Corneal Transplantation for Infectious Keratitis: A Prospective Dutch Registry Study

Purpose: The aim of this study was to analyze real-world practice patterns and graft survival after corneal transplantation for infectious keratitis in the Netherlands. Methods: All consecutive keratoplasties for infectious keratitis registered in the Netherlands Organ Transplant Registry were included. Graft survival was analyzed using Kaplan–Meier survival curves with Cox regression to compare the 3 most common pathogens with subgroup analysis for type and reason of transplantation, sex, and graft size. Multivariable analysis was performed using the same explanatory factors. Results: Between 2007 and 2017, 1111 keratoplasties for infectious keratitis were registered in the Netherlands Organ Transplant Registry. The most common pathogens were viruses (n = 437), bacteria (n = 271), and Acanthamoeba (n = 121). Human leukocyte antigen (HLA) matching did not provide a significant survival benefit, whereas emergency procedures showed worse graft survival [hazard ratio (HR) = 0.40, P = 0.120; HR = 2.73, P < 0.001, respectively]. Graft size >8.5 mm was significantly worse than graft size 8.5 mm (HR = 2.062, P = 0.010). In therapeutic keratoplasty, graft survival was significantly worse for Acanthamoeba than viral keratitis (HR = 2.36, P = 0.008). In the multivariable model, adjusting for graft size, type, and reason for transplantation, viral and bacterial keratitis did not differ significantly in graft survival, and Acanthamoeba showed a significantly worse prognosis (vs. viral keratitis, HR = 2.30, P < 0.001; bacterial keratitis, HR = 2.65, P < 0.001). Conclusions: Viral keratitis was the most common indication for transplantation, followed by bacterial and Acanthamoeba keratitis. HLA matching did not offer protection over elective non-HLA–matched procedures, whereas emergency procedures and grafts sized >8.5 mm showed poor survival. In optical keratoplasty, survival is high for all pathogens, whereas in therapeutic keratoplasty Acanthamoeba shows poor outcome.

I nfectious keratitis is a sight-threatening infection that may require corneal transplantation for infection control, visual rehabilitation, and maintaining globe integrity. 1In one fourth of countries, it is the leading indication for corneal grafting. 2n Europe, corneal transplantation for infectious keratitis is less common, representing 7% of all indications. 3Few large studies have reported graft survival of these high-impact procedures. 4,5In particular, there are little data on the outcomes of emergency transplants and the role of human leukocyte antigen (HLA) in the context of infectious keratitis. 6National quality registries are a valuable tool for improving health outcomes by collecting data from a large number of medical centers. 7Registries are therefore poised to assess practice patterns and outcomes of corneal transplantation for infectious keratitis.
In the current study, we analyzed prospectively collected data from the Netherlands Organ Transplant Registry (NOTR) and report the practice pattern and real-world outcomes of corneal transplantation for infectious keratitis in the Netherlands regarding graft survival and the impact of pathogen, type of surgery (HLA matching, emergency, and elective non-HLA-matched procedures), reason for surgery (optical and therapeutic), sex (recipient, donor, and compatibility), and graft size (8.5 mm, ,8.5 mm, and .8.5 mm).

Graft Registry and Data Collection
Data for this multicenter prospective registry study were obtained from the NOTR, a prospective national database founded by the Netherlands Transplantation Foundation (Nederlandse Transplantatie Stichting [NTS], https:// www.transplantatiestichting.nl/over-de-nts).Donor corneas are centrally allocated and registered in the NOTR in the Netherlands.Using the NOTR, the NTS prospectively captures data related to the recipient, donor, eye bank processing, and surgical procedure of all corneal transplantation performed in the Netherlands.Corneal surgeons completed relevant follow-up data at predefined time points using a standardized electronic data capture system.Data collection was continued until graft failure or loss to follow-up.For this study, the NOTR Steering Group provided institutional review board approval for data extraction and analysis.Informed consent was obtained from all patients to participate in the registry and to use the data for research.The study adhered to the tenets of the Declaration of Helsinki and Dutch legislation.

Study Population
The first surgery registered in the NOTR was performed on January 2 nd , 2007.The study cohort included all consecutive corneal transplantation for infectious keratitis, spanning 10 years until December 24 th , 2017.

Outcome Measures
The primary outcome measure was graft survival.Secondary outcomes pertain to practice patterns, that is, the volume of transplants and causative agents over time.Graft failure was reported by the corneal surgeon or identified in cases of subsequent corneal transplantation in the same eye.The coding guidelines of the NOTR define primary graft failure as corneal edema that never cleared from the immediate postoperative period.Secondary graft failure is a common end point that can be reached through distinctly different pathways.

Statistical Analysis
Statistical analyses were performed using the IBM SPSS Statistics for Windows (version 25.0;IBM Corp., Armonk, NY).To avoid dependency between the 2 eyes, repeat transplants were excluded, and for patients who underwent corneal transplantation in both eyes, only the first eye was included in the graft survival analysis.Baseline characteristics are reported as frequencies with percentages or mean 6 SD.The number of transplants over time was tested using the x 2 goodness-of-fit test.Death-censored graft survival for the total group and subgroups was assessed using Kaplan-Meier survival curves with univariable Cox regression analysis.In addition, a multivariable Cox regression model was performed, including the following explanatory factors: disease-causative agent for the 3 most common pathogens (viral, bacterial, and Acanthamoeba), type of surgery (HLA-matched, emergency, or elective non-HLA-matched procedures), reason for surgery (optical keratoplasty performed for visual rehabilitation or therapeutic keratoplasty performed for infectious debulking and preserving globe integrity), and graft size (8.5 mm, ,8.5 mm, and .8.5 mm).Cox regression analysis was performed over 5 years or 2 years postoperatively, depending on the number of patients still in the study at that time.The proportional hazard assumption was verified using a log(-log) survival function plot.Two-sided P values #0.05 were considered statistically significant.

DISCUSSION
This registry study demonstrated the practice patterns and outcomes of corneal transplantation for infectious keratitis in the Netherlands.Although the volume of corneal transplantation has increased substantially in the last decade due to endothelial keratoplasty, the number of corneal transplants for infectious keratitis has remained stable.Viral, bacterial, and Acanthamoeba keratitis were the most common indications.Most transplants were performed for visual rehabilitation (optical keratoplasty), and a minority for debulking and preserving globe integrity (therapeutic keratoplasty).Two-year graft survival was 72% for therapeutic keratoplasty and was comparable between viral and bacterial keratitis but substantially lower in Acanthamoeba keratitis, even after correction for type, reason for surgery, and graft size.
Infectious keratitis may rapidly deteriorate, necessitating corneal transplantation in an emergency setting, making it a high-risk therapeutic procedure.In our cohort, emergency procedures resulted in significantly worse graft survival rates.Although information on donor parameters for emergency transplantation is available in the registry, because of the relatively small number of cases compared with nonemergent cases, a comparison can be misleading and was therefore not included.The value of matching HLA subtypes for corneal transplantation remains controversial, and there are little data in the context of infectious keratitis.In the current study, HLA-matched grafts did not provide a significant survival benefit compared with elective non-HLA-matched procedures.Similarly, a recent randomized controlled trial on penetrating keratoplasty for any indication did not find a survival benefit of HLA matching. 8However, we do not know what the outcomes would have been, should these highrisk patients have received non-HLA-matched grafts.Nonetheless, it is unlikely that a randomized controlled trial would be conducted in high-risk patients with infectious keratitis, and the registry data may be as close as possible to answer this question.HLA matching in the Netherlands is performed at the discretion of the physician, taking into consideration the characteristics of the recipient and the delay associated with finding a matching donor.Because the use of HLA matching has become rare (,3% according to the EEBA 2008 report), our national registry provides a unique opportunity to explore this topic.A comparison of causative agents within emergency procedures revealed that viral and bacterial keratitis showed promising results, even in so-called high-risk procedures, whereas Acanthamoeba showed significantly worse outcomes.
Fungal and Acanthamoeba keratitis carried a higher risk of repeat transplantation than viral and bacterial keratitis.Half of the cases involved therapeutic procedures, indicating that the primary graft was insufficient for disease management or did not yield the desired outcome.The Australian Graft Registry reported that a consecutive graft has a lower survival rate than the previous graft. 9This trend is confirmed in this study for infectious keratitis and shows the burden on patients and health care.
A much-debated question is the impact of donor-recipient sex matching on graft survival.1][12][13] Against the background of penetrating keratoplasty for infectious keratitis, we failed to detect a significant effect for donor-recipient matching.
Large-diameter corneal grafts have been previously described as a risk factor for graft failure, [14][15][16] but not all studies found a significant association. 17Lower graft survival of larger grafts in our cohort may be related to a higher antigenic load in the proximity of the limbus increasing the risk of rejection and a more severe infection requiring debulking.
In most parts of the developed world, viral keratitis is the most common cause of unilateral infectious corneal blindness, 18 in particular herpes simplex keratitis which affects 1.5 million people globally. 19,202][23] The cause of failure is manifold, for instance, in herpes simplex keratitis, stromal keratitis is associated with deep vascularization which increases rejection risk, 24 and disease recurrence is common after nerves regenerate in the graft.Moreover, herpes keratitis is accompanied by hypoesthesia, which facilitates recurrent trauma and exposure keratopathy. 25The relatively high graft survival in our cohort may be related to standard use of oral prophylaxis to prevent herpes recurrence in the Netherlands. 26n bacterial keratitis, the introduction of newer and more potent antibacterial agents led to a decrease in the number of therapeutic keratoplasties in some centers. 27Although  promising, the US Center for Disease Control estimated that annually 2.8 million people are infected with drug-resistant microbes and resistance is increasing. 28In our cohort, the number of keratoplasties varies over time but does not follow a directional trend.Two-year graft survival of therapeutic keratoplasty for bacterial keratitis was 81%, slightly lower than that reported in previous studies (over 90%). 22,29,30n our cohort, the volume of corneal transplantation for Acanthamoeba keratitis accounted for 14% of all indications and increased from a handful of cases before 2009 to double digits since 2015.This increase may be due to the use of silicone hydrogel contact lenses, 31 multipurpose solutions, 32 or local environmental factors. 335][36] Importantly, Acanthamoeba keratitis showed the worst outcomes of all causative agents even when outcomes were adjusted for type of procedure (HLAmatched, emergency, and elective non-HLA-matched procedure), reason for grafting (optical and therapeutic keratoplasty), and graft size.Age was omitted from the multivariable analysis because Acanthamoeba predominantly affects younger individuals.Since the introduction of biguanides for medical therapy, most cases are treated medically and therapeutic keratoplasty is traditionally reserved for cases of insufficient response to medical therapy or severe complications. 37A much debated question is the value of early therapeutic deep anterior lamellar keratoplasty in Acanthamoeba keratitis. 38However, at the moment, this is not standard of care in the Netherlands, as a result of which there were too few cases available for separate analyses.
Fungal keratitis has a global incidence of more than 1 million cases each year. 39The disease accounts for a significant burden of blindness, 39 causing nearly 5 times as many corneal perforations as bacterial keratitis. 40In our cohort, graft survival for fungal keratitis was 83% 2 years postoperatively, mirroring the outcomes of transplants performed for viral and bacterial keratitis, and comparable to reports in the literature. 41entral graft allocation by the NTS ensured the robustness of our primary outcome measure: graft survival.Nonetheless, our study has the following limitations.The NOTR database is not designed to specifically capture differences in virulence, predisposing factors, extensiveness of keratitis, and ocular surface inflammation.Moreover, to reduce the registration burden, not all parameters are mandatory, for example, corneal neovascularization, sutures, and use of topical and systemic immunosuppressive therapy.The time between disease onset and transplantation is also an interesting factor that was unavailable in this study.However, therapeutic and emergency procedures may be used as surrogates.
In conclusion, this prospective Dutch registry study shows that the volume of corneal transplantation for infectious keratitis has remained stable over the last decade, with the exception of Acanthamoeba.Viral keratitis was the most common indication, followed by bacterial and Acanthamoeba keratitis.Graft survival was promising, except in Acanthamoeba keratitis and grafts larger than 8.5 mm.The benefit of HLA matching is unclear, but our data suggest that it may not provide additional survival benefits.Timely therapeutic keratoplasty should be considered as needed given the relatively successful outcomes in our study, especially for viral and bacterial keratitis.

FIGURE
FIGURE 1. A, Volume of all corneal transplantation (green) compared with corneal transplantation for infectious keratitis (blue) in the Netherlands from 2007 until 2017.The overall volume of corneal transplantation increased over time but remained stable for infectious keratitis.B, Number of transplantation for infectious keratitis per pathogen per year.The number of grafts for Acanthamoeba keratitis increased significantly in the second half of the cohort.(The full color version of this figure is available at www.corneajrnl.com.)

FIGURE 2 .
FIGURE 2. A, Graft survival of primary corneal transplantation and retransplantation for infectious keratitis in the Netherlands.B, Five-year graft survival did not differ between viral and bacterial keratitis but was significantly worse in Acanthamoeba keratitis.C, Emergency procedures showed significantly worse graft survival, whereas human leukocyte antigen (HLA) did not provide significant survival benefit compared with elective non-HLA-matched procedures.D, Graft survival of optical and therapeutic keratoplasty in infectious keratitis.In 49 cases, the reason for transplantation was unknown or unclassifiable.HLA = human leukocyte antigen.E, Graft survival did not differ between donor-recipient sex-matched and sex-mismatched cases.F, Five-year graft survival of grafts sized .8.5 mm was significantly worse compared with grafts sized 8.5 mm, whereas grafts sized ,8.5 mm did not differ statistically from grafts sized 8.5 mm.In 44 cases, the graft size was unknown.(The full color version of this figure is available at www.corneajrnl.com.)

FIGURE 3 .
FIGURE 3. A, In emergency procedures, Acanthamoeba keratitis showed significantly worse graft survival compared with viral and bacterial keratitis.B, In elective non-human leukocyte antigen (HLA)-matched procedures, Acanthamoeba keratitis showed significantly worse graft survival compared with viral and bacterial keratitis.C, In optical keratoplasty, 2-year graft survival did not differ significantly between pathogens.D, In therapeutic keratoplasty, 2-year graft survival was comparable between viral and bacterial keratitis and significantly worse for Acanthamoeba keratitis.HLA = human leukocyte antigen.(The full color version of this figure is available at www.corneajrnl.com.)

TABLE 1 .
Patient, Surgery, and Pathogen Characteristics in All Transplants for Infectious Keratitis N=1111 unless specified otherwise.

TABLE 2 .
Multivariable Analysis of Causative Pathogens for Developing Graft Failure in Infectious Keratitis