Excimer laser smoothing of endothelial keratoplasty grafts

Abstract

Purpose: To use excimer laser smoothing passes to reshape Descemet-stripping automated endothelial keratoplasty (DSAEK) endothelial grafts and to evaluate the effect on the donor endothelium.

Methods: The stromal surface of microkeratome-cut DSAEK grafts was smoothed using excimer laser smoothing passes with masking fluid. Excimer laser hyperopic ablation was used to improve the uniformity of graft thickness within the optical zone. Fourier-domain optical coherence tomography was used to measure endothelial graft pachymetry, plan ablations, and evaluate donor contour. Vital dye staining was performed to assess endothelial cell damage. Scanning electron microscopy images of stromal surfaces were graded on a 5-point scale by masked observers to evaluate surface roughness.

Results: Four grafts underwent excimer laser smoothing. Vital dye staining showed no endothelial damage. Microkeratome-cut surfaces treated with laser smoothing (mean grade = 2.04) were smoother than nonsmoothed microkeratome-cut surfaces (mean grade = 4.07; P < 0.01), surfaces that underwent dry laser ablation (mean grade = 3.63; P < 0.01) and manually dissected interfaces (mean grade = 4.75; P < 0.0001). No difference was observed between stromal beds created by peeling Descemet membrane (mean grade = 1.64) compared with surfaces produced by microkeratome cutting followed by laser smoothing (mean grade = 2.04; P = 0.14). One graft underwent combined excimer smoothing and peripheral hyperopic ablation. The center-periphery thickness difference was 15 μm before ablation and 4 μm afterward.

Conclusions: Laser smoothing passes can be used to improve the contour and smoothness of DSAEK grafts without damaging donor endothelial cells. Clinical trials are needed to determine whether reshaping donors using excimer laser can deliver improved visual outcomes after DSAEK.

Figure 1

OCT images of microkeratome-cut DSAEK donor corneas. A. Shows the interface between the anterior stroma and the DSAEK donor endothelial graft. B. Shows the peripheral edge of the microkeratome cut. Due to the microkeratome cut pattern the graft becomes thicker towards the periphery.

Figure 2

OCT images illustrating the effect of excimer smoothing on DSAEK endothelial grafts. A. Shows the transition from the non-smoothed area on the left to the smoothed area on the right. B. A donor endothelial graft before smoothing. Microscopic surface roughness is evident. Endothelial graft thickness is 94μm. C. The same donor endothelial graft following excimer smoothing passes, thickness is now 68 μm.

Figure 3

Transition from smoothed to non-smoothed areas visible on (A) OCT (arrow) and (B) SEM imaging.

Figure 4

A-F. Scanning electron microscopy images illustrating the quality of stromal surfaces following different preparation methods. . Magnification: (A) 20x, (B) to (F), 150x. (A) SEM image showing a donor endothelial graft where half the central 6mm zone has been smoothed; (B) Illustrates the smooth surface produced by microkeratome cutting followed by excimer smoothing of the stromal surface of the endothelial graft; (C) Illustrates the surface produced by excimer ablation of the dry microkeratome-cut surface; (D) Illustrates the extremely smooth surface produced by peeling Descemet’s membrane; (E) Illustrates the surface produced by microkeratome-cutting, surface irregularities produced by chatter of the microkeratome blade are visible; (F) Shows the rough surface with broken collagen fibrils produced by manual dissection.

Figure 5

Graph comparing the stromal bed smoothness grade of scanning electron microscopy images. DP = Descemet’s peeling; LS= laser with smoothing fluid on microkeratome-cut surface; LD= laser ablation of dry microkeratome-cut surface; MK = microkeratome-cut surface; MN = manual dissection.

Figure 6

Photographs illustrating the results of vital dye staining of 2 endothelial grafts following excimer smoothing. Endothelial cell losses (quantified using Adobe Photoshop software) were less than 2% within the central 9mm diameter zone in both specimens.