The intraoperative impression and postoperative outcomes of gamma-irradiated corneas in corneal and glaucoma patch surgery

Deep Anterior Lamellar Keratoplasty Using Dehydrated versus Standard Organ Culture-Stored Donor Corneas: Prospective Randomized Trial

PURPOSE

To compare the outcomes of deep anterior lamellar keratoplasty (DALK) using dehydrated versus standard organ culture-stored donor corneas for eyes with keratoconus.

DESIGN

Prospective, randomized, single-center trial conducted in Italy.

PARTICIPANTS

Adult patients (age ≥ 18 years) with keratoconus scheduled for elective DALK.

METHODS

Patients undergoing successful type 1 bubble pneumatic dissection using a standard DALK technique were randomized during surgery to receive either dehydrated (n = 30) or standard organ culture-stored (n = 30) donor corneas.

MAIN OUTCOME MEASURES

The primary study outcome was best spectacle-corrected visual acuity (BSCVA) 12 months after surgery. Secondary outcomes were refractive astigmatism (RA), endothelial cell density (ECD), and complication rates.

RESULTS

Postoperative BSCVA did not significantly differ between groups at both time points: mean difference at 6 months was 0.030 logarithm of the minimum angle of resolution (logMAR; 95% confidence interval [CI], -0.53 to 0.10 logMAR; P = 0.471) and at 12 months was -0.013 logMAR (95% CI, -0.10 to 0.08 logMAR; P = 0.764). No significant differences between groups were observed in terms of postoperative RA and ECD at all time points. In the first 3 days after DALK, an epithelial defect was present in 10 patients (33%) in the organ culture cornea group and in 29 patients (97%) in the dehydrated cornea group. Complete re-epithelialization was achieved by day 7 in all patients (100%) in both groups.

CONCLUSIONS

The study provides evidence that the use of dehydrated corneas is noninferior to the use of standard organ culture donor corneas for DALK. Corneal tissue dehydration represents a viable solution that can allow long-term cornea preservation and avoid wastage of unused corneas.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Chemical, Physical, and Biological Corneal Decellularization Methods: A Review of Literature

The cornea is one of the most commonly transplanted tissues worldwide. It is used to restore vision when severe visual impairment or blindness occurs in patients with corneal diseases or after trauma. Due to the global shortage of healthy donor corneas, decellularized corneal tissue has significant potential as an alternative to corneal transplantation. It preserves the native and biological ultrastructure of the cornea and, therefore, represents the most promising scaffold. This article discusses different methods of corneal decellularization based on the current literature. We searched PubMed.gov for articles from January 2009 to December 2023 using the following keywords: corneal decellularization, decellularization methods, and corneal transplantation. Although several methods of decellularization of corneal tissue have been reported, a universal standardised protocol of corneal decellularization has not yet been introduced. In general, a combination of decellularization methods has been used for efficient decellularization while preserving the optimal properties of the corneal tissue.

Acute Sterile Keratolysis After Deep Anterior Lamellar Keratoplasty in a Patient With Keratoconus: A Case Report

PURPOSE

The purpose of this study was to report the outcomes of using gamma-irradiated sterile cornea (GISC) as a deep lamellar keratoplasty (DALK) graft in a patient with keratoconus.

METHODS

This is a case report.

RESULTS

A 33-year-old male patient diagnosed with keratoconus underwent DALK using a GISC and developed a persistent epithelial defect which eventually led to sterile keratolysis necessitating further surgical interventions. Management and slitlamp photography, anterior segment optical coherence tomography (AS-OCT), and histopathological examination of the explanted graft are described in detail.

CONCLUSIONS

This is the first reported case of sterile keratolysis after the use of GISC lenticule in DALK in a healthy patient with keratoconus. The underlying pathophysiology is not clearly understood, and some theories have been proposed in this report. Surgeons need to be aware of this rare complication and are encouraged to have a low threshold for graft replacement to ensure good clinical and visual outcomes. Developing a prospective complication registry to document complications after the use of GISC lenticules in ophthalmic surgery is recommended.

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.

Ultrastructural Analysis of Rehydrated Human Donor Corneas After Air-Drying and Dissection by Femtosecond Laser

Purpose: To evaluate the efficiency of femtosecond laser (FSL) incision of rehydrated human donor corneas after air-drying and its effects on corneal structure.

Methods: We compared the rehydrated and fresh-preserved corneas by microscopy following Victus-Tecnolas FSL treatment for straight-edge anterior lamellar keratoplasty (ALK). The corneas were dehydrated at room temperature under a laminar-flow hood.

Results: To obtain the horizontal cut in rehydrated corneas, we increased the FSL pulse energy to 1.2 μJ from 0.80 μJ applied for the fresh corneas and obtained a clear-cut separation of the lamellar lenticule cap from the corneal bed. Light microscopy showed regular arrangement of stromal collagen lamellae, with spaces in between the fibers in the corneal stroma in the fresh and the rehydrated corneas, but the uppermost epithelial layers in the rehydrated corneas were lost. Transmission electron microscopy (TEM) revealed no signs of thermal or mechanical damage to the corneal structure. The epithelial basal membrane and Bowman's layer maintained their integrity. The epithelial basal layer and cells were separated by large spaces due to junction alteration in the rehydrated corneas. There were gaps between the lamellar layers in the stroma, especially in the rehydrated corneas. Keratocytes displayed normal structure in the fresh corneas but were devoid of microorganules in the rehydrated corneas. Minor irregularities were observed in the vertical incision and the horizontal stroma appeared smooth on scanning electron microscopy.

Conclusion: The corneal stroma of rehydrated corneas maintained morphology and integrity, while corneal cellular components were generally altered. When corneas are intended for FSL-assisted ALK, effective stromal bed incision is best achieved at a laser power higher than that currently adopted for fresh corneas.

Review of Gamma-Irradiated Sterile Cornea: Properties, Indications, and New Directions

ABSTRACT

Gamma-irradiated sterile cornea (GISC) is a relatively new graft tissue that follows the 30-year success of irradiation to other tissues (bone and sclera) to lessen antigenic load and infection transmission. It can serve as a graft to cover glaucoma drainage devices, as graft tissue for frank or impending corneal perforations in tectonic keratoplasty, as graft tissue in lamellar keratoplasty, and as carrier tissue for keratoprosthesis. With the limited availability of fresh corneal tissue in less developed countries, GISC may fill a need for corneal tissue worldwide. It can be used in situations where corneal endothelium is not needed and with a greatly reduced risk of rejection and infection because of the effect of irradiation on corneal tissue.

Factors predicting long-term changes in refraction after lamellar keratoscleroplasty in children with limbal dermoids

OBJECTIVES

The objective of this study is to determine the factors that predict long-term changes in refraction after lamellar keratoscleroplasty in paediatric patients with limbal dermoids.

METHODS

A retrospective study of 66 children with limbal dermoids who had lamellar keratoscleroplasty correction with more than 1-year follow-up. Univariate and multivariate regression analyses were performed to investigate factors associated with the long term in refractive parameters, including spherical equivalent, astigmatism, and mean keratometry. The change value was defined as the postoperative refractive value minus the preoperative refractive value. The lower the value of changes, the more satisfied the effects on the correction of the preoperative refraction.

RESULTS

A total of 66 patients (mean surgical age: 3.5 ± 2.1 years) were assessed with at least 1-year follow-up. Amblyopia treatment duration was the only independent factor predicting the long-term changes in spherical equivalent between baseline and last follow-up visit (β = -0.030, P < 0.001). Lesion encroachment on the central and paracentral cornea (β = 0.502, P = 0.024), suture-related complications (β = 1.571, P < 0.001) and graft rejection (β = 0.983, P = 0.035) were significantly correlated with long-term changes in astigmatism. The long-term changes in refraction were not correlated with surgical age, lesion size, lesion depth, steroid-induced high intraocular pressure and changes in mean keratometry.

CONCLUSION

Suture-related complications and graft rejection should be carefully observed and appropriately treated in order to avoid the possible postoperative increase in astigmatism, especially for patients with lesion encroachment on the central and paracentral cornea. The long-duration amblyopia treatment after surgery appears to have a better correction effect on spherical equivalent in the long term, compared with astigmatism.

Decellularized human corneal stromal cell sheet as a novel matrix for ocular surface reconstruction

The shortage of donor corneas as well as the limitations of tissue substitutes leads to the necessity to develop alternative materials for ocular surface reconstruction. Corneal surface substitutes must fulfill specific requirements such as high transparency, low immunogenicity, and mechanical stability combined with elasticity. This in vitro study evaluates a decellularized matrix secreted from human corneal fibroblasts (HCF) as an alternative material for ocular surface reconstruction. HCF from human donors were cultivated with the supplementation of vitamin C to form a stable and thick matrix. Furthermore, due to enhanced cultivation time, a three-dimensional like multilayered construct which partly mimics the complex structure of the corneal stroma could be generated. The formed human cell-based matrices (so-called cell sheets [CS]) were subsequently decellularized. The complete cell removal, collagen content, ultrastructure, and cell toxicity of the decellularized CS (DCS) as well as biomechanical properties were analyzed. Surgical feasibility was tested on enucleated porcine eyes. After decellularization and sterilization, a transparent, thick, cell free, and sterile tissue substitute resulted, which allowed expansion of limbal epithelial stem cells with no signs of cytotoxicity, and good surgical feasibility. DCS seem to be a promising new corneal tissue substitute derived from human cells without the limitation of donor material; however, future in vivo studies are necessary to further elucidate its potential for ocular surface reconstruction.

A review of long-term corneal preservation techniques: Relevance and renewed interests in the COVID-19 era

The growth of eye banking in India was showing positive trends until the nation was hit by unprecedented times as a result of the COVID-19 pandemic. The impact of this has led to a downward spiraling in eye banking activities globally. Several measures had to be implemented to tide over the crisis and strategies planned for future to prepare for the needs of corneal transplantation. While eye banks in India have been practicing short- term and intermediate storage preservation media, there is a definite need to evolve other methods of very long-term preservation. This review discusses various methods of long term corneal preservation, their relevance and applications in the present times. We reviewed relevant medical literature in English from PUBMED with the key words “Corneal preservation”, “Cryopreservation”, “Glycerol preservation”, Gamma Irradiation”, “Eye Banking” ,”COVID-19”.

Long-term clinical outcomes of keratoplasty using gamma-irradiated corneal lenticules

Objective

To report long-term clinical outcomes of gamma-irradiated corneal lenticules in partial and full-thickness keratoplasty.

Methods and Analysis

This multicentre, retrospective case series includes 23 patients who underwent surgery at three centres (India, Guatemala, and USA) between May 2009 and March 2018. The main outcome measures were epithelialization and retention for therapeutic keratoplasty and best spectacle-corrected visual acuity (BSCVA) for optical keratoplasty.

Results

Patients were categorised according to primary aetiology requiring corneal transplantation: non-inflammatory conditions, infectious keratitis and sterile keratolysis. Nine patients with non-inflammatory conditions underwent anterior lamellar keratoplasty (n=7) and Boston type 1 keratoprosthesis (n=2). All nine grafts remained intact and epithelialized during follow-up (median 24 months). In the seven patients who underwent anterior keratoplasty, the graft stayed optically clear during follow-up (median 12 months), with BSCVA between 20/20 and 20/40 in all but one patient who developed cataract. Nine patients with severe infectious keratitis had emergency patch grafting. Six of those grafts epithelialized and remained intact over a median of 30 months, providing tectonic support until optical keratoplasty with fresh tissue could be performed. Three grafts had recurrent infectious keratitis 1–3 months postoperatively, two of which underwent tectonic keratoplasty with fresh tissue which also eventually became infected during follow-up. In five additional patients with sterile keratolysis who underwent lamellar patch graft, two grafts remained intact during follow-up (median 36 months). Two patients had recurrent corneal melt within 1 month, and both had subsequent corneal surgery with fresh tissue which also failed. There were no donor-related complications.

Conclusion

Gamma-irradiated sterile corneal stromal lenticules can be considered as a viable alternative to fresh tissue in various clinical settings.

Glaucoma Patch Graft Surgery Utilizing Corneas Augmented with Collagen Cross-linking

PURPOSE

Glaucoma drainage device surgery (GDDS) has gained popularity, with outcomes equivalent to trabeculectomy. Erosion of the tube through the overlying conjunctiva may occur in 5%-10% of eyes. Donor corneal tissue has been used as a patch graft for GDDS.

MATERIALS AND METHODS

This was a prospective proof of concept study in 10 patients undergoing GDDS. From patients undergoing endothelial keratoplasty, the donor tissue (approximately 300 μ in thickness) was placed epithelial side down in a well and was allowed to soak in riboflavin solution (VibeX, Avedro, Waltham, MA, USA) for 15 min. This anterior corneal lenticule received 8 mW/cm² ultraviolet (UV) irradiation applied for 15 min (total energy of 7.2 J/cm²). Each lenticule was then bisected and utilized for the two study participants. The tissue was sutured over the tube during the GDDS and then was covered with recipient conjunctiva as per the usual technique. Representative graft tissues were fixed and examined to determine the depth of cross-linking effect. The patients were followed for 1 year.

RESULTS

Histology revealed no apparent demarcation line in the cross-linked grafts; this supported a full-thickness cross-linking treatment effect. There were no intra- or postoperative complications attributed to the graft tissue. No patient developed erosion or exposure of the tube during the 1-year follow-up.

CONCLUSIONS

UV-riboflavin cross-linking of the corneal tissue patch graft material appears to be a safe modification when used in GDDS and warrants ongoing study. This method of patch graft can replace other costy methods used with GDD.

Effects of gamma radiation sterilization on the structural and biological properties of decellularized corneal xenografts

To address the shortcomings associated with corneal transplants, substantial efforts have been focused on developing new modalities such as xenotransplantion. Xenogeneic corneas are anatomically and biomechanically similar to the human cornea, yet their applications require prior decellularization to remove the antigenic components to avoid rejection. In the context of bringing decellularized corneas into clinical use, sterilization is a crucial step that determines the success of the transplantation. Well-standardized sterilization methods, such as gamma irradiation (GI), have been applied to decellularized porcine corneas (DPC) to avoid graft-associated infections in human recipients. However, little is known about the effect of GI on decellularized corneal xenografts. Here, we evaluated the radiation effect on the ultrastructure, optical, mechanical and biological properties of DPC. Transmission electron microscopy revealed that gamma irradiated decellularized porcine cornea (G-DPC) preserved its structural integrity. Moreover, the radiation did not reduce the optical properties of the tissue. Neither DPC nor G-DPC led to further activation of complement system compared to native porcine cornea when exposed to plasma. Although, DPC were mechanically comparable to the native tissue, GI increased the mechanical strength, tissue hydrophobicity and resistance to enzymatic degradation. Despite these changes, human corneal epithelial, stromal, endothelial and hybrid neuroblastoma cells grew and differentiated on DPC and G-DPC. Thus, GI may achieve effective tissue sterilization without affecting critical properties that are essential for corneal transplant survival.

Partial thickness cornea tissue from small incision lenticule extraction: A novel patch graft in glaucoma drainage implant surgery

OBJECTIVE

The aim of the present study was to observe the feasibility and effect of cornea slice acquired from femtosecond laser surgery, small incision lenticule extraction (SMILE) as patch graft for the prevention of drainage tube exposure and to compare with the sclera.

METHODS

The research is a prospective comparative randomized study. Patients who received Ahmed glaucoma valve implantation surgery from August 2015 to January 2017 at the Xiamen Eye Center were randomly divided into 2 groups. Group A (corneal group) included 131 cases (135 eyes), receiving the 3 layers of allogeneic cornea slices as graft. Group B (scleral group) included 124 cases (127 eyes), using the sclera as allograft. The appearance, graft, conjunctiva melting, and tube exposure were the primary observation points.

RESULTS

After followed up for 6 to 20 months, a thinner appearance was seen in 3 eyes (2.2%) in the corneal graft group and 7 eyes (5.5%) in the scleral group. Conjunctiva melted and drainage tube exposed in 0 eyes (0%) in the corneal graft group and 2 eyes (1.6%) in the scleral group. One eye needed repair surgery. There was no statistical difference between the 2 groups (P > .05). After surgery, the intraocular pressure was reduced significantly in both groups (P < .05). The white sclera slice could be seen under the conjunctiva, thereby affecting the cosmetic appearance.

CONCLUSION

The cornea slice acquired from SMILE surgery can effectively prevent drainage tube exposure. Moreover, it is easy to acquire, safe, and cheaper, giving the patient a better cosmetic appearance.

Ocular adhesives: Design, chemistry, crosslinking mechanisms, and applications

Closure of ocular wounds after an accident or surgery is typically performed by suturing, which is associated with numerous potential complications, including suture breakage, inflammation, secondary neovascularization, erosion to the surface and secondary infection, and astigmatism; for example, more than half of post-corneal transplant infections are due to suture related complications. Tissue adhesives provide promising substitutes for sutures in ophthalmic surgery. Ocular adhesives are not only intended to address the shortcomings of sutures, but also designed to be easy to use, and can potentially minimize post-operative complications. Herein, recent progress in the design, synthesis, and application of ocular adhesives, along with their advantages, limitations, and potential are discussed. This review covers two main classes of ocular adhesives: (1) synthetic adhesives based on cyanoacrylates, polyethylene glycol (PEG), and other synthetic polymers, and (2) adhesives based on naturally derived polymers, such as proteins and polysaccharides. In addition, different technologies to cover and protect ocular wounds such as contact bandage lenses, contact lenses coupled with novel technologies, and decellularized corneas are discussed. Continued advances in this area can help improve both patient satisfaction and clinical outcomes.

Etiology of Global Corneal Blindness and Current Practices of Corneal Transplantation: A Focused Review

PURPOSE

The purpose of this focused review was to explore the etiologies of corneal blindness worldwide and compare them with the indications and type of keratoplasties (eg, full-thickness penetrating keratoplasty, anterior lamellar keratoplasty, or endothelial keratoplasty) performed.

METHODS

A literature search of the articles published in the top 10 journals (based on the Altmetrics score) relevant to corneal transplantation within the past 20 years was performed to determine how the focus within corneal transplantation has changed over time. These data were compared with the prevalence and etiology of corneal blindness in each respective region worldwide.

RESULTS

The leading etiologies of corneal blindness worldwide are primarily due to anterior corneal pathology with a normal endothelium, and the prevalence is highest in developing countries. In addition, the number and type of corneal transplantations performed globally indicate that current practices are disproportionately skewed in favor of endothelial keratoplasty, which is targeted for the pathology prevalent in developed countries. Despite the large number of individuals who would benefit from anterior lamellar keratoplasty, this technique seems to be infrequently performed.

CONCLUSIONS

Most corneal blindness worldwide is secondary to anterior corneal pathology because of infections and trauma. However, this does not align with the current trends and practices in the field of corneal transplantation. We discuss potential solutions to address the current leading causes of global corneal blindness, including increasing the number of anterior lamellar keratoplasties performed, using long-term preserved corneas by trained surgeons, and improving eye bank handling and distribution of procured tissues.

Improving the practicality and safety of artificial corneas: Pre-assembly and gamma-rays sterilization of the Boston Keratoprosthesis

PURPOSE

To make the Boston keratoprosthesis (B-KPro), together with its carrier corneal graft, more easily procured, transported and stored, as well as less expensive, easier for the surgeon to implant and safer for the patient, it is proposed that the B-KPro-graft combination be pre-assembled by an expert technician, followed by sterilization with gamma ray irradiation (GI) allowing long-term storage at room temperature. For this to be possible, it must be shown that the B-KPro itself (not only the graft) remains unharmed by the irradiation.

METHODS

Polymethyl methacrylate (PMMA) discs and B-KPros were submitted to either ethylene oxide sterilization or different doses of GI. Cell biocompatibility, mechanical strength and optical quality were evaluated. The feasibility of assembling the B-KPro to a corneal graft, and gamma-radiate afterwards, was also assessed.

RESULTS

There were no differences in cell biocompatibility between the samples. The optical evaluation showed high levels of transparency for all the groups. The absorbance of ultraviolet was higher for the groups treated with GI. The mechanical evaluation by nanoindentation showed no alterations of the PMMA discs after GI. The flexure test revealed a similar mechanical behavior. Technically, pre-assembly and GI of the B-KPro revealed no problems.

CONCLUSIONS

Sterilization of B-KPro using GI has no detrimental influence on the device. The pre-assembly of B-KPro to a donor cornea, followed by gamma sterilization, emerges as an efficient and safe procedure.

Measurement of Gamma-Irradiated Corneal Patch Graft Thickness After Aqueous Drainage Device Surgery

Importance

Exposure of the tube of an aqueous drainage device (ADD) through the conjunctiva is a serious complication of ADD surgery. Although placement of gamma-irradiated sterile cornea (GISC) as a patch graft over the tube is commonly performed, exposures still occur.

Objectives

To measure GISC patch graft thickness as a function of time after surgery, estimate the rate of graft thinning, and determine risk factors for graft thinning.

Design, Setting, and Participants

Cross-sectional study of graft thickness using anterior segment optic coherence tomography (AS-OCT) was conducted at the Wilmer Eye Institute at Johns Hopkins Hospital. A total of 107 patients (120 eyes, 120 ADDs) 18 years or older who underwent ADD surgery at Johns Hopkins with GISC patch graft between July 1, 2010, and October 31, 2016, were enrolled.

Intervention

Implantation of ADD with placement of GISC patch graft over the tube.

Main Outcomes and Measures

Graft thickness vs time after ADD surgery and risk factors for undetectable graft.

Results

Of the 107 patients included in the analysis, the mean (SD) age of the cohort was 64 (16.2) years, 49 (45.8%) were male, and 43 (40.2%) were African American. The mean time of measurement after surgery was 1.7 years (range, 1 day to 6 years). Thinner grafts were observed as the time after surgery lengthened (β regression coefficient, -60 µm per year since surgery; 95% CI, -80 µm to -40 µm). The odds ratio of undetectable grafts per year after ADD surgery was 2.1 (95% CI, 1.5-3.0; P < .001). Age, sex, race, type of ADD, quadrant of ADD placement, diagnosis of uveitis or dry eye, and prior conjunctival surgery were not correlated with the presence or absence of the graft.

Conclusions and Relevance

Gamma-irradiated sterile corneal patch grafts do not always retain their integrity after ADD surgery. Data from this cross-sectional study showed that on average, the longer the time after surgery, the thinner the graft. These findings suggest that placement of a GISC patch graft is no guarantee against tube exposure, and that better strategies are needed for preventing this complication.

Cross-linked decellularized porcine corneal graft for treating fungal keratitis

This study aims to develop a cross-linked decellularized porcine corneal graft (cDPC) as a substitute for lamellar donor corneas and to evaluate the feasibility of using cDPC to treat fungal keratitis. The cDPC was prepared by decellularization, chemical crosslinking and γ-ray irradiation. Transparency, effectiveness of decellularization and biomechanical strength of cDPC were evaluated. The safety and efficacy of using cDPC to treat fungal keratitis were evaluated in the rabbit model. The transparency of cDPC was similar to that of a native porcine cornea (NPC), and no intact cells were observed in cDPC except for an insignificant amount of residual shrinking cellular nucleus. Compared to the NPC, the biomechanical strength of the cDPC was significantly increased. In the rabbit model of lamellar keratoplasty, the implanted cDPC reduced the incidence of corneal perforation, and also maintained transparency in majority. The results of this study suggest that the cDPC is capable of restoring the original transparency of cornea while effectively treating fungal keratitis. The cDPC is a highly promising ideal substitute for the donor human cornea.

Clinical outcomes of gamma-irradiated sterile cornea in aqueous drainage device surgery: a multicenter retrospective study

PurposeThe purpose of the study was to evaluate the safety and efficacy of gamma-irradiated sterile cornea (GISC) for covering the tube in aqueous drainage device (ADD) surgery in a retrospective, multicenter case series.Patients and methodsParticipants included 297 patients (321 procedures) who had undergone ADD surgery for the first time using GISC patch at three clinic centers in the United States between April 2009 and July 2012. The medical records of those consecutive patients were reviewed. Preoperative, intraoperative, and postoperative parameters about GISC were collected and analyzed. The main outcome measures were patch graft failure (PGF) and postoperative complications related to GISC.ResultsThree hundred and nineteen eyes in 295 patients were included in the current analysis. Ten out of the 319 eyes experienced PGF with a mean follow-up of 15.4±9.8 (SD) months. The overall cumulative PGF proportion from Kaplan-Meier analysis was 2.6% (95% CI: 0.6-4.7%) at 18 months. We detected two cases of presumed endophthalmitis related to PGF.ConclusionsGISC appears to have a reasonable success rate for preventing tube exposure related to PGF over an 18-month period. This success rate, in combination with other features of GISC (transparency and storage at room temperature), makes it a viable choice for patch graft material during ADD.

Laboratory Evaluation of Femtosecond Laser Lamellar Cuts in Gamma-Irradiated Corneas

PURPOSE

To evaluate the stromal interface quality after femtosecond laser full lamellar cuts in gamma-irradiated corneas (VisionGraft sterile cornea) and to determine the limits of the cut depth using the VisionGraft as donor corneas for laser-assisted lamellar anterior keratoplasty.

METHODS

Fourteen VisionGraft corneas underwent full lamellar cuts using the femtosecond laser. The percent cut depth was 17% to 21% (100 μm, n = 2), 31% to 35% (n = 3), 38% to 40% (n = 3), 45% to 48% (n = 3), and 50% (n = 3) of the total stromal thickness (not including the epithelium). The cap and stromal bed surfaces were imaged with a scanning electron microscope. The quality of cut surfaces was graded by 2 masked observers based on two indices: ridge and roughness. Ridge grading indicated macroscopic irregularity. Roughness grading indicated microscopic irregularity. The grading was done on a subjective integer scale of 1 to 5 (1 = best and 5 = worst), which was used in a previous study of cut quality in fresh corneas.

RESULTS

The ridge grading ranged from 1.5 for the shallowest cut to 2.2 for the deepest cut and weakly (r = 0.279) but significantly (P = 0.037) correlated with the percent cut depth. The roughness grading ranged from 2.63 to 2.56 and showed no trend with the percent cut depth (r = 0.006, P = 0.968).

CONCLUSIONS

Compared with previously published results of fresh corneas, in which ridge grading exceeded 3 for cuts deeper than 31%, cut quality was better for the VisionGraft. Even at depths up to 48% of the total stromal thickness, ridge grading was not worse than shallow cuts. Thus, gamma-irradiated corneas could provide a smoother interface than do fresh eye bank corneas for laser-assisted lamellar anterior keratoplasty.

Physical and Biological Characterization of the Gamma-Irradiated Human Cornea

PURPOSE

To compare the physical and biological characteristics of commercial gamma-irradiated corneas with those of fresh human corneas and to determine suitability for transplantation.

METHODS

The physical properties of gamma-irradiated and fresh corneas were evaluated with respect to light transmittance, hydration (swelling ratio), elastic modulus (compressive modulus by the indentation method), matrix organization (differential scanning calorimetry), and morphology (light and transmission electron microscopy). The biological properties of the gamma-irradiated cornea, including residual cell content and cellular biocompatibility, were evaluated by quantifying DNA content and measuring the proliferation rate of human corneal epithelial cells, respectively.

RESULTS

The hydration, light transmittance, elastic modulus, and proliferation rate of human corneal epithelial cells were not significantly different between fresh and gamma-irradiated corneas. However, differences were observed in tissue morphology, DNA content, and thermal properties. The density of collagen fibrils of the gamma-irradiated corneal sample (160.6 ± 33.2 fibrils/μm) was significantly lower than that of the fresh corneal sample (310.0 ± 44.7 fibrils/μm). Additionally, in the gamma-irradiated corneas, cell fragments-but not viable cells-were observed, supported by lower DNA content of the gamma-irradiated cornea (1.0 ± 0.1 μg/mg) than in fresh corneas (1.9 μg/mg). Moreover, the denaturation temperature of gamma-irradiated corneas (61.8 ± 1.1 °C) was significantly lower than that of fresh corneas (66.1 ± 1.9 °C).

CONCLUSIONS

Despite structural changes due to irradiation, the physical and biological properties of the gamma-irradiated cornea remain similar to the fresh cornea. These factors, combined with a decreased risk of rejection and longer shelf life, make the gamma-irradiated tissue a viable and clinically desired option in various ophthalmic procedures.

Gamma-Irradiated Sterile Cornea for Use in Corneal Transplants in a Rabbit Model

Purpose:

Gamma irradiated corneas in which the donor keratocytes and endothelial cells are eliminated are effective as corneal lamellar and glaucoma patch grafts. In addition, gamma irradiation causes collagen cross inking, which stiffens collagen fibrils. This study evaluated gamma irradiated corneas for use in corneal transplantations in a rabbit model comparing graft clarity, corneal neovascularization, and edema.

Methods:

Penetrating keratoplasty was performed on rabbits using four types of corneal grafts: Fresh cornea with endothelium, gamma irradiated cornea, cryopreserved cornea, and fresh cornea without endothelium. Slit lamp examination was performed at postoperative week (POW) one, two, and four. Corneal clarity, edema, and vascularization were graded. Confocal microscopy and histopathological evaluation were performed. A P < 0.05 was statistically significant.

Results:

For all postoperative examinations, the corneal clarity and edema were statistically significantly better in eyes that received fresh cornea with endothelium compared to the other three groups (P < 0.05). At POW 1, gamma irradiated cornea scored better than the cryopreserved and fresh cornea without endothelium groups in clarity (0.9 vs. 1.5 and 2.6, respectively), and edema (0.6 vs. 0.8 and 2.0, respectively). The gamma irradiated corneas, cryopreserved corneas and the fresh corneas without endothelium, developed haze and edema after POW 2. Gamma irradiated cornea remained statistically significantly clearer than cryopreserved and fresh cornea without endothelium during the observation period (P < 0.05). Histopathology indicated an absence of keratocytes in gamma irradiated cornea.

Conclusion:

Gamma irradiated corneas remained clearer and thinner than the cryopreserved cornea and fresh cornea without endothelium. However, this outcome is transient. Gamma irradiated corneas are useful for lamellar and patch grafts, but cannot be used for penetrating keratoplasty.

The use of irradiated corneal patch grafts in pediatric Ahmed drainage implant surgery

PURPOSE

To describe the use of irradiated cornea for scleral reinforcement in Ahmed glaucoma valve drainage implant (AGV) devices in children.

METHODS

The medical records of patients <18 years of age who underwent AGV surgery with irradiated cornea as scleral reinforcement were reviewed retrospectively. The primary outcome measure was erosion of the drainage tube through the corneal patch graft. Secondary outcome measures included other major complications: persistent inflammation, wound dehiscence, transmission of infectious disease, endophthalmitis, and tube/plate self-explantation.

RESULTS

A total of 25 procedures (20 patients) met inclusion criteria. Average patient age was 70 months (range, 2 months to 17 years). Mean follow-up was 24.8 months (range, 6 months to 6.2 years). One tube experienced conjunctival exposure through two separate corneal grafts (2/25 cases [8%]), sequentially in the same eye. The first event occurred at month 3.5 after primary implantation of the tube shunt; the second erosion occurred following revision of the existing implant at month 1.5 postoperatively. There were 2 cases of auto-explantation, 2 cases of wound dehiscence, and 1 case of persistent inflammation. There were no cases of endophthalmitis or other infections.

CONCLUSIONS

To our knowledge, this is the first report describing the use of corneal patch grafts in children. Irradiated cornea improves cosmesis and enhances visualization of the tube. The risk of tube exposure was found to be low and comparable to other materials used as a patch graft.

Evaluation of broadband spectral transmission characteristics of fresh and gamma-irradiated corneal tissues

PURPOSE

The aim of this study was to evaluate the clarity of gamma-irradiated sterile corneal donor lenticules.

METHODS

Broadband UV, visible, and near-infrared (200-850 nm) light transmission was measured through gamma-irradiated, sterile partial-thickness, and full-thickness donor lenticules and fresh corneal tissues and compared with standard acrylic intraocular lens (IOL) implants using a conventional spectrophotometer technique.

RESULTS

All tissues had high light transmission (≥ 90%) in the visible and near-infrared regions and very low (<2%) transmission below 290 nm. Differences in light transmission between irradiated and fresh cornea types were observed between 300 and 450 nm, which mirrored differences in light transmission through their respective storage solutions. Light transmission through partial-thickness irradiated donor lenticules was greatest across all wavelengths. All corneal tissues exhibited higher transmission than acrylic IOL implant across all wavelengths.

CONCLUSIONS

Gamma-irradiated donor lenticules are comparable with fresh corneas regarding light transmission, with both partial-thickness and full-thickness lenticules having greater transmission than standard IOL. We would expect the optical performance of gamma-irradiated donor lenticules to be comparable to fresh cornea if used for lamellar corneal procedures that do not require a viable endothelium.

Use of Gamma-Irradiated Cornea to Plug Sclerostomy Site During Tube Shunt Revision

Tube shunt implantation is a common procedure for control of intraocular pressure (IOP). However, tube revision and repositioning must sometimes be performed, and this involves removing the tube from its sclerostomy site. This site is prone to leaking and this may cause postoperative hypotony. We describe a novel and cosmetically acceptable technique of plugging and covering the sclerostomy site with gamma-irradiated corneal tissue.

Tube shunt coverage with gamma-irradiated cornea allograft (VisionGraft)

PURPOSE

To investigate the clinical outcomes of tube shunt coverage using sterile gamma-irradiated cornea allograft.

PATIENTS AND METHODS

The Wills Eye Hospital Glaucoma Research Center retrospectively reviewed the medical records of 165 patients who underwent glaucoma tube shunt procedures using sterile gamma-irradiated cornea allograft (VisionGraft) between December 2012 and November 2013. Demographic characteristics, type of tube shunt, and position were noted. Complications were recorded at 1 day; 1 week; 1, 3, 6, and 12 months; and on the final postoperative visit.

RESULTS

One hundred and sixty-nine eyes of 165 patients were included. The mean follow-up time was 4.8±3.5 (ranging from 1 to 16) months. There was no evidence of immunological reaction, infection, or exposure in 166 eyes (98.2%). Three eyes (1.8%) experienced graft or tube exposure within the first 3 postoperative months. Two of the cases had underlying diseases: bullous pemphigoid and chronic allergic conjunctivitis.

CONCLUSION

Coverage of tube shunts using gamma-irradiated cornea allograft had a low exposure rate and was well tolerated. The graft can be stored long term at room temperature and has an excellent postoperative cosmetic appearance.

Deep anterior lamellar keratoplasty using irradiated acellular cornea with amniotic membrane transplantation for intractable ocular surface diseases

Purpose

To report the clinical outcomes of deep anterior lamellar keratoplasty (DALK) when sterile gamma-irradiated acellular corneal tissues (VisionGraft) are used in combination with amniotic membrane transplantation (AMT) for intractable ocular surface diseases.

Methods

The medical records of fifteen patients who had DALK with AMT were retrospectively reviewed. Indications for surgery included ocular burn, bacterial keratitis, herpes simplex virus keratitis, corneal opacity with Stevens-Johnson syndrome, Mooren's ulcer, idiopathic myxoid degeneration of corneal stroma, and recurrent band keratopathy. DALK was performed using partial-thickness acellular corneal tissue and a temporary amniotic membrane patch was added at the end of the operation.

Results

All cases that underwent DALK with AMT became epithelialized within 2 postoperative weeks. Twelve patients showed favorable outcomes without graft rejection, corneal opacification, or neovascularization. The other three grafts developed corneal opacification and neovascularization, and required additional penetrating keratoplasty (PK). Unlike the results of previous PKs, there were no graft rejections and the graft clarity was well-maintained in these three cases for at least 8 months after PK.

Conclusions

DALK using sterile acellular corneal tissues in combination with AMT may be a good therapeutic strategy for treating intractable ocular surface diseases because of lowered immune rejection, fibroblast activation, and facilitation of epithelialization. Furthermore, DALK can help stabilize the ocular surface, prolong graft survival, and may allow better outcomes when combined with subsequent PK.

Gamma-irradiated corneas as carriers for the Boston type 1 keratoprosthesis: advantages and outcomes in a surgical mission setting

PURPOSE

The Boston keratoprosthesis (KPro) is the most commonly used KPro worldwide. There are limited data on the outcomes when irradiated corneas are used as KPro carriers. We report a retrospective analysis of corneal transplantations performed in a regular surgical mission setting in Beirut, Lebanon, using the Boston KPro type 1 and gamma-irradiated carrier corneas, and we describe visual outcomes, complications, and retention percentage.

METHODS

We conducted a retrospective analysis of 17 consecutive eyes from 16 patients who underwent Boston KPro type 1 implantation at the Beirut Eye Specialist Hospital between December 2010 and July 2012. Patient medical records were reviewed for preoperative, intraoperative, and postoperative details.

RESULTS

Postoperatively, 9 (52.9%), 5 (29.4%), and 2 (11.7%) eyes had a corrected visual acuity of 20/400 or better, 20/100 or better, and 20/40 or better, respectively, at the most recent follow-up visit. A total of 16 eyes (94.1%) improved in corrected visual acuity over the course of follow-up. Overall, 13 eyes (76.4%) developed at least 1 complication after surgery. Retroprosthetic membrane formation was the most common complication, occurring in 10 eyes (58.8%). Neither infectious keratitis nor corneal stromal necrosis was noted during the follow-up period. The retention percentage was 94.1%.

CONCLUSIONS

The visual acuity outcomes, incidence of complications, and retention percentage of the KPro using gamma-irradiated carrier corneas are comparable with the outcomes of KPro implantation reported in the literature using fresh grafts as carriers. KPro with irradiated corneal carrier grafts seems to be an effective option to increase the supply of transplantation suitable corneas in remote areas, where fresh corneal grafts may be scarce.

Treatment of an 8-mm myxoma using acellular corneal tissue

A myxoma is a benign tumor found in the heart and in various soft tissues; however, a corneal myxoma is rare. A mucinous mass of unknown etiology was observed on the left cornea of a 32-year-old male patient. We performed deep anterior lamellar keratoplasty using acellular corneal tissue and concurrent amniotic membrane transplantation. Hematoxylin and eosin staining revealed vacuolation of the parenchyma and myxoid change in the corneal tissue that occurred in the anterior half of the corneal parenchyma. We identified a myxoid stroma by Alcian blue staining and observed collagen fibers with denatured stroma by Masson trichrome staining. The patient's visual acuity improved from light perception to 20 / 200, and the intraocular pressure remained within the normal range for one year after surgery. The transplanted cornea survived successfully with well-maintained transparency, and recurrence was not observed one year after surgery.

Future perspectives for regenerative medicine in ophthalmology

Repair and reconstruction of the cornea has historically relied on synthetic materials or tissue transplantation. However, the future holds promise for treatments using smart biomaterials and stem cells that direct tissue repair and regeneration to ultimately create new ocular structures that are indistinguishable from the original native tissue. The cornea is a remarkable engineering structure. By understanding the physical structure of the tissue and the resulting impact of the structure on biological function, we can design novel materials for a number of ophthalmic clinical applications. Furthermore, by extending this structure-function approach to characterizing corneal disease processes, new therapies can be engineered.

Gamma-irradiation reduces the allogenicity of donor corneas

PURPOSE

To evaluate the utility and allogenicity of gamma-irradiated corneal allografts.

METHODS

Corneal buttons were harvested from C57BL/6 mice and decellularized with gamma irradiation. Cell viability was assessed using TUNEL and viability/cytotoxicity assays. Orthotopic penetrating keratoplasty was performed using irradiated or nonirradiated (freshly excised) C57BL/6 donor grafts and BALB/c or C57BL/6 recipients. Graft opacity was assessed over an 8-week period and graft survival was evaluated using Kaplan-Meier survival curves. Mixed-lymphocyte reactions and delayed-type hypersensitivity assays were performed to evaluate T-cell alloreactivity. Real-time PCR was used to investigate the corneal expression of potentially pathogenic T-helper 1, 2, and 17 cell-associated cytokines.

RESULTS

Corneal cells were devitalized by gamma irradiation as evidenced by widespread cellular apoptosis and plasma membrane disruption. Nonirradiated allograft and isograft rates of survival were superior to irradiated allograft and isograft rates of survival (P < 0.001). Mixed lymphocyte reactions demonstrated that T-cells from irradiated allograft recipients did not exhibit a secondary alloimmune response (P < 0.001). Delayed-type hypersensitivity assays demonstrated that irradiated allografts did not elicit an alloreactive delayed-type hypersensitivity response in graft recipients (P ≤ 0.01). The corneal expression of T-helper 1, 2, and 17 cell-associated cytokines was significantly lower in failed irradiated allografts than rejected nonirradiated allografts (P ≤ 0.001).

CONCLUSIONS

Gamma-irradiated corneas failed to remain optically clear following murine penetrating keratoplasty; however, gamma irradiation reduced the allogenicity of these corneas, potentially supporting their use in procedures such as anterior lamellar keratoplasty or keratoprosthesis implantation.

The use of precut, γ-irradiated corneal lenticules in Boston type 1 keratoprosthesis implantation

PURPOSE

To report the use of a sterile, γ-irradiated corneal tissue without viable endothelium (VisionGraft Sterile Cornea; Tissue Banks International) in lieu of fresh donor cornea in Boston type 1 keratoprosthesis (KPro) implantation.

DESIGN

Retrospective, interventional small case series.

METHODS

Eleven eyes of 11 patients underwent Boston type 1 keratoprosthesis implantation using VisionGraft Sterile Cornea between April 2009 and October 2010. Precut donut-shaped corneal lenticules, using femtosecond laser, measuring 8.5 mm in diameter with a 3-mm central hole were used.

RESULTS

Surgical procedures were uneventful. Complete corneal re-epithelization was noted within 10 days in all cases. No complications related to the donor cornea (eg, stromal necrosis, wound leak, or device extrusion) occurred over an average follow-up of 16.5 months.

CONCLUSIONS

VisionGraft Sterile Cornea eliminates the need for use of fresh donor corneal tissue for Boston type 1 keratoprosthesis procedures, which makes this procedure a viable sight-restoring option when donor corneal tissues are not readily available.