PowerPoint Presentation

Methods

Laser trabeculoplasty was performed on three fresh human donor eyes from different donors using three glaucoma lasers. Each eye was sectioned into thirds such that all lasers were used on each eye. ALT was performed with an argon laser at a wavelength of 488-514nm, exposure duration of 200msec, and spot size diameter of 200 microns; SLT a frequency-doubled Q-switched Nd:YAG laser (532nm; 3 nsec; 400 microns), and TLT a Titanium:Sapphire laser (790nm; 7usec; 200 microns). Three laser exposures of increasing energy/power settings were used with each laser on each eye section: ALT 200/400/800 mW; SLT 0.5/1.0/1/5 mJ; and TLT 30/50/80 mJ as depicted in Figure One.

Figure One: Position of Laser Exposures

Laser Trabeculoplasty with Three Different Lasers

in a Human Donor Eye Model

Gabriel Simon, MD PhD1, Shlomo Melamed, MD2, Thomas Freddo, OD1, Joseph A. Lowery, MSBE3

1Boston University, Boston, MA; 2Tel Aviv University; 3SOLX, Inc., Boston, MA

Figure Three: Pigment dispersion seen during Titanium:Sapphire laser trabeculoplasty (TLT).

Trabecular meshwork (TM) exposed to ALT exhibited the most anatomical alterations consistent with that described in the literature. TLT exhibited some anatomical alteration, with areas of slightly depigmented meshwork., perhaps where debris was separated from trabecular beams. Anatomical or pigmentary changes following SLT were not perceptible.

Results

The three lasers used in this study each provide a unique laser-tissue interaction, with ALT providing the highest thermal effect, and most evident disruption of trabecular architecture. Pigment dispersion seen with TLT may provide an avenue for lowering IOP in a clinical environment. Histology of eyes following SLT showed little change from normal, untreated regions.

Conclusions

The 790 nm near-infrared wavelength of the Titanium:Sapphire is less strongly absorbed by the pigmentation found in the trabecular meshwork allowing it to penetrate deeper into the meshwork. The visible green light from ALT and SLT are strongly absorbed by only the superficial layers. This deeper effect may prove to be more beneficial clinically, by treating the full meshwork thickness, and providing a more sustained IOP reduction as a treatment for open angle glaucoma.

Discussion

Methods (continued)

Eyes were sectioned into thirds prior to laser exposure with a single suture placed centrally to align the laser exposures as depicted in Figure Two. Following laser exposure, all tissue samples were labeled for identification, fixed in 4% glutaraldehyde, and were later processed with hematoxylin and eosin staining for histological analysis by light microscopy.

Figure Two: Sectioned globe with suture for alignment and location of three level laser exposures.

Objective

To study the laser-tissue interaction and depth of penetration associated with three laser trabeculoplasty techniques: Argon Laser Trabeculoplasty (ALT), Selective Laser Trabeculoplasty (SLT), and Titanium:Sapphire Laser Trabeculoplasty (TLT).

Marking Sutures