Corneal Endothelial Morphology and Barrier Function Following Excimer Laser Photorefractive Keratectomy

Abstract

To investigate the effect of deep stromal excimer laser ablation on corneal endothelial morphology and barrier function, excimer laser photorefractive keratectomy (PRK) was performed to obtain residual corneal thickness between 90–250 μm in NZW rabbit corneas (N=50). Corneal endothelium was stained with Alizarin red S for 2 minutes three days after excimer laser ablation, and analyzed morphometrically. Five groups of PRK were performed to obtain three residual corneal thicknesses of 150, 175, and 200 μm in one eye of NZW rabbits (N=30), and also to ablate −6 D and −12 D of correction (N=10). The paired corneas were used as control. Three days after PRK, corneal endothelial permeability was measured according to the method of Watsky et al. and compared to control. Corneas with residual thickness of 90–130 μm showed severe corneal endothelial damage. In 130–200 μm of residual thickness, the damage was inversely proportional to the residual corneal thickness (p 0.1). Three days following PRK, corneal endothelial Pac with residual corneal thickness of 200 μm was 3.28 ± 0.55 × 10−4 cm/min which was also similar to control, whereas Pac with residual thickness of 175 μm and 150 μm were 3.68 ± 0.82, and 3.97 ± 0.58 x 10−4 cm/min, which were significantly different from control (p<0.05). EM showed an intact monolayer of hexagonal endothelial cells, intact intercellular junctions, and normal subcellular organelles, but amorphous granular material appeared within posterior Descemet’s membrane in all excimer laser treated corneas suggesting that the endothelial cells were stimulated to secrete. The results of this study showed that corneal endothelial morphology and barrier function were maintained if ablation level did not go beyond 200 μm of residual corneal thickness. Deeper stromal ablation caused both a morphologic changes and impaired barrier function.