Effect of donor epithelium on corneal transplant survival

Endothelial failure and rejection in recipients of corneas from the same donor

Objective

To determine whether patients who receive corneas from the same donor have similar risks of endothelial failure and rejection.

Methods and Analysis

Patients with Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK) who received their first corneal transplant between 1999 and 2016 were analysed. Patients receiving corneas from donors who donated both corneas for the same indication were defined as ‘paired’. Gray’s test was used to compare the cumulative incidence of endothelial failure and rejection within 5 years post-transplant for ‘paired’ and ‘unpaired’ groups. Cox regression models were fitted to determine whether there was an association between recorded donor characteristics (endothelial cell density (ECD), age and sex and endothelial graft failure and rejection.

Results

10 838 patients were analysed of whom 1536 (14%) were paired. The unpaired group comprised 1837 (69%) recipients of single corneal donors and 7465 (69%) donors who donated both corneas for another indication. ECD was lower for unpaired single cornea donors (p<0.01). There was no significant difference in endothelial graft failure or rejection between paired and unpaired groups for FED (p=0.37, p=0.99) or PBK (p=0.88, p=0.28) nor for donor ECD, age, sex and paired donation after adjusting for transplant factors (across all models p>0.16 for ECD, p>0.32 for donor age, p>0.14 for sex match and p>0.17 for the donor effect).

Conclusion

The absence of a significant difference in graft outcome for corneal transplants for FED and PBK between paired and unpaired donors may reflect a homogeneous donor pool in the UK.

Epithelial Regeneration in Human Corneas Preserved in an Active Storage Machine

Purpose

To characterize the corneal epithelium (CE) and limbal epithelium (LE) of human corneas stored in an innovative active storage machine (ASM) after a period of organ culture (OC).

Methods

Corneas unsuitable for graft and stored in a standard commercial OC medium for 2 to 5 weeks were transferred into our ASM for 14 days. The ASM actively maintained an overpressure on the endothelial side (20 mm Hg) while ensuring medium renewal. We compared three modalities of storage in the ASM's epithelial chamber: (1) alternating exposure to a supplemental hormonal epithelial medium (SHEM) and air (air-lifting), (2) continuous immersion in SHEM, and (3) continuous immersion in OC medium. Passive immersion of the whole cornea in OC medium or of the CE in SHEM with or without airlifting served as controls. Paired corneas were used for better comparability. Histology, differentiation (by immunolabeling), and ultrastructure were analyzed at the end.

Results

The ASM with air-lifting was most effective in regenerating a pluristratified and differentiated CE (apical ZO-1 and MUC16 staining and regeneration of the glycocalyx). In addition, the LE was stratified with preserved expression of ABCB5. The ASM with immersion in SHEM or OC medium gave a less stratified and differentiated CE. In the three control groups, the epithelia, when present, were paucistratified and less differentiated.

Conclusions

In human corneas previously stored in OC, the ASM regenerates a CE with differentiation characteristics close to normal.

Translational Relevance

Regeneration of the epithelium of human corneas discarded by eye banks will increase tissue availability for research.

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.

Prevention and treatment of corneal graft rejection: current practice patterns of the Cornea Society (2011)

PURPOSE

To analyze current practice patterns in the prevention and treatment of corneal graft rejection for both penetrating keratoplasty (PK) and endothelial keratoplasty (EK) and to compare these patterns with previously reported practices.

METHODS

In 2011, an electronic survey was sent to 670 members of the Cornea Society worldwide addressing the routine postoperative management of corneal transplants at different time points, treatment of various manifestations of corneal graft rejection, and preferred surgical techniques.

RESULTS

A total of 204 of 670 surveys (30%) were returned and evaluated. All respondents used topical corticosteroids for routine postoperative management and treatment of endothelial graft rejection. Prednisolone was the topical steroid of choice in all clinical scenarios, similar to previous surveys from 1989 to 2004. Use of subconjunctival and systemic steroids increased for many scenarios of probable and definite graft rejection. Routine use of prednisolone decreased by approximately 10% from previous surveys, whereas difluprednate was used in 13% of high-risk eyes during the first 6 months. Dexamethasone, fluorometholone, and loteprednol use remained stable. Adjunctive topical cyclosporine use increased significantly for PK and EK. EK was the preferred technique for endothelial dysfunction, whereas PK and deep anterior lamellar keratoplasty were both used for keratoconus and anterior scars. Most respondents (75%) felt that graft rejection occurs more frequently after PK than after EK.

CONCLUSIONS

Prednisolone remains the treatment of choice for management and treatment of graft rejection; however, since the introduction of difluprednate, its use has declined slightly since the introduction of difluprednate. Despite perceived differences in rejection rates, there were no differences in prophylactic steroid treatment for PK and EK.

Comparison of galectin expression signatures in rejected and accepted murine corneal allografts

PURPOSE

Although members of the galectin family of carbohydrate-binding proteins are thought to play a role in the immune response and regulation of allograft survival, little is known about the galectin expression signature in failed corneal grafts. The aim of this study was to compare the galectin expression pattern in accepted and rejected murine corneal allografts.

METHODS

Using BALB/c mice as recipients and C57BL/6 mice as donors, a total of 57 transplants were successfully performed. One week after transplantation, the grafts were scored for opacity by slit-lamp microscopy. Opacity scores of 3+ or greater on postoperative week 4 were considered rejected. Grafted corneas were harvested on postoperative week 4, and their galectin expressions were analyzed by Western blot and immunofluorescence staining.

RESULTS

As determined by the Western blot analyses, galectins-1, 3, 7, 8 and 9 were expressed in normal corneas. Although in both accepted and rejected grafts, expression levels of the 5 lectins were upregulated compared with normal corneas, there were distinct differences in the expression levels of galectins-8 and 9 between accepted and rejected grafts, as both the Western blot and immunofluorescence staining revealed that galectin-8 is upregulated, whereas galectin-9 is downregulated in the rejected grafts compared with the accepted grafts.

CONCLUSIONS

Our findings that corneal allograft rejection is associated with increased galectin-8 expression and reduced galectin-9 expression, support the hypothesis that galectin-8 may reduce graft survival, whereas galectin-9 may promote graft survival. As a potential therapeutic intervention, inhibition of galectin-8 and/or treatment with exogenous galectin-9 may enhance corneal allograft survival rates.

Corneal sensation after descemet stripping and automated endothelial keratoplasty

PURPOSE

To measure corneal sensation after Descemet stripping and automated endothelial keratoplasty (DSAEK).

METHODS

Prospective comparative case series involving 52 eyes of 29 patients in the early postoperative period (<6 months) after small-incision DSAEK. Patients' contralateral eye served as a control. The sample size calculation was calculated assuming an alpha error of 0.05 and a beta error of 0.2. This determined that a sample size of 11 patients would be sufficient to detect a difference in corneal sensation of 5 mm as measured with the Cochet-Bonnet esthesiometer. The nylon filament was used to measure threshold sensation at 9 points on the operative eye and 5 points on the control. The data were analyzed using the paired samples test.

RESULTS

Although the results demonstrated mild hypesthesia of the corneal epithelium overlying the donor lenticule, we found no statistically significant difference in corneal sensation at the central point when comparing the DSAEK cornea with the control (57 vs 59 mm, P = 0.13.) In addition, when comparing corresponding points on the epithelium overlying the DSAEK graft and host cornea, no significant difference was found (57 vs 58 mm, P = 0.32). A difference was detected when comparing the average corneal sensation of the DSAEK eye with the control, but careful analysis of the data shows that this was driven by the slight decrease in sensitivity at the temporal incisional point (57 vs 59 mm, P = 0.002).

CONCLUSIONS

The results of this prospective study demonstrate the relative preservation of corneal sensitivity after DSAEK. Preservation of corneal sensation may provide another advantage of DSAEK over traditional penetrating keratoplasty.

'Chimeric' grafts assembled from multiple allodisparate donors enjoy enhanced transplant survival

Certain components of a graft that provoke alloimmunity may not be vital for graft function or critical as targets of rejection. Corneal transplantation is an example of this, because graft epithelium plays a role in allosensitization, whereas corneal graft endothelium-which shares the same alloantigens-is the critical target in allorejection. In this study, we found that exploiting this biology by replacing donor epithelium of an allograft with an allodisparate third-party epithelium yields a marked enhancement in transplant survival. Such 'chimeric' allografts consisted of a C3H/He (H-2(k)) corneal epithelium over a C57BL/6 (H-2(b)) epithelial-denuded cornea (or v.v.) and orthotopically placed on BALB/c (H-2(d)) hosts. Conventional corneal allografts (C3H/He or C57BL/6) or isografts (BALB/c) were also transplanted on BALB/c hosts. Alloreactive T-cell frequencies (CD4(+) interferon [IFN]-gamma(+)) primed to the graft endothelium were strongly diminished in chimeric hosts relative to conventionally allografted hosts. This was corroborated by a decreased T-cell infiltration (p = 0.03) and a marked enhancement of allograft survival (p = 0.001). Our results represent the first successful demonstration of chimeric tissue, epithelial-denuded allograft plus third-party allodisparate epithelium, in the promotion of allograft survival. Moreover, chimeric grafting can be readily performed clinically, whereby corneal allograft rejection remains a significant problem particularly in inflamed graft beds.

The effect of ABO blood incompatibility on corneal transplant failure in conditions with low-risk of graft rejection

PURPOSE

To determine whether corneal graft survival over a 5-year follow-up period was affected by ABO blood type compatibility in participants in the Cornea Donor Study undergoing corneal transplantation principally for Fuchs dystrophy or pseudophakic corneal edema, conditions at low-risk for graft rejection.

DESIGN

Multi-center prospective, double-masked, clinical trial.

METHODS

ABO blood group compatibility was determined for 1,002 donors and recipients. During a 5-year follow-up period, episodes of graft rejection were documented, and graft failures were classified as to whether or not they were attributable to immunologic rejection. Endothelial cell density was determined by a central reading center for a subset of subjects.

RESULTS

ABO donor-recipient incompatibility was not associated with graft failure attributable to any cause including graft failure because of rejection, or with the occurrence of a rejection episode. The 5-year cumulative incidence of graft failure attributable to rejection was 32 (6%) for recipients with ABO recipient-donor compatibility and 12 (4%) for those with ABO incompatibility (hazard ratio, 0.65; 95% confidence interval, 0.33 to 1.25; P = .20). The 5-year incidence for a definite rejection episode, irrespective of whether graft failure ultimately occurred, was 64 (12%) for ABO compatible compared with 25 (8%) for ABO incompatible cases (P = .09). Among clear grafts at 5 years, percent loss of endothelial cells was similar in ABO compatible and incompatible cases.

CONCLUSIONS

In patients undergoing penetrating keratoplasty for Fuchs dystrophy or pseudophakic corneal edema, ABO matching is not indicated since ABO incompatibility does not increase the risk of transplant failure attributable to graft rejection.

Corneal Transplant Rejection Rate and Severity After Endothelial Keratoplasty

PURPOSE

To examine the corneal transplant rejection rate and the rate of graft failure subsequent to rejection in the first 2 years after endothelial keratoplasty (EK) and to compare this to background data for similar cases of penetrating keratoplasty (PK).

METHODS

Anonymized data from consecutive cases of EK [deep lamellar (DLEK) or Descemet stripping (DSEK)] for Fuchs corneal endothelial dystrophy or pseudophakic bullous keratopathy operated on before August 2004 were collected in 4 participating centers. The number and timing of rejection episodes and cases of subsequent graft failure were recorded, together with the time to cessation of topical steroid medication. Two-year postoperative findings were compared with background data for similar patients undergoing PK recorded in the Swedish Corneal Transplant Registry.

RESULTS

Rejection episodes were less frequent after EK than PK (P = 0.035). Fifteen (7.5%) of 199 EK cases had a rejection episode in the first 2 years after surgery versus 92 (13%) of 708 PK cases. Graft failure after rejection in EK may have been less frequent than in PK (P = 0.063), with only 1 (6.7%) case of rejection after EK versus 26 (28.3%) cases of rejection after PK proceeding to graft failure. A strong trend toward continued use of low-dose topical steroid medication was observed in the EK group. Eighty percent of EK patients were still taking topical steroid medication 2 years after surgery, whereas topical steroid medication had been ceased within a year of surgery in almost all PK patients in the comparator group.

CONCLUSIONS

Corneal transplant rejection is less frequent and may be less severe after EK than after PK. It is not yet clear whether these apparent differences are simply a product of relatively prolonged postoperative topical steroid cover in EK patients.

Graft failure: II. Ocular surface complications

Risk factors for corneal transplantation failure include both immunologic factors, such as graft rejection, corneal neovascularization, and peripheral anterior synechiae, as well as non-immunologic factors, such as ocular surface disorders (OSD) and glaucoma. This review highlights the necessity of having healthy ocular surface epithelia, tears, and eyelids. It presents different types of OSD, their underlying pathology, and their impact on native cornea and corneal grafts. In addition, a range of proposed donor and surgical factors influencing surface integrity following corneal transplant are addressed. Current medical and surgical research, both pre- and post-operative that promise to further improve the outcome of corneal grafts in the context of OSD are discussed.

Corneal Graft Rejection

Penetrating keratoplasty is the most widely practiced type of transplantation in humans. Irreversible immune rejection of the transplanted cornea is the major cause of human allograft failure in the intermediate and late postoperative period. This immunological process causes reversible or irreversible damage to the grafted cornea in several cases despite the use of intensive immunosuppressive therapy. Corneal graft rejection comprises a sequence of complex immune responses that involves the recognition of the foreign histocompatibility antigens of the corneal graft by the host's immune system, leading to the initiation of the immune response cascade. An efferent immune response is mounted by the host immune system against these foreign antigens culminating in rejection and graft decompensation in irreversible cases. A variety of donor- and host-related risk factors contribute to the corneal rejection episode. Epithelial rejection, chronic stromal rejection, hyperacute rejection, and endothelial rejection constitute the several different types of corneal graft rejection that might occur in isolation or in conjunction. Corneal graft failure subsequent to graft rejection remains an important cause of blindness and hence the need for developing new strategies for suppressing graft rejection is colossal. New systemic pharmacological interventions recommended in corneal transplantation need further evaluation and detailed guidelines. Two factors, prevention and management, are of significant importance among all aspects of immunological graft rejection. Preventive aspects begin with the recipient selection, spread through donor antigenic activity, and end with meticulous surgery. Prevention of corneal graft rejection lies with reduction of the donor antigenic tissue load, minimizing host and donor incompatibility by tissue matching and suppressing the host immune response. Management of corneal graft rejection consists of early detection and aggressive therapy with corticosteroids. Corticosteroid therapy, both topical and systemic, is the mainstay of management. Addition of immunosuppressive to the treatment regimen helps in quick and long term recovery. Knowledge of the immunopathogenesis of graft rejection may allow a better understanding of the immunological process thus helping in its prevention, early detection and management.

Regeneration of the epithelium in organ-cultured donor corneas with extended post-mortem time

PURPOSE

The maximum post-mortem time limit for obtaining donor corneas varies between eye banks. It is not known for how long a time the epithelial cells survive post-mortem, nor is it known if donor corneas with extended post-mortem time are able to regenerate the epithelium. Therefore, we wanted to examine the epithelium in donor corneas for regenerative ability during storage in an eye bank organ culture system.

METHODS

Twenty-four paired donor corneas with post-mortem time from 28 to 163 hr were obtained. One cornea of a pair was fixed immediately to serve as a control, and the second was cultured in eye bank medium at 32 degrees C for 3 days. Examination of the specimens was performed with light and scanning electron microscopy. Immunohistochemical staining methods with antibodies against K 3, K 19, vimentin and p63 were used to further characterize the cells.

RESULTS

The control corneas showed decreasing amounts of epithelial cells with increasing post-mortem time. All the cultured corneas demonstrated rapid regeneration of the epithelium. After 3 days in organ culture, 10 of 12 donor corneas were covered with epithelium.

CONCLUSION

Even up to 7 days post-mortem, viable cells reside in the corneal epithelium. The study demonstrates the hardiness and enormous regenerative potential of peripheral corneal cells. Donor corneas processed in an eye bank organ culture storage system will obtain an intact epithelial layer within a few days.

A Review of Randomized Controlled Trials of Penetrating Keratoplasty Techniques

PURPOSE

To assess the effects of variations in operative technique on the outcomes of penetrating keratoplasty (PK).

METHOD

Systematic literature review of published randomized controlled trials of operative techniques in PK.

MAIN OUTCOME MEASURES

Visual acuity, refractive error, endothelial cell density, graft rejection, intraocular pressure (IOP), and other surgical complications.

RESULTS

Twenty-seven trials were identified. Many involved small numbers, some of which were probably compromised by inadequate statistical power. There was some limited evidence from a small number of studies (usually 1 or 2) for preoperative cauterization of the cone in keratoconus, excimer laser trephination, taking into account the effect of trephine sizing on postoperative IOP, taking into account the effect of trephine sizing on postoperative spherical equivalent, using sodium hyaluronate, avoiding vitrectomy if possible, using an iris-fixated posterior chamber lens implant in the absence of capsular support, and adjusting a single continuous suture intraoperatively if used. However, there was little convincing evidence for choosing interrupted suturing versus continuous suturing or for an effect of suturing on final sutures-out astigmatism. Likewise, there was no convincing evidence for the superiority of any lamellar alternative to PK for deep stromal disease. Overall, most of the effects of changing technique were small, and there was no evidence for the superiority of any specific technique in terms of improved quality of life or cost-effectiveness.

CONCLUSIONS

There is a need for further studies with which to refine decision-making as regards the choice of operative techniques in PK.

Prevention and Treatment of Corneal Graft Rejection

PURPOSE

This study was designed to analyze current practice patterns in the prevention and treatment of corneal graft rejection and to compare these patterns with previously reported practices.

METHODS

In January 2004, a survey addressing the routine postoperative management of corneal transplants and the treatment of various manifestations of corneal graft rejection was sent to members of The Cornea Society.

RESULTS

Of the 396 surveys, 111 (28%) were returned and analyzed. All respondents used topical corticosteroids for routine postoperative management and treatment of endothelial graft rejection. Prednisolone, in brand or generic form, was used by 37 to 90% for routine management in various clinical scenarios and 81 to 91% for various manifestations of graft rejection at all time points; however, after 6 months, 12 to 26% used loteprednol etabonate for routine management. For routine management of high-risk grafts, 48% used topical cyclosporine in addition to prednisolone. Compared with previous surveys, the use of oral steroids significantly decreased for the routine management of high-risk corneal transplants, and the use of subconjunctival steroids decreased for the management of graft rejection.

CONCLUSIONS

Topical prednisolone remains the mainstay for the prevention and treatment of corneal graft rejection; however, the role of newer agents, loteprednol etabonate and topical cyclosporine, is expanding.

A murine model of interlamellar corneal transplantation

AIMS/BACKGROUND

There are more reagents and information available for immunological studies in the mouse compared with other animals. Unfortunately, the mouse penetrating keratoplasty model is associated with high background inflammation which hinders study of the immune response to the graft. To mitigate this drawback, a murine orthotopic corneal interlamellar transplantation model with mild non-specific inflammation was developed.

METHODS

A 1.5 mm diameter full thickness donor corneal button was placed in a 2 mm diameter recipient corneal interlamellar pocket without placement of a suture. The clinical course of graft status was studied daily for 60 days in 30 allografts (donor strain CBA 101 (H-2k) to recipient NIH (H-2q) and 30 syngeneic grafts (NIH to NIH) by slit lamp biomicroscopy and scored for neovascularisation, opacity, oedema, and granularity. In another cohort of animals, histological observation was performed after 30 minutes and on days 10, 20, 30, and 40 after transplantation (four allografts and four syngeneic grafts per time point). Histological study was also performed on grafts without donor epithelium and on interlamellar pockets without grafts.

RESULTS

There was significantly more neovascularisation (NV), opacity, oedema, and granularity in 24/30 allografts (80%) than in syngeneic grafts. Such grafts were defined as rejected. The median time to rejection was 21 days (range 18 to > 60 days). By histology, some allografts showed moderate to heavy cell infiltration which correlated with clinical scores of NV (4-5), opacity (1-3), oedema (1-3), and granularity (1-3). Such infiltration was absent in other allografts and syngeneic grafts.

CONCLUSION

Surgically, corneal interlamellar transplantation could be accomplished in the mouse and rejection could be clearly defined. The model can therefore be useful for in situ study of cell and molecular aspects of corneal graft rejection.

Systemic cyclosporine in high-risk keratoplasty: long-term results

Systemic cyclosporine (CSA) was given to 43 high-risk keratoplasty patients (vascularisation in three or four quadrants and > 16 stromal vessels): 14 received CSA for 12 months (long CSA group) and 29 for a 4-6 month period (short CSA group). A group of 37 similar high-risk keratoplasty patients received no CSA (no CSA group). In the no CSA group 27 (73%) grafts had rejection episodes compared with 21 (48.8%) in the combined CSA group (p = 0.025). Rejection was reversed in only 23.3% of the no CSA group, compared with 50% and 87.5% in the short (p = 0.06) and long (p = 0.002) CSA groups respectively. Compared with the no CSA group, overall graft survival was better in both the short (p = 0.019) and long (p = 0.0056) CSA groups. This improvement resulted from both a reduction in the incidence, and an increase in the reversal rate, of rejection episodes. The improvement continued after stopping CSA, suggesting that some immunological privilege had been re-established. Acuities of 20/40 or better were achieved by 44.8% and 50% of eyes in the short and long CSA groups respectively, compared with 13.5% of eyes in the no CSA group.

Immunosuppression in corneal transplantation

This paper reviews the clinical post-operative management of keratoplasty and the management of corneal graft rejection. In both instances corticosteroids remain the mainstay of treatment; however, the literature shows a wide range for both route and frequency of administration. Grafts at 'high risk' require more immunosuppressive therapy, but no universally accepted definition of high risk exists and consequently different treatment regimens are difficult to compare and evaluate. Studies using univariate and multivariate survival analysis suggest that recipient corneas can be divided into low, medium and high risk depending on the number of quadrants of vascularisation (avascular, 1-2 quadrants and 3+ quadrants respectively). This wider classification would make the devising and comparing of treatment regimens more consistent. In high-risk cases, corticosteroids alone provide insufficient immunosuppression and systemic cyclosporine is needed in exceptional cases. When managing rejection episodes, a severe reaction involving the endothelium often does not respond to topical steroids alone, and systemic corticosteroids are required. Instead of oral steroids, we now prefer to use an intravenous 'pulse' of 500 mg methylprednisolone: this is at least as effective, avoids prolonged medication, and may confer some long-term benefit.

Progression of visual acuity after penetrating keratoplasty

A consecutive series of 721 eyes was followed for visual acuity changes after keratoplasty in four groups: keratoconus, Fuchs' dystrophy, pseudophakic bullous keratopathy with retained intraocular lenses, and aphakic/pseudophakic bullous keratopathy with secondary implants during keratoplasty. Follow-up ranged from 12 to 84 months. Keratoconus eyes showed the quickest recovery of visual acuity: by 12 months, 91% attained a best-corrected vision of 20/40, and the mean lines of visual acuity for the group plateaued thereafter. The other three groups showed continuing improvement in vision through 24 months. From 3 months through 3 years after keratoplasty, the keratoconus and Fuchs' groups consistently showed better visual acuity levels than either the retained or the secondary implant groups (P less than 0.0001). Reporting changes in visual acuity over time offers multiple advantages compared with providing best-attained or last-recorded visual acuities after keratoplasty.

The use of a single pulse of intravenous methylprednisolone in the treatment of corneal graft rejection. A preliminary report

In corneal graft rejection, rapid reversal of the rejection process is necessary to minimise endothelial cell loss. Ten consecutive patients with acute endothelial rejection were treated with a single 500 mg pulse of methylprednisolone intravenously and topical prednisolone 1% drops hourly. The rejection episode was successfully reversed in eight (80%) of the 10 grafts. This preliminary trial indicates that cortico-steroid pulse therapy may be beneficial in the management of severe corneal graft rejection with the advantage of avoiding prolonged oral corticosteroid therapy.

Immunological aspects of corneal graft rejection

Immunological graft rejection is a major cause of corneal graft failure. HLA class I and II antigens are expressed by various cells within the cornea and during sensitisation of the recipient donor antigens appear to be presented by both donor and recipient antigen presenting cells. Certain donor and host factors have been shown to influence the incidence of corneal graft rejection, and the manipulation of these factors is discussed.

Graft survival in four common groups of patients undergoing penetrating keratoplasty

Graft survival rates and causes of graft failure were evaluated for 1046 consecutive keratoplasties in four groups: keratoconus, Fuchs' dystrophy, pseudophakic bullous keratopathy with retained intraocular lenses (IOLs), and pseudophakic/aphakic bullous keratopathy with secondary lens implants. Patient follow-up averaged 23 months (range, 1-84 months). There was a significant difference in graft survival among the four groups, P less than 0.0001. The keratoconus and Fuchs' groups had the highest survival rates and pseudophakic bullous keratopathy with retained IOLs the lowest rate. Problems with the external surface of the graft caused the largest number of graft failures. Grafts for pseudophakic bullous keratopathy with retained posterior chamber lenses had a significantly higher failure rate from rejection and endothelial decompensation, 5.1%, compared with less than 1.0% in keratoconus, Fuchs' dystrophy, or bullous keratopathy with secondary implants (P less than 0.0005).

Corticosteroids in corneal graft rejection. Oral versus single pulse therapy

Forty-eight patients with corneal grafts with severe endothelial rejection were randomly assigned to two treatment groups. One group of 24 patients received prednisolone acetate 1% drops hourly and a single intravenous pulse of 500 mg methylprednisolone. The other group of 24 patients received the same topical therapy plus oral prednisone 60 to 80 mg daily. Nineteen (79.2%) grafts survived in the group that received pulse therapy compared with 15 (62.5%) grafts in the oral group; the difference was not significant (P = 0.17). However, in patients who sought treatment early (less than or equal to 8 days) survival rates were 92.3% and 54.5%, respectively, which indicated a significant advantage for pulse therapy (P less than 0.05). Pulse therapy also appeared beneficial in preventing subsequent rejection episodes. Five (26.3%) of the 19 surviving grafts in the group that received pulse therapy had a further rejection episode compared with 10 (66.7%) of the surviving 15 grafts in the oral group; the difference is significant (P less than 0.025).

Association between corneal allograft reactions and HLA compatibility

The purpose of this follow-up study is to measure the association between corneal allograft reactions and donor-recipient HLA-A and HLA-B compatibility. Four hundred thirty-eight consecutive adult recipients of corneal grafts with known donor-recipient HLA matching were observed for allograft reactions and failures. Most of the recipients under observation (91%) were well matched for HLA-DR. Of 438 recipients, 158 (36%) completed a 3-year follow-up. Three factors were associated with endothelial allograft reactions: 2 to 4+ corneal vascularization (relative risk, 2.2; P = 0.0006), two mismatched antigens at either the HLA-A or HLA-B locus (relative risk, 2.1; P = 0.0009), and recipient wound size of 8 mm or greater (relative risk, 1.5; P = 0.05). Unexpectedly, a strong association between endothelial allograft reactions and HLA-A or HLA-B incompatibility was found in low-risk recipients defined as unvascularized recipients of a small graft (relative risk, 3.2; P = 0.004). A larger sample size is required to determine if HLA matching offers a solution for recipients with corneal vascularization.

Graft failure after penetrating keratoplasty

Despite the improving results that have been noted with penetrating keratoplasty, graft failure remains a significant problem. The causes of graft failure are quite varied. Primary donor failure, surgical complications, intraocular lens complications, persistent epithelial defects, allograft rejection, infection, glaucoma, trauma, and recurrences of primary corneal dystrophies are common etiologies. In this article, a critical review of the available literature concerned with the factors influencing the many causes of graft failure and their management is provided.

Topical cyclosporine in high-risk corneal transplants

Cyclosporine (cyclosporin A, CsA) is a selective T-cell immunosuppressant that works primarily through inhibition of both antigen presentation and lymphokine production. It has dramatically improved the prognosis for solid organ transplantation. Significant nephrotoxicity has been associated with its systemic use. Topical CsA 2% was used in 11 high-risk corneal transplant patients (8 men; 3 women; average age, 44 years). Ten (91%) of 11 corneas remained clear at an average follow-up of 16 months (range, 6-24 months). All patients had transient epithelial keratitis. Systemic whole blood levels of CsA measured by high-performance liquid chromatography (HPLC) ranged from 14 to 64 ng/ml. All previous reports on the use of topical CsA in high-risk corneal transplant patients have not detected systemic CsA levels.

The role of the limbus in corneal allograft rejection

The state of the recipient peripheral cornea and limbus exerts a strong influence on subsequent corneal graft survival. In particular, graft outcome is influenced by the number of dendritic cells (Langerhans cells) that have infiltrated the graft bed from the limbus. The number of dendritic cells present in the donor button also affects subsequent graft survival.