The mainstay of corneal transplant practice is the transplantation of corneal tissue that has been procured from people who have died and had agreed to donate their tissues after death for the benefit of others. Because the donor and the recipient of the corneal transplant have different tissue types, this is referred to as an “allogeneic transplant” and has potential for immunological complications such as acute rejection. Rejection, mediated by anti-donor immune responses, is the most important contributing factor to corneal transplant failure.
Immune rejection may affect each or all the 3 cellular layers of the cornea and is generally diagnosed by the presence of symptoms (pain, redness and decreased vision) and/or physical signs (hyperaemia, oedema, precipitates and cloudiness). Acute rejection of the endothelium is the most immediately threatening immune complication as the endothelial cell layer has limited ability to regenerate following damage and loss of endothelial integrity results in persistent oedema of the cornea and visual impairment. The occurrence of one or more episodes of acute rejection is associated with reduced long-term graft survival.
Rejection risk is increased considerably by the presence of active inflammatory or infectious eye disease at the time of transplant or during the postoperative period. Furthermore, previously failed transplants are also associated with a heightened risk of rejection of re-transplants, implying that anti-donor immune responses to corneal transplants are long-lived and associated with recurrent and chronic damage.
Immunosuppressive therapy following corneal transplantation is currently tailored to the baseline and peri-operative clinical risk factors for acute rejection. In recipients with low initial rejection risk, topical corticosteroid (steroid eye drops several times a day) is the only routinely prescribed treatment for the first 6 to 12 months after transplantation. Acute rejection is most commonly treated with intensive topical corticosteroid therapy, sometimes accompanied by corticosteroid tablets or intravenous injections.