الفهرس 
Etiology of Corneal Graft RejectionOnly 14 pages are availabe for public view
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Abstract
The immune privilege of corneal allografts relies on disarming each of the three components of the immune reflex arc; afferent, efferent, and central.
Graft rejection is now the leading cause of corneal transplant failure. Compared to other forms of solid organ transplantation, which require systemic immunosuppressive treatment and HLA typing, corneal transplantation commonly enjoys a success rate of up to 90% while relying only on the use of topical corticosteroids as the sole immunosuppressive modality to prevent immune rejection.
The first step in combating graft rejection is to identify high-risk factors, including vascularized corneas, multiple previous corneal grafts, extremes of age, inflamed or, chemical burns. In terms of preoperative care, it is vital to quieten the eye as much as possible whether by using topical steroids or other measures to reduce inflammation.
Vascularization of the graft bed greatly influences the incidence of graft rejection. Treatment of corneal vascularization involves the suppression of vessel growth by the appropriate use of topical steroids. It is important to occlude as many mature blood vessels as possible. Blood vessels can be occluded with an Argon laser.
The importance of human leukocyte antigen (HLA) matching also helps in achieving a successful corneal graft, while ABO blood type matching can also be performed, this is clinically less practical.
Despite the corneal immune privilege, graft rejection is a major complication of PKP as they facilitate subsequent graft failure.
Higher frequency postoperative topical steroids regimen, closer patient follow-up, and more aggressive treatment of suspected or proven episodes of rejection prevent the need for histocompatibility matching.
Treatment of graft rejection depends on the type of rejection; however, in all cases, topical corticosteroids are the mainstay of treatment. Epithelial or stromal rejection without endothelial involvement usually does not progress to graft failure. As previously noted, epithelial rejection may be a self-limited process. Nonetheless, epithelial and stromal rejection should be aggressively treated, because they indicate host immunologic recognition of the graft and may precede to a more severe endothelial rejection.
Postoperative measures to be taken include patient education for symptoms of graft rejection which is important in early diagnosis and initiation of treatment. Topical steroids are essential component of the postoperative care regimen and can be used for much longer than usual – up to 18 months or 24 months. However for high risk keratoplasty topical steroids are not effective in guarding against graft rejection in a high-risk situation, it is crucial not only to work with topical or systemic steroids but to employ immunosuppressive substances systematically.
The management of high-risk keratoplasty continues to be a significant clinical challenge. It is recommend indefinite use of topical steroids and topical CsA in all high-risk grafts. In patients with multiple graft failures, require a multi-drug regimen consisting of oral steroids , CsA or tacrolimus , and azathioprine, MMF, or rapamycin may be considered. The patients will need careful monitoring for the potential side effects. In addition, an investigational slow-release drug implant provides a means for achieving significantly higher local concentration of cyclosporine A in transplanted eyes, compared with levels achieved by either topical or systemic delivery.
Draining lymph nodes removal may help to prevent graft rejection and show promises in reducing the burden of side effects of systemic immunosuppressive drugs.
In terms of surgical measures the surgeons can take steps to help reduce the chances of graft rejection, for example, graft sizing which is very important, suture management, and intraoperative intravenous steroids which is potentially significant.
With continuing advances in molecular biology and immunology, the development of safer and more specific immunosuppressive agents as well as strategies for the immunomodulation of the corneal graft before transplantation can be expected. Until then, early recognition and immunosuppression will continue to be the most important factors in preventing graft failure.
Genetics has always been a very important branch of medicine and recent advances have made a major contribution in understanding and treating many ocular diseases.