Nasal surgery. After constructing a new bypass channel for tear outflow during endoscopic nasal surgery, said Dr. Douglas, the body tries to narrow that new opening. “One of the things we do to put time on our side is to add a pledget laden with 5-FU,” he said. “This slows down the biologic response, which would close the newly created opening.”

Eyelid scars. “Eyelid scars usually aren’t thick, but they’re important because they inhibit the movement of small, delicate structures,” said Dr. Douglas. “5-FU injections given at the first sign of contracture can help minimize scar tissue and dramatically improve eyelid function.”

Eyelid retraction. Another increasingly common use of 5-FU is for cicatricial eyelid retraction in orbit surgery, said Dr. Blaydon. “A patient might have midlamellar scarring to the orbital rim, for example.” Injecting 5-FU softens attachments of these subcutaneous soft-tissue cicatrices to underlying tissues. “Muscles that move the eye are not that strong,” said Dr. Douglas. “But they can be tethered and severely restricted via a scar band. Many times this injection will help those muscles from getting scarred back down to the bone after you release them.” The goal is to allow muscles to move within fat without the restriction of a scar. “It’s like walking in air, as opposed to walking through water.”