Minimally invasive glaucoma surgery promises to deliver modest IOP lowering for mild and moderate stages of open-angle glaucoma with minimal tissue disruption and complications. Narrow angles and advanced glaucoma stages are considered relative contraindications. Questions also remain about how much IOP reduction is truly attributable to MIGS because of the effect of cataract surgery on IOP that is often performed at the same time.
Multiple MIGS devices have been introduced or are currently in development. Ab interno trabeculectomy with the Trabectome (NeoMedix) is the oldest MIGS modality that is FDA approved for adult and pediatric open-angle glaucoma. It lowers IOP by increasing aqueous outflow using plasma-mediated ablation of the trabecular meshwork.
A narrow anterior chamber angle is considered a relative contraindication to MIGS due to concern about angle access and visualization and formation of peripheral anterior synechiae. This precludes a large number of glaucoma patients from a surgery with a highly favorable risk profile and near absence of vision-threatening complications seen in traditional glaucoma surgeries.
Although numerous studies have described the safety and efficacy of Trabectome surgery in the treatment of glaucoma, the relationship between anterior chamber angle grade and outcomes has not been formally examined. Here, we discuss the results of our nonrandomized prospective study regarding how the degree of preoperative angle opening (Shaffer angle grade, SG) relates to IOP outcomes of Trabectome surgery or combined phacoemulsification with Trabectome surgery. We hypothesized that narrow angles would be associated with worse IOP reduction and a higher failure rate.
We evaluated Trabectome and phaco-Trabectome with narrow angles with a SG of 2 or less vs. open angles with a SG of 3 or more. Outcomes included IOP, medications, complications, secondary surgery and success, considered as IOP less 21 mm Hg with a more than 20% reduction without further surgery. Exclusion criteria were missing preoperative data and less than 1 year of follow-up.
From the 671 included cases, at 1 year, 43 Trabectome cases with a SG of 2 or less had an IOP reduction of 42% from 27.3 ± 7.4 mm Hg to 15.7 ± 3 mm Hg (P < .01) vs. 271 Trabectome cases with a SG of 3 or greater with an IOP reduction of 37% from 26.1 ± 7.8 mm Hg to 16.4 ± 3.9 mm Hg (P < .01). In 48 phaco-Trabectome cases with a SG of 2 or less, IOP was reduced 24% from 20.7 ± 7 mm Hg to 15.7 ± 3.6 mm Hg (P < .01) vs. 309 phaco-Trabectome cases with a SG of 3 or greater with an IOP reduction of 25% from 22.6 ± 6.4 mm Hg to 17 ± 3.4 mm Hg (P < .01) (Figure). In addition, there was no statistically significant difference between SG of 2 or less and SG of 3 or greater in reduction of IOP or medications, complications, secondary surgery and success rates.
In separate studies, we examined the contribution of phacoemulsification to the IOP effect of Trabectome surgery. Using Coarsened Exact Matching in 753 patients, phacoemulsification did not contribute significantly. Stratification of results of Trabectome without or with phacoemulsification by glaucoma severity indicated that eyes with severe glaucoma had an IOP reduction of 12 ± 8 mm Hg vs. eyes with mild glaucoma with only 4 ± 5.4 mm Hg. Linear regression showed that IOP reduction was associated with glaucoma severity after adjusting for age, gender, race, diagnosis, cup-to-disc ratio and Shaffer grade.
Narrow angles have previously been seen as a relative contraindication to Trabectome surgery, while phaco-Trabectome has been performed in narrow angles with less concern because removal of the crystalline lens deepens the anterior chamber angle and may resolve angle closure. Phacoemulsification independently has been demonstrated to decrease IOP by up to 3 mm Hg, for a variety of theoretical reasons involving mechanical and sensory pathways involving the trabecular meshwork and Schlemm’s canal. However, after trabecular meshwork ablation, one would not expect an additional IOP reduction via these mechanisms, as suggested by our study.
Our results show that Trabectome surgery can also be considered in the relatively large population of patients with narrow angles. Cataract surgery is not a significant contributor to outcomes in open or narrow angles. Trabectome surgery can be considered in more advanced glaucoma in which it reduces pressure more than in mild glaucoma.
Future of MIGS
UPMC Eye Center continues to try to advance our understanding of ocular outflow and technologies enhancing it. We have previously demonstrated a role for MIGS in the setting of failed trabeculectomy and now present data supporting the use in narrow angles and more advanced glaucoma, both previously seen as contraindications. Our current investigations are focusing on changes of angle structures before and after MIGS to establish anatomically targeted outflow enhancement.
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- For more information:
- Nils A. Loewen, MD, PhD, an associate professor of ophthalmology and the director of the Glaucoma and Cataract Service at UPMC, can be reached at Eye & Ear Institute, 203 Lothrop St., Pittsburgh, PA 15213; email: firstname.lastname@example.org.
Disclosure: Loewen reports he is a Trabectome trainer.