Iontophoresis of Methylene Blue for Gonioscopic Pulsed Dye Laser Sclerostomy

ABSTRACT

Iontophoresis of methylene blue using pipette tip probes is an effective means of scleral staining in preparation for gonioscopic pulsed dye laser sclerostomy. The effects of the surface area of the pipette tip and of the duration of iontophoresis on the concentration and distribution of stain were investigated in rabbit eyes. Iontophoresis of 1% methylene blue was done using currents from 0.2 to 2.0 mAmp, pipette tip probes with surface areas from 0.02 to 7.1 mm², and durations of iontophoresis from 0.5 to 10 minutes. Optimum iontophoresis parameters for delivering methylene blue to the eye were a current of 0.4 mA, a probe tip surface area of 0.19 mm², and a duration of five minutes. The maximal scleral stain concentration, approximately 0.4%, was achieved using these optimal paramaters. Microscopic analysis of frozen tissue sections demonstrated the stain to have penetrated the full thickness of the sclera after five minutes. Tissue samples were analyzed for dye 0.5, 2, 5, 12, and 24 hours after iontophoresis was completed. Decreased dye concentration by over 50% within 2 hours and complete disappearance of dye within 24 hours were demonstrated. Methylene blue concentration thresholds for laser ablation were also examined; the threshold of ablation of methylene blue was 0.0625% when an energy level of 75 mJ was used. We propose that iontophoresis of methylene blue is a useful adjunct to pulsed dye laser sclerostomy formation.