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How much of an opportunity is quarter-DMEK for eye banks?
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Great opportunity for international eye banks
Using quarter segments of a DMEK graft for four separate patients is a great opportunity for eye banks internationally. Unlike in the U.S., where we are lucky enough to have reached saturation, shortage of tissue is a huge, chronic problem in many parts of the world. Quarter-DMEK offers the opportunity to utilize the tissue more effectively, meeting the growing demand for transplantation.
Quarter-DMEK also combines the benefits of descemetorrhexis with a safety net given by a graft. The quarter graft ensures rapid recovery of vision in the central visual axis while the cells migrate and/or repopulate the periphery. Another potential benefit of quarter-DMEK is that it follows the “less is more” idea, which is so true for corneal grafting. PK has a pretty good success rate, but it is still lower than DSAEK, and the success rate of DSAEK is lower than DMEK because the less tissue you are able to transplant, the less likelihood for rejection. With quarter-DMEK, there may be even fewer rejections because you are implanting one-fourth of a DMEK tissue.
There is also an added value for research in this technique. If you have four grafts from the same cornea that are implanted in four different patients and all four fail to attach, it may indicate that failure is more tissue-related than anything else. On the other hand, if two attach and two do not, this may indicate that the failure is more about the technique for instance. So, quarter-DMEK can also be an important source of information.
While I am not a surgeon, I see a lot of benefits for quarter grafts, certainly internationally, where there is a shortage of tissue. It can make a great impact.
Alan Blake, CEBT, CTBS, is executive director of Alabama Eye Bank. Disclosure: Blake reports no relevant financial disclosures.
Not needed in US, may lead to insufficient ECD
Supply of tissue in the U.S. currently exceeds the demand ,and excess corneal tissue is being exported. The number of DMEK grafts is well below the number of DSAEK’s but on the increase. DMEK has a more stringent criteria compared with DSAEK. Surgeons request shorter death-to-preservation, age minimum of 40 to 50 years and up to age 70 years, and endothelial cell density (ECD) of 2,500 cells/mm2 or higher. However, despite the higher criteria and limitations of the donor pool, there is still a supply sufficient to meet the demand for scheduled surgery.
Quarter-DMEK is a smaller area, up to 40% of the size of a standard DMEK, meaning 40% of the possible number of cells available to cover the recipient area of stripped Descemet’s membrane. I think that 125,000 cells to start with a DMEK graft is always going to be preferred over a graft that has only 50,000 cells (calculation based on a 8-mm graft 2,500 ECD). Although DMEK surgery has evolved over a decade in the hands of many skilled surgeons, the amount of cell loss is still significant, up to 30% based on some published papers. So it makes more sense to start off with as many cells as possible and to use a graft that is the same size as the stripped area.
The available donor tissue includes all ages. To increase the availability of tissue for DMEK, techniques that can utilize tissue from donors under age 40 years may be a better choice than either a hemi- or quarter-DMEK. One of them is the DMAEK procedure described by Francis Price, MD. DMAEK grafts may be a solution to increase the donor pool for DMEK-like grafts and provide a graft that can be inserted like a DSAEK and with visual results almost as good as DMEK, providing an even better reserve of younger healthy endothelium.
Mark C. Soper, BS, CEBT, is manager of processing and surgeon relations, VisionFirst, Indiana Lions Eye Bank. Disclosure: Soper reports no relevant financial disclosures.