Minimally invasive glaucoma surgery (MIGS) have filled a gap in the glaucoma treatment algorithm. MIGS have provided doctors and patients a treatment option between traditional, first-line topical glaucoma medications or laser and aggressive filtration surgeries.
These procedures are defined as using an ab-interno approach, minimally traumatic, modestly efficacious, a high safety profile, and rapid recovery.1
The role of the optometrist in the comanagement of MIGS will only increase as more devices are introduced to the market and more patients undergo MIGS procedures.
Let’s review MIGS procedures, ideal patient candidates, and what optometrists need to be prepared for when managing a variety of MIGS procedures postoperatively.
Trabecular meshwork and Schlemm’s Canal devices
The devices and procedures in this category address outflow issues in a variety of ways.
The iStent (Glaukos), iStent Inject (Glaukos), and Hydrus Microstent (Ivantis) gain access to Schlemm’s canal by stenting through the trabecular meshwork.2-4
The ideal patient candidate is someone with a visually significant cataract, mild to moderate glaucoma, and taking one or two topical glaucoma medications.
Ab-interno canaloplasty (AbiC, Ellex) and Visco360 (Sight Sciences) use microcatheters to viscodilate the trabecular meshwork, Schlemm’s canal, and the distal outflow system.5
The ideal patient candidate is someone with mild to moderate glaucoma, on one or two topical glaucoma medications, and is pseudophakic or has a visually significant cataract.
The Kahook Dual Blade (New World Medical) excises or removes roughly three clock hours of trabecular meshwork, giving aqueous direct access to the collector channels and the distal outflow system.6 The device was designed to be used as a standalone procedure but can be combined with cataract surgery.
Trabectome (Neomedix) ablates 120 to 180 degrees of trabecular meshwork and the inner wall of Schlemm’s canal, lowering resistance to aqueous outflow. This procedure can be used as a standalone procedure or in conjunction with cataract surgery.7
The devices-specifically the stents-in this category are placed in the anatomical angle of the eye and typically not visible with only slit-lamp examination. To visualize the angle and the devices, the optometrist must be proficient with gonioscopy.
Although uncommon, a tuft of iris can obstruct the stent, causing the intraocular pressure (IOP) to elevate. If this is identified, return the patient to the surgeon for obstruction removal. I recommend observing the stent at least one time in the first three months postoperatively and then once per year moving forward.
With the devices and procedures in this category, a mild, transient hyphemia is not uncommon. During the preoperative examination, it is important to tell the patient that there is a possibility of cloudy vision for about one week due to a hyphemia.
This hyphemia, which appears on slit-lamp examination similar to an anterior chamber reaction, is not urgent to address, and the patient can be monitored until it resolves. If a large hyphema is present, the patient should be referred to the surgeon for anterior chamber washout.
Hypotony is not a concern with this category of MIGS because they do not bypass episcleral venous pressure. That means IOP should not decrease below 10 mm Hg.
IOP spikes are a concern in this patient population because their optic nerve heads are compromised from the disease. The decision on how aggressive to be with IOP lowering is based on the severity of the glaucoma.
Because most patients in this MIGS category have mild to moderate glaucoma, control can often be obtained with one or two topical glaucoma medications in the postop period. Once IOP is controlled, medication can be removed to assess the efficacy of the MIGS procedure.
If the IOP spike is severe, the addition of an oral anti-glaucoma medication to topical glaucoma medications can help reduce the IOP. Oral agents are only a temporary fix, but they are effective for a short period of time.
In an emergent situation in which the IOP spike could quickly compromise the health of the optic nerve head, an anterior chamber decompression is an effective way to rapidly decrease IOP. The patient should be placed on topical glaucoma medications and followed closely over the next two to seven days to make sure the IOP spike does not reoccur.
Currently no supracillary devices are approved for use. These devices carry the potential to significantly lower IOP because access to the supracillary space allows bypass of episcleral venous resistance.
Episcleral venous pressure is a range from 8 mm Hg to 10 mm Hg. A patient with moderate glaucoma with a visually significant cataract on one, two, or three topical glaucoma medications is an ideal candidate.
Postoperative considerations are the same as trabecular meshwork and Schlemm’s canal devices, except there is a small risk of hypotony with supracillary devices. In the Study of an Implantable Device for Lowering Intraocular Pressure in Glaucoma Patients Undergoing Cataract Surgery (COMPASS) trial, the rate of hypotony was 2.9 percent.8
CyPass Microstent (Alcon) was removed from the market in September 2018 due to complications resulting in corneal endothelial cell loss that occurred around five years postimplantation.9
In the Study to Assess Long-Term Safety of the Transcend CyPass Micro-Stent in Patients Completing the COMPASS (COMPASS XT) trial, 27.2 percent of patients implanted with CyPass Microstent had greater than 30 percent of endothelial cells loss at five years.9 Device position was the only thing strongly correlated with an increase of endothelial cell loss.9
American Society of Cataract and Refractive Surgeons (ASCRS) task force recommended that stent removal should not occur; however, if the surgeon felt it was necessary to intervene due to positioning, trimming the proximal end of the stent is the preferred procedure.10
It is also encouraged that each patient with a stent have endothelial cell count and pachymetry to monitor for changes to the corneal endothelium and monitor for edema.10
Xen gel stent (Allergan) lowers IOP by creating a drainage pathway from the anterior chamber through the intrascleral anatomy and into the subconjunctival space.11 The device is approved as a standalone procedure for refractory glaucoma in phakic or pseudophakic eyes.
Ideal patient candidates are those on maximum medications and have failed with other medical or surgical treatment options.
Subconjunctival devices form a low-lying filtering bleb postoperatively, so optometrists comanaging this device must monitor for bleb-related complications. These include erosion of the stent through the conjunctiva leading to a leaking bleb or blebitis, fibrosis, and encapsulated bleb.
These complications will cause the device to fail and IOP will not be effectively lowered or in the case of a bleb, leak hypotony can occur.
If fibrosis occurs, bleb manipulation or needling will maintain adequate IOP control. In one study, the rate of bleb needling was 32 percent, similar to what is seen with conventional filtration procedures.12
IOP spikes, obstruction, and transient hyphemia occur with subconjunctival devices. They are managed similar to occurances with other MIGS devices.
Hypotony is another postoperative consideration for optometrist when comanaging a subconjunctival device.
The first step in managing hyptony is discontinuing topical glaucoma medications.
Next, examine the anterior chamber to make sure it is formed with no iridocorneal touch. Perform a fundus examination to rule out choroidal effusions. If the anterior chamber is formed and no choroidal effusions exist, the patient can be monitored.
In the setting of a flat anterior chamber or choroid effusions, the patient will need to be referred to the surgeon for intervention. In one study involving a subconjunctival device, the hypotony rate was 24.6 percent.13 The majority of the hypotony suffered in the study was self-resolving, with only two eyes requiring intervention.
Managing MIGS patients
As primary eyecare providers, optometrists will play an integral role in recommending and postoperatively managing MIGS.
It is imperative that ODs understand the mechanism of action of MIGS procedures and what to expect in the postoperative period.
Patient education preoperatively is as important as managing MIGS patients postoperatively. This education includes setting realistic goals, discussing postoperative complications that can occur, and reminding patients that a MIGS procedure doesn’t cure the disease, only manages it-and periodic follow-ups are necessary.
This is an exciting time in the management and treatment of glaucoma. Now, more than ever before, the toolbox available to treat glaucoma patients is growing-MIGS is one of those tools.
1. Saheb H, Ahmed II. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012 Mar;23(2):96-104.
2. Samuelson TW, Katz LJ, Wells JM, Duh YJ, Giamporcaro JE; US iStent Study Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011 Mar;118(3): 459-67.
3. U.S. Food & Drug Administration. Summary of Safety and Effectiveness Data. iStent inject Trabecular Micro-Bypass System. Available at: https://www.accessdata.fda.gov/cdrh_docs/pdf17/P170043b.pdf. Accessed 12/13/18.
4. Samuelson TW, Chang DF, Marquis R, Flowers B, Lim KS, Ahmed IIK, Jampel HD, Aung T, Crandall AS, Singh K; HORIZON Investigators. A Schlemm Canal Microstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON Study.Ophthalmology. 2018 Jun 23. pii: S0161-6420(17)33810-1
5. Lewis RA, von Wolff K, Tetz M, Koerber N, Kearney JR, Shingleton BJ, Samuelson TW. Canaloplasty: Three-year results of circumferential viscodilation and tensioning of Schlemm’s canal using a microcatheter to treat open-angle glaucoma. J Cataract Refract Surg. 2011 Apr;37(4):682-90.
6. Greenwood MD, Seibold LK, Radcliffe NM, Dorairaj SK, Aref AA, RomÃ¡n JJ, Lazcano-Gomez GS, Darlington JK, Abdullah S, Jasek MC, Bahjri KA, Berdahl JP. Goniotomy with a single-use dual blade: Short-term results. J Cataract Refract Surg. 2017 Sep;43(9):1197-1201.
7. Bussel II, Kaplowitz K, Schuman JS, Loewen NA; Trabectome Study Group. Outcomes of ab interno trabeculectomy with the trabectome by degree of angle opening. Br J Ophthalmol. 2015 Jul;99(7):914-919.
8. Vold S, Ahmed II, Craven ER, Mattox C, Stamper R, Packer M, Brown RH, Ianchulev T; CyPass Study Group. Two-year COMPASS trial results: supraciliary microstenting with phacoemulsification in patients with open-angle glaucoma and cataracts. Ophthalmology. 2016 Oct;123(10):2103-12.
9. Lane S. Overview of the results from the 5 yr follow up study of the CyPass MicroStent. Alcon Research, Ltd. Available at: https://augenchirurgie.clinic/content/5-blog/20180922-alcon-nimmt-micro-stent-zur-glaukombehandlung-vom-markt/modules/2-text/cypassoverview.pdf. Accessed 12/13/18.
10. American Society of Cataract and Refractive Surgery. Preliminary ASCRS CyPAss Withdrawal Consensus Statement. Available at: www.ascrs.org/CyPass_Statement. Accessed 12/13/18.
11. Lewis RA. Ab interno approach to the subconjunctival space using a collagen glaucoma stent. J Catarct Refract Surg. 2014 Aug;40(8):1301-6.
12. Allergan. XEN Gel Stent .Available at: www.allergan.com. Accessed 10/7/18.
13. Allergan. Xen Gel Stent. Available at: www.xengelstent.com. Accessed 10/7/18.