Stroma remodelling during healing of corneal surface irregularities induced by PTK

To study the histopathology of the remodelling process in the stroma after excimer-laser-induced corneal irregular injuries.

Seven New Zealand white rabbits received in one eye a transepithelial plano photoablation (60 microm) and an additional plano ablation (25 microm). On the denuded stroma, an electron microscopy specimen grid was placed and another 25 microm ablation was applied to produce surface irregularities. Dichlorotriazinyl aminofluorescein (DTAF) was then applied for 45 seconds. Another seven right eyes of seven rabbits were ablated the same way but without using the grid, resulting in a plano ablation. All the rabbits were killed at weekly intervals after treatment. The harvested corneas from both eyes were further processed for haematoxylin-eosin staining and were also stained with monoclonal antibodies directed against Ki-67 antigen and alpha-smooth muscle actin (alpha-SMA). All specimens were examined under light and fluorescence microscope.

The corneal wounds were covered by epithelium during the first week. The 25 microm x 25 microm x 25 microm stromal irregularities were clearly discernible up to 3 weeks after treatment, during which time they melted and disappeared. A homogeneous zone was formed in which stroma cells laid down an initially disorganized stroma. This was sharply visible under a fluorescence microscope as a dark area between the dichlorotriazinyl aminofluorescein (DTAF) fluorescent stroma and autofluorescent epithelium. Very little response was seen in the plano-ablated wound microscopically and in terms of positive stained cells.

As the irregularities are flattened and the homogenous zone becomes repopulated with keratocytes forming extracellular matrix material (ECM), the cornea regains its previous architecture in both groups. The irregular wound surface promotes wound-healing reactivity, a process that allows the cornea to compensate for the irregularities and heal to a functional state.