Wound healing response in the presence of stromal irregularities after excimer laser treatment

• Purpose: To trace the fate of stromal irregularities after excimer laser treatment and to increase our knowledge of the reasons why surface irregularities in the ablation bed cause inferior postoperative results. Methods: Twelve New Zealand White rabbits received a transepithelial photoablation to a preset depth of 60 ╡m. An electron microscopy specimen grid was then placed on the denuded stroma and another 20 ╡m ablation was applied in order to produce surface irregularities. Another six rabbits received a plano transepithelial photoablation to a preset depth of 80 ╡m. The treated corneas were harvested at various timepoints and differentially further processed for microradiography, hematoxylin-eosin-, hyaluronan (HA)- and leukocyte protein L1 staining. Results: In the grid treated corneas the subepithelial mesh pattern is clearly discernible after 1 week, and after 4 weeks it is replaced by a subepithelial layer containing HA and water. The thinning of this layer between 1 and 12 weeks is statistically significant (p<0.05). After 4 and 8 week the plano treated corneas only exhibit some subepithelial HA- and water accumulation. After 1 day the grid treated corneas show an extensive stromal infiltration of leukocytes. In the plano treated corneas the leukocytes mainly remain on the surface. Conclusions: During the healing process stromal irregularities are flattened, leaving a homogeneous zone with increased water content. This subepithelial layer is rarefying as new subepithelial tissue is forming. Postablational irregularities induce a more pronounced healing reaction when compared to a smooth ablation surface. Leukocyte infiltration seems to play a role in this process.

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