However, despite all of the immune privilege enjoyed by the human cornea, it can be overcome by trauma, infection and chronic inflammation, all very real possibilities in a postsurgical eye. Keeping transplant rejection from becoming failure starts by educating the patient to monitor for symptoms such as discomfort, light sensitivity, redness and decreased vision. Behind the slit lamp, it is vital to recognize signs, including corneal edema, keratic precipitates or KPs (specifically KPs of the corneal graft but not on the peripheral recipient cornea), corneal vascularization, stromal infiltrates, subepithelial infiltrates, iritis and, in extreme cases, a Khodadoust line.
Some define graft failure as immunological rejection that does not clear in 2 months, therefore appropriate treatment is paramount. Anti-VEGF injections can be used to treat corneal neovascularization. For epithelial and subepithelial rejections, which have a higher rate of reversibility, topical corticosteroids can be started at six times per day or every hour (dosage will depend on severity of rejection and strength of steroid prescribed), with a slow, tapered dosing over several months. In contrast, severe endothelial rejection can require topical corticosteroids prescribed as frequently as multiple times an hour with very close monitoring. Significant cases may call for systemic therapy such as oral prednisone. Unsurprisingly, endothelial rejection alone accounts for more than half of corneal transplant failures.
Even without rejection, the longevity of corneal grafts can vary greatly. All donor grafts lose endothelium with transplantation alone, and one should consider that the majority of graft donors are older with subsequent reduced endothelial density even prior to manipulation and transplantation. More than half of U.S. donors are 60 or older, despite the fact that most eye banks have an age limit of 65 for cornea donors. While studies show that donor age is not an important factor in transplant success, eligible donor tissue can have endothelial cell density as low as 2,300 cells/mm2 (Lass et al.). With this in mind, it should be no surprise that PK often decompensate in 30+ years and there is the possible need for repeat corneal transplant surgery in a patient’s lifetime, especially younger patients. (For example, PK transplants a few decades old can present with Fuch’s-like changes. These patients may benefit from a DMEK on their PK!) DMEK and DSAEK can endure for 20 years or longer. DMEK may possibly have less durability than DSAEK, while a DALK leaves the host’s endothelium intact and is likely to last a patient’s lifetime.
To wrap up, there are different risks for different transplant surgeries, and one must consider the level(s) of cornea affected by disease. A PK transplant is full thickness, DSAEK/DMEK replace endothelium, and DALK effectively replaces the stroma. For these patients, surgical planning is always a balance between the most appropriate transplant, graft longevity, recovery time, potential visual outcome and risk of complication, including the different rates of rejection for different corneal transplants.
When it comes down to it, the cornea remains a great tissue for transplantation with immune privilege as an avascular and alymphatic tissue with ACAID, all of which increases immune tolerance to an ocular antigen such as transplanted tissue. When taking all of these factors into account and selecting and treating our patients appropriately, these can be life-changing surgeries.
Join us next month when we’ll discuss corneal transplant suture manipulation, transplant-specific risks, recovery and expected time to visual stability.
Anshu A, et al. Ophthalmology. 2012;doi:org/10.1016/j.ophtha.2011.09.019.
Gorovoy MS. Cornea. 2014;doi:10.1097/ICO.0000000000000023.
Lass J, et al. Arch Ophthalmol. 2010;doi:org/10.1001/archophthalmol.2010.128.63.
Rahman I, et al. Eye. 2009;doi:10.1038/eye.2008.305.
Sari E, et al. Am J Ophthalmol. 2013;doi:org/10.1016/j.ajo.2013.03.007.