THE SCARIFICATION PROCESS IN RABBIT LASER SCLEROSTOMIES

Background Obliteration of sclerostomy canals during the course of hea ling is of course undesirable, but before interference with the proces s 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. Methods Two cw-Nd:YAG laser sclerostomies were created ab intern o on one eye in each of ten rabbits; the unoperated fellow-eyes served as controls. IOP was monitored daily over a twelve-day period. Change s incurred within the canals and to collaterally damaged scleral tissu e were analyzed at two-day intervals by light and electron microscopy. Results 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 postoper ative day, the blebs had disappeared. Within five days of surgical int ervention, 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 modera te thermal insult, suggests that collagen fibrils undergo a process of repolymerization. Conclusions Although the time course of repair is m ore rapid in rabbits than in humans, the data gleaned nonetheless yiel d valid information respecting the sequence of events involved in the scarification process. The loose nature of the tissue occluding the ca nal 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.