Physicochemical characteristics of a microfiltered 0.4% trypan blue solution when applied to the anterior capsule

This letter highlights some of the physico-chemical characteristics of a microfiltered 0.4% solution of trypan blue, CAPSULblue (Excel-Lens, Los Gatos California USA). This dye is used to stain the anterior capsule to enhance its visibility and the stained capsule acts a target for a 590nm laser during selective laser capsulotomy. The characteristics of the 0.4% solution are compared to commercially available 0.06% trypan blue solutions. There is a striking variability seen in purity, pH, osmolality and monoazo-dye concentration in the 0.06% solutions when compared with the microfiltered 0.4% solution. Particulate matter is seen in one of the non-filtered examples which may induce toxic anterior segment syndrome (TASS). The speed of staining the anterior capsule is also compared demonstrating the much more rapid effect with the 0.4% solution. Finally, the rate of removal of the dye from the eye through the uveoscleral and trabecular outflow pathways after surgery is demonstrated.