Postoperative complications can have multiple causes and preventative measures
N. Douglas Baker, MD, reviews some of his surgical strategies for avoiding complications after trabeculectomy or a glaucoma tube procedure.
Reviewed by N. Douglas Baker, MD
Complications after glaucoma surgery include a number of different entities-and for each, there is variety of potential causes as well as preventive strategies. N. Douglas Baker, MD, discussed issues relating to site of the trabeculectomy filtering bleb and of the tube location in cases of drainage device surgery.
“I used to think my trabeculectomy procedure was successful if it effectively achieved a low IOP,” said Dr. Baker, in private practice at Ophthalmic Surgeons and Consultants of Ohio, Columbus. “It is also important, however, to create a comfortable bleb, and that requires keeping the aqueous filtration site 3 mm to 4 mm posterior to the limbus.”
He outlined several measures that will help direct aqueous fluid drainage posteriorly and avoid formation of a thin elevated bleb. Dr. Baker explained that he creates a larger scleral flap (5 mm at the limbus and 3 mm at the apex of a trapezoidal configuration). He also recommended suturing the scleral flap with tighter horizontal limbal sutures and leaving the posterior sutures looser.
“For postoperative suture lysis, the posterior sutures should be cut first in order to encourage posterior aqueous filtration,” Dr. Baker said. Achieving meticulous closure of Tenons at the limbus is also valuable.
Dr. Baker said he places three or four episcleral bites nasally when doing the conjunctival and Tenons closure to prevent nasal extension of the filtration bleb. He added that by design, subconjunctival minimally invasive glaucoma surgery devices direct fluid posteriorly and promote formation of a flat limbal bleb.
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To avoid tube exposure, Dr. Baker advised placing the tube perpendicular to the limbus, creating a scleral tunnel with a 23-gauge needle and entering the sclera 4 mm posterior to the limbus.
“It is not uncommon for me to see patients on referral with a tube that was placed just 2 mm posterior to the limbus,” he said. “In that situation, the lid rubs against the tube so that erosion and tube exposure is likely to occur over time even with placement of a patch graft.”
To overcome the risk of endothelial cell loss over time, Dr. Baker said that instead of placing the tube in the anterior chamber, in a pseudophakic patient he places the tube in the posterior chamber, posterior to the iris and anterior to the IOL. The goal is to place the tip of the tube at the pupillary margin and have the tube bevel directed posteriorly to help avoid iris capture.
To prevent early hypotony in a case with posterior chamber placement, Dr. Baker said he usually stents the tube lumen with a 3-0 polypropylene (Prolene) suture and places a non-expansive 14% perfluoropropane (C3F8) gas bubble in the anterior chamber, which will persist for about 10 days.
“Some surgeons will put sodium hyaluronate (Healon) in the anterior chamber, but C3F8 works better to prevent hypotony because it provides outward forces, and unlike the viscoelastic, the gas can also be easily removed with a 1/2-inch, 30-gauge needle paracentesis if the IOP starts to rise because of increased aqueous production,” he explained.
When placing the tube in the vitreous, Dr. Baker said he first places the tube in the vitreous cavity, entering the sclera and vitreous cavity with a 23-gauge needle 4 mm posterior to the limbus.
Then, he has a retinal surgeon perform a complete vitrectomy with air and fluid exchange and placement of a 20% sulfur hexafluoride (SF6) gas bubble into the vitreous cavity. SF6 also lasts for 10 to 14 days, decreasing the risk for early hypotony, Dr. Baker said.
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N. Douglas Baker, MD
This article is adapted from Dr. Baker’s presentation at the 2019 American Glaucoma Society annual meeting. Dr. Baker is a consultant to Molteno and Santen.