Erbium-YAG laser-assisted preparation of deep sclerectomy

Background: Deep sclerectomy and viscocanalostomy an becoming more and more popular as non-penetrating filtering procedures. The purpose of the presen t study was to simplify the technique of this procedure and to reduce the r ate of unintended perforations during the preparation of the deep lamella. Methods: 20 enucleated porcine eyes were used. A superficial lamellar scler al flap with an area of 5x5 mm as for trabeculectomy was surgically prepare d. Using a pulsed erbium:YAG laser the deep lamella (220+/-40 mu m) with an area of 4x3 mm was removed. Ablation was performed with an energy of 40-10 0 mJ, a frequency of 1-10 Hz and a spot size of 500 mu m and I mm (divergen t beam). During the procedure the intraocular pressure was kept constant by continuous infusion. Finally the eyes were analyzed histologically. Results: After initial trials it was possible to ablate the remaining deep corneoscleral lamella with the erbium:YAG laser without perforating into th e anterior chamber. Starting with an energy of 70-85 mJ and a reduction to 40-60 mJ when reaching deeper layers, a spot size of 500 mu m and a 10 Hz r epetition rate gave the highest safety and efficiency in preparation. After a learning curve it was possible to preserve Descemet's membrane and intac t trabecular meshwork in 10 consecutive operations as demonstrated by histo logy. Conclusion: Erbium:YAG laser-assisted deep sclerectomy offers an alternativ e to microsurgical preparation of the deep scleral lamella. The thermal dam age is minimal (10-40 mu m) and scarring may therefore not be stimulated.