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New Technique

The E-DMEK procedure can make a world of difference to the DMEK surgeon

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Descemet's membrane endothelial keratoplasty (DMEK) is a new type of endothelial transplantation described first by Gerrit Melles in 2006. It comprises the transplantation of only the donor Descemet's membrane with endothelium unlike Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) which also transplants donor stroma. DMEK has major advantages over DSAEK in that it provides better vision as well as very low rates of graft rejection. As there is no stroma transplanted, there is also no induced hyperopia. However, it has still not become a widely practised technique the world over mainly due to the steep learning curve associated with it.

The DMEK graft is thin and flimsy and is difficult to handle with ease in the anterior chamber. It is vital to correctly identify the Descemetic side of the graft in order to orient the graft with Descemet's side up. Since the Descemet's membrane is an elastic structure, the graft always curls towards the Descemetic side. During surgery, the final graft orientation should be such that its edges curl upwards. The graft can be stained with Trypan blue dye to enhance visibility, however wash-off of dye can occur during surgery, especially with longer surgical times. Even with a well-stained graft, it is often difficult to identify the Descemetic side as the microscope light falling vertically on the graft passes through the transparent graft without giving much additional information about the graft morphology, orientation or direction of curling. A purely vertical view affects three-dimensional perception and makes surgical decisions difficult. One technique to determine edge curl is by passing a cannula into the anterior chamber to see if the cannula lies below or above the blue stained graft.

However, this is a touch technique, can lead to shallowing of the anterior chamber and can disturb an oriented graft. The hand-held slit lamp may also be used very effectively but this gives only a slit view and not a view of the entire graft simultaneously. It therefore needs to be scanned across the graft and surgical manoeuvres cannot be done simultaneously with slit viewing. Hence, for rapid, easy and successful surgery, it is important to be able to determine in an easy, non-touch manner, without confusion, the way the graft lies within the anterior chamber. It is also important to be able to see and comprehend clearly the graft dynamics as it is attempted to be unfolded so that the surgeon is sure that he/she is doing the right manoeuvre. The entire scenario is worsened by corneal oedema which often co-exists in such patients or increases with increasing duration of surgery.

New technique

A new technique that I have described for making DMEK easier and less dependent on guesses is the Endoilluminator assisted DMEK or E-DMEK. An endoilluminator or light pipe that is used for vitreo-retinal surgeries is used for this purpose. The DMEK graft is prepared and stained. The host Descemet's membrane is scored and stripped and the DMEK graft is injected into the anterior chamber. The microscope light is then switched off and the endoilluminator is held obliquely at the limbus in such a manner that the light is shone into the anterior chamber and onto the DMEK graft. The tangential light from the endoilluminator is used to comprehend details of the DMEK graft, its position, folds in the graft and orientation of Descemet's membrane versus endothelium with respect to overlying stroma. The angle of incident light can be changed and the probe may be moved around the limbus to help comprehend the entire graft morphology.

As the light is incident from an angle and not vertical, striking three-dimensional depth perception is obtained secondary to reflexes from the light bouncing off the edges of the graft as well as by seeing the movement induced in the graft by fluid currents/gentle tapping. The direction of curvature of graft edges, and thereby graft orientation is confirmed by tapping the host cornea gently and appreciating light reflexes (see figures; Video file). As and when required, the surgeon may switch between working with either the endoilluminator or the microscope light or both.

However, best three-dimensionality is obtained with only the endoilluminator light alone. The endoilluminator probe may be held by the surgeon or the assistant. Using E-DMEK, the graft is thus oriented the right way up, unfolded and centred following which it is floated up with air. Surgery is finished by checking IOP and light perception and the patient is asked to maintain a supine position for 24 hours.

The major advantage that E-DMEK gives is that the entire extent of the graft can be easily visualised three-dimensionally, thus clearing any doubts in the mind of the surgeon regarding orientation, morphology, position etc. Graft dynamics can be better comprehended leading to easier and faster surgery. This has the advantage of decreasing graft damage secondary to prolonged surgery, excessive fluidics and unnecessary manipulation. Though the increased visibility and three-dimensional depth perception that is obtained is very useful in DMEK with relatively clear corneas, it becomes even more invaluable when visibility is already compromised secondary to corneal oedema or dye washout. Graft orientation can be checked by seeing the reflexes bouncing off the edge of the graft on very gently tapping the cornea thus helping the surgeon to conclusively determine whether or not the graft is flipped. This is done while maintaining a no-touch technique, thus decreasing cell loss in the graft. Surgery can be sped up because of better visualisation of the whole graft, thereby decreasing graft damage.

The E-DMEK technique can also be translated into the latest form of endothelial keratoplasty – Pre-Descemetic endothelial keratoplasty (PDEK) as Endoilluminator assisted PDEK or E-PDEK. Prof Agarwal, who brought out the technique of PDEK which includes transplantation of the Pre-Descemetic or Dua's layer with the Descemet's membrane and endothelium says, "The E-DMEK technique makes a world of difference to the DMEK surgeon. It is extremely helpful in all the intracameral steps of surgery. I use it in every single case of both DMEK and PDEK as I know it will make all the difference to the surgery and the postoperative outcomes."

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