Thinning of corneal grafts with excimer laser for posterior lamellar keratoplasty – where are the limits?

Abstract

Purpose : The ultrathin DSAEK methods have superior visual results comparing to conventional DSAEK. We have newly introduced an ultrathin DSAEK technique of corneal graft thinning and smoothing using excimer laser (Microkeratome and Excimer Laser assisted Endothelial Keratoplasty - MELEK), which showed good clinical results. The described group of ultrathin graft lamellas had the mean thickness above 100 µm and no damage of endothelial cells after laser treatment was reported. In this experimental study we wanted to proof the possibilities and limitations of the further graft thinning respecting endothelial damage and graft thickness.

Methods : Ten experimental human donor corneas, not suitable for the transplantation, were prepared by a single cut of a microkeratome (Moria, 350 µm) and mounted on an artificial anterior chamber. Afterwards they were smoothed and thinned with an excimer laser (Esiris, Schwind) using an ablation profile of phototherapeutic keratectomy (PTK). A half of each cornea was treated with excimer laser and the other half was covered with a metal mask and served as a control group. The corneal grafts were thinned to 100/80/60/40 and 20 µm. The graft thickness was measured using optical coherence tomography (3D OCT, TopCon) before and after the excimer laser smoothing. We analyzed the thickness of the graft and endothelial cell count of the ablated and control side. We examined the endothelium using trypan blue staining and described the histology and morphology of the corneas.

Results : The mean graft thickness before laser treatment was 263±55 µm and after smoothing and thinning was 53±27 µm (20-96). Three corneal grafts with the thickness of 20 µm, 26 µm and 31 µm were perforated. There were no differences in the endothelial cell count after excimer laser treatment between the ablated group (1663±300 cells/mm²) and the control group (1673±509 cells/mm² ). There was no distinction in morphologic and histopathologic results between the two groups, the trypan blue staining shown no damages of the endothelium in both groups.

Conclusions : The thinning and smoothing of the corneal grafts to the thickness of 40 µm is predictable and safe. The lamella below 30 µm shows a greater risk of perforation. The treatment of the corneal grafts with excimer laser does not influence the endothelial cell count.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.