5-fluorouracil is a medication that can help prevent scar tissue from forming. Scar tissue forms naturally as a wound heals. Scar tissue that forms near the new drainage opening created during glaucoma surgery can narrow or close it completely. 5-fluorouracil is injected under the lining of the eye (conjunctiva) at the first sign that the opening may be closing off after surgery. It may be used during surgery to prevent scar tissue from forming.

Treatment with 5-fluorouracil can be painful. Numbing medications (anesthetics) can be applied to the eye to decrease pain when the 5-fluorouracil is injected.

5-fluorouracil has side effects, which are generally mild and do not last long. However, sometimes these side effects can be quite serious. Serious side effects include:

• Bleeding and scarring of the clear covering (cornea) over the colored part of the eye (iris).
• Separation of the nerve layer inside the eye (retinal detachment). This is rare.
• Excess loss of fluid from the eye (hypotony). This can cause softening of the eyeball, possibly leading to clouding of the lens (cataract).
• Buildup of fluid behind the colored lining (choroid) under the nerve layer (retina).
• Poor healing in the area of the injection, causing a thin bleb (the small bubble of tissue that forms when a new drainage opening is created in some types of surgery for glaucoma).

Injections of 5-fluorouracil can be given daily, and the effects of each injection are carefully watched before it is decided to inject more medication.

Another medication, mitomycin-C, is more commonly used during glaucoma surgery to prevent scarring, but it cannot be injected after surgery as 5-fluorouracil can.