Does Corneal Topography Using 3-Dimensional Optical Coherence Tomography Suggest Different Subtypes of Terrien Marginal Degeneration?

PURPOSE: The aim of this study was to analyze corneal topography relative to astigmatism, higher order aberrations, and corneal curvatures in Terrien marginal degeneration using 3-dimensional anterior-segment optical coherence tomography. METHODS: Twenty-nine eyes of 15 Finnish patients from a tertiary referral center had topographic axial power maps classified into 4 patterns by visual grading: crab claw (CC), mixed (M), arcuate (A), and normal. Regular astigmatism, keratometry, higher order aberrations, maximal corneal thinning, apex thickness, and curvature changes relative to best fit sphere toward maximal peripheral thinning were compared. RESULTS: Four, 9, and 12 eyes were classified as CC, M, and A, respectively; 1 as normal with clinical disease; and 3 as normal with unilateral disease. Median follow-up was 2.3 (range, 0-7.2) years. Three eyes changed pattern. Patients with the CC pattern were the youngest when diagnosed, progressed more rapidly, exhibited cavities in superior quadrants with anterior bulging, and had greater higher order posterior aberrations. Patients with the M pattern were older, progressed slower, and showed superonasal asymmetric corneal steepening extending centrally, often with asymmetric bow tie. Patients with pattern A showed little progression and were the oldest when diagnosed, with maximal corneal thinning equally in all quadrants. According to the Wang classification, the median stage was 4, 2, and 2 in CC, M, and A patterns, respectively, whereas it was always 2 by the Süveges classification. CONCLUSIONS: Terrien marginal degeneration is characterized by distinct corneal topographic patterns that differ in tomographic features, suggesting existence of subtypes in addition to different stages of disease. Patients representing CC and M patterns might benefit from more frequent monitoring.

Longitudinal Optical Coherence Tomography Measurement of Retinal Ganglion Cell and Nerve Fiber Layer to Assess Benign Course in Multiple Sclerosis.

A benign form of multiple sclerosis (BMS) is not easily diagnosed, but changes of the retinal ganglion cell layer-inner plexiform layer (GCL-IPL) and retinal nerve fiber layer (RNFL) may be sensitive to the disease. The aim of this study was to use optical coherence tomography (OCT) to investigate longitudinal changes of GCL-IPL and RNFL in BMS. Eighteen patients with BMS and 22 healthy control (HC) subjects were included, with a mean follow-up period of 32.1 months in BMS and 34.3 months in HC. Mean disease duration in BMS was 23.3 years, with 14 patients left untreated. Unilateral optic neuritis (ON) was found in eight patients. Non-ON eyes showed thinner GCL-IPL layer in the BMS group relative to HC (p < 0.001). The thinning rate of GCL-IPL in non-ON BMS, however, was -0.19 ± 0.15 µm/year vs. 0 ± 0.11 µm/year for HC (p = 0.573, age-adjusted). Thinning rate of RNFL in non-ON BMS was -0.2 ± 0.27 µm/year vs. -0.05 ± 0.3 µm/year for HC (p = 0.454, age adjusted). Conclusions: Thinning rate of the GCL-IPL and RNFL in BMS is similar to the healthy population but differs from the thinning rate in relapsing-remitting MS, presenting a non-invasive OCT-based criterion for assessing a benign course in multiple sclerosis.

Bioengineered corneal tissue for minimally invasive vision restoration in advanced keratoconus in two clinical cohorts.

Visual impairment from corneal stromal disease affects millions worldwide. We describe a cell-free engineered corneal tissue, bioengineered porcine construct, double crosslinked (BPCDX) and a minimally invasive surgical method for its implantation. In a pilot feasibility study in India and Iran (clinicaltrials.gov no. NCT04653922 ), we implanted BPCDX in 20 advanced keratoconus subjects to reshape the native corneal stroma without removing existing tissue or using sutures. During 24 months of follow-up, no adverse event was observed. We document improvements in corneal thickness (mean increase of 209 ± 18 µm in India, 285 ± 99 µm in Iran), maximum keratometry (mean decrease of 13.9 ± 7.9 D in India and 11.2 ± 8.9 D in Iran) and visual acuity (to a mean contact-lens-corrected acuity of 20/26 in India and spectacle-corrected acuity of 20/58 in Iran). Fourteen of 14 initially blind subjects had a final mean best-corrected vision (spectacle or contact lens) of 20/36 and restored tolerance to contact lens wear. This work demonstrates restoration of vision using an approach that is potentially equally effective, safer, simpler and more broadly available than donor cornea transplantation.

Phosphorylcholine and KR12-Containing Corneal Implants in HSV-1-Infected Rabbit Corneas.

Severe HSV-1 infection can cause blindness due to tissue damage from severe inflammation. Due to the high risk of graft failure in HSV-1-infected individuals, cornea transplantation to restore vision is often contraindicated. We tested the capacity for cell-free biosynthetic implants made from recombinant human collagen type III and 2-methacryloyloxyethyl phosphorylcholine (RHCIII-MPC) to suppress inflammation and promote tissue regeneration in the damaged corneas. To block viral reactivation, we incorporated silica dioxide nanoparticles releasing KR12, the small bioactive core fragment of LL37, an innate cationic host defense peptide produced by corneal cells. KR12 is more reactive and smaller than LL37, so more KR12 molecules can be incorporated into nanoparticles for delivery. Unlike LL37, which was cytotoxic, KR12 was cell-friendly and showed little cytotoxicity at doses that blocked HSV-1 activity in vitro, instead enabling rapid wound closure in cultures of human epithelial cells. Composite implants released KR12 for up to 3 weeks in vitro. The implant was also tested in vivo on HSV-1-infected rabbit corneas where it was grafted by anterior lamellar keratoplasty. Adding KR12 to RHCIII-MPC did not reduce HSV-1 viral loads or the inflammation resulting in neovascularization. Nevertheless, the composite implants reduced viral spread sufficiently to allow stable corneal epithelium, stroma, and nerve regeneration over a 6-month observation period.

Pathologic epithelial and anterior corneal nerve morphology in early-stage congenital aniridic keratopathy.

OBJECTIVE: To document the clinical and morphologic corneal findings in the early stages of congenital aniridic keratopathy in Swedish families. DESIGN: Prospective, observational, comparative case series. PARTICIPANTS: A total of 16 eyes of 16 subjects with congenital aniridic keratopathy and a clear central cornea, and 6 eyes from 6 healthy controls (unaffected relatives). Nine of the 16 eyes with aniridia came from 5 families with a documented familial history of aniridia. METHODS: Detailed ophthalmic examinations included best spectacle-corrected visual acuity (BSCVA), tear film production, tear break-up time (BUT), corneal touch sensitivity, intraocular pressure measurement, ultrasound pachymetry, slit-lamp biomicroscopy, and laser scanning in vivo confocal microscopy (IVCM). MAIN OUTCOME MEASURES: Confirmed stage of aniridic keratopathy, clinical parameters of cornea and tear film (visual acuity, sensitivity, corneal thickness, tear production, and BUT), and the morphologic status of corneal epithelium, sub-basal nerves, and limbal palisades of Vogt. RESULTS: In early-stage aniridic keratopathy, BSCVA and tear BUT were reduced relative to controls (P < 0.001 for both), and corneal thickness was increased (P=0.01). Inflammatory dendritic cells were present in the central epithelium in aniridia, with significantly increased density relative to controls (P = 0.001). Discrete focal opacities in the basal epithelial region were present in 5 of 11 aniridia cases with an otherwise clear cornea. Opacities were associated with dendritic cells and harbored structures presumed to be goblet cells. Sub-basal nerves were extremely dense in 3 aniridia cases, and a prominent whorl pattern of nerves and epithelial cells was observed in 1 case. Normal limbal palisade morphology was absent in aniridia but present in controls. CONCLUSIONS: Early-stage aniridic keratopathy is characterized by the development of focal opacities in the basal epithelium, altered sub-basal nerves, infiltration of the central epithelium by dendritic cells, tear film instability, and increased corneal thickness and degradation of limbal palisade architecture. These findings may help to elucidate the pathogenesis of aniridic keratopathy.

Electron-Beam Irradiated Recombinant Human Collagen-Phosphorylcholine Corneal Implants Retain Pro-Regeneration Capacity.

Sterilization of biodegradable, collagen-based implants is challenging as irradiation sterilization methods can alter their mechanical properties. Electron beam (EB) irradiation is a terminal sterilization method that has been used for biologically-derived implants. Here, recombinant human collagen type III-phosphorylcholine (RHCIII-MPC) hydrogels were irradiated with EB doses of 17, 19, or 21 kGy and their subsequent biocompatibility and ability to promote regeneration in rabbit corneas was evaluated. Unirradiated hydrogels stored in 1% chloroform in phosphate-buffered saline (C-PBS) were the controls. There were no significant differences between irradiated and non-irradiated samples in optical or physical properties (tensile strength, modulus, elasticity), or the ability to support cell growth. However, irradiated implants were more sensitive to high levels of collagenase than unirradiated controls and the C-PBS implants had increased cell growth compared to EB and controls at 72 h. Corneal implants e-beamed at 17 kGy or e-beamed and subsequently frozen (EB-F) to increase shelf-life showed no adverse biological effects of the irradiation. EB, EB-F, and C-PBS implanted corneas all rapidly re-epithelialized but showed mild neovascularization that resolved over 6 months. The regenerated neo-corneas were transparent at 6 months post-operation. In vivo confocal microscopy confirmed normal morphology for the epithelium, stroma, sub-basal nerves and unoperated endothelium. Histology showed that all the regenerated corneas were morphologically similar to the normal. Immunohistochemistry indicated the presence of a differentiated corneal epithelium and functional tear film. In conclusion, the e-beamed corneal implants performed as well as non-irradiated control implants, resulting in fully regenerated neo-corneas with new nerves and without blood vessels or inflammation that may impede vision or corneal function. Therefore, a complete validation study to establish EB irradiation as an effective means for corneal implant sterilization prior to clinical application is necessary as a next step.

Cellular level characterization of capillary regression in inflammatory angiogenesis using an in vivo corneal model.

In this study, we introduce a technique for repeated, microscopic observation of single regressing capillaries in vivo in inflamed murine corneas. Natural capillary regression was initiated by removal of inflammatory stimulus during an active pro-angiogenic phase, while the additional impact of anti-angiogenic treatment with triamcinolone or bevazicumab was investigated. Capillaries regressed naturally within 1 week and treatments did not further enhance the natural regression. Morphologically, early-phase regression was characterized by significant lumen narrowing and a significant reduction in CD11b+ myeloid cell infiltration of the extracellular matrix. By 1 week, vascular remodeling occurred concomitant with CD11b+CD68+KiM2R+ mature macrophage localization on capillary walls. Empty conduits without blood flow, positive for collagen IV and devoid of vascular endothelium and pericytes, were apparent in vivo and by 3 weeks were more numerous than perfused capillaries. By 3 weeks, macrophages aggregated around remaining perfused capillaries and were observed in apposition with degrading capillary segments. Abrupt termination of capillary sprouting in our regression model further revealed vascular endothelial abandonment of sprout tips and perfused capillary loop formation within a single angiogenic sprout, possibly as an intussusceptive response to cessation of the stimulus. Finally, we observed lumen constriction and macrophage localization on capillary walls in vivo in a clinical case of corneal capillary regression that paralleled findings in our murine model.

Clinical outcome and recurrence of epithelial basement membrane dystrophy after phototherapeutic keratectomy a cross-sectional study.

OBJECTIVE: To evaluate the outcome of phototherapeutic keratectomy (PTK) treatment of epithelial basement membrane dystrophy (EBMD) patients and to examine clinical and morphologic signs of recurrent dystrophy. DESIGN: Cross-sectional, clinic-based study. PARTICIPANTS: Fifty-two eyes of 39 patients diagnosed with EBMD who underwent PTK between 2001 and 2008. METHODS: Preoperative symptoms, best spectacle-corrected visual acuity (BSCVA), and refraction data were collected. At follow-up, refraction and BSCVA were measured, symptoms were noted, and slit-lamp biomicroscopy and in vivo confocal microscopy (IVCM) were performed. MAIN OUTCOME MEASURES: Best spectacle-corrected visual acuity and signs of recurrent EBMD based on symptoms and morphologic features. An assessment of EBMD severity after PTK additionally was considered. RESULTS: Mean follow-up time was 43 months (range, 7-100 months). After PTK, BSCVA remained unchanged or improved in 49 (98%) of 51 eyes. Twenty-four (46%) of 52 eyes had recurrence of some form, and recurrence was correlated positively with postoperative time (P<0.001). Symptomatic recurrence occurred in 7 eyes (13%), whereas morphologic recurrence occurred in 21 eyes (40%). Symptoms were coupled with positive IVCM findings in 3 (43%) of 7 cases and with slit-lamp findings in 1 (14%) of 7 cases. Of 17 eyes with morphologic recurrence by IVCM, 9 eyes (53%) were classified as having grade 1 recurrence, 8 eyes (47%) were classified as having grade 2 recurrence, and none were classified as having grade 3 recurrence. Morphologic recurrence was associated with epithelial removal by laser ablation before PTK. CONCLUSIONS: Although PTK is an effective method of alleviating the clinical symptoms of EBMD, the dystrophy can recur with time. The relationship between the postoperative development of clinical symptoms and the corneal morphologic features is complex and requires further investigation.

Diagnostic Criteria for Terrien Marginal Degeneration: Nordic Terrien Degeneration Study.

PURPOSE: To refine the diagnostic criteria for Terrien marginal degeneration (TMD) based on experience in 3 Nordic countries. METHODS: This is a retrospective, multicenter, hospital-based cross-sectional study of 49 eyes of 29 white patients in tertiary referral centers in Finland, Sweden, and Denmark from 1998 to January 2018. The median follow-up was 3 years. Symptoms, best corrected visual acuity, astigmatism, corneal thickness, curvature and cavities, stage, and progression were analyzed. RESULTS: TMD was diagnosed equally likely between 15 and 86 years of age (median, 47 years). Twenty patients (69%) had bilateral disease, and 62% were men. Seventeen patients (59%) had symptoms including blurred vision and ocular surface disease symptoms without inflammatory signs. Eight patients (28%) had slightly reduced corneal sensitivity. Median best corrected visual acuity was 20/25 (range, 20/16-20/200) and astigmatism was 2.6 diopters (D) (range, 0-10) with a mean progression of 0.41 D per year (range, 0-5.4). Age and astigmatism were not correlated. All eyes had peripheral vascularization, lipid deposits, and hyperreflectivity throughout thinned peripheral stroma and its anterior edge. The thinning progressed in 15 patients (52%). Of 26 patients, 8 (31%) had single or confluent paralimbal intrastromal cavities, most commonly superiorly. By Süveges classification, the stage was 2 (92%) or 3 (8%). Minimum corneal thickness and corneal curvature were loosely associated, leading to different stages in Wang classification in 34 eyes (69%). CONCLUSIONS: TMD is defined by peripheral corneal thinning, superficial neovascularization, lipid deposition at the leading edge, absence of ulceration and inflammation, and frequently cavitation. The most sensitive way to follow its progression is anterior segment optical coherence tomography.

Collagen analogs with phosphorylcholine are inflammation-suppressing scaffolds for corneal regeneration from alkali burns in mini-pigs.

The long-term survival of biomaterial implants is often hampered by surgery-induced inflammation that can lead to graft failure. Considering that most corneas receiving grafts are either pathological or inflamed before implantation, the risk of rejection is heightened. Here, we show that bioengineered, fully synthetic, and robust corneal implants can be manufactured from a collagen analog (collagen-like peptide-polyethylene glycol hybrid, CLP-PEG) and inflammation-suppressing polymeric 2-methacryloyloxyethyl phosphorylcholine (MPC) when stabilized with the triazine-based crosslinker 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The resulting CLP-PEG-MPC implants led to reduced corneal swelling, haze, and neovascularization in comparison to CLP-PEG only implants when grafted into a mini-pig cornea alkali burn model of inflammation over 12 months. Implants incorporating MPC allowed for faster nerve regeneration and recovery of corneal sensation. CLP-PEG-MPC implants appear to be at a more advanced stage of regeneration than the CLP-PEG only implants, as evidenced by the presence of higher amounts of cornea-specific type V collagen, and a corresponding decrease in the presence of extracellular vesicles and exosomes in the corneal stroma, in keeping with the amounts present in healthy, unoperated corneas.

Collagen-based scaffolds with infused anti-VEGF release system as potential cornea substitute for high-risk keratoplasty: A preliminary in vitro evaluation.

Currently the only widely accepted corneal blindness treatment is human donor cornea transplantation. However, increasing shortage of donor corneas as well as high risk of rejection in some corneal diseases remain two major problems, which limit the success of corneal transplantation. Corneal neovascularization is considered as one of the main risk factors of graft failure. Different cell-free biosynthetic scaffolds fabricated from collagens or collagen-like peptides are being tested as donor cornea substitutes (DCS). Here, we report for the first-time composite biosynthetic DCS with integrated sustained release system of anti-VEGF drug, bevacizumab and their preliminary in vitro validation. We have tethered gold nanoparticles with bevacizumab and integrated into a collagen-based cell-free hydrogel scaffold. Developed grafts preserved good optical properties and were confirmed not toxic to human corneal epithelial cells. Bevacizumab has been shown to constantly releasing from the DCS up to 3 weeks and preserved its anti-angiogenic properties. These results provide background for further use of infused composite biosynthetic DCS with integrated nanosystem of bevacizumab sustained release in corneal disease accompanied by neovascularisation where conventional corneal transplantation might fail.

A porous collagen-based hydrogel and implantation method for corneal stromal regeneration and sustained local drug delivery.

Biomaterials designed to replace the diseased cornea could be used to treat corneal blindness where human donor tissue is in short supply, but challenges are the integration of biomaterials with host tissue and cells, avoiding a rapid material degradation and maintaining corneal transparency. Additionally, implantation surgery often triggers an aggressive wound healing response that can lead to corneal thinning and opacity. Here, we report a collagen-based hydrogel with transparency and mechanical properties suitable for replacing a substantial portion of a damaged or diseased corneal stroma. The porous hydrogel permitted migration and population by host cells while maintaining transparency and thickness six months after surgical implantation in an in vivo model of human corneal surgery. With a novel hybrid surgical implantation technique inspired by LASIK refractive surgery, rapid wound healing occurred around implants to maintain biomaterial integrity, transparency and function. Host stromal cell repopulation and regeneration of host epithelium and nerves were observed, as necessary steps towards corneal regeneration. Finally, as a proof-of-principle, the hydrogel loaded with a neuroregenerative drug achieved sustained slow-release drug delivery in vitro. The proposed hydrogel and novel implantation technique together represent a therapeutic approach with translational potential for replacing and regenerating diseased corneal stromal tissue.

LiQD Cornea: Pro-regeneration collagen mimetics as patches and alternatives to corneal transplantation.

Transplantation with donor corneas is the mainstay for treating corneal blindness, but a severe worldwide shortage necessitates the development of other treatment options. Corneal perforation from infection or inflammation is sealed with cyanoacrylate glue. However, the resulting cytotoxicity requires transplantation. LiQD Cornea is an alternative to conventional corneal transplantation and sealants. It is a cell-free, liquid hydrogel matrix for corneal regeneration, comprising short collagen-like peptides conjugated with polyethylene glycol and mixed with fibrinogen to promote adhesion within tissue defects. Gelation occurs spontaneously at body temperature within 5 min. Light exposure is not required-particularly advantageous because patients with corneal inflammation are typically photophobic. The self-assembling, fully defined, synthetic collagen analog is much less costly than human recombinant collagen and reduces the risk of immune rejection associated with xenogeneic materials. In situ gelation potentially allows for clinical application in outpatient clinics instead of operating theaters, maximizing practicality, and minimizing health care costs.

High fluence PACK-CXL as adjuvant treatment for advanced Acanthamoeba keratitis.

PURPOSE: To describe the outcome of adjuvant high fluence photoactivated chromophore for infectious keratitis cross-linking (PACK-CXL) used to treat an advanced form of refractory Acanthamoeba keratitis (AK) diagnosed several months after initial presentation. OBSERVATIONS: An otherwise healthy 24-year old female presented with a severe unilateral keratitis. The diagnosis eluded clinicians for several months and when finally confirmed as AK, anti-amoebic therapy was instated and only appeared to be effective after addition of high fluence PACK-CXL. CONCLUSION AND IMPORTANCE: In this case of advanced AK, high fluence PACK-CXL treatment given adjuvant to pharmacologic anti-amoebic therapy resulted in lasting pain relief, re-epithelization and eradication of the Acanthamoeba parasite. Given adjuvant to anti-amoebic pharmacotherapy, high fluence PACK-CXL might be a useful method for treating typically refractory advanced AK.

PEG-stabilized carbodiimide crosslinked collagen-chitosan hydrogels for corneal tissue engineering.

Implantable biomaterials that mimic the extracellular matrix (ECM) in key physical and physiological functions require components and microarchitectures that are carefully designed to maintain the correct balance between biofunctional and physical properties. Our goal was to develop hybrid polymer networks (HPN) that combine the bioactive features of natural materials and physical characteristics of synthetic ones to achieve synergy between the desirable mechanical properties of some components with the biological compatibility and physiological relevance of others. In this study, we developed collagen-chitosan composite hydrogels as corneal implants stabilized by either a simple carbodiimide cross-linker or a hybrid cross-linking system comprised of a long-range bi-functional cross-linker (e.g. poly(ethylene glycol) dibutyraldehyde (PEG-DBA)), and short-range amide-type cross-linkers (e.g. 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS)). Optimum hybrid hydrogel demonstrated significantly enhanced mechanical strength and elasticity by 100 and 20%, respectively, compared to its non-hybrid counterpart. It demonstrated excellent optical properties, optimum mechanical properties and suturability, and good permeability to glucose and albumin. It had excellent biocompatibility and when implanted into pig corneas for 12 months, allowed seamless host-graft integration with successful regeneration of host corneal epithelium, stroma, and nerves.

Recombinant human collagen for tissue engineered corneal substitutes.

We successfully fabricated transparent, robust hydrogels as corneal substitutes from concentrated recombinant human type I and type III collagen solutions crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). White light transmission through these gels is comparable or superior to that of human corneas. Hydrogels from both type I and type III collagens supported in vitro epithelium and nerve over-growth. While both these biocompatible hydrogels have adequate tensile strength and elasticity for surgical manipulation, type III collagen hydrogels tended to be mechanically superior. Twelve-month post-implantation results of type I recombinant collagen-based corneal substitutes into mini-pigs showed retention of optical clarity, along with regeneration of corneal cells, nerves and tear film. For clinical use, implants based on fully characterized, recombinant human collagen eliminate the risk of pathogen transfer or xenogeneic immuno-responses posed by animal collagens.

Stage-related central corneal epithelial transformation in congenital aniridia-associated keratopathy.

PURPOSE: To relate central corneal epithelial phenotype to degree of keratopathy in a limbal stem cell deficient population. METHODS: 37 patients (67 eyes) with aniridia-associated keratopathy (AAK) underwent corneal examination including slit lamp biomicroscopy to determine the Grade of AAK, Cochet-Bonnet esthesiometry, and in vivo confocal microscopy (IVCM) to assess morphology of the central corneal epithelium and subepithelial region. RESULTS: AAK Grade ranged from 1 (limbal involvement only) to 4 (total conjunctivalization), with progression from Grade 1 occurring after the age of 20. 30% of subjects had an asymmetric Grade between eyes. In early-stage AAK (Grades 1-2), central epithelial cells had mixed corneal-conjunctival phenotype, touch sensitivity and subbasal nerves diminished, and mature dendritic cells, inflammatory leukocytes, and blood vessels were present despite central transparency in the slit lamp. In later stages (Grades 3-4) of the LSCD, neural deficit and nerve function worsened, immune cell invasion increased, and lymphatic vessels were detected in several cases. Goblet cells and epithelial cysts were observed to varying degrees in all stages, but without clear association to AAK severity. The clinical grade and progression of AAK was strongly associated with the central corneal epithelial phenotype. CONCLUSIONS: AAK is associated with degradation of epithelial phenotype, a neural deficit, and immune compromised status even in the clear central cornea in the earliest stages. IVCM can aid in assessing whether the conditions for limbal stem cell maintenance are likely to exist, based on morphology of the central epithelial microenvironment.

Collagen-Based Fillers as Alternatives to Cyanoacrylate Glue for the Sealing of Large Corneal Perforations.

PURPOSE: To describe the use of collagen-based alternatives to cyanoacrylate glue for the sealing of acute corneal perforations. METHODS: A collagen analog comprising a collagen-like peptide conjugated to polyethylene glycol (CLP-PEG) and its chemical crosslinker were tested for biocompatibility. These CLP-PEG hydrogels, which are designed to act as a framework for corneal tissue regeneration, were then tested as potential fillers in ex vivo human corneas with surgically created full-thickness perforations. Bursting pressures were measured in each of 3 methods (n = 10 for each condition) of applying a seal: 1) cyanoacrylate glue with a polyethylene patch applied ab externo (gold standard); 2) a 100-µm thick collagen hydrogel patch applied ab interno, and 3) the same collagen hydrogel patch applied ab interno supplemented with CLP-PEG hydrogel molded in situ to fill the remaining corneal stromal defect. RESULTS: Cyanoacrylate gluing achieved a mean bursting pressure of 325.9 mm Hg, significantly higher than the ab interno patch alone (46.3 mm Hg) and the ab interno patch with the CLP-PEG filler (86.6 mm Hg). All experimental perforations were sealed effectively using 100 µm hydrogel sheets as an ab interno patch, whereas conventional ab externo patching with cyanoacrylate glue failed to provide a seal in 30% (3/10) cases. CONCLUSIONS: An ab interno patch system using CLP-PEG hydrogels designed to promote corneal tissue regeneration may be a viable alternative to conventional cyanoacrylate glue patching for the treatment of corneal perforation. Further experimentation and material refinement is required in advance of clinical trials.

Biomaterials-enabled cornea regeneration in patients at high risk for rejection of donor tissue transplantation.

The severe worldwide shortage of donor organs, and severe pathologies placing patients at high risk for rejecting conventional cornea transplantation, have left many corneal blind patients untreated. Following successful pre-clinical evaluation in mini-pigs, we tested a biomaterials-enabled pro-regeneration strategy to restore corneal integrity in an open-label observational study of six patients. Cell-free corneal implants comprising recombinant human collagen and phosphorylcholine were grafted by anterior lamellar keratoplasty into corneas of unilaterally blind patients diagnosed at high-risk for rejecting donor allografts. They were followed-up for a mean of 24 months. Patients with acute disease (ulceration) were relieved of pain and discomfort within 1-2 weeks post-operation. Patients with scarred or ulcerated corneas from severe infection showed better vision improvement, followed by corneas with burns. Corneas with immune or degenerative conditions transplanted for symptom relief only showed no vision improvement overall. However, grafting promoted nerve regeneration as observed by improved touch sensitivity to near normal levels in all patients tested, even for those with little/no sensitivity before treatment. Overall, three out of six patients showed significant vision improvement. Others were sufficiently stabilized to allow follow-on surgery to restore vision. Grafting outcomes in mini-pig corneas were superior to those in human subjects, emphasizing that animal models are only predictive for patients with non-severely pathological corneas; however, for establishing parameters such as stable corneal tissue and nerve regeneration, our pig model is satisfactory. While further testing is merited, we have nevertheless shown that cell-free implants are potentially safe, efficacious options for treating high-risk patients.

Short peptide analogs as alternatives to collagen in pro-regenerative corneal implants.

Short collagen-like peptides (CLPs) are being proposed as alternatives to full-length collagen for use in tissue engineering, on their own as soft hydrogels, or conjugated to synthetic polymer for mechanical strength. However, despite intended clinical use, little is known about their safety and efficacy, mechanism of action or degree of similarity to the full-length counterparts they mimic. Here, we show the functional equivalence of a CLP conjugated to polyethylene glycol (CLP-PEG) to full-length recombinant human collagen in vitro and in promoting stable regeneration of corneal tissue and nerves in a pre-clinical mini-pig model. We also show that these peptide analogs exerted their pro-regeneration effects through stimulating extracellular vesicle production by host cells. Our results support future use of CLP-PEG implants for corneal regeneration, suggesting the feasibility of these or similar peptide analogs in clinical application in the eye and other tissues. STATEMENT OF SIGNIFICANCE: Although biomaterials comprising full-length recombinant human collagen and extracted animal collagen have been evaluated and used clinically, these macromolecules provide only a limited number of functional groups amenable to chemical modification or crosslinking and are demanding to process. Synthetic, customizable analogs that are functionally equivalent, and can be readily scaled-up are therefore very desirable for pre-clinical to clinical translation. Here, we demonstrate, using cornea regeneration as our test bed, that collagen-like-peptides conjugated to multifunctional polyethylene glycol (CLP-PEG) when grafted into mini-pigs as corneal implants were functionally equivalent to recombinant human collagen-based implants that were successfully tested in patients. We also show for the first time that these materials affected regeneration through stimulation of extracellular vesicle production by endogenous host cells that have migrated into the CLP-PEG scaffolds.