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Constructing the cornea: hopes and challenges for regenerative medicine

The need for alternatives to cadaveric cornea transplant The first corneal transplant was performed in 1905. Since then corneal transplant surgery has improved greatly. In the past decade, advances in lamellar keratoplasty have made it possible to transplant post erior corneas for corneal endothelial disease or anterior corneas for stromal disease. Limbal stem cell grafts are used for corneal epithelial disease. With improvements in technique come increases in the demand for corneal tissue as more conditions are readily treatable. The WHO estimates that 4.9 million people worldwide suffer from corneal blindness. This number is staggering, even before we consider the estimates for people who are merely visually impaired in one or both eyes due to corneal disease. Currently, the USA (population 313 million) has the most extensive eye banking system of the developed world. The Eye Bank Association of America keeps detailed records of transplants performed annually. In 2011, 46,196 corneal transplants were performed [1]. If a similar rate of transplants were performed worldwide (population seven billion), approximately 1,000,000 transplants would be performed annually. Based on those numbers, it is apparent that there is a worldwide need for donor corneal tissue. There is room for improvement in the USA as well. For those 46,196 corneal transplants that were performed, 114,348 corneas were donated and 18,307 of these corneas were exported internationally. A total of 29,407 corneas were disqualified because they did not meet standards [1]. The leading reasons for disqualification included poor tissue quality on slit lamp exam, positive serology for communicable diseases and medical record or autopsy findings. While the USA sets the standards very high for donor tissue, there is a range of quality of the tissue that meets these standards. Age parameters of acceptability are set, but it is generally believed that younger tissue is preferable. Minimum endothelial cell counts on donor tissue is set, but more is better. Death to preservation time of donor tissue is best when short. The list goes on. Many potential donor corneas are rejected due to positive serology for communicable diseases. Even with testing, the possibility of disease transmission through transplantation remains. Currently not all communicable diseases are testable. Additionally, with these standards comes significant cost. In the USA, the average cost of harvesting, clearing and supplying a cornea for penetrating keratoplasty is roughly US$3000. Preparing corneas for endothelial keratoplasty has additional steps and consequently adds US$1000–1500 to the cost. As the numbers of transplants continue to increase, the annual healthcare costs become increasingly significant. The data are compelling for the need of a substitute for the traditional donor cornea. Worldwide, the lack of donor tissue relative to corneal disease is staggering. In Constructing the cornea: hopes and challenges for regenerative medicine