Managing Corneal Grafts
BY WILLIAM L. MILLER, OD, MS, PHD, FAAO
Corneal transplantation is largely successful, with a nearly 90% success rate in low-risk cases lacking vascularization, even without systemic immunosuppressive drugs (Qazi and Hamrah, 2013). This is largely due to the cornea’s avascular nature, which protects it from the inflammatory effects of vascular elements. This also limits the possibility of corneal graft rejection. The younger the patient is at the time of graft transplantation, the greater the risk of graft failure over the patient’s lifetime due to the robust nature of the immune system in younger patients.
Signs and Symptoms
The Corneal Research Foundation advises patients to think of “RSVP” when monitoring the success of their corneal graft. The acronym stands for redness, sensitivity, vision, and pain.
Graft rejection can occur within weeks or months postoperatively. Practitioners should monitor the cornea at each exam. This becomes more essential in high-risk patients, including those who have vascularization in two or more quadrants that extends 2mm or more into the stroma; previous graft rejection; and inflammation as a result of bacterial, fungal, or viral keratitis. Additional high-risk issues include ocular surface disease such as severe dry eye, Sjögren’s syndrome, Stevens-Johnson syndrome, or neuroparalytic disease.
Involvement based on corneal anatomical position can also be used to assess the seriousness of the graft rejection. Stromal and endothelial involvement dictate a more aggressive approach to treatment and management due to the more guarded prognosis in these cases. Epithelial rejection can be asymptomatic with only slight inflammation. It represents the mildest form of graft rejection and is treated the least aggressively. Look for neovascularization into the donor graft as well as signs of conjunctival or circumlimbal hyperemia, subepithelial infiltrates in the donor tissue, stromal edema or haze, keratic precipitates (KPs), and cells or flare (Maumenee, 1962; Krachmer and Alldredge, 1978). KPs lined up on the endothelium is classically known as a Khodadoust rejection line (Khodadoust and Silverstein, 1969); an increase in corneal thickness, an endothelial rejection line, and more than five KPs are indicative of severe graft rejection.
Pre- and Post-Op Care
High-risk host corneas typically undergo preoperative steroid administration q.i.d. for one week prior to surgery. Routine post-op use of topical steroids can consist of instillation every hour for a few days followed by q2h for two weeks, q.i.d. for two months, b.i.d. for three months, and q.d. for four months (Panda et al, 2007). Intraocular pressure should be measured throughout the treatment regimen because of the effects of long-term use of topical steroids.
If the stroma or endothelium is involved, incorporate additional treatment regimens while increasing topical steroid instillation. Additional treatments can include subconjunctival steroid injections, oral steroids (60mg to 80mg daily, continued for as long as two weeks) and intravenous (IV) steroids (given in a pulsed therapeutic single IV dose of 500mg methylprednisolone). Topical cyclosporine A has also been used with topical or IV steroids in cases of more severe graft rejections. Other immunomodulators reported in the literature include oral forms of tacrolimus, rapamycin, and mycophenolate mofetil (MMF) (Joseph et al, 2007; Birnbaum et al, 2006; Reinhard et al, 2005; Birnbaum et al, 2009). In cases of increasingly severe rejection that are not responding to therapy, refer patients to a corneal specialist for management and possible repeat graft surgery if the donor cornea fails. CLS
For references, please visit www.clspectrum.com/references and click on document #226.
Dr. Miller is an associate professor and chair of the Clinical Sciences Department at the University of Houston College of Optometry. He is a consultant or advisor to Alcon and Vistakon and has received research funding from Alcon and CooperVision and lecture or authorship honoraria from Alcon and B+L. You can reach him at email@example.com.