Transplantation

Thinner lamellar endothelial grafts result in better visual outcomes sooner after surgery compared to thick lamellar grafts or penetrating keratoplasty (PKP), according to a study presented at the 2013 Congress of the European Society of Ophthalmology. “According to our results on a relatively small number of eyes, the thinner lamellar endothelial grafts obtained using ultra-thin Descemet’s stripping automated endothelial keratoplasty (UT-DSAEK) provides faster and more complete visual rehabilitation as compared to conventional DSAEK,” Iva Dekaris MD, PhD told delegates. While corneas with thicker grafts do eventually improve in terms of visual results, they do not, however, attain the level of best-corrected vision obtained with ultra-thin grafts, noted Prof Dekaris, and the advantage of quicker visual recovery is lost. Although PKP has been the mainstay of treatment for corneal diseases for the best part of a century, lamellar surgery has become increasingly popular in recent years, said Prof Dekaris, and now makes up about half of all corneal transplants in the US and approximately 25 per cent of those in Europe, with DSAEK the most commonly used lamellar technique. The advantages of DSAEK have already been well established in the scientific literature, said Prof Dekaris, highlighting the fact that it is safe and technically straightforward compared to more complex surgical procedures such as Descemet’s membrane endothelial keratoplasty (DMEK), in which only Descemet’s membrane is transplanted. Although technically more difficult, the principal advantage of DMEK over DSAEK is its superior visual outcomes, said Prof Dekaris. “There are pros and cons to every medical procedure and the biggest drawback of DSAEK is the fact that many patients do not obtain postoperative vision of 20/20, and in DMEK we know that they do,” she said. Understanding why DMEK patients obtain better visual results prompted Prof Dekaris and other researchers to explore possible links between graft thickness and postoperative outcomes. “When we started to prospectively follow our DSAEK cases we asked ourselves whether graft thickness matters, but at the time in 2010 there were only two scientific papers with small patient numbers that sought to address this issue. We knew for sure that DMEK patients do better regarding vision and perhaps it was not just coincidence that the thinnest graft is that produced in DMEK procedures,” she said. To test the hypothesis, Prof Dekaris and co-workers carried out a prospective case study of 20 eyes that underwent UT DSAEK (group 1) and 30 eyes that had conventional DSAEK (group 2), all for the treatment of pseudophakic bullous keratopathy (Figure 1). Both surgeon-cut and “pre-cut” tissue obtained from certified eye banks was used and all patients underwent serial central graft thickness measurements with non-contact optical coherence tomography (Zeiss Visante™ AS-OCT) at various time points after surgery.   The eyes in the conventional DSAEK group were further subdivided into three subgroups based on first day postoperative endothelial graft thickness, said Prof Dekaris: thin grafts with a lamellar thickness less than180 μm, medium-thick grafts of between 180 and 250 μm and thick grafts over 250 μm. The differences between the groups regarding best spectacle-corrected visual acuity (BSCVA) and endothelial cells density loss were recorded. Noting that there was no statistically significant difference in age, sex, or preoperative BSCVA between groups, Prof Dekaris said that the median postoperative graft thickness in group 1 was 78 μm and 190 μm for group 2, with a follow-up of between three and 36 months. In terms of visual outcomes, the UT DSAEK group achieved better postoperative BCVA both in quantity and speed of recovery (mean BCVA of 0.75 and 0.8 at one and three months, respectively), compared to all conventional DSAEK groups, said Prof Dekaris. The thin DSAEK grafts of less than 180 microns recorded the best visual acuity among the three DSAEK subgroups and attained a mean BCVA of 0.6 at six months postoperatively. By contrast, thick grafts never reached the same BCVA score of either ultra-thin or thin DSAEK grafts, she said (Figure 2). To illustrate the difference in visual recovery, Prof Dekaris showed one case study of a patient who had PKP in one eye and ultra-thin DSAEK in his fellow eye. At three months he had BCVA of 0.35 in PKP and 0.95 in the UT-DSAEK eye (Figure 3). “We can see that the speed of visual recovery is drastically different between the PKP and UT-DSAEK eyes. The tempo of visual recovery between conventional DSAEK and ultrathin DSAEK in different eyes of the same patients was objectively better in UT-DSAEK, reaching BCVA of 0.9 at one month, as compared to 0.7 in conventional DSAEK. However, patient observations were that they do not see much difference between the two operated eyes,” she said. Summing up, Prof Dekaris said that the study showed that only lamellar grafts of 180 microns and less obtain good visual quality in conventional DSAEK with results superior to PK eyes over the long term. Furthermore, ultra-thin DSAEK provides faster and more complete visual rehabilitation compared to conventional DSAEK. “I would echo Dr Melles’ saying that 'not only one road leads to Rome' and at this time the range of different endothelial keratoplasty procedures allow us to manage each case based on the patient's individual needs. We would emphasise, however, that DMEK is safer regarding graft rejection and we do need more data going forward to see how ultra-thin DSAEK performs in this respect,” she concluded.