Caution urged with anti-scarring medications

"One cannot do a technically unsatisfactory filtration procedure and expect an anti-scarring medication to rescue a basic surgical error," said Dr. Parrish, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami.

"But I would caution surgeons to remember that having to deal with a flat chamber, mature cataract, and intumescent cornea with irreversible endothelial damage as a result of anti-metabolite use is a far worse outcome of filtration surgery than bleb scarring with loss of IOP control," Dr. Parrish added.

"Those concepts were critical before we had anti-scarring agents and still are today," Dr. Parrish said.

He credited Paul Palmberg, MD, PhD, of the Bascom Palmer Eye Institute, Miami, with observing that mitomycin-C (MMC, Mutamycin, Bristol-Myers Squibb) or 5-fluorouracil (5-FU, Adrucil) do not cause hypotony themselves, but their use will preserve any hypotony the surgeon creates.

"If a patient leaves the operating room with a very low IOP, the wound healing process that might scar down the filtration site without antimetabolite use will not occur, and the hypotony the patient is left with will persist," Dr. Parrish explained.

However, the use of anti-scarring medications enables the use of a "different operation" to reduce the risk of hypotony as compared with that performed 30 years ago. The "different" technique involves setting the IOP by adjusting the scleral resistance with sutures and then applying the antimetabolite to prevent the formation of additional resistance at the conjunctiva-Tenon's interface.

Safe glaucoma surgery also mandates aggressive treatment of early and late conjunctival wound leaks that are a significant risk factor for intraocular infection. In addition, patients should be instructed about the signs and symptoms of late-onset bleb infection so that they will seek prompt attention.

For that purpose, Dr. Parrish explained that the mnemonic "RSVP" (red eye, sensitivity to light, vision changes, pain) introduced by corneal surgeon Henry Gelender, MD, of Dallas, is a helpful tool.

Lessons learned

Experience with anti-scarring agents has taught several lessons for optimizing their safe use. The first is the importance of never placing the filtration site inferiorly since inferior blebs are at increased risk to leak and thereby increase the risks of bacterial blebitis and subsequently endophthalmitis.

In addition, in order to create a more diffuse posterior bleb, the flap should be fornix-based, not limbus-based, and the intraoperative MMC should be applied over a larger area (3 or 4 clock hours) versus a more limited region, he said.

"The fornix-based flap [may be] associated with less of an ischemic bleb because it causes less disruption of the conjunctival blood supply," Dr. Parrish said.

Other safety considerations include the use of intraoperative 5-FU 50 mg/ml for 5 minutes as an alternative to MMC in older Caucasians undergoing primary surgery. However, if the choice is made to use MMC in such cases, then a lower concentration, 0.2 or 0.4 mg/ml versus 0.5 mg/ml, and for a shorter exposure time, 2 minutes versus 5 minutes, might also be considered to reduce the likelihood of creating a very thin, avascular conjunctiva.