Prevention and treatment of corneal graft rejection: current practice patterns of the Cornea Society (2011). Cornea. 2015;34:609-614. [PMID: 25811719 DOI: 10.1097/ico.0000000000000403]

Nanoparticle-hydrogel composite as dual-drug delivery system for the potential application of corneal graft rejection

Immune rejection remains the major cause of corneal graft failure. Immunosuppressants (such as rapamycin; RAPA) adjunctive to antibiotics (such as levofloxacin hydrochloride; Lev) are a clinical mainstay after corneal grafts but suffer from poor ocular bioavailability associated with severe side effects. In this study, we fabricated a Lev@RAPA micelle loaded cationic peptide-based hydrogel (NapFFKK) as a dual-drug delivery system by integrating RAPA micelles with Lev into a cationic NapFFKK hydrogel to potentially reduced the risk of corneal graft rejection. The properties of the resulting hydrogels were characterized using transmission electronmicroscopy and rheometer. Lev@RAPA micelles loaded NapFFKK hydrogel provided sustained in vitro drug release without compromising their inherent pharmacological activities. Topical instillation of Lev@RAPA micelles loaded NapFFKK hydrogel resulted in the great ocular tolerance and extended precorneal retention over 60 min, thus significantly enhancing the ocular bioavailability of both Lev and RAPA. Overall, such dual-drug delivery system might be a promising formulation for the suppression of corneal graft failure.

Retinal transplant immunology and advancements

Several gaps and barriers remain for transplanting stem cells into the eye to treat ocular disease, especially diseases of the retina. While the eye has historically been considered immune privileged, recent thinking has identified the immune system as both a barrier and an opportunity for eye stem cell transplantation. Recent approaches leveraging scaffolds or cloaking have been considered in other tissues beyond immune suppression. This perspective paper outlines approaches for transplantation and proposes opportunities to overcome barriers of the immune system in stem cell transplantation in the eye.

Myeloid-derived suppressor cells promote allograft survival by suppressing regulatory T cell dysfunction in high-risk corneal transplantation

Highly inflamed and neovascularized corneal graft beds are known as high-risk (HR) environments for transplant survival. One of the primary factors leading to this rejection is reduction in the suppressive function of regulatory T cells (Treg). Our results show that myeloid-derived suppressor cells (MDSC) counteract interleukin-6-mediated Treg dysfunction by expressing interleukin-10. Additionally, MDSC maintain forkhead box P3 stability and their ability to suppress IFN-γ+ Th1 cells. Administering MDSC to HR corneal transplant recipients demonstrates prolonged graft survival via promotion of Treg while concurrently suppressing IFN-γ+ Th1 cells. Moreover, MDSC-mediated donor-specific immune tolerance leads to long-term corneal graft survival as evidenced by the higher survival rate or delayed survival of a second-party C57BL/7 (B6) graft compared to those of third-party C3H grafts observed in contralateral low-risk or HR corneal transplantation of BALB/c recipient mice, respectively. Our study provides compelling preliminary evidence demonstrating the effectiveness of MDSC in preventing Treg dysfunction, significantly improving graft survival in HR corneal transplantation, and showing promising potential for immune tolerance induction.

Topical tacrolimus in high-risk corneal transplants

PURPOSE

The purpose of this study was to assess the use of topical tacrolimus ointment in preventing rejection in high-risk corneal grafts, when added to the standard immunosuppressive regimen.

METHODS

We conducted an observational, retrospective study using clinical data of high-risk patients subjected to penetrating keratoplasty, who were treated with topical tacrolimus ointment 0.2 mg/g twice a day plus topical dexamethasone 0.1 mg/ml 6 id and compared it with a similar control group treated with topical dexamethasone 0.1 mg/ml 6 id alone. High-risk status was attributed to patients with previous ipsilateral corneal graft failure, two or more quadrants with corneal neovascularization or an infectious or inflammatory corneal disease.

RESULTS

We analysed 53 patients in the trial group versus 53 patients in the control group, with similar age, baseline diagnosis and risk factors, and median follow-up times of 30 and and 24 months, respectively. Survival analysis showed a higher graft survival rate at all follow-up periods for patients treated with topical tacrolimus (p < 0.01). No adverse reactions were reported.

DISCUSSION

This study shows that topical tacrolimus ointment increases the survival rate of the graft if added to the previous topical steroid regimen in high-risk patients.

CONCLUSION

Topical tacrolimus is safe and effective in prolonging graft survival in high-risk patients.

2021 Survey of Keratoplasty Postoperative Steroid Management

PURPOSE

The aim of the study is to investigate US-based ophthalmologists' preferred corneal transplant techniques and postoperative steroid regimen.

METHODS

Ophthalmologists attending the 2021 Cornea and Eye Banking Forum and/or Cornea Subspecialty Day were surveyed in person.

RESULTS

Ninety-two ophthalmologists with a median of 13 years (range of 1-35; mean of 14.5; ±9.05 mean ± SD) of experience as attending clinicians were surveyed. One hundred percent of the surgeons performed penetrating keratoplasty, which was followed by 96.7% for Descemet stripping endothelial keratoplasty, 90.2% for Descemet membrane endothelial keratoplasty, and 72.8% for deep anterior lamellar keratoplasty. Prednisolone 1% for postoperative care was the preferred choice across all surveyed keratoplasty techniques and postsurgery time intervals. All surgeons reported steroid administration frequency of 4 times a day in the first month and once a day after 12 months postkeratoplasty. To manage ocular hypertension after corneal transplantation, the leading approach was adding a glaucoma medication (44.6%), and beta-adrenergic antagonists were ranked as the most preferred choice by 59 (66.3%) of the respondents. For graft rejection after corneal transplantation, topical steroids (79.8%) were the initial treatment of choice with hourly administration being the most common frequency prescribed (87.4%). Most surgeons either agreed or strongly agreed (78.4%) that a randomized clinical trial evaluating the safety and efficacy of different steroid regimens after corneal transplantation would influence their clinical decision making.

CONCLUSIONS

Prednisolone remains the predominantly used steroid across different keratoplasties. Steroid regimens are similar for non-high-risk penetrating keratoplasty, Descemet membrane endothelial keratoplasty, Descemet stripping endothelial keratoplasty, and deep anterior lamellar keratoplasty. To treat graft rejection, surgeons tend to initially add a glaucoma medication than to reduce the potency or frequency of the steroid.

Management and prevention of corneal graft rejection

The management of an episode of corneal graft rejection (CGR) is primarily by corticosteroids. Immunomodulators are useful for long-term immunosuppression and in dealing with cases of high-risk (HR) corneal grafts. The classical signs of CGR following penetrating keratoplasty (PKP) include rejection line, anterior chamber (AC) reaction, and graft edema. However, these signs may be absent or subtle in cases of endothelial keratoplasty (EK). Prevention of an episode of graft rejection is of utmost importance as it can reduce the need for donor cornea significantly. In our previous article (IJO_2866_22), we had discussed about the immunopathogenesis of CGR. In this review article, we aim to discuss the various clinical aspects and management of CGR.

Dual-crosslinked regenerative hydrogel for sutureless long-term repair of corneal defect

Corneal transplantation is the most effective clinical treatment for corneal defects, but it requires precise size of donor corneas, surgical sutures, and overcoming other technical challenges. Postoperative patients may suffer graft rejection and complications caused by sutures. Ophthalmic glues that can long-term integrate with the corneal tissue and effectively repair the focal corneal damage are highly desirable. Herein, a hybrid hydrogel consisting of porcine decellularized corneal stroma matrix (pDCSM) and methacrylated hyaluronic acid (HAMA) was developed through a non-competitive dual-crosslinking process. It can be directly filled into corneal defects with various shapes. More importantly, through formation of interpenetrating network and stable amide bonds between the hydrogel and adjacent tissue, the hydrogel manifested excellent adhesion properties to achieve suture-free repair. Meanwhile, the hybrid hydrogel not only preserved bioactive components from pDCSM, but also exhibited cornea-matching transparency, low swelling ratio, slow degradation, and enhanced mechanical properties, which was capable of withstanding superhigh intraocular pressure. The combinatorial hydrogel greatly improved the poor cell adhesion performance of HAMA, supported the viability, proliferation of corneal cells, and preservation of keratocyte phenotype. In a rabbit corneal stromal defect model, the experimental eyes treated with the hybrid hydrogel remained transparent and adhered intimately to the stroma bed with long-term retention, accelerated corneal re-epithelialization and wound healing. Giving the advantages of high bioactivity, low-cost, and good practicality, the dual-crosslinked hybrid hydrogel served effectively for long-term suture-free treatment and tissue regeneration after corneal defect.

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Double-network hydrogel contains regenerative decellularized corneal stroma matrix.

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Suture-free easy operation, high transparency, strong attachment to stroma bed.

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Long-term retention on corneal defect with excellent force and pressure resistance.

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Rapid re-epithelialization, minimal scar formation, sustained cornea regeneration.

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A functional biomaterial-based strategy for in situ corneal wound healing.

Dropless penetrating keratoplasty using a subconjunctival dexamethasone implant: safety pilot study

BACKGROUND/AIM

Rejection is the main cause of graft failure after penetrating keratoplasty (PK). Its prevention by repeated instillation of steroid eye-drops has not evolved in decades. Poor adherence and discontinuous nature of eye-drop treatment may explain some PK failures. In a rabbit model, we previously demonstrated that a subconjunctival dexamethasone implant was well tolerated and prevented rejection efficiently in the first 5-6 weeks. This clinical trial investigates its tolerance and safety after PK.

METHODS

Single-centre, phase II non-randomised tolerance and safety pilot study (NCT02834260). Designed to analyse the risk of elevated intraocular pressure (IOP), discomfort and resorption time. Fourteen patients with a low rejection risk indication of PK were enrolled between January 2017 and August 2018. The implant was injected in the 12 o'clock position, 5 mm from the limbus, at the end of PK. A steroid eye-drop treatment was planned when implant resorption was complete. Patients were monitored regularly for 12 months: IOP (main outcome measure at 1 month), discomfort and redness scores, implant status, rejection episode and central corneal thickness by optical coherence tomography. An independent data safety monitoring committee verified safety aspects.

RESULTS

No increase in IOP or other adverse event related to the implant was observed. Average resorption time was 6 weeks. The switch to steroid eye-drops was uneventful. One patient, included despite preoperative corneal neovascularisation (unintended protocol deviation) experienced a rejection.

CONCLUSIONS

This is the first proof of concept that dropless immunosuppression is possible after low rejection risk PK.

TRIAL REGISTRATION NUMBER

NCT02834260.

Impact of gender mismatch on corneal graft rejection and rejection-related graft failure in repeat penetrating keratoplasty

PURPOSE

To explore the impact of gender mismatch on corneal allograft rejection and rejection-related graft failure in patients with repeat penetrating keratoplasty (PK).

METHODS

A retrospective cohort was conducted at Ramathibodi Hospital, Bangkok, Thailand. Patients with repeat PK and follow-up period of at least 6 months were recruited. Demographic data, pre-operative ocular findings and donor information were collected. Patients were divided into 2 groups according to gender mismatch between donor and recipient (male to female vs others). Survival analysis was performed using the Kaplan-Meier method. The association between risk factors and the outcomes of graft rejection and rejection-related graft failure were analyzed using Cox proportional hazards regression.

RESULTS

Of 68 patients with repeat PK, 26 patients (38.2%) were gender mismatched. There was no difference in 3-year rejection-free survival and graft survival between patients with gender mismatch and others (p = 0.698 and p = 0.402, respectively). Younger recipients (< 40 years) showed a significantly higher rejection rate compared to older recipients (hazard ratio; HR = 3.14, 95% confidence interval; CI 1.15 to 8.58), while patients with multiple PK (> 2 times) were found to be significantly associated with higher rejection-related graft failure compared to patients with 2 times or less PK (HR = 2.72, 95% CI 1.03 to 7.21). After multivariate analysis, only younger recipients demonstrated a statistical significance on graft rejection (adjusted HR = 2.86, 95% CI 1.04 to 7.84).

CONCLUSIONS

Gender mismatch might not impact corneal graft rejection or rejection-related graft failure in patients with repeat PK. Younger age was found to be a strong factor associated with graft rejection. Gender matching might not be compulsory for repeat PK.

Management and Treatment Outcomes of High-Risk Corneal Transplantations

Corneal transplantation is the most effective treatment for corneal blindness. Standard planned keratoplasties have a high success rate. Conditions such as active inflammation at the time of surgery, the presence of ocular surface disease, previous graft disease, or neovascularization make them more susceptible to rejection. These are so-called high-risk corneal transplantations. In our study, we selected 52 patients with a higher risk of graft rejection. A total of 78 procedures were performed. The main indications for the first keratoplasty were infections (59.6%) and traumas (21.2%). Visual acuity (VA) significantly improved from 2.05 logMAR on the day of keratoplasty to 1.66 logMAR in the latest examination (p = 0.003). An analysis of the graft survival showed a 1-year survival of 54% and a 5-year survival of 19.8% of grafts. The mean observation time without complications after the first, second, and third surgery was 23, 13, and 14 months, respectively. The best results were noted among patients with infectious indications for keratoplasty (p = 0.001). Among them, those with bacterial infection had the best visual outcomes (p = 0.047).

Acute corneal allograft rejection following SARS-CoV-2 vaccination-A systematic review

All documented cases of acute corneal allograft rejection following SARS-CoV-2 vaccination were examined, to characterize possible risk factors and graft outcomes. Comprehensive search (4 electronic databases: PubMed, CENTRAL, ClinicalTrials.gov, Google Scholar, plus manual search in articles' reference lists) until March 1st 2022 to identify studies reporting acute corneal allograft rejection following SARS-CoV-2 vaccination; study protocol was developed in line with PRISMA statement. We analysed demographics, allograft type, rejection prophylaxis regime at the time of vaccination, transplantation-to-vaccination time (G-Vt), vaccination-to-immune reaction onset time (V-Rt), management, best-corrected visual acuity before and after rejection, and graft survival. Of 169 titles/abstracts screened, 16 studies (n  = 36 eyes) met the inclusion criteria. Fourteen eyes (38.9%) had received >1 graft, and 11.1% of cases had history of immune reactions; 52.9% of cases occurred after the first dose. Median (P25-P75) G-Vt was 48 (10-78) months; median V-Rt was 9 (7-14) days. In eyes with resolved rejection, median time-to-resolution was 3 (1-4) weeks. Four eyes (11.1%) had partial resolution of corneal decompensation, and 5 grafts (13.9%) failed. Acute corneal allograft rejection after SARS-CoV-2 vaccination is a rare event, but may occur any time post-keratoplasty. Early recognition and prompt, aggressive treatment is warranted to optimize vision and graft survival. Well-known risk factors for rejection may be confounding factors, including the high proportion of cases with a history of previous grafts and the rejection prophylaxis regimes at the time of vaccination. Increasing immunosuppressants in the peri-vaccination period may decrease the risk of immune reactions, especially in high-risk cases.

Preventive treatment of allograft rejection after endothelial keratoplasty: A systematic review and meta-analysis

PURPOSE

To evaluate the efficacy of preventive treatment against allograft rejection after endothelial keratoplasty (EK), we conducted a systematic review and meta-analysis.

METHOD

PubMed, Cochrane Library, Embase and ScienceDirect databases were searched until May 2021. We computed a random-effect meta-analysis on graft rejection rate stratified by the intervention (i.e. Descemet membrane EK (DMEK) and Descemet stripping (Automated) EK (DS(A)EK) or ultrathin (UT)-DSAEK), and postoperative treatment. Meta-regressions were performed to compare intervention, treatment and influence of putative confusion factors.

RESULTS

We included 49 studies and 12 893 EK (6867 DMEK and 6026 DS(A)EK/UT-DSAEK). Topical steroids were merged in two efficacy regimens: standard steroids (prednisolone acetate 1% or dexamethasone 0.1%) and soft steroids (fluorometholone 0.1% or loteprednol etabonate 0.5%). Globally, DMEK had a lower graft rejection rate than DS(A)EK/UT-DSAEK (coefficient - 3.3, 95 CI, -4.60 to -1.90; p < 0.001). No significant differences were observed between standard and soft steroids to prevent graft rejection after DMEK. After EK, the rate of ocular hypertension was 20% (95 CI, 14 to 26%) with the use of standard steroids and 7% (5 to 9%) with soft steroids. Comparisons of treatments were not feasible in DS(A)EK/UT-DSAEK due to a lack of studies.

CONCLUSIONS

Descemet membrane endothelial keratoplasty (DMEK) has less risk of graft rejection compared with DS(A)EK/UT-DSAEK. Furthermore, soft steroids seemed to be a valuable alternative to standard steroids to prevent graft rejection after DMEK, involving a safe profile against ocular hypertension. Further studies are needed to compare other drugs in the prevention of graft rejection after EK.

Surgical Outcomes of Ahmed Glaucoma Valve Implantation with Postoperative Use of Prednisolone Acetate Versus Difluprednate

PURPOSE

To evaluate the effect of postoperative topical prednisolone acetate and difluprednate on surgical outcomes of Ahmed Glaucoma Valve (AGV) implantation.

DESIGN

Retrospective comparative case series PARTICIPANTS: The study population consisted of 102 eyes of 90 patients, including 52 eyes that received prednisolone acetate 1% (PF group) and 50 eyes that received difluprednate 0.05% (DZ group).

METHODS

The medical records of consecutive patients who underwent AGV implantation at the University of California San Francisco were retrospectively reviewed. Patients in the PF group received prednisolone acetate 1% 6-8 times per day tapered over 5-6 months, and patients in the DZ group received difluprednate 0.05% 4 times daily tapered over 4 months postoperatively.

MAIN OUTCOME MEASURES

Intraocular pressure (IOP), number of glaucoma medications, visual acuity (VA), postoperative complications, and rate of treatment success.

RESULTS

At 1 year, IOP (mean ± standard deviation) was 12.4 ± 3.7 mmHg in the DZ group and 13.0 ± 4.0 mmHg in the PF group (P = 0.49). The number of glaucoma medications was 0.72 ± 0.71 in the DZ group and 1.09 ± 0.91 in the PF group (P = 0.04), with a reduction from baseline of 2.5 ± 1.0 glaucoma medications in the DZ group and 1.8 ± 1.6 medications in the PF group (P = 0.01). LogMAR VA (mean ± SD) was 0.55 ± 0.80 in the DZ group and 0.59 ± 0.65 in the DZ group after 1 year of follow-up (P = 0.81). The cumulative probability of success was 95.8% in the DZ group and 93.5% in the PF group at 1 year (P = 0.61). Postoperative complications occurred in 4 eyes (7.7%) in the DZ group and 6 eyes (12%) in the PF group (P = 0.52).

CONCLUSIONS

After 1 year, postoperative treatment with difluprednate 0.05% following AGV implantation resulted in similar IOP with use of fewer glaucoma medications compared with prednisolone acetate 1%. The rates of treatment success and surgical complications were comparable between the two groups during the first year of follow-up.

Topical administration of tacrolimus and corticosteroids in tapering doses is effective in preventing immune rejection in high-risk keratoplasty: a 5-year follow-up study

Background

To evaluate the efficacy of the topical administration of immunosuppressants and corticosteroids in tapering doses in the management of patients with high-risk keratoplasty.

Methods

One hundred and six patients treated with topical immunosuppressants (50 eyes in the FK506 group and 56 eyes in the CsA group) and corticosteroid eye drops in tapering doses were enrolled in the study. The rates of rejection episodes, irreversible rejection, graft survival, and related influential factors were evaluated.

Results

The mean follow-up period was 48.1 ± 7.9 months (range, 36–60 months). The rates of rejection episodes and irreversible rejection were 14.0% and 6.00% in the FK506 group and 37.5% and 7.1% in the CsA group, respectively. Kaplan-Meier survival analysis demonstrated a significantly higher graft survival rate in the FK506 group (81.6%±5.3%, 71.1%±6.3%) compared with that in the CsA group (71.1%±6.3%, 57.5%±7.5%) at 3 and 5 years after surgery (P = 0.006). Multivariate logistic regression revealed that preoperative risk score ≥ 3 (P = 0.016) and endothelial immune rejection (P = 0.033) were risk factors associated with graft survival.

Conclusions

Topical administration of tacrolimus and corticosteroids in tapering doses is effective in decreasing the incidence of immune rejection in high-risk keratoplasty. Careful instruction of patients on the reasonable use of topical tacrolimus is critical to avoid immune rejection induced by sudden discontinuation of medication.

Objective measurement of adherence to topical steroid medication after penetrating keratoplasty using an electronic monitoring aid: A pilot study

Objectives

Corneal transplantation is the most common transplant worldwide and its success critically depends on the management of corneal graft rejection through topical steroid therapy during the first 12 months after surgery. There is currently no published data on adherence after keratoplasty. This pilot study aims to explore the adherence to topical steroid after penetrating keratoplasty using a smart electronic device.

Methods

Thirty patients undergoing penetrating keratoplasty were included to evaluate the adherence to topical dexamethasone medication for 12 months after surgery. Patients received the usual post-transplantation treatment (topical dexamethasone) and follow-up after surgery (day 15, months 1, 2, 3, 4, 5, 6, 9, and 12). Adherence to treatment was monitored using the KaliJAR device (Kali Care, Santa Clara, CA, USA), which recorded the number of single-dose units (SDU) discarded. At control visits, data recorded by the device were compared to the manually count of SDU. Adherence ratio and individual adherence curve were explored for all patients.

Results

Data from 27 patients showed a high agreement between adherence ratio calculated based on the device data and obtained from manual counting of the discarded SDU (intraclass coefficient correlation of 0.87 [95% CI: 0.738–0.938]). Mean adherence to the treatment over the 12-month study period was 95.2 ± 4%.

Conclusions

Adherence to topical dexamethasone for 12 months after corneal transplantation was high. The connected device was able to record accurately the discarded SDU. This approach would be a particular interest in the early identification and personalized follow-up of poorly adherent patients.

Systemic Immunosuppression in Cornea and Ocular Surface Disorders: A Ready Reckoner for Ophthalmologists

Purpose: Many diseases of the cornea and ocular surface are manifestations of an underlying autoimmune process and require systemic immunosuppression for their management. These cases often present to a general ophthalmologist before being referred to an ocular immunologist or rheumatologist. However, the patients do need to be followed by the ophthalmologist to assess disease progression or for management of ocular co-morbidities and for taking care of ocular complications of the disease. Undeniably, there is a certain hesitance to promptly initiate them on systemic therapy because the literature regarding the indications, dosages, and side effects of this group of drugs is vast and dispersed.The aim of this review is to provide a source of ready reference for the general ophthalmologist as well as trainees and residents, on systemic immunosuppression for corneal and ocular surface disease. Methods: This review included 153 studies which were published as randomized controlled trials, systematic reviews, or as nonrandomized comparative studies (cohort or case-control series) on the topic of systemic immunosuppression in cornea and ocular surface disorders.Results: This review provides a concise summary of both the types of drugs and the common indications where they would be indicated, along with treatment and monitoring algorithms for each specific disease condition. The most used group of drugs are corticosteroids, which have significant side effects, particularly when administered systemically or for longer periods of time. To overcome this, steroid-sparing immunosuppressants are recommended. The four main classes of immunosuppressants used today are antimetabolites, T-cell inhibitors, alkylating agents and biologic agents. This review details the use of these drugs in ocular surface inflammation, including the dosing schedule, side effects and monitoring in allergic conjunctivitis, mucous membrane pemphigoid, peripheral ulcerative keratitis, immunological rejection against corneal allografts, anterior scleritis and aqueous deficiency dry eyes. Conclusions: This review provides an uncluttered and wholesome understanding of systemic immunosuppression in cornea and ocular surface diseases, with the hope that this will serve as a ready reckoner and help bridge the gap between ophthalmology and rheumatology for the betterment of our patients.

Topical corticosteroids with topical cyclosporine A versus topical corticosteroids alone for immunological corneal graft rejection

PURPOSE

To assess the efficacy and safety of supplementing topical cyclosporine A (CsA) to topical corticosteroids (CS), in the prophylaxis and treatment of corneal graft rejection following penetrating keratoplasty (PK).

METHODS

Meta-analysis. Search was performed in PubMed, CENTRAL, ClinicalTrials.gov, reference lists of articles and conference proceedings. Primary outcomes: 1-year rejection-free survival rate (prophylaxis); resolution rate of rejection episodes (treatment). Secondary outcomes: 6- and 24-month rejection-free graft survival rate, number of rejection episodes during follow-up, time-to-resolution of rejection episode, 12- and 24-months graft survival rate, adverse events. Subgroup analyses were planned for high-risk grafts; primary vs. secondary prophylaxis of graft rejection episodes; and CsA concentrations of 0.05%, 1%, and 2%.

RESULTS

Five studies of moderate methodological quality were included (one retrospective, four RCT), assessing 459 eyes (CS + CsA 226, CS 233). In the prophylaxis setting, supplemental CsA was associated with a higher rejection-free survival rate at 12-months (RR 1.25, 95% CI: 1.00-1.56, p = 0.05) and 24-months post-PK (RR 1.56, 95% CI: 1.15-2.11, p < 0.01), though no differences were found at the 6-months timepoint (p = 0.93). This effect was mostly verified using CsA 2% in the high-risk subset of patients. In the treatment setting, no differences were found in the resolution rate of rejection episodes (p = 0.23). No differences existed on drug-related adverse events.

CONCLUSION

In the prophylaxis of rejection episodes post-PK, the combined regimen of CS + CsA was associated with a higher 1- and 2-year rejection-free graft survival rate. Subgroup analysis mostly supported the use of CsA 2% for high-risk grafts. Further studies are needed to validate these results.

Effectiveness of matching human leukocyte antigens (HLA) in corneal transplantation: a systematic review protocol

BACKGROUND

Corneal transplantation is the most frequently performed transplantation in the UK. Despite this, the therapeutic value of matching human leukocyte antigen (HLA) subtypes for transplanted corneas remains controversial. Ocular immune privilege was originally deemed to render matching unnecessary; however, more recently, matching has demonstrated improved outcomes including graft success, amongst others. This systematic review aims to evaluate the effectiveness of major and minor antigen matching on graft outcomes in corneal transplantation.

METHODS

Standard systematic review methodology will be used to identify, select and extract data from observational studies and clinical trials assessing the effects of HLA matching on corneal graft outcomes. Bibliographic databases (Cochrane Library, EMBASE, MEDLINE, Web of Science, Scopus), clinical trial registers, abstract and conference proceedings, in addition to dissertation, thesis and grey literature will be searched. Neither date of publication nor language will be restricted, and non-English articles will be translated where necessary. The primary outcome will be to assess corneal graft success for different degrees of HLA matching/mismatching. The precise end outcome measure varies amongst studies and includes graft rejection, immunoreaction, failure and survival. Therefore, data will be extracted across all relevant outcome parameters and grouped for subsequent statistical tests. Risk of bias assessment will be completed, appropriate to each study design. Study selection, data extraction and risk of bias assessment will be independently completed by two reviewers. Data will be tabulated, and a narrative synthesis presented. Meta-analysis will be performed where there is sufficient homogeneity between studies to warrant its effective completion. Subgroup and sensitivity analysis will be undertaken if appropriate.

DISCUSSION

Many studies have investigated the effectiveness of HLA matching for corneal transplantation. A systematic review is needed to collate and analyse this evidence. Findings of this systematic review may form the basis of evidence-based recommendations on pre-operative HLA typing and matching of corneal grafts for transplantation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO reference CRD42020198882.

Randomized, Double-Masked Trial of Netarsudil 0.02% Ophthalmic Solution for Prevention of Corticosteroid-Induced Ocular Hypertension

PURPOSE

To assess whether prophylactic use of netarsudil 0.02% ophthalmic solution reduces the risk of intraocular pressure (IOP) elevation associated with prolonged use of topical corticosteroids to prevent cornea transplantation rejection.

DESIGN

Prospective, randomized clinical trial.

METHODS

In this study, 120 subjects were randomized to use netarsudil (off-label) or placebo once daily for 9 months after Descemet membrane endothelial keratoplasty, and 71 fellow eyes were enrolled and assigned to the opposite treatment arm. Participants concurrently used topical prednisolone acetate 1% 4× daily for 3 months, 3× daily for a month, twice daily for a month, and once daily for 4 months. The main outcome was IOP elevation (defined as IOP ≥24 mm Hg or an increase of ≥10 mm Hg over baseline) assessed by Kaplan-Meier and proportional hazards analyses, taking loss to follow-up into consideration.

RESULTS

Overall, 95 eyes were assigned to netarsudil and 96 to placebo; 15 eyes (16%) were withdrawn early from the netarsudil arm because of ocular irritation. The rate of IOP elevation was 14% with netarsudil and 21% with placebo (relative risk: 0.6; 95% confidence interval: 0.3-1.3; P = .23). IOP was >30 mm Hg in 7.8% assigned to netarsudil versus 7.4% assigned to placebo (P = .84). Median 6-month central endothelial cell loss was 31% versus 29% with netarsudil versus placebo, respectively (P = .49).

CONCLUSIONS

Netarsudil did not produce a statistically significant reduction in the risk of steroid-induced IOP elevation after corneal transplantation relative to placebo.

Corneal Transplant Follow-up Study II: a randomised trial to determine whether HLA class II matching reduces the risk of allograft rejection in penetrating keratoplasty

PURPOSE

A randomised trial to test the hypothesis that human leucocyte antigen (HLA) class II matching reduces the risk of allograft rejection in high-risk penetrating keratoplasty (PK).

METHODS

All transplants were matched for HLA class I antigens (≤2 mismatches at the A and B loci) and corneas were allocated to patients by cohort minimisation to achieve 0, 1 or 2 HLA class II antigen mismatches. The corneal transplants (n=1133) were followed for 5 years. The primary outcome measure was time to first rejection episode.

RESULTS

Cox regression analysis found no influence of HLA class II mismatching on risk of immunological rejection (HR 1.13; 95% CI 0.79 to 1.63; p=0.51). The risk of rejection in recipients older than 60 years was halved compared with recipients ≤40 years (HR 0.51; 95% CI 0.36 to 0.73; p=0.0003). Rejection was also more likely where cataract surgery had been performed after PK (HR 3.68; 95% CI 1.95 to 6.93; p<0.0001). In univariate analyses, preoperative factors including chronic glaucoma (p=0.02), vascularisation (p=0.01), inflammation (p=0.03), ocular surface disease (p=0.0007) and regrafts (p<0.001) all increased the risk of rejection. In the Cox model, however, none of these factors was individually significant but rejection was more likely where≥2 preoperative risk factors were present (HR 2.11; 95% CI 1.26 to 3.47; p<0.003).

CONCLUSIONS

HLA class II matching, against a background of HLA class I matching, did not reduce the risk of allograft rejection. Younger recipient age, the presence of ≥2 preoperative risk factors and cataract surgery after PK all markedly increased the risk of allograft rejection.

TRIAL REGISTRATION NUMBER

ISRCTN25094892.

Corneal transplantation after failed grafts: Options and outcomes

Corneal transplantation is the most commonly performed human tissue transplantation procedure worldwide. Because of the large number of transplants, corneal graft failure has become one of the most common indications for corneal transplantation. The relatively recently developed lamellar transplant techniques have brought about specific potential complications leading to graft failure that may require different approaches to repeat transplantation other than penetrating keratoplasty. On the other hand, these new lamellar techniques also provide novel ways of rescuing failed penetrating grafts, with potential advantages over successive penetrating keratoplasties, such as reduced intraoperative risks and faster visual rehabilitation. We summarize the incidence and risk factors of graft failure for penetrating and lamellar (stromal and endothelial) corneal transplants and discuss the various surgical alternatives currently available to rescue such failed grafts, with a focus on the reported outcomes and limitations.

Initial High-Dose Prophylaxis and Extended Taper for Mushroom Keratoplasty in Vascularized Herpetic Scars

PURPOSE

To report the outcomes of initial high-dose and extended taper of antiviral and steroid prophylaxis for the treatment of eyes with high-risk vascularized herpetic corneal scars that underwent 2-piece mushroom keratoplasty (MK).

DESIGN

Prospective interventional case series.

METHODS

In this single-center study, 52 consecutive eyes with vascularized (≥2 quadrants) herpetic corneal scars underwent 2-piece microkeratome-assisted MK. Initial high-dose and extended taper of combined oral and topical antiviral and steroid prophylaxis was administered. Outcome measures were best spectacle-corrected visual acuity (BSCVA), refractive astigmatism (RA), endothelial cell density, immunologic rejection, herpetic recurrence, and graft failure rates.

RESULTS

Excluding patients with vision-impairing comorbidities, baseline BSCVA (1.73 ± 0.67 logMAR) significantly improved annually during the first 2 years (P < .001, P = .016), reaching 0.17 ± 0.18 logMAR at year 2, and remaining stable up to 10 years (P = .662). At 2 years, 86% of eyes saw ≥20/40, 55% saw ≥20/25, and 18% saw ≥20/20 Snellen BSCVA. RA exceeded 4.5 diopters in 7% of cases after wound revision for high-degree astigmatism in 7 cases. Endothelial cell loss was 40.9% at 1 year with an annual decline of 3.1% over 10 years. The 10-year cumulative risk for immunologic rejection, herpetic recurrence, and graft failure was 9.7%, 7.8%, and 7.6%, respectively.

CONCLUSIONS

Initial high dose and extended taper of antiviral and steroid prophylaxis for MK in high-risk, vascularized herpetic corneal scars achieves clinical outcomes that remain stable for up to 10 years after surgery with minimal risk of immunologic rejection, herpetic recurrence and graft failure.

Tacrolimus dye drop treatment for the management of early post-operative intraocular inflammation after therapeutic keratoplasty for severe infectious keratitis

The current study investigated the anti-inflammatory effect of 0.1% tacrolimus eye drops for the treatment of therapeutic penetrating keratoplasty (TPK) for severe infectious keratitis during early disease stages and reported the long-term clinical outcomes. The present retrospective study included 20 eyes from patients diagnosed with severe keratitis who underwent TPK surgery. Patients were followed-up for up to 12-18 months. Tacrolimus eye drops were administered 4 times/day starting on the first day post-surgery. Glucocorticoid eye drops were subsequently added to treatment plans one-month post-surgery. All patients were followed-up for the first 3 post-operative days, then examined once a week thereafter for the first month. In early post-operative stages, the states of the grafts (ΔS) and the absorption of intraocular inflammation (S) were observed. ΔS was defined as the difference between the states of the grafts on the first post-operative day (SS1d) and those at one month post-surgery (SS1m). S was calculated as the difference between the inflammation score mean one day post-surgery (T1d) and the mean one-month post-surgery (T1m). For long term clinical outcomes, graft failure rates and complications were recorded. Among the 20 eyes analyzed, the mean T1d, T1m and S were 7.4±2.06, 2.0±2.47 and 5.4±2.13 (P<0.01), respectively. The mean SS1d, SS1m and ΔS were 5.3±1.56, 3.8±1.24 and 1.5±1.5 (P<0.01), respectively. During follow-up, there were 6 cases of corneal graft failure, 4 of which were due to immune rejection and 2 of which were due to complications. The current study concluded that tacrolimus eye drops facilitated the absorption of intraocular inflammation in the early post-operative period of TPK and may extend long term survival of grafts in cases of severe infectious keratitis.

Corneal graft failure: an update

Corneal graft surgery is one of the most successful forms of human solid-tissue transplantation, and nowadays, there is a worldwide expansion of the surgical volume of corneal grafts. This surgery is continuously evolving, with new surgical techniques and postoperative treatments that have considerably increased the chance of survival for the grafts. Despite the high rate of success, corneal transplantation is still complicated by a relevant risk of graft failure. This study investigates the causes that lead to the failure of the different corneal graft surgical techniques and provides an updated synthesis on this topic. A comprehensive review of the main pathological pathways that determine the failure of corneal grafts is provided, analysing the main risk factors and disclosing the survival rates of the principal form of corneal grafts. Our results revealed that penetrating keratoplasty has higher failure rates than lamellar keratoplasty, with immunological rejection being the leading cause of graft failure, followed by late endothelial failure (LEF) and ocular surface disorders. Postoperative glaucoma and dehiscence of the surgical wound represent other important causes of failure. Endothelial keratoplasty showed the lowest rates of failure in the mid-term, with LEF, detachment of the graft and primary graft failure representing the most common pathological reasons for failure.

High-risk Corneal Transplantation: Recent Developments and Future Possibilities

Human corneal transplantation (keratoplasty) is typically considered to have superior short- and long-term outcomes and lower requirement for immunosuppression compared to solid organ transplants because of the inherent immune privilege and tolerogenic mechanisms associated with the anterior segment of the eye. However, in a substantial proportion of corneal transplants, the rates of acute rejection and/or graft failure are comparable to or greater than those of the commonly transplanted solid organs. Critically, while registry data and observational studies have helped to identify factors that are associated with increased risk of corneal transplant failure, the extent to which these risk factors operate through enhancing immune-mediated rejection is less clear. In this overview, we summarize a range of important recent clinical and basic insights related to high-risk corneal transplantation, the factors associated with graft failure, and the immunological basis of corneal allograft rejection. We highlight critical research areas from which continued progress is likely to drive improvements in the long-term survival of high-risk corneal transplants. These include further development and clinical testing of predictive risk scores and assays; greater use of multicenter clinical trials to optimize immunosuppressive therapy in high-risk recipients and robust clinical translation of novel, mechanistically-targeted immunomodulatory and regenerative therapies that are emerging from basic science laboratories. We also emphasize the relative lack of knowledge regarding transplant outcomes for infection-related corneal diseases that are common in the developing world and the potential for greater cross-pollination and synergy between corneal and solid organ transplant research communities.

Local delivery of corticosteroids in clinical ophthalmology: A review

Locally administered steroids have a long history in ophthalmology for the treatment of inflammatory conditions. Anterior segment conditions tend to be treated with topical steroids whilst posterior segment conditions generally require periocular, intravitreal or systemic administration for penetration. Over recent decades, the clinical applications of periocular steroid delivery have expanded to a wide range of conditions including macular oedema from retino-vascular conditions. Formulations have been developed with the aim to provide practical, targeted, longer-term and more efficacious therapy whilst minimizing side effects. Herein, we provide a comprehensive overview of the types of periocular steroid delivery, their clinical applications in ophthalmology and their side effects.

Long-term Outcomes on de novo Ocular Hypertensive Response to Topical Corticosteroids After Corneal Transplantation

PURPOSE

To determine incidence, demographics, management, and outcomes of topical steroid-induced ocular hypertension after penetrating keratoplasty (PKP) and to establish effects on intraocular pressure (IOP) and graft rejection when alternate corticosteroids are used.

METHODS

A single-center, retrospective review of 568 consecutive PKPs performed between 1997 and 2010 was conducted. Data were collected on demographics, best-corrected visual acuity, surgical indications, lens status, IOP, postoperative management, and incidence of rejection.

RESULTS

Eighty eyes (14.1%) of 74 patients were included. The most common indication was keratoconus (28.8%). Twenty-seven eyes (33.8%) were phakic, 46 (57.4%) had a posterior chamber intraocular lens, and 7 (8.8%) had an anterior chamber intraocular lens. Mean postoperative IOP increase was only significant in the anterior chamber intraocular lens group (18.7 mm Hg, SD 10.4; P = 0.02). The average time for developing hypertension was 9.8 months (SD 14.8) postoperatively, with an average IOP increase of 13.3 mm Hg (SD 5.9). Prednisolone acetate 1% was switched to rimexolone 1% in 64 eyes (80%) and to fluorometholone 0.1% in 16 eyes (20%), which alone achieved IOP normalization in 26 eyes (32.5%) (P < 0.01). Fifty-four eyes (67.5%) required additional antiglaucoma medication. An average IOP reduction of 12.3 mm Hg (SD 6.9) was achieved at an average of 2.3 months (SD 5.2) after the switch. Seventeen eyes (21%) developed glaucoma and 13 eyes (16.3%) developed graft rejection after switching formulations, with no statistically significant differences between rimexolone and fluorometholone (P > 0.05).

CONCLUSIONS

The use of alternate topical corticosteroids may be considered in cases of steroid-induced ocular hypertension after PKP because they offer good antiinflammatory prophylaxis with reduced hypertensive response.

Rejection Prophylaxis in Corneal Transplant

BACKGROUND

Graft rejection. Twenty to thirty percent of patients with corneal transplants experience at least one rejection episode in the first 5 years after transplantation. Prophylaxis through matching for human leukocyte antigens (HLA) is controversial. We herein report the results of the Functional ANtigen matChing in keratoplastY (FANCY) trial.

METHODS

FANCY was a randomized, double-blind, multicenter clinical trial. The primary objective was to evaluate superiority of HLA matching versus random graft assignment. The primary endpoint was rejection-free graft survival. We included both normal-risk and high-risk indications. The study is registered with ClinicalTrials. gov (NCT00810472).

RESULTS

721 patients were included, 639 patients were randomized. 474 patients underwent keratoplasty within the study; 165 patients received grafts outside the trial. One patient died and one patient was lost to follow up. We observed 33 graft rejections in the HLA matching arm (n = 224). The corresponding estimated cumulative incidence rate of immune reactions after two years was 15.7%. We observed 40 rejections in the control arm (n = 249). After two years this yields an estimated cumulative incidence rate of 17%.

CONCLUSION

In our heterogenous study group, HLA matching did not show a significant advantage compared to random graft assignment. The rejection rate in our sample was lower than expected. Therefore no definite conclusions can be drawn as to whether HLA matching is beneficial in corneal transplantation.

Literature review and suggested protocol for prevention and treatment of corneal graft rejection

Effective prophylaxis and treatment of corneal graft rejection are essential to improve outcomes in corneal transplantation. To date, there has been no standardized protocol published that outlines the optimal prophylactic and therapeutic approaches and, furthermore, the published controlled trials on this subject are limited. Likewise, no study has addressed how the level of antigen exposure varies between different types of keratoplasties. The aim of this paper is to provide a simple evidence-based protocol for the prevention and treatment of corneal graft rejection.

In vivo effect of bevacizumab-loaded albumin nanoparticles in the treatment of corneal neovascularization

Corneal neovascularization (CNV) is associated with different ocular pathologies, including infectious keratitis, trachoma or corneal trauma. Pharmacological treatments based on the topical application of anti-VEGF therapies have been shown to be effective in the treatment and prevention of CNV. The aim of this work was to evaluate the effect of bevacizumab-loaded albumin nanoparticles in a rat model of CNV. Bevacizumab-loaded nanoparticles, either "naked" (B-NP) or coated with PEG 35,000 (B-NP-PEG), were administered once a day in the eyes of animals (10 μL, 4 mg/mL every 24 h) during 7 days. Bevacizumab and dexamethasone were employed as controls and administered at the same dose every 12 h. At the end of the study, the area of the eye affected by neovascularization was about 2-times lower for animals treated with B-NP than with free bevacizumab. In the study, dexamethasone did not demonstrate an inhibitory effect on CNV at the employed dose. All of these results were confirmed by histopathological analysis, which clearly showed that eyes treated with nanoparticles displayed lower levels of fibrosis, inflammation and edema. In summary, the encapsulation of bevacizumab in human serum albumin nanoparticles improved its efficacy in an animal model of CNV.

Sutureless repair of corneal injuries using naturally derived bioadhesive hydrogels

Corneal injuries are common causes of visual impairment worldwide. Accordingly, there is an unmet need for transparent biomaterials that have high adhesion, cohesion, and regenerative properties. Herein, we engineer a highly biocompatible and transparent bioadhesive for corneal reconstruction using a visible light cross-linkable, naturally derived polymer, GelCORE (gel for corneal regeneration). The physical properties of GelCORE could be finely tuned by changing prepolymer concentration and photocrosslinking time. GelCORE revealed higher tissue adhesion compared to commercial adhesives. Furthermore, in situ photopolymerization of GelCORE facilitated easy delivery to the cornea, allowing for bioadhesive curing precisely according to the required geometry of the defect. In vivo experiments, using a rabbit stromal defect model, showed that bioadhesive could effectively seal corneal defects and induce stromal regeneration and re-epithelialization. Overall, GelCORE has many advantages including low cost and ease of production and use. This makes GelCORE a promising bioadhesive for corneal repair.

"Therapeutic Penetrating Keratoplasty: A Retrospective Review"

PURPOSE

To report the indications, outcomes, and complications of therapeutic penetrating keratoplasty (Th PK) in patients with corneal perforation and/or nonhealing corneal ulceration.

METHODS

A retrospective review was conducted of 51 eyes of 51 patients undergoing Th PK between January 1, 2006 and April 15, 2016. Data collected included patient demographics, visual acuity (VA), size of the corneal infiltrate and epithelial defect, degree of corneal thinning/perforation, microbiological results, surgical details, and postoperative complications.

RESULTS

The average age at presentation was 56.0 years (range 6-92 years), and most of the patients were females (n=31, 60.8%). Th PK was performed for corneal perforation in 28 eyes (54.9% of cases), nonhealing corneal ulcer in 16 eyes (31.4% of cases), and imminent risk of corneal perforation in 7 eyes (13.7% of cases). Infection was the most common reason for performing a Th PK and was present in 92.3% (47/51) of all cases. Of the infectious cases, the most common etiologies were bacterial (44.7%, 21/47) and fungal (31.9%, 15/47). The most common identifiable risk factor for undergoing a Th PK was a history of contact lens wear, which was seen in 32.7% of patients. Initial anatomic success was achieved in all patients after performing Th PK. Most patients (33/51; 64.7%) had clear grafts at their last follow-up examination. There was an improvement in VA in 70.2% (33/47, where data were available) of the patients at the final postoperative visit compared with the preoperative visit. Average best postoperative VA (1.14±0.88 logarithm of the minimum angle of resolution [LogMAR]; 20/276) was significantly better than the presenting (1.98±0.68 LogMAR; 20/1910) and preoperative (2.18±0.55 LogMAR; 20/3,027) visual acuities (P<0.0001). The most common complication after Th PK was cataract, which was present in 81.8% (27/33) of phakic eyes in which lens status could be assessed, followed by graft failure (47.1%; 24/51), and secondary glaucoma (45.1%; 23/51). Five eyes developed infection in the therapeutic graft, four eyes had persistent corneal epithelial defect at their last follow-up visit, and two eyes underwent evisceration.

CONCLUSIONS

Therapeutic penetrating keratoplasty achieves anatomic success and it is a useful procedure for restoring a stable cornea in cases in which infection fails to heal or when the cornea perforates. Furthermore, Th PK achieves corneal clarity and improves vision in most patients.

Third-Party Allogeneic Mesenchymal Stromal Cells Prevent Rejection in a Pre-sensitized High-Risk Model of Corneal Transplantation

High-risk cornea transplant recipients represent a patient population with significant un-met medical need for more effective therapies to prevent immunological graft rejection due to heightened anti-donor immune response. In this study, a rat model of pre-existing anti-donor immunity was developed in which corneal allografts were rejected earlier than in non-pre-sensitized recipients. In this model, third-party (non-donor, non-recipient strain) allogeneic mesenchymal stromal cells (allo-MSC) were administered intravenously 7 and 1 days prior to transplantation. Rejection-free graft survival to 30 days post-transplant improved from 0 to 63.6% in MSC-treated compared to vehicle-treated control animals (p = < 0.0001). Pre-sensitized animals that received third-party allo-MSC prior to transplantation had significantly higher proportions of CD45⁺CD11b⁺ B220⁺ monocytes in the lungs 24 h after the second MSC injection and significantly higher proportions of CD4⁺ FoxP3⁺ regulatory T cells in the graft-draining lymph nodes at the average day of rejection of control animals. In in vitro experiments, third-party allo-MSC polarized primary lung-derived CD11b/c⁺ myeloid cells to a more anti-inflammatory phenotype, as determined by cytokine profile and conferred them with the capacity to suppress T cell activation via prostaglandin E₂ and TGFβ1. In experiments designed to further validate the clinical potential of the protocol, thawed cryopreserved, third-party allo-MSC were shown to be similarly potent at prolonging rejection-free corneal allograft survival as their freshly-cultured counterparts in the pre-sensitized high-risk model. Furthermore, thawed cryopreserved third-party allo-MSC could be co-administered with mycophenolate mofetil without adversely affecting their immunomodulatory function. In conclusion, a clinically-relevant protocol consisting of two intravenous infusions of third-party allo-MSC during the week prior to transplantation, exerts a potent anti-rejection effect in a pre-sensitized rat model of high-risk corneal allo-transplantation. This immune regulatory effect is likely to be mediated in the immediate post-transplant period through the promotion, by allo-MSC, of alternatively-activated macrophages in the lung and, later, by enhanced regulatory T-cell numbers.

Transplantation of photoreceptors into the degenerative retina: Current state and future perspectives

The mammalian retina displays no intrinsic regenerative capacities, therefore retinal degenerative diseases such as age-related macular degeneration (AMD) or retinitis pigmentosa (RP) result in a permanent loss of the light-sensing photoreceptor cells. The degeneration of photoreceptors leads to vision impairment and, in later stages, complete blindness. Several therapeutic strategies have been developed to slow down or prevent further retinal degeneration, however a definitive cure i.e. replacement of the lost photoreceptors, has not yet been established. Cell-based treatment approaches, by means of photoreceptor transplantation, have been studied in pre-clinical animal models over the last three decades. The introduction of pluripotent stem cell-derived retinal organoids represents, in principle, an unlimited source for the generation of transplantable human photoreceptors. However, safety, immunological and reproducibility-related issues regarding the use of such cells still need to be solved. Moreover, the recent finding of cytoplasmic material transfer between donor and host photoreceptors demands reinterpretation of several former transplantation studies. At the same time, material transfer between healthy donor and dysfunctional patient photoreceptors also offers a potential alternative strategy for therapeutic intervention. In this review we discuss the history and current state of photoreceptor transplantation, the techniques used to assess rescue of visual function, the prerequisites for effective transplantation as well as the main roadblocks, including safety and immune response to the graft, that need to be overcome for successful clinical translation of photoreceptor transplantation approaches.

Immunosuppression by a subconjunctival implant releasing dexamethasone in a rabbit model of penetrating keratoplasty

AIMS

To evaluate the efficacy of a subconjunctival dexamethasone-releasing implant in preventing rejection of penetrating keratoplasty (PK) in an animal model.

METHODS

Twenty-two rabbits underwent allogenic PK. After randomisation, they received either a 700 µg dexamethasone implant under the conjunctiva at the end of surgery (n=10), one dexamethasone 1 mg/mL eye-drop thrice daily (n=6) or a placebo thrice daily (n=6). The suture was left in place. Animals were observed weekly by slit-lamp and optical coherence tomography with quantification of transparency, neovascularisation and central corneal thickness (CCT). At 5-6 weeks, they were euthanised for histology. The residual dexamethasone concentration in ocular tissues was measured with an ultra-performance liquid chromatography-tandem mass spectrometer.

RESULTS

Placebo group: early neovascularisation was systematic, penetrating the graft by 270-360° at 5-6 weeks. Rejection occurred in 50% of cases. Eye-drop and implant groups: similar course without rejection at 6 weeks and normal CCT. Neovascularisation was observed in 5/6 rabbits in the eye-drop group and in 6/8 in the implant group, with two cases of new vessels penetrating the graft from week 3. Neovascularisation scores did not differ significantly between the two treatments and were significantly lower than for the placebo. Histology was in agreement in all cases. Implants disappeared after 3-5 weeks. No local side effect was observed. Tissue concentrations were all higher at day 8 (n=2) in the implant group than in the eye drop group and lower at 6 weeks (n=8).

CONCLUSIONS

In this PK model characterised by a high rejection rate, a subconjunctival dexamethasone implant was for 6 weeks as effective as the topical form in preventing allograft rejection.

Angiogenesis and lymphangiogenesis in corneal transplantation-A review

Corneal transplantation has been proven effective for returning the gift of sight to those affected by corneal disorders such as opacity, injury, and infections that are a leading cause of blindness. Immune privilege plays an important role in the success of corneal transplantation procedures; however, immune rejection reactions do occur, and they, in conjunction with a shortage of corneal donor tissue, continue to pose major challenges. Corneal immune privilege is important to the success of corneal transplantation and closely related to the avascular nature of the cornea. Corneal avascularity may be disrupted by the processes of angiogenesis and lymphangiogenesis, and for this reason, these phenomena have been a focus of research in recent years. Through this research, therapies addressing certain rejection reactions related to angiogenesis have been developed and implemented. Corneal donor tissue shortages also have been addressed by the development of new materials to replace the human donor cornea. These advancements, along with other improvements in the corneal transplantation procedure, have contributed to an improved success rate for corneal transplantation. We summarize recent developments and improvements in corneal transplantation, including the current understanding of angiogenesis mechanisms, the anti-angiogenic and anti-lymphangiogenic factors identified to date, and the new materials being used. Additionally, we discuss future directions for research in corneal transplantation.

[Immunosuppression after corneal transplantation : Clinical standards and novel approaches]

Corticosteroid eye drops are the mainstay of immunosuppressive therapy after routine lamellar and perforating corneal transplantation. Commonly occurring side effects are cataract formation and increased intraocular pressure. Alternative immunosuppressive agents could allow the dosage of glucocorticoids to be reduced. The antibiotic azithromycin is a candidate drug that showed anti-inflammatory properties in cell cultures and animal models and has positive effects on transplant rejection.

Tacrolimus Eye Drops as Adjunct Therapy in Severe Corneal Endothelial Rejection Refractory to Corticosteroids

PURPOSE

To evaluate the safety and efficacy of tacrolimus eye drops as adjunctive therapy in the treatment of severe corneal endothelial rejection after penetrating keratoplasty refractory to corticosteroids.

METHODS

In this prospective interventional case series, 11 eyes of 11 patients assessed for severe corneal endothelial rejection, with an inadequate response to topical, local, and systemic corticosteroids, were treated with either 0.01% or 0.05% tacrolimus eye drops 4 times daily. Improvement in signs of rejection, visual function, and development of complications were monitored.

RESULTS

The duration of steroid treatment before intervention was 8.1 ± 1.4 days (range = 7-11). Patients were subsequently administered topical tacrolimus 0.01% or 0.05% qid. The time to clinical improvement was 10.3 ± 3.4 days (range = 3-17). The time to rejection reversal was 27.8 ± 16.3 days (range = 7-52). After 3 months, 10 patients (90.8%) demonstrated clinical improvement, and complete restoration of graft clarity was achieved in 5 patients (45.4%). In responsive cases, steroid therapy was successfully tapered off after 60.2 ± 19.7 days (range = 36-93). The best spectacle-corrected visual acuity improved from 1.7 ± 0.9 to 0.8 ± 0.5 logMAR (P = 0.0016). Reported side effects included stinging on drop instillation and punctate epithelial keratopathy.

CONCLUSIONS

Tacrolimus eye drops may be able to play an adjunctive therapeutic role in patients with severe corneal endothelial rejection refractory to conventional steroid treatment. Controlled studies are needed to further investigate the role of tacrolimus in this setting.

Subconjunctival injectable dendrimer-dexamethasone gel for the treatment of corneal inflammation

Corneal inflammation is often encountered as a key pathological event in many corneal diseases. Current treatments involve topical corticosteroids which require frequent instillations due to rapid tear turnover, causing side-effects such as corneal toxicity and elevated intraocular pressure (IOP). Hence, new interventions that can reduce side effects, dosing frequency, and increase patient compliance can be highly beneficial. In this study, we explore a subconjunctival injectable gel based on G4-PAMAM dendrimer and hyaluronic acid, cross-linked using thiol-ene click chemistry, incorporated with dendrimer dexamethasone (D-Dex) conjugates as a potential strategy for sustained delivery and enhanced bioavailability of corticosteroids. The efficacy of the injectable gel formulation was evaluated in a rat mild alkali burn model. Fluorescently-labelled dendrimers (D-Cy5) incorporated in the gel release D-Cy5 in vivo. The released D-Cy5 selectively targets and localizes within corneal macrophages in inflamed rat cornea but not in healthy controls. This pathology dependent biodistribution was exploited for drug delivery, by incorporating D-Dex in the injectable gel. The attenuation of corneal inflammation by D-Dex gels was assessed using various clinical and biochemical parameters over a 2-week period. Subconjunctival D-Dex gel treatment resulted in favorable clinically-relevant outcomes with reduced central corneal thickness and improved corneal clarity compared to free-Dex and placebo gel controls. The extent of corneal neovascularization was significantly reduced in the D-Dex group. These findings suggest that D-Dex attenuates corneal inflammation more effectively than free-Dex by attenuating macrophage infiltration and pro-inflammatory cytokines expression. A significant elevation in IOP was not observed in the D-Dex group but was observed in the free-Dex group. This novel injectable D-Dex gel may be a potential drug delivery platform for the treatment of many inflammatory ocular surface disorders such as dry eye, auto-immune keratitis and post-surgical complications where frequent steroid administration is required.

Update on the Management of High-Risk Penetrating Keratoplasty

PURPOSE OF REVIEW

In this article, we review the indications and latest management of high-risk penetrating keratoplasty.

RECENT FINDINGS

Despite the immune-privilege status of the cornea, immune-mediated graft rejection still remains the leading cause of corneal graft failure. This is particularly a problem in the high-risk graft recipients, namely patients with previous graft failure due to rejection and those with inflamed and vascularized corneal beds. A number of strategies including both local and systemic immunosuppression are currently used to increase the success rate of high-risk corneal grafts. Moreover, in cases of limbal stem cell deficiency, limbal stem cells transplantation is employed.

SUMMARY

Corticosteroids are still the top medication for prevention and treatment in cases of corneal graft rejection. Single and combined administration of immunosuppressive agents e.g. tacrolimus, cyclosporine and mycophenolate are promising adjunctive therapies for prolonging graft survival. In the future, cellular and molecular therapies should allow us to achieve immunologic tolerance even in high-risk grafts.

Systemic Immunomodulatory Strategies in High-risk Corneal Transplantation

The cornea is the most commonly transplanted tissue in the body. Although corneal grafts generally have high success rates, transplantation onto inflamed and vascularized host beds, or so-called high-risk corneal transplantation, has a high rate of graft rejection. The management of this high-risk corneal transplantation is challenging and involves numerous measures. One of the key measures to prevent graft rejection in these cases is the use of systemic immunosuppressive agents. In this article, we will review the systemic immunosuppressive agents most commonly used for high-risk corneal transplantation, which include corticosteroids, cysclosporine A, tacrolimus, mycophenolate mofetil, and rapamycin. Benefits, risks, and published data on the use of these medications for high-risk corneal transplantation will be detailed. We will also summarize novel immunoregulatory approaches that may be used to prevent graft rejection in high-risk corneal transplantation.

Management of high-risk corneal transplantation

The cornea is the most commonly transplanted tissue in medicine. The main cause of corneal graft failure is allograft rejection. The incidence of graft rejection depends on the presence of high-risk characteristics, most notably corneal neovascularization. Although corneal grafting has high success rates in the absence of these risk factors, high-risk keratoplasty is associated with low success rates because of a high incidence of immune-mediated graft rejection. To improve the survival of high-risk corneal transplantation, various preoperative, intraoperative, and postoperative measures can be considered; however, the key step in the management of these grafts is the long-term use of local and/or systemic immunosuppressive agents. Although a number of immunosuppressive agents have been used for this purpose, the results vary significantly across different studies. This is partly due to the lack of an optimized method for their use, as well as the lack of a precise stratification of the degree of risk in each individual patient. New targeted biologic treatments, as well as tolerance-inducing methods, show promising horizons in the management of high-risk corneal transplantation in near future.

High-risk corneal allografts: A therapeutic challenge

Corneal transplantation is the most common surgical procedure amongst solid organ transplants with a high survival rate of 86% at 1-year post-grafting. This high success rate has been attributed to the immune privilege of the eye. However, mechanisms originally thought to promote immune privilege, such as the lack of antigen presenting cells and vessels in the cornea, are challenged by recent studies. Nevertheless, the immunological and physiological features of the cornea promoting a relatively weak alloimmune response is likely responsible for the high survival rate in “low-risk” settings. Furthermore, although corneal graft survival in “low-risk” recipients is favourable, the prognosis in “high-risk” recipients for corneal graft is poor. In “high-risk” grafts, the process of indirect allorecognition is accelerated by the enhanced innate and adaptive immune responses due to pre-existing inflammation and neovascularization of the host bed. This leads to the irreversible rejection of the allograft and ultimately graft failure. Many therapeutic measures are being tested in pre-clinical and clinical studies to counter the immunological challenge of “high-risk” recipients. Despite the prevailing dogma, recent data suggest that tissue matching together with use of systemic immunosuppression may increase the likelihood of graft acceptance in “high-risk” recipients. However, immunosuppressive drugs are accompanied with intolerance/side effects and toxicity, and therefore, novel cell-based therapies are in development which target host immune cells and restore immune homeostasis without significant side effect of treatment. In addition, developments in regenerative medicine may be able to solve both important short comings of allotransplantation: (1) graft rejection and ultimate graft failure; and (2) the lack of suitable donor corneas. The advances in technology and research indicate that wider therapeutic choices for patients may be available to address the worldwide problem of corneal blindness in both “low-risk” and “high-risk” hosts.