Introduction
The cornea differs from other tissues or organs in that in its healthy state it is a relatively privileged site for transplantation due to the absence of blood and lymphatic vessels (except for the marginal corneal arcades)1 and a relative paucity of mature antigen presenting cells.2 Despite this, corneal graft failure remains significant with an overall 5-year graft survival for Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK) of 79% (95% CI 76% to 81%), and 59% (95% CI 55% to 63%), respectively.3 4 Corneal transplants fail predominantly from endothelial failure as these cells do not divide and depend on survival of the donor endothelium. Corneal graft rejection and/or inflammation in the recipient are significant causes of endothelial graft failure.3 5
Both donor and recipient factors play a role in graft rejection and failure. Many of the recipient risk factors associated with rejection are well recognised, including young recipient age, number of previous transplants, vascularisation, previous rejection episodes and the indication and type of transplant.6 7 Similarly, donor factors such as endothelial cell density (ECD), donor age, H-Y incompatibility have been shown to play variable roles in graft rejection and failure. Many donor factors such as race,8 lens status,9 harvesting10–12 and preservation techniques8 9 11 13–19 have been studied, but the evidence is often conflicting. A comprehensive summary of the donor factors that have been investigated to influence graft outcome and the associated evidence is provided in online supplemental table 1.8–68
Brightbill and Kaufman drew attention to investigating the outcomes of penetrating keratoplasty (PK) between recipients of paired donor eyes.69 This was based on the findings that pairs of donor eyes have minimal differences in ECD.70 They found that despite a range of recipient corneal diseases, paired grafted corneas showed remarkable similarity in postoperative central corneal thickness.
In this study, the demographics and endothelial outcomes for ‘paired’ corneal transplants were compared with ‘unpaired’ single corneal donor transplants and from donors who donated both corneas but for an alternative indication or regraft. An association between cause of failure and type of rejection for each patient of paired donor transplants was also investigated. The potential similarity in outcomes between transplant recipients of the same donor as well as potential differences between single corneal donors was of interest. It is unclear if corneas from donors where only one eye is suitable for transplant, differ in quality from corneas from donors where both eyes are issued for transplantation and whether this has a bearing on graft outcome. Patients with FED and PBK patients were selected because rejection and failure is due to endothelial failure and in particular, patients with FED are a relatively homogeneous group with few risk factors. Additionally, other donor factors were explored such as donor age, ECD and gender mismatch to determine whether these factors were associated with an increased hazard of endothelial graft failure and rejection. As well as recorded donor factors, an unknown donor effect was fitted to account for unexplained donor to donor variation and for any correlation between pairs of corneas from the same donor.