THE REPAIR RESPONSE FOLLOWING ND-YAG LASER SCLEROSTOMY AB INTERNO IN RABBITS

This study was undertaken to examine ultrastructurally the course of t issue regeneration after thermally-induced laser sclerostomy and compa re it with the post-operative clinical events in a rabbit model. Apply ing a continuous wave neodymium:YAG (Nd:YAG) laser, two sclerostomies were created ab interno on one eye in each of ten pigmented rabbits us ing a 200-mu m-diameter quartz optical fiber; the unoperated fellow-ey es served as controls. Intraocular pressure (IOP) was measured daily b efore and after surgery. Animals were observed post-operatively for up to 16 days. Well-defined filtering blebs and a low complication rate demonstrated the success of the procedure. IOP was significantly lower ed during the entire course of the observation period but after the fi fth day, the conjunctival blebs had disappeared. The morphology of the changes in the sclerostomy fistulas were analysed at 2-day intervals by light and electron microscopy. Immediately after surgery, the canal was ensheathed by an approximately 100-mu m-thick layer of coagulated collagenous tissue in which two zones could be distinguished accordin g to the intensity of damage. Within 5 days, the inner and outer canal openings were invaded by macrophages and fibroblasts originating from the iris root and episclera, respectively. The former cells were enga ged in the phagocytosis of disintegrated collagen adjacent to the lume n. More distally located fibrils which had incurred less severe damage , had retained their fibrillar structure but had lost banding periodic ity. After thermal stress had faded, they appeared to undergo a proces s of repolymerisation. By day 10, the lumen had become occluded by a l oose meshwork of phagocytes, fibroblasts and proliferating capillaries . These new vessels and the loose nature of the canal-occluding framew ork and of the surrounding regenerating collagenous tissue could have further permitted percolation and transport of aqueous humor, since IO P remained low, despite the disappearance of filtering blebs. Although the time course of repair is more rapid in rabbits than in humans, th e data gleaned nonetheless yield valid information respecting the sequ ence of events following thermally-induced scleral fistula. (C) 1995 A cademic Press Limited.