B A Weber1, L Gan, P Fagerholm. 1. St. Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden; Dept. of Ophthalmology, University Hospital, Linköping, Sweden. beat.weber@bluemail.ch
Abstract
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 microm. An electron microscopy specimen grid was then placed on the denuded stroma and another 20 microm ablation was applied in order to produce surface irregularities. Another six rabbits received a plano transepithelial photoablation to a preset depth of 80 microm. 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.
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 microm. An electron microscopy specimen grid was then placed on the denuded stroma and another 20 microm ablation was applied in order to produce surface irregularities. Another six rabbits received a plano transepithelial photoablation to a preset depth of 80 microm. 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.