Introduction 1 2 3 The prevailing storing technique today is the storage of the corneoscleral button. The storage time can be extended by removing the corneoscleral button from the globe. A longer storage time permits greater flexibility in the use of the donor tissue and prevents wastage. In addition in many countries, for different reasons, legal or ethical, corneoscleral disc excision in situ is preferred to the removal of the whole globe. Moreover, the preparation of lamellae and mushroom-shaped grafts from a corneoscleral button is nowadays possible with help of an artificial anterior chamber. With the introduction of the preservation media, corneal surgeons have to rely on highly skilled technicians employed in eye banks selecting and storing the donor tissue. The original hypothermic storage solution, the M–K medium, has been succeeded by other solutions claiming better and longer maximum storage results. The hypothermic method is common all over the world. 3 4 5 6 7 Both storage methods, hypothermic and organ culture will be compared considering technical aspects, tissue evaluation possibilities, storage time, microbiological safety, graft survival and future applications with regard to the increased interest in lamellar grafting. Technical aspects General Procurement and storage techniques have to be performed under aseptic conditions. Increasingly, eye banks have a formally established quality assurance program. This and the increasing regulation may affect banks working on a smaller scale. For example in France the number of operating eye banks reduced form 226 in 1993 to 43 in 2004. Hypothermic storage 1 Fig. 1 Corneoscleral buttons in different vials for hypothermic storage (left) and in the incubator during organ culture (right)  The medium consists of a tissue culture medium, supplemented with antibiotics, deturgescent agents like dextran and chondroitin sulphate to prevent corneal swelling in vitro, and other additives such as energy sources, antioxidants, membrane stabilizing and growth factors to improve the storage capacity. Inspection of the tissue by slit-lamp and/or specular microscope can be performed in a closed system. Organ culture The technique is relatively complicated, despite the fact that nowadays the storage solutions are commercially available. 1 8 9 7 8 7 The necessary transfer of the cornea from the storage to the transport solution averts a stored cornea from being directly available for use. Besides, a minimal storage period is required for microbiological testing. All this makes the technique more complicated than the hypothermic storage method. Tissue evaluation General Irrespective of the storage method(s) used the donor should be adequately screened. Tissue that is potentially hazardous to eye bank personnel and the recipient should be excluded in addition to tissue that poses a risk for the success of the surgery. Physical assessment, serologic testing and evaluation of medical and social history of the donor are mandatory. Routine inspection of the endothelium is also part of the donor evaluation. Moreover, it can play an important role in setting higher and more-uniform quality standards for tissue acceptance. It may also help to increase the donor supply by assessing corneas that may otherwise be arbitrarily excluded for transplantation on the basis of age or time post mortem. The possibilities for evaluation of the endothelium are dependent of the storage method used. 10 Hypothermic storage 2 Fig. 2 Evaluation of the endothelium by specualr microscopy (left) and light microscopy after artificial swelling of the intercellular space (right)  11 Most specular microscopes are equipped with software programs to determine parameters describing the endothelial mosaic in terms of variation in cell shape andthe percentage of hexagonal cells in addition to the assessment of the cell density. The obtained morphometric results may help to standardize descriptions, but only provided the microscopes are well calibrated and the necessary interactive manipulation is performed by an experienced observer. Organ culture 2 12 13 7 14 15 16 17 18 19 20 Storage time General 21 3 22 24 Fig. 3 y x y x y x  Hypothermic storage 25 26 27 28 7 25 7 Organ culture 29 4 30 31 32 33 32 35 Fig. 4 Percentage endothelial cell loss (endothelial cell density before storage minus the cell density after divided by the cell density before multiplying by 100) during routine storage by organ culture is plotted for a given year  Microbiological safety General 36 37 Hypothermic storage 38 39 40 41 42 43 44 43 45 46 38 Organ culture 7 47 7 Sterility may be better with organ culture since microbial contamination will become more readily evident. Organ culture might be considered as the method of choice in circumstances where corneas are suspected of being at a higher risk of contamination. The mandatory reporting of adverse reactions and the central registration of these within the EU area where both the hypothermic and the organ culture techniques are used will demonstrate in time whether the incidence of endophthalmitis really differs between organ culture and hypothermic storage. Graft survival 48 49 33 50 34 35 51 Future aspects 52 53 55 56 57 Conclusions 58 To permit these possibilities the organ culture procedure is more complicated than the hypothermic storage. Well qualified personnel, advice of microbiological laboratory staff, and a well suited facility are essential for a proper organ culture procedure but may also be valuable for hypothermic storage. The higher costs of organ culture have to be balanced against the offered advantages and possibilities not permitted by the hypothermic storage. Whether organ culture will also be the proper storage technique for surgically manipulated corneoscleral buttons remains to be investigated.