Glaucoma
December 2023
by Ellen Stodola
Editorial Co-Director
When performing cataract surgery on patients who have a functioning trabeculectomy, there may be an increased risk of trabeculectomy failure. Michael Boland, MD, PhD, and Erin Boese, MD, discussed this risk and how to approach patients.
Dr. Boland said it’s important to be sure patients are aware that there is an increased risk that the trabeculectomy will fail if you do surgery, including cataract surgery. In some cases, the trabeculectomy may not be working optimally preop, and cataract surgery may be a good opportunity to revive it. Dr. Boland would consider some sort of bleb needling procedure at the time of cataract surgery.
He said that since MIGS procedures generally don’t get the pressure as low as trabeculectomy, he usually wouldn’t choose to do cataract surgery plus MIGS if the trabeculectomy failed. He usually tries the needling procedure first because if the patient needed lower pressures to begin with, you’re much less likely to get that with a MIGS procedure. However, the caveat that Dr. Boland mentioned was patients who may have had trabeculectomy a long time ago when fewer surgical options were available. If you decide that the pressure doesn’t need to be that low, Dr. Boland suggested that the surgeon try a less invasive procedure if that trabeculectomy fails. “If your target is not 12 but maybe 18, I would potentially consider some other kind of procedure at the same time,” he said. “I tend to think of MIGS as important for certain targets, but they’re not currently interchangeable with trabeculectomy.”
Source: Michael Boland, MD, PhD
Erin Boese, MD, said that cataract surgery with a well-functioning trabeculectomy can be particularly tricky for a couple of reasons: the risk of bleb failure and errors/variability in the IOL calculations. In both cases, a good preoperative conversation is necessary to manage expectations appropriately. “What I worry about the most is that the cataract surgery may cause the trabeculectomy to not work as well or to fail entirely,” she said. “There are things that can be done to minimize this, but it can still happen even when all precautions are taken.”
Another important preoperative consideration has to do with IOL calculations. If the IOP is on the low side from a well-functioning bleb, Dr. Boese said two things may cause the IOL calculations to be off. One is that a softer eye is often a bit shorter. “If the IOP increases following the surgery and the axial length increased, you may have a myopic surprise, sometimes by a significant amount,” she said. The other aspect that can be off is the astigmatism. “A soft eye will often have regular with-the-rule astigmatism, something that resolves when the IOP is increased,” she said. “I am especially careful not to place a toric lens in these patients if I suspect that the trabeculectomy may be responsible for part of the astigmatism I’m seeing.”
Dr. Boland said he won’t perform cataract surgery until the patient has visually significant symptoms because of the increased risk for trabeculectomy failure. He noted that there’s some evidence that the earlier you do cataract surgery, the more likely you are to cause failure of the trabeculectomy. There’s a concept of the trabeculectomy getting established over months to years, and the longer you can wait, the less likely it is to fail.
Dr. Boese agreed that you should wait to do cataract surgery until there’s a visual impact. “If the cataract is not bothering the patient, I won’t remove it because every extra year that we can get from a well-functioning bleb is a win,” she said. “However, every patient reaches a point where they are ready, and there isn’t any use delaying. I’d much prefer a straightforward and uncomplicated surgery to waiting so long that I’m dealing with a brunescent lens.”
Dr. Boese said ideally cataract surgery would be performed prior to a trabeculectomy; the second best option is to do a combined phacoemulsification/trabeculectomy. “Whenever a patient has a cataract that I anticipate will be visually significant within the next couple of years, I’m typically planning to do a combined phacoemulsification/trabeculectomy so I don’t have to worry about running the risk of doing the phacoemulsification later,” she said. “Of course, this is not always possible. When you have patients with a functioning trabeculectomy who need cataract surgery, I wait at least 6 months until the trabeculectomy is more mature.” Dr. Boese added that there is a high risk of failure within those first 6 months. “Beyond that, I don’t think it matters much if the trabeculectomy is 6 months old or 25 years old—in all cases of a bleb, you still have a risk of trabeculectomy failure with cataract surgery.”
While cataract surgery alone may lower IOP to some extent, Dr. Boland said the impact on trabeculectomy is less clear in this setting. He thinks this factor is less important in these cases. If you have a functioning trabeculectomy, most of the aqueous is going out that way, and the native drainage system may not be functional. He wouldn’t expect the pressure to improve just because you’re adding cataract surgery.
Dr. Boese also said to be cautious when considering studies that show that cataract surgery alone can reduce the IOP. “This is not the case in glaucomatous eyes with a trabeculectomy,” she said. “Studies have shown that even with careful monitoring, IOP on average climbs 2–4 mm Hg following a cataract surgery in an eye with a functioning bleb and sometimes much more than this.” This is thought to be because the small amount of intraocular inflammation stirred up with surgery is enough to scar down the bleb. It can be managed with close postoperative follow-up and steroids. “In cataract surgery following a trabeculectomy, I will often have patients start prednisolone dosing at every 2 hours while awake, rather than my typical QID dosing,” she said.
Dr. Boese noted two preoperative factors that help her prepare for trabeculectomy failure after cataract surgery. “One is where the IOP is compared to our target, and the other is the bleb morphology,” she said. “If the IOP is much lower than our target, we have enough buffer to accept a small reduction in bleb function. However, if we are just at target or if the patient is requiring additional use of glaucoma drops, I am more worried that it will fail. With regard to the bleb morphology, I worry much more about very shallow or flat blebs than taller, diffuse blebs with robust conjunctiva.”
There are also intraoperative risks. A short and uncomplicated cataract surgery will have a much lower risk than a long and complicated cataract surgery, Dr. Boese said, adding that intraoperative iris manipulation increases the risk of inflammation and bleb failure. “Anything intraoperatively that increases inflammation will increase the risk of postop failure, but many of these factors are unavoidable,” she said.
“You can’t treat a cataract after a trabeculectomy the same way as a cataract in someone without a bleb,” Dr. Boese said. “You wouldn’t be faulted to send the patient to have the cataract surgery done by a glaucoma specialist or even better, the person who performed the trabeculectomy. The most important thing is to increase the postoperative steroid regimen significantly. Even a quick, straightforward cataract surgery can lead to enough inflammation to scar down the bleb.” She doesn’t rely on intracameral antibiotics and will often have patients use topical antibiotics after the surgery for a week.
Dr. Boland didn’t note any particular technologies to reduce the risk of the trabeculectomy failing, but he did say it’s important to minimize the surgery time because you want to create the least amount of inflammation possible. He injects an antimetabolite adjacent to the bleb after the cataract surgery and uses frequent topical steroids to reduce inflammation and any fibrosis that may occur.
Bleb failure following cataract surgery is always disappointing, Dr. Boese said, but sometimes unavoidable. “We can add back glaucoma drops, revise/needle the bleb, or in some cases, perform another trabeculectomy or tube,” she said. “I typically find that bleb needling is less effective in mature blebs, but I have had a lot of success with needling a mature bleb failing shortly after cataract surgery. If the conjunctiva is healthy enough to withstand a needling, this is where I’d start, often with an antimetabolite like mitomycin-C. If we just need the IOP down slightly, adding back glaucoma drops is a possibility.”
Dr. Boese said that intraoperatively, she doesn’t find that the fluidics change much following a trabeculectomy, as long as it is a mature bleb. “However, I often use a lower infusion pressure with the goal of causing less bleb turbulence,” she said. “I used to try to put a dollop of cohesive viscoelastic material near the sclerostomy, but this never made any difference. I am a bit more careful not to disturb the trabeculectomy externally as well. This means not using a fixation ring, toothed forceps on the conjunctiva, or nicking the bleb with your main or paracentesis wounds.”
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Lessons learned
Valerie Trubnik, MD, Glaucoma Editorial Board member, shared lessons she has learned to “level up”:
- In order to improve flow in a busy glaucoma clinic, I have learned from senior colleagues that it may be helpful to split up the exam into two parts on separate visits. Perform an OCT RNFL, gonioscopy, and a non-dilated exam with a 90 D lens on the first visit, and bring the patient back for a visual field, dilated exam, and disc photos on follow-up. Portable VR visual field sets may also help improve efficiency.
- I’ve learned that it’s critical to be firm with patients about their set target pressures and IOP control and to hold them accountable regularly during their visits.
- My cornea colleagues have taught me that cyclosporine drops are often underutilized in glaucoma in improving dry eye, which is ubiquitous among our patients, and to help quiet inflamed eyes, especially prior to any filtering surgery.
About the physicians
Erin Boese, MD
Clinical Assistant Professor of Ophthalmology and Visual Sciences
Carver College of Medicine
University of Iowa
Iowa City, Iowa
Michael Boland, MD, PhD
Associate Professor of Ophthalmology
Mass Eye and Ear
Harvard Medical School
Boston, Massachusetts
Relevant disclosures
Boese: None
Boland: Allergan, Carl Zeiss Meditec, Janssen, Topcon Healthcare
Contact
Boese: erin-boese@uiowa.edu
Boland: Michael_Boland@meei.harvard.edu
