. The sophisticated structural and functional proteins which maintain the unique high precision physical properties of stereocilia in the detection, transmittance and interpretation of acoustic signals in the hearing process are important. The maintenance of the material properties of stereocilia are essential in sound transmission processes. Specific, emerging roles for low sulfation KS in sensory bioregulation are contrasted with the properties of high charge density KS isoforms. Some speculations are made on how the molecular and electrical properties of KS may be of potential application in futuristic nanoelectronic, memristor technology in advanced ultrafast computing devices with low energy requirements in nanomachines, nanobots or molecular switches which could be potentially useful in artificial synapse development. Application of KS in such innovative areas in bioregulation are eagerly awaited.

A PEDF peptide mimetic effectively relieves dry eye in a diabetic murine model by restoring corneal nerve, barrier, and lacrimal gland function

PURPOSE

The study investigated effectiveness of a novel PEDF peptide mimetic to alleviate dry eye-like pathologies in a Type I diabetic mouse model established using streptozotocin.

METHODS

Mice were treated topically for 3-6 weeks with Ppx (a 17-mer PEDF mimetic) 2x/day or vehicle. Corneal sensitivity, tear film, epithelial and endothelial injury were measured using Cochet-Bonnet esthesiometer, phenol red cotton thread wetting, fluorescein sodium staining, and ZO1 expression, respectively. Inflammatory and parasympathetic nerve markers and activation of the MAPK/JNK pathways in the lacrimal glands were measured.

RESULTS

Diabetic mice exhibited features of dry eye including reduced corneal sensation and tear secretion and increased corneal epithelium injury, nerve degeneration, and edema. Ppx reversed these pathologies and restored ZO1 expression and morphological integrity of the endothelium. Upregulation of IL-1β and TNFα, increased activation of P-38, JNK, and ERK, and higher levels of M3ACHR in diabetic lacrimal glands were also reversed by the peptide treatment.

CONCLUSION

The study demonstrates that topical application of a synthetic PEDF mimetic effectively alleviates diabetes-induced dry eye by restoring corneal sensitivity, tear secretion, and endothelial barrier and lacrimal gland function. These findings have significant implications for the potential treatment of dry eye using a cost-effective and reproducible approach with minimal invasiveness and no obvious side effects.

Single cell analysis of short-term dry eye induced changes in cornea immune cell populations

Background

Dry eye causes corneal inflammation, epitheliopathy and sensorineural changes. This study evaluates the hypothesis that dry eye alters the percentages and transcriptional profiles of immune cell populations in the cornea.

Methods

Desiccating stress (DS) induced dry eye was created by pharmacologic suppression of tear secretion and exposure to drafty low humidity environment. Expression profiling of corneal immune cells was performed by single-cell RNA sequencing (scRNA-seq). Cell differentiation trajectories and cell fate were modeled through RNA velocity analysis. Confocal microscopy was used to immunodetect corneal immune cells. Irritation response to topical neurostimulants was assessed.

Results

Twelve corneal immune cell populations based on their transcriptional profiles were identified at baseline and consist of monocytes, resident (rMP) and MMP12/13 high macrophages, dendritic cells (cDC2), neutrophils, mast cells, pre T/B cells, and innate (γDT, ILC2, NK) and conventional T and B lymphocytes. T cells and resident macrophages (rMP) were the largest populations in the normal cornea comprising 18.6 and 18.2 percent, respectively. rMP increased to 55.2% of cells after 5 days of DS. Significant changes in expression of 1,365 genes (adj p < 0.0001) were noted in rMP with increases in cytokines and chemokines (Tnf, Cxcl1, Ccl12, Il1rn), inflammatory markers (Vcam, Adam17, Junb), the TAM receptor (Mertk), and decreases in complement and MHCII genes. A differentiation trajectory from monocytes to terminal state rMP was found. Phagocytosis, C-type lectin receptor signaling, NF-kappa B signaling and Toll-like receptor signaling were among the pathways with enhanced activity in these cells. The percentage of MRC1+ rMPs increased in the cornea and they were observed in the basal epithelium adjacent to epithelial nerve plexus. Concentration of the chemokine CXCL1 increased in the cornea and it heightened irritation/pain responses to topically applied hypertonic saline.

Conclusion

These findings indicate that DS recruits monocytes that differentiate to macrophages with increased expression of inflammation associated genes. The proximity of these macrophages to cornea nerves and their expression of neurosensitizers suggests they contribute to the corneal sensorineural changes in dry eye.

Fuchs endothelial corneal dystrophy: an updated review

PURPOSE

The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current  therapeutic approaches, and future treatment perspectives.

METHODS

Literature review.

RESULTS

Fuchs' endothelial corneal dystrophy (FECD) is the most common bilateral corneal dystrophy and accounts for one-third of all corneal transplants performed in the US. FECD is caused by a combination of genetic and non-heritable factors, and there are two types: early-onset FECD, which affects individuals from an early age and is usually more severe, and late-onset FECD, which is more common and typically manifests around the age of 40. The hallmark findings of FECD include progressive loss of corneal endothelial cells and the formation of focal excrescences (guttae) on the Descemet membrane. These pathophysiological changes result in progressive endothelial dysfunction, leading to a decrease in visual acuity and blindness in later stages. The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current therapeutic approaches, and future treatment perspectives.

CONCLUSION

With the characterization and understanding of FECD-related genes and ongoing research into regenerative therapies for corneal endothelium, we can hope to see more significant improvements in the future in the management and care of the disease.

Cryopreservation-induced delayed injury and cell-type-specific responses during the cryopreservation of endothelial cell monolayers

The cryopreservation of endothelial cell monolayers is an important step that bridges the cryopreservation of cells in suspension to that of tissues. Previous studies have identified clear distinctions in freezing mechanisms between cells in suspension and in monolayers, as well as developed novel protocols for monolayer cryopreservation. Recently, our group has shown that human umbilical vein endothelial cell (HUVEC) and porcine corneal endothelial cell (PCEC) monolayers grown on Rinzl plastic substrate can be cryopreserved in 5% dimethyl sulfoxide, 6% hydroxyethyl starch, and 2% chondroitin sulfate, following a slow-cooling protocol (-1 °C/min) with rapid plunge into liquid nitrogen from -40 °C. However, membrane integrity assessments were done immediately post thaw, which may result in an overestimation of cell viability due to possible delayed injury responses. Here, we show that for the optimal protocol condition of plunge at the -40 °C interrupt temperature, HUVEC and PCEC monolayers exhibited no significant immediate post-thaw injuries nor delayed injury responses during the 24-h post-thaw overnight culture period. HUVEC monolayers experienced no significant impact to their natural growth rate during the post-thaw culture, while PCEC monolayers experienced significantly higher growth than the unfrozen controls. The difference in the low-temperature responses between HUVEC and PCEC monolayers was further shown under high temperature plunge conditions. At these suboptimal plunge temperatures, HUVEC monolayers exhibited moderate immediate membrane injury but a pronounced delayed injury response during the 24-h post-thaw culture, while PCEC monolayers showed significant immediate membrane injury but no additional delayed injury response during the same period. Therefore, we provide further validation of our group's previously designed endothelial monolayer cryopreservation protocol for HUVEC and PCEC monolayers, and we identify several cell-type-specific responses to the freezing process.

Temperature Dependence of Membrane Permeability Parameters for Five Cell Types Using Nonideal Thermodynamic Assumptions to Mathematically Model Cryopreservation Protocols

Cryopreservation is the process of preserving biological matter at subzero temperatures for long-term storage. During cryopreservation, cells are susceptible to various injuries that can be mitigated by controlling the cooling and warming profiles and cryoprotective agent (CPA) addition and removal procedures. Mathematical modeling of the changing cell volume at different temperatures can greatly reduce the experiments needed to optimize cryopreservation protocols. Such mathematical modeling requires as inputs the cell membrane permeabilities to water and CPA and the osmotically inactive fraction of the cell. Since the intra- and extracellular solutions are generally thermodynamically nonideal, our group has been incorporating the osmotic virial equation to model the solution thermodynamics that underlie the cell volume change equations, adding the second and third osmotic virial coefficients of the grouped intracellular solute to the cell osmotic parameters that must be measured. In our previous work, we reported methods to obtain cell osmotic parameters at room temperature by fitting experimental cell volume kinetic data with equations that incorporated nonideal solution thermodynamics assumptions. Since the relevant cell volume excursions occur at different temperatures, the temperature dependence of the osmotic parameters plays an important role. In this work, we present a new two-part fitting method to obtain five cell-type-specific parameters (water permeability, dimethyl sulfoxide permeability, osmotically inactive fraction, and the second and third osmotic virial coefficients of the intracellular solution) from experimental measurements of equilibrium cell volume and cell volume as a function of time at room temperature and 0 °C for five cell types, namely, human umbilical vein endothelial cells (HUVECs), H9c2 rat myoblasts, porcine corneal endothelial cells (PCECs), the Jurkat T-lymphocyte cell line, and human cerebral microvascular endothelial cells (hCMECs/D3 cell line). The fitting method in this work is based on both equilibrium and kinetic cell volume data, enabling us to solve some technical challenges and expand our previously reported measurement technique to 0 °C. Finally, we use the measured parameters to model the cell volume changes for a HUVEC cryopreservation protocol to demonstrate the impact of the nonideal thermodynamic assumptions on predicting the changing cell volume during freezing and thawing.

Corneal wound healing following infrared laser irradiation at the wavelengths of 1.319 and 10.6 μm

OBJECTIVES

To investigate the wound healing of rabbit cornea following infrared laser irradiations at the wavelengths of 1.319 and 10.6 μm.

MATERIALS AND METHODS

Twelve New Zealand rabbits were selected to establish a corneal injury model. The right and left eyes were irradiated with a neodymium-doped yttrium aluminum garnet laser at the wavelength of 1.319 μm (140 J/cm2 ) for 0.7 s and a CO2 laser at the wavelength of 10.6 μm (5.94 J/cm2 ) for 0.14 s, respectively. The incident spot diameter was 3 mm. Optical coherence tomography (OCT) was used to monitor injuries at 0 h, 0.5 h, 1 h, 3 h, 6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, 48 h, 54 h, 60 h, 66 h, 3 d, 7 d, 14 d, 28 d, 3 m, and 6 m postexposure. Meanwhile, slit-lamp microscopy and histopathology were performed at 6 h, 24 h, 3 d, 7 d, 14 d, 28 d, 3 m, and 6 m postexposure.

RESULTS

After the two types of infrared laser injuries, distinct white circular lesions on the corneal surface were directly observed. Deeper corneal injury, more severe edema, and faster migration of new epithelium were found for the wavelength of 1.319 μm, compared to the wavelength of 10.6 μm.

CONCLUSIONS

OCT combined with histopathology and slit-lamp microscopy can clearly observe the dynamic process of corneal wound healing after infrared laser irradiation. The damage characteristics for the two different wavelengths were visibly different, but the whole wound healing process was similar. The obtained results may provide references for the diagnosis, treatment, and evaluation of laser-induced damages.

The potential benefits of polyphenols for corneal diseases

The cornea functions as the primary barrier of the ocular surface, regulating temperature and humidity while providing protection against oxidative stress, harmful stimuli and pathogenic microorganisms. Corneal diseases can affect the biomechanical and optical properties of the eye, resulting in visual impairment or even blindness. Due to their diverse origins and potent biological activities, plant secondary metabolites known as polyphenols offer potential advantages for treating corneal diseases owing to their anti-inflammatory, antioxidant, and antibacterial properties. Various polyphenols and their derivatives have demonstrated diverse mechanisms of action in vitro and in vivo, exhibiting efficacy against a range of corneal diseases including repair of tissue damage, treatment of keratitis, inhibition of neovascularization, alleviation of dry eye syndrome, among others. Therefore, this article presents a concise overview of corneal and related diseases, along with an update on the research progress of natural polyphenols in safeguarding corneal health. A more comprehensive understanding of natural polyphenols provides a novel perspective for secure treatment of corneal diseases.

Single-cell transcriptomic analysis of corneal organoids during development

Corneal organoids are useful tools for disease modeling and tissue transplantation; however, they have not yet been well studied during maturation. We characterized human iPSC-derived corneal organoids at 1, 2, 3, and 4 months of development using single-cell RNA sequencing to determine the cellular heterogeneity at each stage. We found pluripotent cell clusters committed to epithelial cell lineage at 1 month; early corneal epithelial, endothelial, and stromal cell markers at 2 months; keratocytes as the largest cell population at 3 months; and a large epithelial cell population at 4 months. We compared organoid to fetal corneal development at different stages and found that 4-month organoids closely resemble the corneal cellular complexity of the fetal (16 post conception week) and adult cornea. Using RNA velocity trajectory analysis, we found that less differentiated cells appear to give rise to corneal epithelial cells during development.

Permeation kinetics of dimethyl sulfoxide in porcine corneoscleral discs

The cornea is the transparent tissue in front of the eye that bends light to help the eye focus. More than five million people's vision can be restored by a corneal transplant (keratoplasty), but there is a scarcity of suitable donor tissue. Cryopreservation could potentially increase the on-demand availability of corneas by reducing expiration and contamination during hypothermic storage, and allow equitable distribution. Understanding the transport of water and cryoprotectants across the tissue is important in developing effective cryopreservation protocols. Here, we first measured the shrinking and swelling kinetics at 22 °C and 0 °C of porcine corneoscleral discs when exposed to phosphate-buffered saline and to a cryoprotectant vehicle solution containing 2.5% chondroitin sulfate and 1% dextran. Other valuable measurements were made including the density and osmolality of the vehicle solution at 0 °C, and the water fraction of porcine cornea and sclera. Using the knowledge gained from this first part to minimize background swelling, we then examined permeation kinetics of dimethyl sulfoxide (Me2SO) in porcine corneoscleral discs at 0 °C, the temperature at which cryoprotectant loading typically occurs. The concentration data obtained as a function of time were fitted to a Fick's law model of one-dimensional diffusion to measure an effective diffusion coefficient of Me2SO, which was found to be 5.306×10-11 m2/s. We further quantified permeation kinetics of Me2SO in sclera alone at 0 °C to support our hypothesis that our measurements for corneoscleral discs will not be affected by the presence of the sclera. The obtained effective diffusion coefficient can be used in modelling aimed at developing cryopreservation protocols that minimize the exposure time of the corneas during the cryoprotectant loading step.

Efficacy of topical insulin for recurrent epithelial corneal erosions

BACKGROUND

Topical insulin can promote and accelerate corneal regeneration, even in eyes with serious comorbidities, and offers several benefits over other treatment options.

AIMS

The aim of this study is to evaluate the effect of topical insulin in treatment of recurrent epithelial corneal erosion.

METHODS

Patients with recurrent epithelial erosions were included in a prospective non-randomized hospital-based study, divided into two groups, one of them received persistent epithelial defects (PEDs) conventional treatment and the other received the same treatment with insulin eye drops 4 times/day. All patients were examined carefully by slit lamp. Patients during the 1st, 2nd, 3rd, and 4th weeks as well as after 2 months. Demographics, etiology, therapy, comorbidities, and the healing time of PED were performed.

RESULTS

Area shows significant improvement after 2 weeks (p = 0.006), 2 months (p = 0.046), and 3 months (p = 0.002) in group II (cornetears gel and topical insulin) as compared to group I (cornetears gel). The recurrence was statistically significant decreased with cornetears gel and topical insulin (group II) by 0.0%, as compared to cornetears gel (group I) by 3 patients (21.4%).

CONCLUSION

Topical insulin can promote corneal reepithelization in recurrent epithelial erosion and decreases recurrence in these cases. Other advantages include excellent tolerance, availability, and cost-effectiveness.

Comparison of corneal endothelial cell density and morphology with Optisol GS and Life4C storage media in the eye bank: a 5-year retrospective analysis

Purpose

Optisol GS and Life4C are corneal storage media used by eye banks worldwide. We sought to determine if either solution was associated with superior corneal endothelial cell density (ECD) or morphology in a large cohort of donor corneas.

Methods

From January 2016 through December 2020, 10,316 corneas from 5,624 unique donors were acquired and analyzed at Rocky Mountain Lions Eye Bank. In April 2019, Life4C replaced Optisol GS as the sole storage medium. We compared ECD and morphology before and after April 2019, and excluded corneas processed within the transition period. Univariable and multivariable regression analyses accounted for age, sex, tobacco use, heavy alcohol use, and diabetes. Only right corneas were analyzed to account for the correlation between eyes.

Results

Of 5042 right corneas analyzed, 3486 were stored in Optisol GS and 1556 in Life4C. There was no significant difference in ECD across groups (2794 vs. 2793 cells/mm2 in Optisol GS and Life4C, p=0.88). In multivariate analyses, there was no significant difference in corneal ECD (0.6 cells/mm2 higher with Life4C, p=0.96) or hexagonality (0.22% higher with Life4C, p=0.31). However, the coefficient of variation was significantly lower in the Life4C group (-0.0039, p=0.03). After adjustment for above factors, corneas in Life4C demonstrated a 3.1% decreased likelihood of exhibiting CV values greater than 0.40 (p=0.009).

Conclusions

This study demonstrates comparable and favorable outcomes using both storage media and confirms their overall efficacy. The decreased CV in Life4C is not of clinically significant magnitude, but merits further research in clinical and long-term settings.

Nano Self-Assemblies of Caffeic Acid-Fibronectin Mimic a Peptide Conjugate for the Treatment of Corneal Epithelial Injury

Rapid corneal re-epithelialization is important for corneal wound healing. Corneal epithelial cell motility and oxidative stress are important targets for therapeutic intervention. In this study, we covalently conjugated the antioxidant caffeic acid (CA) with a bioactive peptide sequence (PHSRN) to generate a CA-PHSRN amphiphile, which was formulated into nanoparticular eye drops with an average size of 43.21 ± 16 nm. CA-PHSRN caused minimal cytotoxicity against human corneal epithelial cells (HCECs) and RAW264.7 cells, exhibited an excellent free radical scavenging ability, and remarkably attenuated reactive oxygen species (ROS) levels in H2O2-stimulated HCECs. The antioxidant and anti-inflammatory activities of CA-PHSRN were assessed in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. The results show that CA-PHSRN treatment effectively prevented LPS-induced DNA damage and significantly reduced the levels of LPS-induced pro-inflammatory cytochemokines (i.e., iNOS, NO, TNF-α, IL-6, and COX-2) in a dose-dependent manner. Moreover, using a rabbit corneal epithelial ex vivo migration assay, we demonstrated that the proposed CA-PHSRN accelerated corneal epithelial cell migration and exhibited high ocular tolerance and ocular bioavailability after topical instillation. Taken together, the proposed CA-PHSRN nanoparticular eye drops are a promising therapeutic formulation for the treatment of corneal epithelial injury.

Development and validation of a reliable rabbit model of limbal stem cell deficiency by mechanical debridement using an ophthalmic burr

A simple and reproducible method is necessary to generate reliable animal models of limbal stem cell deficiency (LSCD) for assessing the safety and efficacy of new therapeutic modalities. This study aimed to develop and validate a rabbit model of LSCD through mechanical injury. The corneal and limbal epithelium of New Zealand White rabbits (n = 18) were mechanically debrided using an ophthalmic burr (Algerbrush II) with a 1.0-mm rotating head after 360° conjunctival peritomy. The debrided eyes were serially evaluated for changes in corneal opacity, neo-vascularization, epithelial defect and corneal thickness using clinical photography, slit lamp imaging, fluorescein staining, and anterior segment optical coherence tomography scanning (AS-OCT). Following this, an assessment of histopathology and phenotypic marker expression of the excised corneas was conducted. The experimental eyes were grouped as mild (n = 4), moderate (n = 10), and severe (n = 4) based on the grade of LSCD. The moderate group exhibited abnormal epithelium, cellular infiltration in the stroma, and vascularization in the central, peripheral, and limbal regions of the cornea. The severe group demonstrated central epithelial edema, peripheral epithelial thinning with sparse goblet cell population, extensive cellular infiltration in the stroma, and dense vascularization in the limbal region of the cornea. A significant decrease in the expression of K12 and p63 (p < 0.0001) was observed, indicating the loss of corneal epithelium and limbal epithelial stem cells in the LSCD cornea. This study demonstrates that the Alger brush-induced mechanical debridement model provides a reliable model of LSCD with comprehensive clinic-pathological features and that is well suited for evaluating novel therapeutic and regenerative approaches.

Overview of Recent Advances in Nano-Based Ocular Drug Delivery

Ocular diseases profoundly impact patients' vision and overall quality of life globally. However, effective ocular drug delivery presents formidable challenges within clinical pharmacology and biomaterial science, primarily due to the intricate anatomical and physiological barriers unique to the eye. In this comprehensive review, we aim to shed light on the anatomical and physiological features of the eye, emphasizing the natural barriers it presents to drug administration. Our goal is to provide a thorough overview of various characteristics inherent to each nano-based drug delivery system. These encompass nanomicelles, nanoparticles, nanosuspensions, nanoemulsions, microemulsions, nanofibers, dendrimers, liposomes, niosomes, nanowafers, contact lenses, hydrogels, microneedles, and innovative gene therapy approaches employing nano-based ocular delivery techniques. We delve into the biology and methodology of these systems, introducing their clinical applications over the past decade. Furthermore, we discuss the advantages and challenges illuminated by recent studies. While nano-based drug delivery systems for ophthalmic formulations are gaining increasing attention, further research is imperative to address potential safety and toxicity concerns.

Characterization of the Limbal Epithelial Stem Cell Niche

Purpose

Limbal epithelial stem cells (LESCs) reside within a LSC niche (LSCN). We recently identified that hyaluronan (HA) is a major constituent of the LSCN, and that HA is necessary for maintaining LESCs in the "stem cell" state, both in vitro and in vivo. Herein, we characterized the LSCN to identify key components of the HA-specific LSCN.

Methods

The cornea and limbal rim were dissected from mouse corneas, subjected to mRNA extraction, and sequenced using a NextSeq 500 (Illumina) and data processed using CLC Genomics Workbench 20 (Qiagen) and the STRING database to identify key components of the LSCN. Their expression was confirmed by real-time PCR, Western blotting, and immunohistochemistry. Furthermore, the differential expression of key compounds in different corneal cell types were determined with single-cell RNA sequencing.

Results

We identified that the hyaladherins inter-alpha-inhibitor (IαI), TSG-6 and versican are highly expressed in the limbus. Specifically, HA/HC complexes are present in the LSCN, in the stroma underlying the limbal epithelium, and surrounding the limbal vasculature. For IαI, heavy chains 5 and 2 (HC5 and HC2) were found to be the most highly expressed HCs in the mouse and human limbus and were associate with HA-forming HA/HC-specific matrices.

Conclusions

The LSCN contains HA/HC complexes, which have been previously correlated with stem cell niches. The identification of HA/HC complexes in the LSCN could serve as a new therapeutic avenue for treating corneal pathology. Additionally, HA/HC complexes could be used as a substrate for culturing LESCs before LESC transplantation.

Whole-Exome Sequencing of 24 Spanish Families: Candidate Genes for Non-Syndromic Pediatric Keratoconus

Keratoconus is a corneal dystrophy that is one of the main causes of corneal transplantation and for which there is currently no effective treatment for all patients. The presentation of this disease in pediatric age is associated with rapid progression, a worse prognosis and, in 15-20% of cases, the need for corneal transplantation. It is a multifactorial disease with genetic variability, which makes its genetic study difficult. Discovering new therapeutic targets is necessary to improve the quality of life of patients. In this manuscript, we present the results of whole-exome sequencing (WES) of 24 pediatric families diagnosed at the University Hospital La Paz (HULP) in Madrid. The results show an oligogenic inheritance of the disease. Genes involved in the structure, function, cell adhesion, development and repair pathways of the cornea are proposed as candidate genes for the disease. Further studies are needed to confirm the involvement of the candidate genes described in this article in the development of pediatric keratoconus.

Mapping nanoscale topographic features in thick tissues with speckle diffraction tomography

Resolving three-dimensional morphological features in thick specimens remains a significant challenge for label-free imaging. We report a new speckle diffraction tomography (SDT) approach that can image thick biological specimens with ~500 nm lateral resolution and ~1 μm axial resolution in a reflection geometry. In SDT, multiple-scattering background is rejected through spatiotemporal gating provided by dynamic speckle-field interferometry, while depth-resolved refractive index maps are reconstructed by developing a comprehensive inverse-scattering model that also considers specimen-induced aberrations. Benefiting from the high-resolution and full-field quantitative imaging capabilities of SDT, we successfully imaged red blood cells and quantified their membrane fluctuations behind a turbid medium with a thickness of 2.8 scattering mean-free paths. Most importantly, we performed volumetric imaging of cornea inside an ex vivo rat eye and quantified its optical properties, including the mapping of nanoscale topographic features of Dua's and Descemet's membranes that had not been previously visualized.

Twelve-Month Clinical and Histopathological Performance of a Novel Synthetic Cornea Device in Rabbit Model

Purpose

To report the biological stability and postoperative outcomes of a second-generation, single-piece, flexible synthetic cornea in a rabbit model.

Methods

Device materials and design were amended to enhance biointegration. Optic skirt design devices were made from compact perfluoroalkoxy alkane with porous expanded polytetrafluoroethylene ingrowth surface overlying the skirt and optic wall. Sixteen devices were implanted into intrastromal pocket in rabbit eyes. Rabbits were randomly assigned to 6- and 12-month follow-up cohorts (n = 8 in each) postoperatively. Monthly examinations and optical coherence tomography assessed cornea-device integration, iridocorneal angle, optic nerve, and retina.

Results

There were no intraoperative complications. All devices were in situ at exit, with clear optics. No retroprosthetic membrane, glaucoma, cataract formation, or retinal detachment was observed. Two rabbits in the 6-month group had mild, focal anterior lamella thinning without retraction adjacent to the optic near tight sutures. Three postoperative complications occurred in the 12-month group. One rabbit diagnosed with endophthalmitis was euthanized on day 228. Mild sterile focal retraction of anterior lamella occurred in two rabbits, which were terminated on days 225 and 315. Light microscopic examination of enucleated globes demonstrated fibroplasia with new collagen deposition into the porous scaffold without significant inflammation, encapsulation, or granuloma formation.

Conclusions

Clinical evaluations, imaging, and histopathological findings indicate favorable outcomes of this synthetic corneal device in a rabbit model. Early feasibility studies in humans are being planned.

Translational Relevance

Favorable 12-month results of the device in rabbits demonstrate vision-restoring potential in corneally blind individuals at high risk of failure with donor keratoplasty.

Genome editing in the treatment of ocular diseases

Genome-editing technologies have ushered in a new era in gene therapy, providing novel therapeutic strategies for a wide range of diseases, including both genetic and nongenetic ocular diseases. These technologies offer new hope for patients suffering from previously untreatable conditions. The unique anatomical and physiological features of the eye, including its immune-privileged status, size, and compartmentalized structure, provide an optimal environment for the application of these cutting-edge technologies. Moreover, the development of various delivery methods has facilitated the efficient and targeted administration of genome engineering tools designed to correct specific ocular tissues. Additionally, advancements in noninvasive ocular imaging techniques and electroretinography have enabled real-time monitoring of therapeutic efficacy and safety. Herein, we discuss the discovery and development of genome-editing technologies, their application to ocular diseases from the anterior segment to the posterior segment, current limitations encountered in translating these technologies into clinical practice, and ongoing research endeavors aimed at overcoming these challenges.

Nanotechnology-based ocular drug delivery systems: recent advances and future prospects

Ocular drug delivery has constantly challenged ophthalmologists and drug delivery scientists due to various anatomical and physiological barriers. Static and dynamic ocular barriers prevent the entry of exogenous substances and impede therapeutic agents' active absorption. This review elaborates on the anatomy of the eye and the associated constraints. Followed by an illustration of some common ocular diseases, including glaucoma and their current clinical therapies, emphasizing the significance of drug therapy in treating ocular diseases. Subsequently, advances in ocular drug delivery modalities, especially nanotechnology-based ocular drug delivery systems, are recommended, and some typical research is highlighted. Based on the related research, systematic and comprehensive characterizations of the nanocarriers are summarized, hoping to assist with future research. Besides, we summarize the nanotechnology-based ophthalmic drugs currently on the market or still in clinical trials and the recent patents of nanocarriers. Finally, inspired by current trends and therapeutic concepts, we provide an insight into the challenges faced by novel ocular drug delivery systems and further put forward directions for future research. We hope this review can provide inspiration and motivation for better design and development of novel ophthalmic formulations.

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.

Application of Hydrogels in the Device of Ophthalmic Iontophoresis: Theory, Developments and Perspectives

The human eye is a consolidated organ with delicate structures and unique immune privileges. Ocular diseases are intractable due to the intrinsic biological barriers within the eyeball. Hydrogels are excellent drug-carrying substances with soft material and excellent properties. They have been extensively used to deliver drugs into ocular tissue via iontophoresis devices. Ophthalmic iontophoresis is an electrochemical technique using tiny electrical currents to deliver drugs into the eye non-invasively. The early infantile iontophoresis technique often required long applying time to achieve therapeutic dose in the posterior ocular segment. The potential limitations in the initial drug concentration and the maximum safe currents would also impede the efficiency and safety of iontophoresis. Moreover, the poor patient compliance always leads to mechanical damage to the cornea and sclera during application. Advantageously, the flexible drug-carrying hydrogel can be in direct contact with the eye during iontophoresis, thereby reducing mechanical damage to the ocular surface. Moreover, the water absorption and adjustable permeability of hydrogels can reduce the electrochemical (EC) reactions and enhance the efficiency of iontophoresis. In this review, we focus on recent developments of hydrogels iontophoresis in ophthalmologic practice. Refinements of the knowledge would provide an outlook for future application of hydrogels in treating ocular disease.

Optimization of method for achieving a single-cell suspension from mouse corneas

The single-cell RNA-sequencing (scRNA-seq) technique is used to explore the biological characteristics of tissues under pathological and physiological conditions that include certain chronic eye diseases. Harvesting of single-cell suspensions is one challenge inherent to scRNA-seq procedures. This study aimed to use an optimized method to digest a whole mouse cornea to harvest single-cell suspensions. We utilized five different mouse cornea digestion methods to obtain single-cell suspensions: (1) 5 dissected mouse corneas were cut into pieces (∼0.5 mm) and digested in trypsin for 10 min, and this digestion was repeated for 10 cycles; (2) 5 dissected mouse corneas were cut into pieces and incubated with 5 mg/ml collagenase A at 37 °C for 1h and then further digested in trypsin at 37 °C for 10 min; (3) used the same approach as that used in method 2, but the second digestion step was performed in TrypLE for 20 min; (4) used the same approach as that used in method 2, but the concentration of collagenase A was 2 mg/ml and the incubation time was 2h; (5) used the same approach as that used in method 3, but the corneas were incubated in 2 mg/ml collagenase A at 37 °C for 2h. Trypan blue staining was used to calculate the cell viability and agglomeration rate. The cell types and percentages were determined using immunofluorescence staining. RNA integrity number (RIN) was measured by Agilent 2100. Method 1 showed the lowest cell yield (0.375 × 10⁵), epithelial cell percentage, and less than 70% cell viability, thus not a proper protocol. Method 2 showed the highest cell viability (over 90%), percentage of single-cell (89.53%), and high cell quantity (1.05 × 10⁵). Method 3 had a significantly lower cell viability (55.30%). Cell agglomeration rates of method 4 and 5 reached up to 20% and 13%, and with lower cell viability (72.51%, 59.87%, respectively) and decreased epithelial cell rate compared to method 2 and 3. The results suggest that method 2 (5 mg/ml collagenase A and trypsin) is a preferred protocol for digesting mouse cornea to obtain single-cell suspension which achieves the criterion of single-cell RNA sequencing.

Pharmacological Functions, Synthesis, and Delivery Progress for Collagen as Biodrug and Biomaterial

Collagen has been widely applied as a functional biomaterial in regulating tissue regeneration and drug delivery by participating in cell proliferation, differentiation, migration, intercellular signal transmission, tissue formation, and blood coagulation. However, traditional extraction of collagen from animals potentially induces immunogenicity and requires complicated material treatment and purification steps. Although semi-synthesis strategies such as utilizing recombinant E. coli or yeast expression systems have been explored as alternative methods, the influence of unwanted by-products, foreign substances, and immature synthetic processes have limited its industrial production and clinical applications. Meanwhile, macromolecule collagen products encounter a bottleneck in delivery and absorption by conventional oral and injection vehicles, which promotes the studies of transdermal and topical delivery strategies and implant methods. This review illustrates the physiological and therapeutic effects, synthesis strategies, and delivery technologies of collagen to provide a reference and outlook for the research and development of collagen as a biodrug and biomaterial.

Biomechanics of a Plant-Derived Sealant for Corneal Injuries

Purpose

The corneal epithelium has a glycocalyx composed of membrane-associated glycoproteins, mucins, and galactin-3. Similar to the glycocalyx in visceral tissues, the corneal glycocalyx functions to limit fluid loss and minimize frictional forces. Recently, the plant-derived heteropolysaccharide pectin has been shown to physically entangle with the visceral organ glycocalyx. The ability of pectin to entangle with the corneal epithelium is unknown.

Methods

To explore the potential role of pectin as a corneal bioadhesive, we assessed the adhesive characteristics of pectin films in a bovine globe model.

Results

Pectin film was flexible, translucent, and low profile (80 µm thick). Molded in tape form, pectin films were significantly more adherent to the bovine cornea than control biopolymers of nanocellulose fibers, sodium hyaluronate, and carboxymethyl cellulose (P < 0.05). Adhesion strength was near maximal within seconds of contact. Compatible with wound closure under tension, the relative adhesion strength was greatest at a peel angle less than 45 degrees. The corneal incisions sealed with pectin film were resistant to anterior chamber pressure fluctuations ranging from negative 51.3 ± 8.9 mm Hg to positive 214 ± 68.6 mm Hg. Consistent with these findings, scanning electron microscopy demonstrated a low-profile film densely adherent to the bovine cornea. Finally, the adhesion of the pectin films facilitated the en face harvest of the corneal epithelium without physical dissection or enzymatic digestion.

Conclusions

We conclude that pectin films strongly adhere to the corneal glycocalyx.

Translational Relevance

The plant-derived pectin biopolymer provides potential utility for corneal wound healing as well as targeted drug delivery.

Meta-analysis of corneal endothelial changes after phacoemulsification in diabetic and non-diabetic patients

BACKGROUND

Currently, there is still controversy about the differential changes in corneal endothelium function and morphology after phacoemulsification between Diabetes Mellitus (DM) and non-Diabetes Mellitus (non-DM) patients. In this study, we aimed to evaluate the influence of phacoemulsification on the corneal endothelium in DM and non-DM patients.

METHODS

Databases of PubMed, Embase, Web of Science, and the Cochrane Library were searched for studies published between January 1, 2011 and December 25, 2021. The weighted mean difference and 95% confidence interval were used to estimate the outcomes of statistical analyses performed.

RESULTS

Thirteen studies involving 1744 eyes were included in this meta-analysis. No significant difference was observed in the central corneal thickness (CCT), endothelial cell density (ECD), coefficients of variation (CV), or hexagonal cell percentage (HCP) between the DM and non-DM groups (CCT: P = 0.91; ECD: P = 0.07; CV: P = 0.06; HCP: P = 0.09) preoperatively. The CCT was significantly thicker in the DM group at 1 month (P = 0.003) and 3 months (P = 0.0009) postoperatively, and there was no significant difference at 6 months postoperatively (P = 0.26) than non-DM group. The CV was significantly higher and HCP was significantly lower in the DM group at 1 month (CV:P < 0.0001, HCP: P = 0.002), with no significant difference at 3 months (CV: P = 0.09, HCP: P = 0.36) and 6 months (CV: P = 0.32, HCP: P = 0.36) postoperatively than non-DM group. DM patients had lower ECD than non-DM patients at all postoperative time points (1 month, 3 months: P < 0.00001, 6 months: P < 0.0001).

CONCLUSIONS

The influence of phacoemulsification on corneal endothelial damage is greater in diabetic patients. Moreover, the recovery of corneal endothelial function and morphology is delayed in these patients. Clinicians should be more attentive to the corneal health of DM patients when considering phacoemulsification.

The roles of autophagy and mitophagy in corneal pathology: current knowledge and future perspectives

The cornea is the clear dome that covers the front portion of the globe. The primary functions of the cornea are to promote the refraction of light and to protect the eye from invading pathogens, both of which are essential for the preservation of vision. Homeostasis of each cellular layer of the cornea requires the orchestration of multiple processes, including the ability to respond to stress. One mechanism whereby cells respond to stress is autophagy, or the process of "self-eating." Autophagy functions to clear damaged proteins and organelles. During nutrient deprivation, amino acids released from protein breakdown via autophagy are used as a fuel source. Mitophagy, a selective form of autophagy, functions to clear damaged mitochondria. Thus, autophagy and mitophagy are important intracellular degradative processes that sustain tissue homeostasis. Importantly, the inhibition or excessive activation of these processes result in deleterious effects on the cell. In the eye, impairment or inhibition of these mechanisms have been associated with corneal disease, degenerations, and dystrophies. This review summarizes the current body of knowledge on autophagy and mitophagy at all layers in the cornea in both non-infectious and infectious corneal disease, dystrophies, and degenerations. It further highlights the critical gaps in our understanding of mitochondrial dysfunction, with implications for novel therapeutics in clinical practice.

Expansion and characterization of human limbus-derived stromal/mesenchymal stem cells in xeno-free medium for therapeutic applications

BACKGROUND

Mesenchymal stem cells (MSCs) have been proven to prevent and clear corneal scarring and limbal stem cell deficiency. However, using animal-derived serum in a culture medium raises the ethical and regulatory bar. This study aims to expand and characterize human limbus-derived stromal/mesenchymal stem cells (hLMSCs) for the first time in vitro in the xeno-free medium.

METHODS

Limbal tissue was obtained from therapeutic grade corneoscleral rims and subjected to explant culture till tertiary passage in media with and without serum (STEM MACS XF; SM), to obtain pure hLMSCs. Population doubling time, cell proliferation, expression of phenotypic markers, tri-lineage differentiation, colony-forming potential and gene expression analysis were carried out to assess the retention of phenotypic and genotypic characteristics of hLMSCs.

RESULTS

The serum-free medium supported the growth of hLMSCs, retaining similar morphology but a significantly lower doubling time of 23 h (*p < 0.01) compared to the control medium. FACS analysis demonstrated ≥ 90% hLMSCs were positive for CD90⁺, CD73⁺, CD105⁺, and ≤ 6% were positive for CD45^-, CD34^- and HLA-DR^-. Immunofluorescence analysis confirmed similar expression of Pax6⁺, COL IV⁺, ABCG2⁺, ABCB5⁺, VIM⁺, CD90⁺, CD105⁺, CD73⁺, HLA-DR^- and CD45^-, αSMA^- in both the media. Tri-lineage differentiation potential and gene expression of hLMSCs were retained similarly to that of the control medium.

CONCLUSION

The findings of this study demonstrate successful isolation, characterization and culture optimization of hLMSCs for the first time in vitro in a serum-free environment. This will help in the future pre-clinical and clinical applications of MSCs in translational research.

Digital light processing-based multi-material bioprinting: Processes, applications, and perspectives

In the past decade, three-dimensional (3D) printing technology based on digital light processing (DLP) has developed rapidly and shown application prospects in several fields such as pneumatic robotics, flexible electronics, and tissue engineering. In particular, DLP-based multi-material printing has been capable of constructing heterogeneous 3D structures with characteristic gradients. DLP 3D printing technology has a wide range of applications in the field of bioprinting due to its high precision and mild printing conditions, including functionalized artificial tissues, medical models, and bioreactors. This paper focuses on the development of DLP-based multi-material 3D printing technology and its applications in the field of bioprinting, followed by giving an outlook on future efforts on overcoming the challenges and obstacles of this promising technique.

Mobile-CellNet: Automatic Segmentation of Corneal Endothelium Using an Efficient Hybrid Deep Learning Model

PURPOSE

The corneal endothelium, the innermost layer of the human cornea, exhibits a morphology of predominantly hexagonal cells. These endothelial cells are believed to have limited regeneration capacity, and their density decreases over time. Endothelial cell density (ECD) can therefore be used to measure the health of the corneal endothelium and the overall cornea. In clinical settings, specular microscopes are used to image this layer. Owing to the unavailability of reliable automatic tools, technicians often manually mark the cell centers and borders to measure ECD for such images, a process that is time and resource-consuming.

METHODS

In this article, we propose Mobile-CellNet, a novel completely automatic, efficient deep learning-based cell segmentation algorithm to estimate ECD. This uses 2 similar image segmentation models working in parallel along with image postprocessing using classical image processing techniques. We also compare the proposed algorithm with widely used biomedical image segmentation networks U-Net and U-Net++.

RESULTS

The proposed technique achieved a mean absolute error of 4.06% for the ECD on the test set, comparable with the error for U-Net of 3.80% ( P = 0.185 for difference), but requiring almost 31 times fewer floating-point operations (FLOPs) and 34 times fewer parameters.

CONCLUSIONS

Mobile-CellNet accurately segments corneal endothelial cells and reports ECD and cell morphology efficiently. This can be used to develop tools to analyze specular corneal endothelial images in remote settings.

Nanofibers in Ocular Drug Targeting and Tissue Engineering: Their Importance, Advantages, Advances, and Future Perspectives

Nanofibers are frequently encountered in daily life as a modern material with a wide range of applications. The important advantages of production techniques, such as being easy, cost effective, and industrially applicable are important factors in the preference for nanofibers. Nanofibers, which have a broad scope of use in the field of health, are preferred both in drug delivery systems and tissue engineering. Due to the biocompatible materials used in their construction, they are also frequently preferred in ocular applications. The fact that they have a long drug release time as a drug delivery system and have been used in corneal tissue studies, which have been successfully developed in tissue engineering, stand out as important advantages of nanofibers. This review examines nanofibers, their production techniques and general information, nanofiber-based ocular drug delivery systems, and tissue engineering concepts in detail.

Hyperosmolar Potassium Inhibits Corneal Myofibroblast Transformation and Prevent Corneal Scar

PURPOSE

Corneal myofibroblasts play a crucial role in the process of corneal scarring. Potassium has been documented to reduce skin scar tissue formation. Herein, we investigated the ability of potassium to prevent corneal fibrosis in cell culture and in vivo.

METHODS

Corneal fibroblasts (CFs) were isolated from the corneal limbus and treated with TGF-β1 to transform into corneal myofibroblasts. Corneal myofibroblast markers were detected by quantitative real-time PCR, Western blot, and immunofluorescence. The contractive functions of corneal myofibroblast were evaluated by the scratch assay and the collagen gel contraction assay. RNA sequencing in corneal fibroblasts was performed to explore the mechanisms underlying hyperosmolar potassium treatment. GO and KEGG analysis were performed to explore the underlying mechanism by hyperosmolar potassium treatment. The ATP detection assay assessed the level of cell metabolism. KCl eye drops four times per day were administered to mice models of corneal injury to evaluate the ability to prevent corneal scar formation. Corneal opacity area was evaluated by Image J software.

RESULTS

Treatment with hyperosmolar potassium could suppress corneal myofibroblast transformation and collagen I synthesis induced by TGF-β1 in cell culture. Hyperosmolar potassium could inhibit wound healing and gel contraction in CFs. RNA sequencing results suggested that genes involved in the metabolic pathway were downregulated after KCl treatment. ATP levels were significantly decreased in the KCl group compared with the control group. Hyperosmolar potassium could prevent corneal myofibroblast transformation after corneal injury and corneal scar formation in mice.

CONCLUSION

Potassium can suppress corneal myofibroblast transformation and collagen I protein synthesis. Moreover, given that KCl eye drops can prevent corneal scar formation, it has been suggested to have huge prospects as a novel treatment approach during clinical practice.

Cell-Laden Marine Gelatin Methacryloyl Hydrogels Enriched with Ascorbic Acid for Corneal Stroma Regeneration

Corneal pathologies from infectious or noninfectious origin have a significant impact on the daily lives of millions of people worldwide. Despite the risk of organ rejection or infection, corneal transplantation is currently the only effective treatment. Finding safe and innovative strategies is the main goal of tissue-engineering-based approaches. In this study, the potential of gelatin methacryloyl (GelMA) hydrogels produced from marine-derived gelatin and loaded with ascorbic acid (as an enhancer of the biological activity of cells) was evaluated for corneal stromal applications. Marine GelMA was synthesized with a methacrylation degree of 75%, enabling effective photocrosslinking, and hydrogels with or without ascorbic acid were produced, encompassing human keratocytes. All the produced formulations exhibited excellent optical and swelling properties with easy handling as well as structural stability and adequate degradation rates that may allow proper extracellular matrix remodeling by corneal stromal cells. Formulations loaded with 0.5 mg/mL of ascorbic acid enhanced the biological performance of keratocytes and induced collagen production. These results suggest that, in addition to marine-derived gelatin being suitable for the synthesis of GelMA, the hydrogels produced are promising biomaterials for corneal regeneration applications.

Pentacam corneal topography and densitometry features of PCOS patients

BACKGROUND

To evaluate corneal topography and densitometry features in patients with polycystic ovary syndrome (PCOS) and compare them with healthy individuals.

METHODS

53 eyes of 53 female patients diagnosed with PCOS and 53 eyes of 53 age-matched female volunteers were analyzed in the study. In addition to the detailed ophthalmological and gynecological examination, anterior segment analysis was performed using Pentacam. A complete analysis of aberrometric, keratometric, topometric, and, densitometric values between the groups was performed, and the results were outlined.

RESULTS

According to the results, although Kmax-front, Kmean-front, ISV, IVA, IHA, BAD_D and PI-Avg values were slightly higher in PCOS group along with a slight thinning in the thinnest location, there was no statistically significant difference between the groups. Moreover, correlation analysis between PCOS clinical parameters and keratometric/topometric/aberrometric data were found to be almost normal. Yet, when Pentacam tomography maps of all cases are examined in detail, mild ectatic changes were observed in 5 cases in PCOS group. Furthermore, a significant increase in thickness across all densitometry values except anterior (10-12 mm), central (10-12 mm), and total (10-12 mm) was found in PCOS group.

CONCLUSIONS

Our study showed that an intensification of corneal densitometry values ​​and various changes in keratometry data implying ectasia can be observed in patients with PCOS. Prospective studies with larger patient series are needed to reveal any potential relationship between PCOS and corneal abnormalities.

Targeting Type I IFN/STAT1 signaling inhibited and reversed corneal squamous metaplasia in Aire-deficient mouse

Corneal transparency and integrity are essential for obtaining good vision; nevertheless, squamous metaplasia (SQM) of ocular epithelium is a kind of serious blinding corneal diseases, without therapeutic medication in clinic. Here, we found that deficiency of the autoimmune regulator (AIRE) in corneas spontaneously developed corneal plaques. Using corneal abrasion model, we revealed that deletion of Aire not only resulted in delayed corneal re-epithelialization, but also promoted a cell-fate transition from transparent corneal epithelium to keratinized epithelium, histopathologically characterized with SQM based on the transcriptomic analysis. Mechanistically, Aire-deficient corneas led to the heightened Type I interferon (IFN-I)/STAT1 signaling after abrasion. Pharmacological blockade of IFN-I/JAK/STAT1 signaling in Aire-knockout (KO) corneas not only accelerated epithelial wound healing, but also alleviated corneal plaques and SQM. Collectively, our findings revealed critical roles of AIRE in governing corneal epithelial homeostasis and pathologic keratinization, and further identified IFN-I/STAT1 signaling as a potential target for treating ocular surface diseases with SQM, and even for treating pathological scenarios related to SQM in other tissues.

"Groove and Peel" Deep Anterior Lamellar Keratoplasty: How Deep Can You Go?

PURPOSE

The aim of the current research was to measure the thickness of the residual central corneal bed after performing the manual "Groove and Peel" deep anterior lamellar keratoplasty (GP-DALK) technique on human cadaveric eyes.

METHODS

The manual GP-DALK technique was performed on 6 human cadaver eyes by an experienced corneal surgeon. After surgery, the eye globes were fixed in 10% buffered formalin and embedded in paraffin. For each eye, 4-μm-thick hematoxylin and eosin sections involving the pupillary axis were obtained and examined. Using an image-processing software, 2 observers measured the corneal thickness of the residual central corneal bed and the peripheral corneal rims.

RESULTS

The overall mean central corneal bed thickness was 35.5 ± 12.9 μm, whereas the mean right and left peripheral rim thicknesses were 993.0 ± 141.1 and 989.3 ± 147.1 μm, respectively ( P = 0.0006 ). In most corneas, the level of dissection reached almost to the pre-Descemetic collagen (Dua) layer.

CONCLUSIONS

The GP-DALK technique is effective in removing most of the corneal stroma and may be non-inferior to "big-bubble" deep anterior lamellar keratoplasty in some cases.

Outcomes of keratolimbal allograft from ABO compatible donors for severe bilateral limbal stem cell deficiency

PURPOSE

To report outcomes of keratolimbal allograft (KLAL) compatible for both human leukocyte (HLA) and/or blood type using oral prednisone, mycophenolate, and tacrolimus, with basiliximab if panel reactive antibodies (PRA) are present. Intravenous immunoglobulin (IVIG) was used post-operatively if donor-specific anti-HLA antibodies (DSA) were present.

METHODS

Retrospective interventional series of consecutive patients with KLAL for limbal stem cell deficiency (LSCD) from HLA and/or blood type compatible deceased donors with a minimum follow-up time of 12 months. Main outcome measures were ocular surface stability, visual acuity and systemic immunosuppression (SI) adverse events.

RESULTS

Eight eyes of eight patients with mean age of 48.6 ± 10.1 years (range 34-65 years) were included. Mean follow-up time was 37.3 ± 22.7 months (range 12-71 months) following KLAL; four (50%) had combined LR-CLAL surgery. The etiologies of LSCD were Stevens-Johnson Syndrome (n = 4/8), aniridia (n = 2/8), chemical injury (n = 1/8) and atopic eye disease (n = 1/8). All patients had PRA present and received basiliximab infusions. 5/8 patients received IVIG based on DSA identified pre-operatively. At last follow-up, 7 eyes (87.5%) had a stable ocular surface; 1 eye (12.5%) developed failure and had keratoprosthesis implantation. There was a significant improvement in visual acuity from 1.65 ± 0.48 to 0.68 ± 0.34 logMAR (p = 0.01). SI was tolerated well with minimal adverse events.

CONCLUSIONS

Preliminary outcomes of KLAL with ABO compatible tissue using the Cincinnati protocol, preoperative basiliximab (when PRA present) and post-operative IVIG (when DSA present) are encouraging. This protocol may allow for utilization of deceased donor tissue with results approximating those of living donor tissue transplanted for severe bilateral LSCD.

Roles of early events in the modifications undergone by bovine corneal endothelial cells during wound healing

A mechanical injury in bovine corneal endothelial (BCE) cells in culture induces: (1) a fast calcium wave (FCW); (2) slow increases in cytosolic sodium and calcium, critical for the healing process, and (3) a rise in the apoptotic rate with respect to quiescent cells. In order to investigate the nature of the stimuli that determine the ionic changes and apoptotic response, we performed here studies on a non-injury model of tissue restitution in BCE monolayers. For this, we employed cell cultures grown to confluence in the presence of a Parafilm strip. We observed that, previously to strip removal, most of the border cells had already developed the slow ionic modifications, while in the scratch wounds these changes gradually occur after several hours of healing. This finding suggests that, in BCE cells, the presence of a free edge is sufficient to trigger ionic modifications necessary for wound healing and to elicit an augmented apoptotic response. The apoptotic index of the migrating cells in the Parafilm model (PF) was determined to be approximately two-fold the one of scratch wounds, a result that, in agreement with our previous observations, we attributed to the absence of the FCW in the PF experiments. The findings of this work further contribute to the understanding of epithelial wound healing, a crucial adaptive, and homeostatic response.

Nutraceuticals: A Promising Therapeutic Approach in Ophthalmology

Oxidative stress represents one of the main factors driving the pathophysiology of multiple ophthalmic conditions including presbyopia, cataracts, dry eye disease (DED), glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR). Currently, different studies have demonstrated the role of orally administered nutraceuticals in these diseases. For instance, they have demonstrated to improve lens accommodation in presbyopia, reduce protein aggregation in cataracts, ameliorate tear film stability, break up time, and tear production in dry eye, and participate in the avoidance of retinal neuronal damage and a decrease in intraocular pressure in glaucoma, contribute to the delayed progression of AMD, or in the prevention or treatment of neuronal death in diabetic retinopathy. In this review, we summarized the nutraceuticals which have presented a positive impact in ocular disorders, emphasizing the clinical assays. The characteristics of the different types of nutraceuticals are specified along with the nutraceutical concentration used to achieve a therapeutic outcome in ocular diseases.