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The first successful penetrating keratoplasty in a human was performed as early as 1906 by Zirm.1 The tissue was obtained from the eye of a living donor requiring enucleation. Much has changed since then. Advances in surgical instrumentation and techniques and the introduction of antibiotics and corticosteroids in the 1950s significantly improved the success rate of corneal transplantation. Consequently, the demand for donor tissue increased. On the one hand, the supply was enhanced by the possibility of using eyes from human cadavers.2 On the other hand, attempts were made to increase the storage time for cadaveric tissue while maintaining the integrity of the endothelial layer. The importance of the corneal endothelium for the maintenance of corneal clarity was convincingly demonstrated by Stocker.3 At about the same time in the 1970s two methods for storage of excised human corneoscleral buttons were introduced in the USA and are currently still applied: hypothermic storage45 and organ culture preservation.6-8
Storage techniques and storage time
In hypothermic storage corneas are preserved at 4°C in tissue culture medium supplemented with antibiotics and with dehydrating agents (dextran, chondroitin sulphate) to prevent corneal swelling. The original M-K medium45 has been succeeded by solutions such as K-sol, Dexsol, and Likorol potentially allowing a storage time exceeding the 4 days thought to be the maximum for the M-K medium. In organ culture preservation corneas are incubated in tissue culture medium supplemented with fetal calf serum, antibiotics, and antimycotics at 30–37°C. The swelling of the cornea, due to the absence of dehydrating agents in the medium, is reversed shortly before transplantation by placing the cornea, in the first instance, in M-K medium at 4°C.9 Currently the swelling is reversed by transferring the corneas to a culture medium supplemented with dextran (4–8%) at room temperature to 37°C. Because …