A composition containing Brilliant Blue G (BBG) or a pharmaceutically acceptable salt thereof, and a positional isomer of Brilliant Blue G (BBG) or a pharmaceutically acceptable salt thereof, the composition containing 90 wt % or more and 100 wt % or less of one or both of Brilliant Blue G (BBG) and the pharmaceutically acceptable salt thereof in the total of the Brilliant Blue G (BBG), the pharmaceutically acceptable salt of Brilliant Blue G (BBG), the positional isomer of Brilliant Blue G (BBG), and the pharmaceutically acceptable salt of the positional isomer of Brilliant Blue G (BBG), a method for producing said composition, and a method of removing the ocular membrane of a human patient.
