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The purpose of this study was to verify the feasibility of ab externo layer-by-layer excimer laser photoablative removal of limbal tissue down to the trabecular meshwork and to assess the damage caused by this procedure to the neighbouring structures. Excimer laser photoablation (193 nm) can remove layers of corneal tissue effectively with little or no damage to the adjacent areas. Previous experimental studies have demonstrated a decrease in outflow resistance after ab-externo photoablative removal of juxtacanalicular tissue. We have performed ab-externo photoablative removal of limbal tissue overlying the trabecular meshwork in four freshly enucleated eyes from our Eye Bank. The beam of an excimer laser (wavelength 193 nm; fluence 180 mJ/Sq.cm) was shaped using a metal mask with a rectangular opening of 1.2 x 2.5 mm. After removing the conjunctiva, photoablation was carried out at maximum surgical microscope magnification (40 x) until trabecular meshwork appeared at the bottom of the crater. Light microscopy showed that craters had smooth walls and their base reached the Schlemm's canal area; all structures appeared of normal morphology. Transmission electron microscopy showed a thin layer of amorphous material or pseudomembrane on the side walls of the crater; corneoscleral collagen fibers were abruptly interrupted and undistorted. At the bottom of the crater the trabecular meshwork and Schlemm's canal tissues appeared normal.

We have performed ab-externo photoablative filtration surgery on 19 patients affected by uncontrolled primary open-angle glaucoma. All cases had wide open angles, were previously treated with argon laser trabeculoplasty and were considered good candidates for trabeculectomy. After topical and peribulbar anesthesia, a limbus-based conjunctival flap was dissected. Photoablation of a rectangular area at the limbus was performed with an argon fluoride excimer laser (193 nm), at 180 mJ x sq cm fluence. The beam was shaped in the appropriate fashion using a custom-made metal mask. Photoablation was continued until aqueous appeared percolating through the juxtacanalicular tissue at the bottom of the crater; a water-tight closure of conjunctiva was then performed. Postoperatively, the anterior chamber reaction was minimal; in no case a flat chamber or choroidal detachment was observed. In 18 of the 19 cases the IOP was significantly lowered, and a filtering bleb developed. Mean preoperative IOP was 26.4 (+/- 7) mmHg. At a median follow-up of 9 months (range 4-15) the IOP is < or = 18 mmHg on no medications in 16 (84%) of the eyes, with a mean value of 13.3 (+/- 6) mmHg. Our short-term results support excimer laser photoablative filtration as a relatively safe and effective procedure for primary open-angle glaucoma.