Surgical innovations

Two of the latest iterations of endothelial keratoplasty have the potential to simplify surgery and to make more efficient use of donor tissue, Gerrit Melles MD, PhD, Director, Netherlands Institute for Innovative Ocular Surgery (NIIOS), told a session of the World Cornea Congress VII in San Diego, USA.

Dr Melles, who played a key role in the development of Descemet’s membrane endothelial keratoplasty (DMEK), discussed hemi-DMEK and Descemet’s membrane mediated endothelial transfer (DMET).

“The first problem facing our field is that we have a tendency to produce more acronyms than Apple can produce apps,” he said.

“With all these new innovations you have to evaluate from a starting point, probably DMEK, which produces very good results for us. If you want to come up with something new it really has to be much better, otherwise why do it?”

DMET involves injecting free-floating donor Descemet graft in the recipient anterior chamber following Descemetorhexis on the host. The cornea clears over a period of weeks, with endothelial tissue covering the exposed posterior stroma. Patients undergoing DMET experience visual results similar to those seen with DMEK. Results seen in the treatment of Fuchs' dystrophy have caused Dr Melles to question the nature of that disorder.

“We’ve seen a lot of evidence that host cells in Fuchs’ are still potent, and capable of migrating. If you remove the Descemet’s membrane, the cells in Fuchs’ may be capable of clearing the cornea. We have seen cases where a large detachment clears up sometimes with a visual acuity of 20/20. This does not happen in bullous keratopathy,” he said.

He hypothesises that something in the host endothelium is determining whether the cornea is going to clear. The host endothelium in Fuchs’ might be lacking some factor they need, and when that factor is introduced with donor tissue, it functions in the normal way.

“If that is true then the whole concept of Fuchs' as dystrophy is called into question. In my opinion Fuchs' is not a dystrophy. It is a dysfunctional state of the cell. If we can reverse that state with cell injection or donor to the interior chamber, we may actually solve the problem,” added Dr Melles.

However, Dr Melles stopped short of calling DMET the next big step, noting that from the clinical point of view it takes much longer for cornea to clear when using the free-floating donor. Patients might wait months to achieve good vision, while with DMEK patients are doing well after one month.

Another innovation, hemi-DMEK, originated as a way for use of donor tissue that was previously going to waste. Hemi-DMEK involves dissecting the entire Descemet’s membrane, then cutting it in half so that there are two half moon shaped grafts. The surgical technique is the same as DMEK, but requires a different technique at the eye bank. Visual acuity results are also similar to those seen with standard DMEK procedure, with the principal advantage being that one donor cornea can be used for two procedures.

Dr Melles emphasised that DMEK provides faster and better visual rehabilitation, and is associated with a similar pattern of reduction in endothelial cell density compared with traditional keratoplasty. The complication rates seen early on with DMEK were affected by the surgical learning curve, but it now appears that after proper training the rates of complications were significantly reduced to low levels.

“I always thought we could have done a better job of standardising the deep lamellar endothelial keratoplasty (DLEK) and Descemet’s stripping endothelial keratoplasty (DSEK) procedures. We are now standardising the way we teach DMEK. Students can learn the nuances at course taught at NIIOS and at conferences such as the ESCRS, and can follow up by watching many good videos available at NIIOS, YouTube and elsewhere. It is easy to learn and the learning curve is not too long. If you want to start with DMEK now you can learn and understand every step and learn every little detail.

“DMET may not really compete well with DMEK, but it may be a most interesting next step from a scientific point of view, because it opens the door to other treatment options, that is, not a ‘keratoplasty’ per se as we know it, but more towards a tissue-directive therapy,” said Dr Melles.

Gerrit Melles: melles@niios.com