Laser discectomy. Comparison of systems.

Percutaneous methods of lumbar disc removal have gained wide popularity since the introduction of the automated suction device. Newer methods to enter this field include the Nd:YAG and Ho:YAG lasers. To date, no experimental model exists to compare the efficacy of disc removal of these devices. An in vitro disc elastance (pressure/volume) model was designed that accurately reflects the mass of dry disc removed after any type of discectomy procedure. The experimental design consists of an infusion pump compressing a static column of air in line with the disc through a 12-gauge needle. Both mechanical and laser devices exhibited a reproducible treatment plateau, beyond which no disc removal was effected. Total energy, as opposed to power, was found to be the main determinant of the extent of disc removal during laser discectomy. Finally, in the experimental model of juvenile swine the automated suction device exhibited superior disc removal compared to the two lasers, but the clinical applicability of this is debatable. Disc space elastance offers a rapid and reproducible method to quantitate the extent of disc removal after intradiscal treatment methods and if employed in human cadaver spines may minimize the need for clinical trials to compare different devices and techniques.

Ab-interno erbium (Er):YAG laser sclerostomy with iridotomy in Dutch cross rabbits.

An ab-interno technique using a pigmented rabbit model has been developed that uses a pulsed erbium:YAG laser to create an iridotomy with a sclerostomy through the same corneal incision. Laser energy was delivered with an articulated arm terminating in side-firing (850 or 650 microns OD) or end-firing (850 or 400 microns OD) fiber optic endoprobes, which allowed iridotomies and sclerostomies, respectively, to be created. Initially, sclerostomies (8-10, 8 mJ/300 microseconds pulses) and basal iridotomies (1-3, 4 mJ/200 microseconds pulses) were created with the larger probes. Problems encountered with this technique included corneal decompensation and rapid formation of peripheral anterior synechiae with occlusion of sclerostomies. The smaller endoprobes were then used to create mid-peripheral iridotomies and sclerostomies utilizing the same energy parameters. Sclerostomies created in this manner remained patent in the first postoperative week until the animals were sacrificed to obtain material for histologic study.

Effects of pulse width on erbium:YAG laser photothermal trabecular ablation (LTA).

An erbium (Er):YAG laser can remove trabecular meshwork (TM) by photothermal ablation with minimal contiguous thermal damage. A variable pulse width Er:YAG laser was used to investigate the effect of varying pulse width on ablation of human TM. Trabecular photothermal ablation was performed on tissue obtained from eye bank eyes at pulse widths of 50, 150, and 250 microseconds, with energy held constant at 4 mJ. At this energy, a single laser pulse was sufficient for full-thickness ablation of TM. Laser energy was delivered through a 200-microns diameter optical fiber held in apposition to the tissue sample, which was immersed in physiologic saline. High-speed photography of the resultant steam bubbles also was performed. Light microscopy and scanning electron microscopy of TM ablated at 50 microseconds revealed the greatest variability in size (0-140 microns) of the full-thickness ablated areas and demonstrated blast effects, tissue shredding and < or = 10 microns thermal damage. At 150 microseconds, the full-thickness ablated areas were more consistent size (115-120 microns), showed no blast effects and 10 to 20 microns thermal damage. At 250 microseconds, the largest ablations were found (180-220 microns) and showed no blast damage; however, a significant amount of thermal damage (< or = 50 microns) was evident. The steam bubbles produced by the laser energy were largest at 50 microseconds and did not begin to collapse until well over twice the original pulse interval. At 150 and 250 microseconds, the steam bubbles were successively smaller and dissipated at the end of the laser pulse.(ABSTRACT TRUNCATED AT 250 WORDS)

Percutaneous laser discectomy with the Ho:YAG laser.

A prototype Ho:YAG (2.15 microns) laser operating at 2-J/pulse, 3 Hz through a 600-microns fiber was employed to perform laser discectomies at the L3-4 disc through an 18G needle in five juvenile pigs. No temperature elevations were recorded in the posterior longitudinal ligament at the disc level and all animals recovered fully with no adverse sequelae, even immediately upon awakening from anesthesia. Pathologic examination demonstrated a wide swath of coagulation necrosis confined to the disc space. The Ho:YAG laser, owing to its close approximation to the intense 2.0 microns absorption band of water, appears to be a viable candidate for clinical trials of laser discectomy.

Light transport in planar luminescent solar concentrators: the role of DCM self-absorption.

The influence of self-absorption in a 4-dicyano-methylene-2-methyl-6-p-dimethyl amino-styrl-4H-pyran (DCM) doped polymethylmethacrylate (PMMA) optical waveguide on the light transport efficiency has been evaluated. A Monte Carlo technique was used to simulate intermolecular energy transfer and calculate the energy emission profile of an active waveguide. The calculated and measured edge emission profiles were found to be in excellent agreement. The edge emission spectra for various distances of excitation from the edge were used to estimate the DCM self-absorption cross section.

Use of the thermal lens technique to measure the luminescent quantum yields of dyes in PMMA for luminescent solar concentrators.

The thermal lens technique has been used to measure absolute luminescent quantum yields of dyes in liquid and solid (PMMA) solutions. The validity of the approach has been established by measuring quantum yields of known compounds, and we stress the application to dye/polymer systems that would be suitable for luminescent solar concentrators. Our results for rhodamine 6G and Fluorol 555 give 0.93 +/- 0.04 and 0.88 +/- 0.03, respectively, for their quantum yield in PMMA.

Organic dyes in PMMA in a planar luminescent solar collector: a performance evaluation.

The performance of organic dyes in PMMA has been evaluated in a three-layer planar luminescent solar concentrator. The single plate and combined three-plate efficiencies have been measured for a number of dyes, and results of one typical combination are reported here. A detailed characterization of the spectroscopic properties of the dye molecules as well as the device dependent and device independent parameters of the plates allow comparison between measured and predicted efficiency. Our results demonstrate the presence of a significant positive synergism for the multilayer device.