The Fundamental Research Of Femtosecond Laser Photodisruption For Minimally Invasive Laser Sclerostomy

Objective Femtosecond laser technology, used as a minimally invasive tool in intrastromal refractive surgery, may also have potential as a useful instrument for glaucoma filtration surgery. The purpose of the present study was to evaluate the feasibility of minimally invasive laser sclerostomy by femtosecond laser photodisruption and seek the appropriate patterns of laser ablation and relevant laser parameters.Method A femtosecond laser (800 nm/50 fs/1 kHz), focused by a 0.1 numerical aperture (NA) objective lens, with different pulse energies and exposure times was applied to ablate hydrated rabbit sclera in vitro. The irradiated samples were examined by scanning electron microscopy (SEM).Results By moving a three-dimensional, computer-controlled translation stage to which the sample was attached, the femtosecond laser could produce three types of ablation patterns, including linear ablation, cylindrical aperture and rectangular cavity. With pulse energies ranging from 37.5 to 150μJ, the linear lesions were consistently observed at the inner surface of sclera, whereas it failed to make any photodisruption if pulse energy was below the threshold value of 31.25μJ, with the corresponding threshold intensity of 4.06×1014 W/cm2. The depths of the linear lesions increased linearly with both pulse energy (37.5-150μJ) and exposure time (0.1-0.4 s). Histological examination showed the incisions produced by femtosecond laser photodisruption had precise geometry and the edges were sharp and smooth, with no evidence of collateral damage to the surrounding tissue.Conclusions Our results predict the potential application of femtosecond laser pulses in minimally invasive laser sclerostomy for glaucoma treatment. Objective To explore the feasibility, efficacy and safety of performing ab externo sclerostomy with a femtosecond laser in rabbits with chronic ocular hypertension.Method The chronic ocular hypertension model was induced by injecting a-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 1,000 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.Results A 2×1mm2 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 15s-16s. There was a significant difference (F=117.46,39.96,15.17,11.62, 15.31,11.10; P<0.01) in 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.Conclusions The current study demonstrates that ab externo femtosecond laser sclerostomy is a feasible, safe and effective option for the treatment of glaucoma. Objective To experimentally compare the surgical outcomes and healing patterns of the external sclerostomy produced using a femtosecond laser with that made by a surgical knife, and to evaluate the efficacy and advantages of femtosecond laser sclerostomy.Method In a randomized, prospective, masked-observer study, twenty pigmented rabbits underwent external sclerostomy in the right eye, and the fellow eye remained as the unoperated control. Ten rabbits underwent sclerostomy with a femtosecond laser, and ten underwent sclerostomy with a surgical superblade. The survival of filtration blebs, intraocular pressure (IOP) and clinical manifestation were observed for 1 month after surgery. Six additional rabbits underwent external femtosecond laser sclerostomy in the right eye and mechanical sclerostomy in the left eye, and were killed on day 14 after surgery. Histologic staining, immunohistochemistry and scanning electron microscopy were performed to assess the appearance of the filtering fistula. The titanium-sapphire femtosecond laser was operating at a repetition rate of 1,000 per second,0.4 mJ pulse energy, a central wavelength of 800 nm and a pulse duration of 50 femtoseconds. Mann-Whitney and Kaplan-Meier tests were used for statistical analysis.Results Successful complete sclerostomy was achieved in each laser-treated eye which was ablated only once by the laser. The laser treated time was approximately 15s-16s. In the laser-treated group (n=16),3 eyes (19%) developed mild hyphema at the site of entry and 8 eyes (50%) showed transient edema in the corneal periphery adjacent to the laser impact zone. The differences between the groups in duration of function blebs and pressure reduction were statistically significant (Mann-Whitney U=24.000 and 20.000, respectively; P=0.025 and 0.016, respectively). The success rate of the laser-treated group was significantly higher than the knife group (χ2=7.785, P=0.005). Histologically, the subconjunctival connective tissue was loosely arranged and contained clear spaces with partially patent sclerostomy in the laser-treated eyes on postoperative day 14. This contrasted with the completely scarred sclerostomy tract in the knife group. The mean numbers of fibroblasts and new vessels as well as the amount of new collagen deposition were significantly decreased in the laser group, compared with the knife group (Mann-Whitney U=5.500,2.500 and 7.000, respectively; P=0.045,0.013 and 0.036, respectively).Conclusions The current study demonstrates that external femtosecond laser sclerostomy may offer a safe and effective alternative in the minimally invasive surgical management of glaucoma.