be replaced. Possible scenarios include blockage, where a particle becomes logged in the tube line blocking flow; retraction, where the tube line slips out of correct position such that flow is inhibited or halted; valve failure, where the valve stops working blocking flow completely. Surgical failure occurs due to the ongoing scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using anti-fibrotic medication like 5-fluorouracil (5FU) or Mitomycin-C (during the procedure), or creating a necessity for revision surgery with the sole or combinative use of biodegradable spacer or collagen matrix implant. A Cochrane Review comparing aqueous shunt surgery with and without Mitomycin-C did not find benefit or harm associated with the intervention. See also Eye surgery Glaucoma surgery References External links Glaucoma Valves website at Brown University Implants (medicine) Ophthalmology