In short

In up to 50% of all penetrating keratoplasty (PK) procedures the indication for surgery is endothelial decompensation and provided there are no stromal opacities or high-degree astigmatism (i.e. in failed grafts), new endothelial cells are all that is needed for the cornea to clear up.

For this reason Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) was developed and in recent years it has gained widespread popularity. With this procedure the recipient cornea is maintained, with the exception of the complex Descemet membrane and endothelium, which are removed from the central part (usually 9 mm in diameter) of the posterior corneal surface. The donor graft consists of a thin lamella (usually between 100 µm and 200 µm in thickness) of deep stroma carrying the donor Descemet membrane and endothelium and is attached to the recipient cornea by means of an air bubble. Although cornea clarity is re-established by DSAEK in a relatively short period of time, the resulting stromal interface is considered by some authors a limiting factor for final visual acuity (VA).

From DSAEK to DMEK

In 2006, to overcome the supposed limitations of DSAEK, Dr Gerrit Melles from Holland presented a new procedure, which he named Descemet membrane endothelial keratoplasty (DMEK). With this procedure only donor Descemet and endothelium are transplanted onto the posterior corneal surface of the recipient eye. Manual stripping and dissection by means of specially designed micro-instruments (spatula, hook, etc.) are employed to separate the donor Descemet's membrane together with the endothelium from the overlying stroma. The donor endothelial graft can then be preserved rolled up in a special syringe and shipped to the surgeon for transplantation.

Technical obstacles

To date, several technical problems relating to Dr Melles's technique have limited the popularity of DMEK among corneal surgeons. In particular, waste of donor tissue when detaching Descemet from overlying stroma should be avoided, while manipulation of donor tissue during delivery and positioning should be minimized.

Figure 1: The Descemet membrane and endothelium are removed from the central part of the posterior surface of the recipient cornea.

We have developed a new technique to prepare and transplant donor endothelial grafts which minimizes the waste of donor tissue and allows safe transportation as well as easy manipulation.

First steps

Figure 2: A 25 G needle connected to a 5 cc syringe is inserted into the donor cornea, endothelium face-up.

At the beginning of surgery, the Descemet membrane and endothelium are removed from the central part (8 to 9 mm in diameter) of the posterior surface of the recipient cornea (Figure 1). Then the donor cornea is laid with the endothelium facing up and a 25 G needle connected to a 5 cc syringe is inserted bevel up into its periphery at about 1 mm from the limbus and immediately beneath the endothelium for about 2 mm (Figure 2). Air is then injected until detachment of Descemet membrane is achieved and a large bubble is obtained (Figure 3).

Figure 3: Injected air detaches the Descemet membrane.

This part of the preparation can be performed either by the surgeon at the table or by a technician in the eye bank. In the former case, surgery will follow according to the technique described below, while in the latter case the cornea with the 'endothelial-Descemet bubble' can be stored in tissue culture medium for up to seven days before delivery to the surgeon.