Preliminary study of femtosecond laser sclerostomy ab externo in a rabbit model of chronic ocular hypertension

Abstract

To explore the feasibility, efficacy and safety of performing ab externo sclerostomy with a femtosecond laser in rabbits with chronic ocular hypertension. The chronic ocular hypertension model was induced by injecting α-chymotrypsin into posterior chamber. Twenty rabbits with chronic ocular hypertension were randomly divided into experiment and control groups, each group consisting of 10 rabbits. An ab externo sclerostomy using a femtosecond laser was performed in the right eyes in the experiment group. The right eyes in control group were unoperated. The laser was a pulsed titanium-sapphire laser, operating at a repetition rate of 1000 per second, 0.4 mJ pulse energy, a central wavelength of 800 nm and a pulse duration of 50 femtoseconds. The survival of filtration blebs, clinical manifestation and intraocular pressure (IOP) were observed for 1 month after surgery. Animals were killed on days 3, 7, 14 and 30 post-operatively. Hematoxylin and eosin (HE) staining and scanning electron microscopy (SEM) were performed to evaluate the histopathologic changes in filtering tracts. The differences in IOP between the experiment and control groups were analyzed by repeated measures analysis of variance. A 2 mm × 1 mm clear full-thickness scleral incision was created in each eye in the experiment group which was hit only once by the laser. The laser treated time was approximately 15 - 16 s. There was a significant difference (F = 117.46, 39.96, 15.17, 11.62, 15.31, 11.10; P < 0.01). IOP between experiment and control groups at post-operatively day 1, 3, 7, 14, 21, 30. No serious intra- or post-operative complications happened in the treated eyes except for anterior chamber hemorrhage in 2 eyes triggered by laser injury to iris root. A conjunctival bleb was successfully formed in all treated eyes at 1 day after surgery and lasted from 14 to 21 days. Histopathology showed that the perforating scleral incisions created by femtosecond laser were sharply defined, with almost no collateral damage to the surrounding tissue. The tissue repair response in the filtering tracts was characterized by mild hyperplasia of fibroblasts and the loose deposition of a small amount of new collagen fibers. The current study demonstrates that ab externo femtosecond laser sclerostomy is a feasible, safe and effective option for the treatment of glaucoma.