P.P. Van Saarloos

Quantitative measurement of the ablation rate of poly(methyl methacrylate) with 193‐nm excimer laser radiation

The ablation rate of poly(methyl methacrylate) (PMMA) from two different producers has been measured as a function of fluence, and the result compared with other published work. The two PMMA samples had distinctly different ablation rates. Differences between these two samples and the previously published work demonstrate the difficulties of obtaining quantitative ablation rate data. Possible sources of error in obtaining these data are discussed.

Laser microsclerostomy for primary open angle glaucoma: a review of laser mechanisms and delivery systems.

A number of different lasers and delivery systems are currently used in experimental sclerostomy procedures. These are discussed with reference to their performance in terms of cutting accuracy and trauma to the adjacent tissues. Lasers emitting wavelengths close to the absorption peaks of water in the mid-infrared region and organic polymers in the far ultraviolet region have a short absorption pathlength in the sclera and produce the least adjacent thermal tissue trauma. These ablating lasers cannot be delivered gonioscopically, and contact endoscopic techniques trap hot expanding gases within the forming sclerostomy channel causing secondary thermal and mechanical damage. Optimal results should be obtained using an ablating laser delivered either through an open mask or a modified endoscopic system incorporating an adequate exhaust mechanism.

193-nm excimer laser sclerostomy using a modified open mask delivery system in rhesus monkeys with experimental glaucoma

Excimer laser sclerostomy is a new glaucoma filtration procedure in which the argon fluoride excimer laser at 193 nm is delivered ab externo through a modified open mask system incorporating an en-face air jet to dry the target area and preserve hemostasis during ablation and a conjunctival plication mechanism, which allows the conjunctival and scleral wounds created by through-and-through ablation to separate once the mask is removed. No preparatory dissection of the conjunctiva is required. Five 200-μm and five 500-gmm sclerostomies were formed by ablation at a pulse repetition rate of 20 Hz and a fluence per pulse of 400 mJ/cm2 in fellow eyes of five rhesus monkeys with experimental glaucoma. Overall, seven of the ten eyes attained a functional result, with intraocular pressures remaining below 21 mmHg for 6 ± 1 days and rising to the pre-operative level after 10 ± 3 days without adjunctive antifibroblast medication. The duration of filtration for 200-μm and 500-μm sclerostomies was similar, and parallels that previously observed for posterior lip sclerostomy in the same animal model. The three eyes with no functional result all had incorrectly positioned sclerostomies. Choroidal detachment and significant shallowing of the anterior chamber did not occur. Excimer laser sclerostomy appears to be a viable technique for filtration, provided that mask placement is accurate.

Excimer laser sclerostomy: The in vitro development of a modified open mask delivery system

The argon fluoride (ArF) excimer laser at 193 nm ablates the ocular tissues with a new order of precision and virtually no adjacent damage. A glaucoma filtration operation has been designed in which small-bore sclerostomies are created using the ArF excimer laser delivered through an open mask. The mask plicates the conjunctiva at the limbus prior to ablation. Removing the mask at the end of the procedure allows the conjunctiva to relax back to its original position, separating the conjunctival and scleral wounds. Formal conjunctival dissection is thus avoided. Feasibility studies in cadaver pig eyes, using a fluence per pulse of 400 mJ/cm2 and a pulse repetition rate of 20 Hz, indicate that sclerostomies of 300 µm diameter can be reliably formed if an en-face air jet is built into the mask to raise the pressure in the target area, preventing aqueous flooding.