University of Texas (UT) Southwestern Medical Center ophthalmologists have identified an important cause of why secondary corneal transplants are rejected at triple the rate of first-time corneal transplants. The cornea, the most frequently transplanted solid tissue, has a first-time transplantation success rate of about 90 percent. But second corneal transplants undergo a rejection rate three times that of first transplants. "Understanding why these rejections occur is important to further improving the ways in which corneal transplants are performed," said the study's senior author Dr. Jerry Niederkorn, Professor and Vice Chair of Research of Ophthalmology, and Professor of Microbiology. "In the future, ophthalmologists may be able to implement processes, and eventually prescribe medications, that can lower the rates of rejection." More than 40,000 transplants are performed annually to replace the cornea, the clear outer lens at the front of the eye, with tissue from a donor. Most corneal transplants are done to correct severe visual impairments caused by keratoconus, a condition in which the normally dome-shaped cornea progressively thins and becomes cone-shaped, according to the American Academy of Ophthalmology. The high success rate of first-time corneal transplants is attributed to a process called immune privilege, which allows transplants to be successfully performed without matching the donor tissue to that of the recipient, as is required for organ transplants. Although immune privilege accounts for the initial high success rate, it can occasionally fail, leading to the rejection of corneal transplants in approximately 10 percent of patients. In patients requiring a second transplant, the incidence of immune rejection rises to almost 70 percent.
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