Patients with moderate, severe glaucoma may benefit from MIGS
The Xen gel stent has been shown to reduce IOP and the number of medications in this group.
The goal in the management of primary open-angle glaucoma is to effectively lower IOP with the least invasive approach. Thus, the micro-invasive glaucoma surgeries are becoming more popular.
Micro-invasive glaucoma surgery (MIGS) promotes a greater safety profile with a quicker recovery while lowering IOP. Many of the MIGS procedures can be combined with cataract surgery to allow for a two-in-one procedure. They use an ab-interno approach that typically allows the conjunctiva to remain intact in case future glaucoma filtration surgeries are needed.
One specific type of MIGS is the Xen Glaucoma Treatment System (Allergan), which the FDA approved in November 2016. This procedure lowers IOP by draining aqueous humor into the subconjunctival space rather than using the traditional pathways such as the trabecular meshwork or the uveoscleral pathway.
The ideal candidate for this procedure is a patient whose glaucoma is still advancing with the maximum topical and surgical therapy.
The Xen Glaucoma Treatment System consists of the Xen 45 gel stent and the disposable Xen injector. The gel stent is 6 mm in length and consists of gelatin cross-linked with glutaraldehyde that is stiff when dehydrated but becomes flexible and conforms to the appropriate space when hydrated by the aqueous humor. This hydration leads to a secure gel stent that has less risk of fibrosis or erosion due to its flexible and inert nature. The cross-linking of the gelatin with the glutaraldehyde inhibits degradation of the stent over time. All of these factors lead to a stable structure of the gel stent that appropriately regulates the flow of aqueous humor.
The surgical procedure of the Xen Glaucoma Treatment System can be performed with or without cataract surgery. A corneal incision is made where the Xen injector is inserted. The injector goes through the anterior chamber to the targeted angle. The needle, bevel up, goes through the trabecular meshwork and sclera to end up in the subconjunctival space where the gel stent is released. The Xen gel stent lowers IOP by draining aqueous via the subconjunctival space. A bleb is formed as the aqueous drains, and mitomycin C is recommended to prevent scar formation. The bleb is typically lower and more diffuse than with a trabeculectomy. The properly placed Xen gel stent can be visualized in the angle and in the subconjunctiva. Postoperative complications include hyphema, malposition, conjunctival perforation, hypotony and erosion.
In a clinical trial performed by Allergan, baseline mean IOP was 25.1 (±3.7) mm Hg with the usage of 3.5 (±1.0) hypotensive medications. After 12 months, the mean IOP was 15.9 (±5.2) mm Hg, with the subjects using a mean of 1.7 (±1.5) hypotensive medications with no serious adverse reactions. However, 32.3% of the subjects required bleb needling, mostly due to fibrosis of the bleb (18.5%).
Another study was performed evaluating Xen gel stent implantation in conjunction with cataract surgery (Sheybani). Patients in the study had a mean baseline IOP of 20.8 (± 4.6) mm Hg and used 2.7 (±1.0) hypotensive medications. At 12 months, the mean IOP was 13.1 (±3.6) mm Hg, 0.9 (±1.1) hypotensive medications were used, and there were no significant ocular complications.
A 76-year-old male with primary open-angle glaucoma (POAG) presented for a glaucoma follow-up evaluation. The patient had previous argon laser trabeculoplasty in both eyes. The patient was using brimonidine three times a day, dorzolamide three times a day and pilocarpine three times a day. His IOPs were in the thirties, with POAG progression.
The Octopus G-TOP (Haag Streit) perimetry revealed nasal steps in both eyes, with the right eye being more significant as well as having a superior arcuate defect. Using the Hodapp, Parish and Anderson classification system, both visual fields have a mean deviation of less than -6 dB, which would be considered an early defect. However, both involve the central 5° of fixation, thus should be graded as moderate field defects in both eyes.
The Optovue OCT provided evidence of thinning of the superior and inferior temporal areas of the nerve fiber layer. The OCT also displayed significant ganglion cell complex thinning in the right eye greater than the left. The focal loss volume (FLV) and global loss volume (GLV) are flagged in this patient. Based on these test results, it can be determined that this patient has moderate to severe POAG in the right eye and moderate POAG in the left eye. Lowering of the patient’s IOP is a priority to prevent progression of this disease.
The next step in the treatment of the POAG was phacoemulsification with intraocular lens implantation in combination with Kahook Dual Blade (KDB) goniotomy. This was performed in both eyes in 2017. The IOP lowered to the mid-to-high twenties in both eyes after cataract surgery but was not enough of a pressure reduction considering the severity of the patient’s glaucoma.
Xen was performed on his right eye first, and at the 1-day postoperative visit his IOP was 8 mm Hg OD, and at the 1-week visit his IOP was 15 mm Hg OD. This is a significant decrease in IOP compared to the cataract surgery and KDB goniotomy. The left eye will undergo the Xen procedure in the near future.
Xen in particular is a MIGS that targets patients with moderate to severe glaucoma. The Xen 45 gel stent is designed to accurately regulate the flow of aqueous with its hydrophilic nature. In multiple studies, the Xen gel stent proved to be effective at lowering IOP with less risk of significant side effects (Lavin et al., Fea, Pfeiffer et al.). With all of this in mind, Xen is an important MIGS in 2018.
- Allergan. Directions for use for the Xen Glaucoma Treatment System. Instruction pamphlet. 2017.
- Fea AM. J Cataract Refract Surg. 2010;doi:10.1016/j.jcrs.2009.10.031.
- Keskin AM, et al. Austin Ophthalmol. 2016;1(1):1002.
- Lavin-Dapena C, et al. 12-month results from a minimally invasive, 45 m lumen ab interno gelatin stent in combination with a preoperative MMC from a multicenter study conducted in Spain. Presented at: World Glaucoma Congress; Hong Kong; June 2015.
- Pfeiffer N, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2015.03.031.
- Pillunat LE, et al. Clin Ophthalmol. 2017;doi.org/10.2147/OPTH.S160409.
- Sheybani A AI. Ab interno gelatin stent with mitomycin-C combined with cataract surgery for treatment of open-angle glaucoma: 1-year results. Presented at: American Society for Cataract and Refractive Surgery; Boston; April 18, 2015.
- Voskanyan L, et al. Adv Ther. 2014;doi:10.1007/s12325-014-0095-y.
- For more information:
- Michael Cymbor, OD, is a partner at Nittany Eye Associates and is co-director of the Glaucoma Institute of State College. He can be reached at: firstname.lastname@example.org.
- Gretta Ghaner, OD, is a 2018 graduate of Salus University who practices at Family Eyecare in Johnstown, Pa.
Disclosures: Cymbor is a speaker for Optovue and has received unrestricted research grants from Optovue, Heidelberg and Zeiss. Ghaner reports no relevant financial disclosures.