Transmural iontophoresis of fluorescein into rabbit retinal veins
Purpose. Branch or central retinal vein occlusions (RVO) are common vascular disorders for which there are no effective treatments. We propose the novel idea that iontophoresis, the transport of ions by an electric current, might be useful in propelling drugs locally into the vascular lumen without the need for mechanical penetration of the vessel. We tested the hypothesis by demonstrating that iontophoresis can be used to inject fluorescein into the lumen of rabbit retinal veins. Methods. Retinal veins in albino rabbits were first occluded near the optic nerve by photothrombosis or diathermy to obstruct the flow of blood through the vessels. After a limited vitrectomy, a transvitreal glass micropipette with a 20 micron tip containing 10% fluorescein was apposed to each retinal vein distal to the occlusion site; twenty microamperes of constant-current was delivered (except in four sham control experiments) through the pipette tip for ten minutes. Color and red-free photographs, as well as photographs with the fluorescein filters in place were taken immediately after each procedure. The animals were euthanized and the eyes processed for light and electron microscopy. Results. Retrograde filling of the retinal veins with fluorescein was noted in nine out of the ten veins treated and was absent in the four sham control veins. Fluorescein stained the retinal tissue around the injection site in all veins treated. Complications of treatment include clot formation at the site of iontophoresis. Conclusions. Fluorescein can be transported transmurally into retinal veins by iontophoresis. These results suggest that iontophoresis could be developed as a method for localized delivery of thrombolytic drugs into retinal veins of patients with RVO.