Gonioscopic laser sclerostomy of sclera dyed with methylene blue and reactive black: A tracer study in cats using cationized ferritin

Gonioscopic sclerostomy using laser ablation of dye-enhanced sclera was performed in 14 eyes of seven non-glaucomatous cats. Prior to laser delivery, the sclera at the limbal region had been stained by iontophoresis, using 3% solutions of methylene blue in five eyes and reactive black in nine eyes. The laser used was the flash lamp pumped pulse dye laser which emitted red light at a wavelength of 590 nm at high energy (up to 400 mJ) per pulse. Successful sclerostomy, defined as immediate reduction of intraocular pressure (IOP) to levels below 10 mmHg, was achieved in all eyes treated. Mean preoperative IOP was 24.35 mmHg, while immediately post-laser it was reduced to 5.21 mmHg. Despite sharp reduction of IOP in all eyes, large spontaneous filtration blebs were only detected in two eyes immediately after laser sclerostomy, while no such blebs could be demonstrated in the other eyes. Two eyes displayed subconjunctival hemorrhage with hyphema and one eye had shallowing of the anterior chamber. In six eyes subconjunctival gas bubbles could be demonstrated, indicating an open scleral fistula. Two eyes had conjunctival holes. Cationized ferritin (CF) was injected intracamerally in ten eyes, and in nine eyes a large filtration bleb was immediately raised with diffuse staining of the subconjunctival space with the tracer, indicating an open sclerostomy. In four eyes, histological specimens disclosed various sizes and shapes of complete (in two eyes) and incomplete sclerostomy (two eyes). There was no major difference in the level of energy required for sclerostomy in the methylene blue versus the reactive black stained eyes. However, in eyes stained with reactive black there was less bleaching of stained tissue following laser impact, allowing better absorption of laser energy in external parts of the sclera. Gonioscopic laser sclerostomy of sclera dyed with 3% methylene blue or 3% reactive black is a non-invasive method to achieve a functional sclerostomy with subsequent reduction of IOP in the cat.