Gonioscopic laser sclerostomy: comparing the ablation capacities of methylene blue and reactive black stains in vitro and in vivo

Abstract

Aim: Gonioscopic laser sclerostomy requires staining of the sclera by an iontophoresis technique to permit the absorption of the laser energy. The ablation ability of a pulsed dye laser using methylene blue as scleral stain was compared to that using reactive black in order to evaluate which stain is more effective for achieving a full-thickness sclerostomy, both in vitro and in vivo.

Materials and Methods: lontophoresis with methylene blue and reactive black, 1% and 3% each, was performed in vitro on sclera from 31 autopsy human eyes. The performance of methylene blue and reactive black was studied in vivo both clinically and histologically. lontophoresis of 1 eye with reactive black 3% and the fellow eye with methylene blue 3% was performed on 11 rabbits.

Results: In vitro, the creation of a full-thickness sclerostomy using a pulsed dye laser was significantly higher for reactive black 3% (71%) than for methylene blue 1% (40%) (p=0.017, McNemar's test) and  methylene blue 3% (35.5%) (p=0.0078). In vivo the intraocular pressure drop (mean ± SD) was greater for reactive black 3% (-4.6±6 mm Hg) th an methylene blue 3% (-0.3 ± 12.9 mm Hg) (p=0.015, paired t-test). The frequency of bleb formation, flattening of the anterior chamber, or visible subconjunctival hole was significantly higher for reactive black (82%) than for methylene blue (18%) (p=0.015 , McNemar's test). Histologic study in 14 rabbits immediately following GLS demonstrated 5 full-thickness sclerostomies in the reactive black­ stained eyes. and 2 full-thickness sclerostomies in the methylene blue-stained eyes. The difference between reactive black and methylene blue, based on histology, was not statistically significant (Fisher's exact test).

Conclusion: Reactive black is better than methylene blue for achieving full-th ickness sclerostomy in vitro and in vivo.