Many glaucoma specialists and comprehensive ophthalmologists have developed an increased comfort with the management of mild to even moderate glaucoma. This is due largely to the growing list of effective topical medications and less invasive surgical options, such as microinvasive glaucoma surgery (MIGS), which have expanded the glaucoma treatment arsenal.1
Despite these advances, we have all encountered patients with worsening structural and functional damage and intraocular pressures above goal or patients with advanced glaucoma at initial presentation. The management of these patients can be more difficult. And, while a MIGS procedure may be considered in select cases, more invasive glaucoma surgeries are often necessary to achieve very low IOP targets. Even seasoned glaucoma specialists grapple with the decision of when to operate on these patients.
Furthermore, ask a handful of experienced glaucoma specialists which procedure to perform in one of these cases and you are likely to get as many different answers as surgeons you ask. This is because there are a lot of variables to consider when making this decision. The associated risks of these procedures can also weigh heavily on decision-making.
Here we will review some key factors to consider when deciding how to manage patients with advanced glaucoma.
First things first: the glaucoma patient
The first thing to consider when making any clinical decision is, of course, the patient. There are a number of patient variables that should contribute to your choice, including patient demographics, disease severity, and patient compliance with drop therapy and follow-up.
The age of the patient and the presence of comorbidities alters the risk profile of incisional glaucoma surgery. Older patients are at higher risk of complications from anesthesia, are more likely to have other systemic health conditions, such as hypertension and diabetes, and are more likely to be on anticoagulation therapy. All of these factors may increase the risk of serious complications, like choroidal hemorrhage and hyphema. While we generally don’t stop anticoagulants before glaucoma surgery, it should be considered in high-risk individuals, such as monocular patients, when approved by their primary care physician or cardiologist.
It is also important to consider disease severity when deciding which surgical intervention is best for your patient. First, consider the status of both eyes: Is the patient monocular? How severe is the disease in the other eye? What is the patient’s visual function?
The decision to perform a high-risk surgery can be difficult in a monocular patient in whom a vision-threatening or even vision-reducing complication can be devastating. Sometimes in these patients, less is more, and the risks of an advanced surgery, like a trabeculectomy, outweigh the potential benefits. However, if the patient is losing vision quickly and at risk for losing functional vision in their only seeing eye, the risks may be worth it. Additionally, if the patient has severe disease in one eye and mild to moderate disease in the other, the benefits of a more invasive glaucoma surgery in the worse eye may outweigh the risks.
Another important consideration is the patient’s current visual function. Phakic patients should be counseled that they may lose a line or two of visual acuity due to cataract formation. Similarly, trabeculectomy blebs may produce or worsen corneal astigmatism. Patients should understand that the goal of advanced glaucoma surgery is to prevent irreversible vision loss from disease progression and not to improve vision.
It is important that patients have realistic expectations about goals of care. If a significant cataract is already present, the patient may be best served by a combination of cataract removal with glaucoma surgery.
Last, but certainly not least, is patient compliance. Poor patient compliance with medical therapy may cause you to opt for incisional surgery sooner, especially in patients with severe glaucoma who are at risk of vision loss. On the other hand, these patients may have a more complicated postoperative course if they miss drops and follow-up appointments. Trabeculectomy, in particular, requires frequent follow-up with careful postoperative tweaking in order to optimize function and reduce the likelihood of failure.
In patients in whom you suspect noncompliance, it may be helpful to schedule a few appointments to ensure consistent follow-up or to enlist the regular help of family and friends before deciding on a glaucoma surgery.
This list is certainly not all-inclusive, and there are a number of other variables that may affect your surgical decision making in these difficult cases. Sometimes discussing these patients with a colleague will help you realize potential factors that might impact your clinical decision making.
Glaucoma drainage implant versus filtering surgery
When considering an incisional surgery for advanced glaucoma, there are two main options: traditional filtering surgery and glaucoma drainage implants. Traditional filtering surgery includes trabeculectomy or EX-PRESS minishunt (Alcon, Forth Worth, Texas). Glaucoma drainage implants can incorporate the Ahmed Glaucoma Valve (New World Medical, Rancho Cucamonda, CA) or non-valved tubes such as the Baerveldt (Johnson and Johnson Vision, Jacksonville, Florida) or the Ahmed ClearPath (New World Medical, Rancho Cucamonda, CA). In addition to the above-mentioned patient factors, it is important to consider which of these options offers your patients the highest likelihood of success.
Since the publication of the original Tube Versus Trabeculectomy (TVT) study, many glaucoma specialists have migrated towards glaucoma drainage implants and away from trabeculectomy. The TVT compared outcomes of glaucoma drainage implants versus trabeculectomy in patients who had undergone previous ocular surgery.
This study randomized patients to receive either trabeculectomy or placement of a non-valved Baerveldt 350 glaucoma tube. The results demonstrate lower rates of failure with glaucoma drainage implants versus trabeculectomy in this patient population. It is important to note that patients included in this study had undergone previous ocular surgery. In fact, most had undergone previous glaucoma surgery, likely impacting these results.2
The recently published Primary Tube Versus Trabeculectomy (PTVT) study, on the other hand, addressed the question of trabeculectomy or non-valved glaucoma tube as the initial incisional glaucoma procedure in patients with advanced glaucoma.
This study demonstrated no difference in failure rate between trabeculectomy and a non-valved glaucoma device implantation when used as the initial surgical procedure for advanced glaucoma.3 Patients who underwent trabeculectomy also had statistically lower IOP and were on fewer drops at three-year follow-up.3 In summary, while trabeculectomy and tube shunts have similar success rates as primary glaucoma surgeries, glaucoma drainage devices may be better for patients who have already had a prior ocular surgery, and trabeculectomy may be better for patients who need a lower pressure.
Non-valved versus valved glaucoma drainage implants
Glaucoma drainage implants (GDI) can be broadly categorized as either valved or non-valved. The most commonly used valved glaucoma implant is the Ahmed Glaucoma Valve (AGV). Commonly used non-valved tube shunts are the Baerveldt glaucoma implant and Ahmed ClearPath non-valved glaucoma implant. After implantation of a glaucoma drainage implant, a capsule forms around the plate of the device, serving as a reservoir for aqueous fluid, thus reducing IOP. Capsule formation takes approximately six weeks and is necessary to regulate outflow in non-valved implants.
Valved implants have a mechanism that prevents flow across the tube at a set IOP, which eliminates the need for capsule formation to regulate outflow. This allows for immediate pressure lowering and avoids hypotony. Non-valved tubes require surgical modification of the tube to delay flow through the tube for six weeks, until capsule formation occurs in order to avoid hypotony. This may play an important factor in which GDI you choose. In patients with extremely elevated IOPs or in those who need immediate IOP lowering, consider using a valved GDI. Patients with reasonable pre-operative IOP who can wait a few weeks for pressure lowering effect may be candidates for non-valved devices.
Another important consideration is the patient’s goal IOP. While both valved and non-valved implants offer great IOP lowering, there are subtle differences in outcomes. The Ahmed Versus Baerveldt (AVB) study and the Ahmed Baerveldt Comparison (ABC) study compared outcomes of these two GDIs. Both studies show greater IOP lowering and fewer post-operative IOP lowering medications required with the Baerveldt GDI.4,5 However, both studies demonstrated a higher rate of complications with the Baerveldt GDI. In your patients that need a lower IOP, non-valved implants may be a better choice, but you might want to stick to AGVs in monocular patients and patients hesitant about the risk profile of advanced glaucoma surgery.
The type of glaucoma may also impact your choice of GDI.
Patients with neovascular glaucoma often present with a high IOP and need immediate pressure reduction, making an AGV is your best bet. Patients with uveitic glaucoma and steroid-induced glaucoma may also do better with a valved implant to allow for quick IOP lowering and to avoid the potential of future hypotony.
Trabeculectomy versus Ex-PRESS glaucoma shunt
Many glaucoma specialists still consider trabeculectomy to be the gold standard of glaucoma surgery. It offers superior pressure lowering compared to any other glaucoma surgery and is your best bet to achieve a sustainable IOP of 10 or less. But remember, trabeculectomies take work, and they often require a combination of laser suture lysis, needling, or bleb revisions to achieve and maintain target pressures. Hypotony from over-filtration or wound leaks may also complicate recovery and require other post-operative maneuvers and medications to resolve. This requires frequent post-operative appointments and close monitoring, which may be difficult for the patient and for the provider, especially now in the COVID era.
Another fact, which causes great hesitation, is the risk of serious postoperative complications, such as hypotony, choroidal effusions, and choroidal hemorrhage. In order to reduce this risk, some surgeons use the EX-PRESS glaucoma minishunt. This small arrowhead-shaped stent is placed under a scleral flap in a surgical procedure that is otherwise remarkably, similar to trabeculectomy. Studies have shown similar IOP lowering, yet a slightly reduced risk profile, with the EX-PRESS glaucoma shunt when compared to traditional trabeculectomy.6 However, other studies have demonstrated the need for more frequent postoperative manipulations.7 Many surgeons find the EX-PRESS glaucoma shunt implantation technically easier, as it avoids the need for a large sclerostomy and iridectomy.
XEN gel stent
A newer and less invasive option for filtering surgery is the XEN Gel stent (Allergan, Madison, NJ), which received FDA approval in 2016. The XEN Gel stent is a 6-mm porcine gelatin tube with a 45-micron diameter lumen that is implanted in the sclera and provides an outflow of aqueous from the anterior chamber to the subconjunctival space. The procedure is less invasive, allows for a faster recovery, and offers a lower risk profile, making it a good option for high-risk patients.
The XEN Gel implant is ideal for patients with glaucoma refractory to medical therapy who have not undergone previous trabeculectomy or GDI implantation, who have open angles on gonioscopy, and are at a low risk of scarring. The XEN gel stent should be reserved for patients with IOP goals in the mid to low teens, as average IOP lowering at two years is around 14mmHg.9 It is important to counsel these patients on the high risk of postoperative needling, which has been demonstrated to be as high as 50%.9
Cyclophotocoagulation for advanced glaucoma
There is also the option of cyclodestructive procedures to treat patients with advanced glaucoma. Traditionally, transscleral cyclophotocoagulation (CPC) has been reserved for refractory glaucoma in patients who have failed trabeculectomy or GDI implantation, patients who are not surgical candidates due to systemic medical conditions, and in patients with blind painful eyes.8
CPC has a scary list of potential risks, including hypotony, prolonged iridocyclitis, and phthisis bulbi, which has led many glaucoma specialists to reserve CPC for either end-stage eyes or systemically ill patients who can’t tolerate other procedures.
However, more recent treatment protocols with an 810nm diode laser have shown a much lower incidence of serious adverse events. Micropulse CPC (mpCPCP) was also introduced in 2015 and is a less destructive procedure with an improved safety profile compared to traditional CPC. For elderly patients and patients with systemic illnesses that preclude the option of other glaucoma surgeries, mpCPC is an attractive option.
Micropulse treatments can be titrated according to the amount of IOP reduction desired but frequently require one or more retreatments to achieve goal IOP. However, because of the risk of prolonged iridocyclitis, both CPC and mpCPC should be used with caution in patients with inflammatory conditions or uveitis.
Surgical management experience
Finally, there is a lot to be said for a surgeon’s experience. At the end of the day, there are usually a number of good surgical options for a given patient, and your comfort level and skill may be the deciding factor. While it is almost always helpful to discuss patients with colleagues, remember what works well in their hands may not always be what works best in yours. Don’t underestimate the importance of feeling comfortable with the surgical procedure and the postoperative care required, as this is essential for a successful outcome no matter which advanced glaucoma surgery you choose.
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- Boland MV, Corcoran KJ, Lee AY. Changes in performance of glaucoma surgeries 1994-2017 based on claims and payment data for US Medicare beneficiaries. Ophthalmology Glaucoma 2021, doi: https://doi.org/10.1016/j.ogla.2021.01.004
- Geddes SJ, Schiffman JC, Feuer WJ, et al. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study After Five Years of Follow-up. Am J Ophthalmol. 2012 153 (5):789-803.
- Gedde SJ, Feuer WJ, Lim KS, et al. Treatment Outcomes in the Primary Tube Versus Trabeculectomy Study after 3 Years of Follow-up. Ophthalmology 2020; 127:33-345.
- Christakis PG, Kalenak JW, Tsai JC, et al. The Ahmed Versus Baerveldt Study: Five-Year Treatment Outcomes. Ophthalmology 2016; 123: 2093-2102.
- Budenz DL, Barton K, Gedde SJ, et al. Five-Year Treatment Outcomes in the Ahmed Baerveldt Comparison Study. Ophthalmology 2015; 122: 308-316.
- Maris PJ, Ishida K, Netland PA. Comparison of trabeculectomy with Ex-PRESS miniature glaucoma device implanted under scleral flap. J Glaucoma 2007; 16(1): 14-19.
- Tojo N, Otsuka M, Hayashi A. Conventional trabeculectomy versus trabeculectomy with the Ex-PRESS mini-glaucoma shunt: differences in postoperative interventions. Clinical Ophthalmology 2018; 12: 643-650.
- Pastor SA, Singh K, Lee DA, et al. Cyclophotocoagulation: A report by the American Academy of Ophthalmology. Ophthalmology 2001; 108 (11): 2130-2138.
- Mansouri K, Bravetti GE, Gillmann K, et al. Two-Year Outcomes of XEN Gel Stent Surgery in Patients with Open-Angle Glaucoma. Ophthalmology Glaucoma 2019;2: 309-318.