Descemet's membrane endothelial keratoplasty and corneal transplantation

Descemet's membrane endothelial keratoplasty (DMEK) is emerging as the best technique for eyes requiring cornea transplantation because of endothelial dysfunction and taking a little extra care in each stage of the procedure can make it a lot easier, said Friedrich Kruse MD, University of Erlangen, Germany. Dr Kruse, delivering the Keynote Lecture at the Annual Cornea Day, noted that endothelial keratoplasty offers the advantage of an unchanged anterior corneal surface and therefore better visual outcomes. However, results with Descemet’s membrane stripping automated endothelial keratoplasty (DSAEK) have been somewhat marred by the stroma-to-stroma interface. Better visual results have been achieved with DMEK, in which only the Descemet’s membrane and the corneal endothelium is transplanted. However, many surgeons find the technique technically difficult. Dr Kruse told the congress that many of those difficulties can be largely overcome through the use of stepwise approach to patient selection, donor tissue preparation and implantation surgery. The ideal patients for surgeons who are just learning the technique include those with myopia or emmetropia and those with larger than normal corneal diameters. Patients best avoided are those with shallow anterior chambers, significant hyperopia, thick crystalline lenses, aphakia, iris defects or vitrectomised eyes. When selecting donor tissue older eyes with high endothelial cell counts are best, due to the tendency of younger donor endothelial buttons to roll up excessively. Organ cultured eyes also appear to be the best source for donor tissue, he said. Steps to facilitate preparation of donor buttons for DMEK procedure include the placement of the corneoscleral buttons onto a suction block, such as is commonly used to prepare DSAEK tissue, in conjunction with the use of a Moria DSAEK trephination system. In addition, to prevent placing donor button upside down, he suggested making three circular marks in an identifiable order at the edge of the donor disc. As regards the insertion of the graft, Dr Kruse said that after trying various techniques, he has found that injecting the rolled tissue with an air bubble already inside it with an IOL injector of the type used for micro-incision IOLs seems to be the best approach. He added that his results to date seem to bear out the theory behind the technique. For example, at 12 months’ follow-up visual acuity is 20/40 or better in 90 per cent of patients and 20/25 or better in 90 per cent. However, endothelial cell density is a cause for concern, in his first patients it fell to 1420 cells/mm2 at 12 months’ follow-up. “With this technique we can tell our patients that by three months their refraction will be stable and they can be fitted for glasses. As regards the loss of endothelial cell density this represents our learning curve and I think the results we are currently achieving are much better,†he concluded.