Peripheral blood immune cell profiling of acute corneal transplant rejection.

Acute rejection (AR) of corneal transplants (CT) has a profound effect on subsequent graft survival but detailed immunological studies in human CT recipients are lacking. In this multi-site, cross-sectional study, clinical details and blood samples were collected from adults with clinically diagnosed AR of full-thickness (FT)-CT (n = 35) and posterior lamellar (PL)-CT (n = 21) along with Stable CT recipients (n = 177) and adults with non-transplanted corneal disease (n = 40). For those with AR, additional samples were collected 3 months later. Immune cell analysis was performed by whole-genome microarrays (whole blood) and high-dimensional multi-color flow cytometry (peripheral blood mononuclear cells). For both, no activation signature was identified within the B cell and T cell repertoire at the time of AR diagnosis. Nonetheless, in FT- but not PL-CT recipients, AR was associated with differences in B cell maturity and regulatory CD4+ T cell frequency compared to stable allografts. These data suggest that circulating B cell and T cell subpopulations may provide insights into the regulation of anti-donor immune response in human CT recipients with differing AR risk. Our results suggest that, in contrast to solid organ transplants, genetic or cellular assays of peripheral blood are unlikely to be clinically exploitable for prediction or diagnosis of AR.

Defining the optimal cryoprotectant and concentration for cryopreservation of limbal stem cells.

Limbal stem cell (LSC) deficiency causes progressive loss of vision but may be treated by transplant of autologous LSCs. Cryopreservation has the potential to indefinitely extend the lifespan of LSCs allowing re-transplant in case of graft failure. In this study, we aimed to identify the optimal cryoprotectant and cryoprotectant concentration for LSC cultures. Suspension cultures derived from cadaveric corneoscleral rims were cooled to 4 °C with Me2SO, propylene glycol or ethylene glycol at a concentration of 5%, 10% or 15%. Cell tolerance was measured in terms of membrane integrity, colony-forming efficiency and alamarBlue® reduction. Increasing cryoprotectant concentration above 5% reduced membrane integrity, metabolism and colony-forming efficiency. Cryoprotectant choice did not significantly influence these characteristics. Cells demonstrating Side Population were maintained after cryopreservation with 5% propylene glycol in vapour phase liquid nitrogen for 1 week, indicating that cryopreservation of LSCs with relatively low cryoprotectant concentration (5%) has promise in low-temperature eye banking.

Endophthalmitis after penetrating keratoplasty.

PURPOSE: To determine the incidence of endophthalmitis after penetrating keratoplasty (PK) and patient and donor risk factors. DESIGN: Retrospective cohort study using national transplant registry data. PARTICIPANTS: All corneal transplant recipients (n = 11 320) registered on the United Kingdom Transplant Registry undergoing their first PK between April 1999 and December 2006. METHODS: Patients who developed endophthalmitis were identified on the transplant registry. In addition, cases where the fellow cornea from the same donor had been transplanted were included. Clinical information regarding donor and recipient characteristics, surgical details, and postoperative outcomes were collected and analyzed. In cases where endophthalmitis was reported, the diagnosis was verified by a follow-up supplementary questionnaire to the surgeon. Logistic regression was used to investigate differences in the factors associated with the development of endophthalmitis. MAIN OUTCOME MEASURES: Incidence of endophthalmitis and graft survival. RESULTS: The overall incidence of endophthalmitis occurring after primary PK in the UK was 0.67%. The incidence of endophthalmitis occurring within 6 weeks of surgery was 0.16%. Graft survival after endophthalmitis was 27% (95% confidence interval, 16-38) at 5 years, with a mean best-corrected visual acuity of 1.13 (logarithm of the minimum angle of resolution) for surviving grafts. Factors associated with endophthalmitis were donor cause of death (infection), high-risk cases, and indication for corneal transplantation. CONCLUSION: Endophthalmitis remains a serious issue, with those affected having reduced graft survival and poor visual outcomes. Management of the identified recipient and donor risk factors are important to reduce endophthalmitis risk. In particular, the increased incidence of endophthalmitis when the donor dies of infection requires further explanation and review of current donor eye retrieval and eye bank practices. The delayed presentation of endophthalmitis cases also raises questions regarding possible sequestration of microbes within the corneal tissue and the effect of antimicrobials in storage media.

Outcomes after reversed corneal graft rejection: a report from the European VISICORT project.

OBJECTIVE: This study aims to describe the outcome of corneal grafts, both low risk and high risk, after successfully reversed immunological rejection. METHODS: Datasets on reversed rejection episodes in penetrating and endothelial keratoplasties between 2014 and 2019 (n=876) were extracted from the Adverse Immune Signatures and their Prevention in Corneal Transplantation database, which contains the prospectively and consecutively collected corneal transplants from five European centres. Stratified by the preoperatively determined risk status for immunological rejection, the outcome parameters analysed included visual acuity, intraocular pressure, endothelial cell density and central corneal thickness before and after reversed rejection episodes. RESULTS: Fourty-seven (52%) out of a total of 91 identified rejection episodes were successfully reversed and were available for analysis (23 penetrating and 24 endothelial keratoplasties). No statistically significant change was found for any of the parameters studied between the values before and the values 3 months after the rejection episode, irrespective of the preoperative risk status. CONCLUSION: The outcome of corneal grafts that survive immunological rejection may be clinically indistinguishable from the state before immunological rejection, irrespective of graft type and risk status. These findings support clinicians by providing information on prognosis after reversed rejection episodes and by giving patients realistic expectations regarding the outcome.

A pilot to examine the logistical and feasibility issues in testing deceased tissue donors for vCJD using tonsil as the analyte.

Transplanted tissues have transmitted transmissible spongiform encephalopathies and in the UK there have been more cases of variant Creutzfeldt-Jakob disease (vCJD) than elsewhere in the world. A pilot study was undertaken to look at the feasibility of testing for vCJD in deceased donors using tonsillar tissue. This pilot showed that obtaining consent for removal and testing tonsil tissue was feasible. Donor eligibility for inclusion in the pilot was limited to tissue donors from the National Health Service Blood and Transplant, Tissue Services and to donors shared with the Corneal Transplant Service Eye Banks. Obtaining tonsillar tissue in the immediate post-mortem period was limited by the presence of rigor mortis. Tonsillar tissue was suitable for routine analysis for the presence of prion associated with vCJD in deceased tissue donors. Production and processing of tissue was straightforward and a low assay background was obtained from most samples. Since palatine and lingual tonsil tissue can be obtained in pairs it was possible, in the majority of cases, to set aside an intact sample for confirmatory testing if required. In one instance a sample was reactive by Western blot. However, the pattern of reactivity was not typical for that obtained from vCJD patients. Unfortunately the sample was not of sufficient quality for the confirmatory test to provide a conclusive result.

Long-Term Graft Survival and Decline in Endothelial Cell Density Following Penetrating Keratoplasty with Organ-Cultured Corneas.

INTRODUCTION: Endothelial cell density (ECD) changes long after penetrating keratoplasty (PKP) of organ-cultured corneas have been little studied. We aim to calculate the point when ECD decline stabilises following PKP with organ culture stored corneas. METHODS: This is an observational study of first-ever PKPs and first-ever re-grafts, performed over 17 years under a single surgeon. ECDs were acquired at 3 and 6 months, 1 year post-graft and annually thereafter by specular microscopy. Time-dependent ECD data was fitted to a log-biexponential model. RESULTS: We studied 465 first-ever grafts and 128 re-grafts. Mean recipient age was 59 years (range 0-96 years; SD 22). Median follow-up was 5.7 (range 0.2-17.1) years. Probability of ED at 5 years in first grafts and re-grafts was 4.4% (2.6-7.1%) and 14.8% (8.3-23.2%). In first grafts, ECD loss reached 0.6% per annum at 7.9 (6.2-9.6) years post-operatively. The half-lives of ECD loss during the immediate post-operative period for first grafts, re-grafts, dystrophies, ectasias, and previous ocular surgery are 20.1 (14.9-30.9), 12.8 (6.9-79.4), 19.5 (13.1-37.7), 26.2 (16.2-68), and 11.6 (6.7-41.3) months, respectively. The half-life during this rapid phase of ECD loss has an inverse correlation with graft survival at 10 years (r = - 0.89, p = 0.02). CONCLUSIONS: Rate of endothelial decompensation is higher in first grafts than re-grafts. ECD decline stabilises 7.9 years post-operatively in first grafts but then becomes lower than the physiological loss expected. Further work is needed to verify whether organ-cultured grafts reach physiological levels of ECD loss faster than hypothermically stored grafts.

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.

One threat, different answers: the impact of COVID-19 pandemic on cornea donation and donor selection across Europe.

OBJECTIVES: To assess to which extent the COVID-19 pandemic affected corneal transplantation by virtue of donor selection algorithms in different European countries. DESIGN: Survey. SETTING: 110 eye banks in 26 European countries. PARTICIPANTS: 64 eye banks covering 95% of European corneal transplantation activity. INTERVENTIONS: A questionnaire listing the number of corneas procured and distributed from February to May 2018-2020 was circulated to eye banks. MAIN OUTCOME MEASURES: The primary outcome was the number of corneal procurements. Additional outcomes were national algorithms for donor selection, classified according to their stringency (donors with COVID-19 history, suspected for COVID-19, asymptomatic, PCR testing) and the pandemic severity in each country. We calculated Spearman's correlation coefficient to determine, two by two, the relationship between the 3-month decline in eye banking activity (procurement), the stringency of donor selection algorithm and the grading of pandemic severity (cases and deaths). A partial correlation was run to determine the relationship between decline and stringency while controlling for pandemic severity. RESULTS: Procurements decreased by 38%, 68% and 41%, respectively, in March, April and May 2020 compared with the mean of the previous 2 years, while grafts decreased, respectively, by 28%, 68% and 56% corresponding to 3866 untreated patients in 3 months. Significant disparities between countries and the decrease in activity correlated with stringency in donor selection independent of pandemic severity. CONCLUSIONS: Our data demonstrate significant differences between countries regarding donor screening algorithms based on precautionary principles and, consequently, a decrease in the donor pool, already constrained by a long list of contraindications. Fundamental studies are needed to determine the risk of SARS-CoV-2 transmission by corneal transplantation and guide evidence-based recommendations for donor selection to justify their substantial medical and economic impact.

Preservation of Human Cornea.

SUMMARY: The successful outcome of the majority of corneal transplants depends on the presence of a viable corneal endothelium. This monolayer of cells lines the inner surface of the cornea and its primary function is to maintain corneal transparency by controlling the hydration of the collagenous stromal layer. Since human corneal endothelial cells do not readily proliferate, preservation of the endothelium is a primary aim of methods of corneal storage. Although some cryopreserved corneas have been transplanted successfully, the complexity of the cryopreservation technique and its potential for causing endothelial damage have limited its application. Hypothermia (2-8 °C) is the most commonly applied method of storage, which allows storage for 7-14 days. Organ culture (28-37 °C), which extends storage time to 4 weeks, is used widely in European eye banks. Graft outcomes for corneas stored by these two techniques appear similar.

Practice patterns of corneal transplantation in Europe: first report by the European Cornea and Cell Transplantation Registry.

PURPOSE: To report practice patterns of corneal transplantation in Europe. SETTING: Corneal clinics in 10 European member states (MS), the United Kingdom, and Switzerland. DESIGN: Multinational registry study. METHODS: Corneal transplant procedures registered in the European Cornea and Cell Transplantation Registry were identified. Preoperative donor and recipient characteristics, indication and reason for transplantation, and surgical techniques were analyzed. RESULTS: A total of 12 913 corneal transplants were identified from 10 European Union MS, the United Kingdom, and Switzerland. Most countries were self-sufficient with regard to donor tissue. Fuchs endothelial corneal dystrophy was the most common indication (41%, n = 5325), followed by regraft (16%, n = 2108), pseudophakic bullous keratopathy (12%, n = 1594), and keratoconus (12%, n = 1506). Descemet stripping automated endothelial keratoplasty (DSAEK, 46%, n = 5918) was the most commonly performed technique, followed by penetrating keratoplasty (30%, n = 3886) and Descemet membrane endothelial keratoplasty (9%, n = 1838). Vision improvement was the main reason for corneal transplantation (90%, n = 11 591). Surgical technique and reason for transplantation differed between indications. CONCLUSIONS: This report provides the most comprehensive overview of corneal transplantation practice patterns in Europe to date. Fuchs endothelial dystrophy is the most common indication, vision improvement the leading reason, and DSAEK the predominant technique for corneal transplantation.

Outcomes of corneal transplantation in Europe: report by the European Cornea and Cell Transplantation Registry.

PURPOSE: To analyze real-world graft survival and visual acuity outcomes of corneal transplantation in Europe. SETTING: Corneal clinics in 10 European Union member states, the United Kingdom, and Switzerland. DESIGN: Multinational registry study. METHODS: All corneal transplant procedures registered in the European Cornea and Cell Transplantation Registry (ECCTR) were identified. Graft survival of primary corneal transplants were analyzed using Kaplan-Meier survival curves with log-rank test and Cox regression. Corrected distance visual acuities (CDVAs) are reported at baseline and 2 years postoperatively using the Lundström distribution matrix. RESULTS: A total of 12 913 corneal transplants were identified. Overall, 32-year graft survival of corneal transplants was high (89%) but differed between indications, ranging from 98% in keratoconus and 80% for trauma. Overall, CDVA improved postoperatively, but the risk for losing vision ranged from 7% (baseline vision ≤0.1 Snellen) to 58% (baseline vision ≥1.0 Snellen). CONCLUSIONS: This report provides a comprehensive overview of graft survival and visual outcomes of corneal transplantation in Europe. In addition, it provides real-world estimates of outcomes for a variety of indications and surgical techniques to support benchmarking and demonstrates the relationship between baseline and postoperative vision.

A UK scheme for reporting serious adverse events and reactions associated with ocular tissue transplantation.

Reporting and investigation of serious adverse events and reactions associated with tissue and cell transplantation is a fundamental aspect of ensuring adequate levels of safety and quality and is a requirement of the European Union Directives on tissues and cells. In the UK, a system for the reporting and analysis of events and reactions associated with ocular tissue transplantation is well established. It is operated by a network of individuals and organisations, each with clearly defined roles and responsibilities, following written procedures for reporting and investigation. Analysis of reports indicates that the most important adverse reactions associated with this type of tissue transplantation are endophthalmitis (0.58%) and primary graft failure (0.3%). This system allows the analysis of all types of events and reactions by the professionals involved so that trends can be identified and services improved. Tools to evaluate the severity and imputability of individual events or reactions, such as those developed by the EUSTITE project, can be utilised to facilitate the selection of those cases meeting the criteria for reporting to the Competent Authority. This vigilance model has been shown to be effective and could be applied in other fields of tissue or cell transplantation.

Long-term topical steroid treatment after penetrating keratoplasty in patients with pseudophakic bullous keratopathy.

PURPOSE: To assess the use of long-term topical corticosteroid treatment in patients with pseudophakic bullous keratopathy (PBK) after penetrating keratoplasty (PK). DESIGN: Retrospective cohort study. PARTICIPANTS: This study considered patients with PBK undergoing an initial PK procedure for visual reasons in the United Kingdom between April 1999 and March 2004. There were 1274 initial PK procedures for PBK reported to United Kingdom Transplant in this period, of which 1184 (91%) were grafted for visual reasons. Of these 1184 grafts, follow-up was reported in 1033 instances (87%). METHODS: A Cox regression model was used to investigate the combined effects of all preoperative factors (recipient age, human leukocyte antigen [HLA] matching, trephine size, deep stromal vascularization, surgeon activity) on graft failure. The model was fitted using all preoperative factors first, and subsequently, factors associated with corticosteroid and other medications were included. MAIN OUTCOME MEASURES: Graft survival. RESULTS: Three-year survival of grafts for PBK was 65% (95% confidence interval [CI], 59%-70%). Topical corticosteroids were still being used beyond 18 months after surgery in 378 (37%) of the 1033 corneal grafts included in this study. The grafts of patients not currently receiving steroids were 1.5 times as likely to fail (hazard ratio [HR], 1.5; 95% CI, 1.0-2.2; P<0.03). Lack of HLA matching (P = 0.006), trephine size or=8.00 mm (P = 0.03), recipient age younger than 65 years (P = 0.003), and corneal vascularization (P = 0.04) all increased the risk of graft failure. CONCLUSIONS: The use of long-term postoperative corticosteroids improved graft survival after PK for PBK. Barring patient contraindications for long-term topical corticosteroid use, clinicians should consider maintaining patients with PBK on long-term postoperative corticosteroid maintenance.

Corneal transplant follow-up study II (CTFS II): a prospective clinical trial to determine the influence of HLA class II matching on corneal transplant rejection: baseline donor and recipient characteristics.

PURPOSE: To describe a study to determine the influence of HLA class II matching on allograft rejection of high-risk, full-thickness corneal transplants. METHODS: A prospective, longitudinal, clinical trial (ISRCTN25094892) with a primary outcome measure of time to first clinically determined rejection episode. Tissue typing used DNA-based techniques. Corneas were allocated to patients with ≤2 human leucocyte antigen (HLA) class I antigen mismatches by cohort minimisation to achieve 0, 1 or 2 HLA class II (HLA-DR) antigen mismatches. Transplants were to be followed up at 6 months and then annually on the anniversary of surgery for 5 years. Power calculations estimated a sample size of 856 transplants to detect a 0.1 difference in probability of rejection at 1 year between HLA class II matched and mismatched transplants at the 5% level of significance with 80% power. RESULTS: To allow for loss to follow-up, 1133 transplants in 980 patients were accrued to the study between 3 September 1998 and 2 June 2011. 17% of transplants had 0 HLA-DR mismatches. The most frequent indication was bullous keratopathy, accounting for 27% of transplants and 54% of the transplants were regrafts. Median waiting time for a matched graft was 3 months. Donor and recipient characteristics were distributed evenly across the study groups. CONCLUSION: Recruitment to the CFS II has closed with 1077/1133 transplants meeting all the study criteria. Follow-up has been completed and final analysis of the data has started. TRIAL REGISTRATION NUMBER: ISRCTN25094892 andUKCRNID9871, Pre-results.

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.

Fungal infection after endothelial keratoplasty: association with hypothermic corneal storage.

PURPOSE: To compare the incidence of fungal infection after endothelial keratoplasty (EK) when donor tissue had been stored in hypothermic medium or organ culture. METHODS: We describe the clinical features of 10 cases of fungal infection (keratitis or endophthalmitis) following EK identified at three European centres. Case definition was the culture of fungus or a positive PCR from the host cornea or anterior chamber after EK. A survey of the incidence of infection after EK was conducted by the European Eye Bank Association. The main outcome measure was the number of cases in which donor tissue had been stored in hypothermic medium compared with organ culture. RESULTS: The 10 cases occurred between 2014 and 2017. All donor corneas had been stored in hypothermic medium sourced from three US eye banks. Three pairs of mate corneas caused infections in six recipients. Candida spp were identified from nine cases, with one isolate of Purpureocillium lilacinum. Data on 16 862 corneas supplied for EK were available from 16 European eye banks for the 5-year period from 2012. There were 17 reported cases of infection, of which 15 (88%) were fungal infections and 14 (82%) were Candida spp. Fungal infection was reported from 3 of 14 476 (0.02%) corneas supplied in organ culture compared with 12 of 2386 (0.50%) corneas supplied in hypothermic medium (p<0.0001). The incidence of infection after hypothermic storage was similar for material sourced from Europe (0.52%) or the USA (0.61%). CONCLUSIONS: Infection after EK is strongly associated with Candida spp. The possible explanations for the higher incidence of infection when tissue is stored in hypothermic medium are discussed.

Outcomes of same-sizing versus oversizing donor trephines in keratoconic patients undergoing first penetrating keratoplasty.

PURPOSE: To investigate whether use of same-size donor and recipient trephines reduced myopia after penetrating keratoplasty for keratoconus. DESIGN: Retrospective cohort study. PARTICIPANTS: Eight hundred seventy-eight first grafts for keratoconus were reported to UK Transplant between April 1999 and December 2003. There were 234 and 644 grafts in the same-size and oversize donor trephine groups, respectively. At 1 year, mean spherical equivalent (SE) data were available for 116 eyes (50%) and 295 eyes (46%) in the same-size and oversize groups. At 2 years, mean SE data were available for 64 eyes (27%) and 148 eyes (23%) in the same-size and oversize groups. METHODS: Logistic regression and univariate analysis of follow-up data submitted to UK Transplant. MAIN OUTCOME MEASURES: At 1 and 2 years postoperatively, mean SE, magnitude of the cylindrical component of the refraction, postoperative uncorrected visual acuity (VA), postoperative best-corrected VA, and postoperative complications were recorded. RESULTS: The mean SEs for the same-size and oversize donor trephine groups, respectively, were -1.45 diopters (D) and -1.41 D at 1 year (P = 0.6) and -1.74 D and -2.19 D at 2 years postoperatively (P = 0.3). Although there were no differences in graft survival between the groups at 1 and 2 years, there was a higher incidence of postoperative wound leaks in the same-size group (P = 0.03). CONCLUSION: Use of same-size donor and recipient trephines did not reduce myopia and was associated with an increased risk of postoperative complications.

Astigmatism and the impact of relaxing incisions after penetrating keratoplasty.

PURPOSE: To determine the impact of relaxing incisions for correcting postoperative astigmatism following penetrating keratoplasty. METHODS: Data were collected through the Swedish Corneal Transplant Register. Of the 1161 grafts with complete 2-year follow-up, 131 underwent relaxing incisions. Stepwise multiple regression was used to determine the factors that influenced the extent of astigmatism in diopters (D) (square root transformed). The change in astigmatism brought about by relaxing incisions was evaluated both by subtraction (ie, ignoring angle) and vector analysis. RESULTS: The overall mean astigmatism was 4.56 D (95% confidence interval [CI]: 4.40-4.73, n = 1161). The final regression model explained only a small proportion of the overall variability of the data (< 5%). There was a slight increase in postoperative astigmatism with recipient age (P = .025), and two of the seven participating clinics achieved lower levels of astigmatism (P = .001 and P = .036, respectively). In patients who underwent relaxing incisions, astigmatism was reduced from 8.40 D (95% CI: 8.0-9.0, n = 131) to 3.80 D (95% CI: 3.5-4.3). The mean difference by subtraction was 4.50 D (95% CI: 4.0-5.0, P < .001, paired t test). Vector analysis showed the overall reduction of astigmatism due to surgery to be 7.90 D (95% CI: 7.2-8.7). Compared with grafts with no refractive surgery, a trend was noted that suggested corrected visual acuity was improved following relaxing incisions. CONCLUSIONS: Relaxing incisions were found to be a safe and effective method for reducing postoperative astigmatism and may improve visual acuity.