[Healing of laser-induced sclerostomy channels in the rabbit]

Obliteration of sclerostomy canals during the course of healing is of course undesirable, but before interference with the process can hope to be successful, a stepwise ultrastructural delineation of the course of events provoked by surgucal intervention is essential. In the current study, such an analysis is undertaken, and the changes in tissue morphology discerned correlated with observed modulations in IOP.

Two cw-Nd:YAG laser sclerostomies were created ab interno on one eye in each of ten rabbits; the unoperated fellow-eyes served as controls. IOP was monitored daily over a twelve-day period. Changes incurred within the canals and to collaterally damaged scleral tissue were analyzed at two-day intervals by light and electron microscopy.

The development of well-defined filtering blebs demonstrated the success of the procedure. IOP was significantly lowered during the entire course of the observation period, but after the fifth postoperative day, the blebs had disappeared. Within five days of surgical intervention, morphological analysis revealed the canal to be invaded by macrophages originating from both the iris root and episcleral tissue; these were actively engaged in the phagocytosis of intensely damaged collagen abutting on the lumen. A few days later, the lumen had become occluded by fibroblasts and a dense capillary network. The course of regeneration observed within scleral tissue which had undergone moderate thermal insult, suggests that collagen fibrils undergo a process of repolymerization.

Although the time course of repair is more rapid in rabbits than in humans, the data gleaned nonetheless yield valid information respecting the sequence of events involved in the scarification process. The loose nature of the tissue occluding the canal lumen apparently permits the percolation of fluid through it, thus accounting for the clinical discrepancy between a continuing decrease in IOP and the disappearance of a filtering bleb.