The green dye (ICG) is used to help the surgeon visiualize particular parts of the retina, such as the ILM. It's controversial, but many surgeons believe that it can be toxic to the retina and may cause permanent damage.
Dyes that stain structures inside the eye are frequently used. In the quantitites used they are not considered toxic and make the surgery safer. Other than that you will need to ask the surgeon for more clarification. We use a blue dye in cataract surgery
JCH MD