A simple and cost effective method for preparing FL and LG solutions

The purpose of this study was to develop a clinically feasible method for obtaining dye concentrations of 2% fluorescein (FL) and 1% lissamine green (LG) by soaking commercially available dye impregnated strips in saline.

Calibration curves were established to related known concentrations of dye to prepared FL fluorescence and LG absorbance. To determine the optimum number of dye strips and soaking times (preliminary testing), 1, 2, 3 FL or LG strips were soaked in 200 μl commercially available saline for 0.5, 1, 2, 3, 4 and 5 min, using calibration curves to determine FL and LG concentrations. The best combination of number of dye strips and soaking time was soaking 3FL and 3LG strips for 5 min and these were finally tested in 2 ml centrifuge tubes, selected for ease of use in a clinical setting.

Preliminary testing indicated that soaking 3 FL or 3 LG strips for 5 min in saline yielded an average (±standard deviation) of 2.0 ± 0.000% FL and 0.93 ± 0.010% LG. Final testing of FL in centrifuge tubes (strips soaked for 3-15 min) yielded an average of 1.99 ± 0.040% FL, with no significant difference among time periods or dye lots tested. However, LG showed more variable results with an average of 0.80 ± 0.160% LG (5-15 min), with significant differences among dye lots and times (2-way ANOVA, p < 0.05).

This simple, reliable and relatively inexpensive method involves soaking 3 FL or LG strips in saline solution, yielding concentrations close to the 2%FL and 1%LG recommended for clinical trials, although LG showed more variability.