Safety Profile of Minimally Invasive Glaucoma Surgery

Kateki Vinod; Steven J. Gedde


Curr Opin Ophthalmol. 2021;32(2):160-168. 

In This Article

Trabecular Meshwork/Schlemm's Canal-based Minimally Invasive Glaucoma Surgery

Trabecular meshwork/Schlemm's canal-based MIGS facilitate aqueous egress from the anterior chamber into collector channels via excision, cleavage, dilation, or microstenting.[6] A minimal degree of blood reflux from Schlemm's canal is an expected intraoperative event indicating that the correct anatomical target has been accessed.


Trabectome (NeoMedix Inc., Tustin, CA, USA) is a handheld electrocautery device with its own irrigation/aspiration system that ablates up to 180 degrees of the trabecular meshwork and inner wall of Schlemm's canal. Ab interno trabeculectomy using Trabectome may be performed with or without concomitant phacoemulsification (phaco) cataract surgery. In a metaanalysis of 5091 patients who underwent phaco-Trabectome or Trabectome alone, the most common complications were hyphema (up to 100%), peripheral anterior synechiae (PAS; 14% of 101 eyes), and intraocular pressure (IOP) spikes (6% of 1127 eyes).[7] Spontaneous, delayed hyphema was reported in 12 of 262 (4.6%) patients up to 31 months after uncomplicated Trabectome in one retrospective case series.[8] Additional glaucoma surgery may be required to control IOP elevation resulting from delayed hyphema after Trabectome.[8,9] Intraoperative blood reflux has also been described during cataract surgery[10] and trabeculectomy[11] in patients with a history of prior Trabectome. Recurrent hyphema was implicated as a potential contributor to nocturnal IOP spikes measured using the Sensimed Triggerfish (Sensimed AG, Lausanne, Switzerland) contact lens sensor in a patient who reported nightly pain symptoms following Trabectome, which resolved with topical IOP-lowering therapy.[12]

Corneal injury, including trauma to Descemet's membrane, occurred in 6 of 101 (6%) patients in a study by Minckler et al..[13] Mean endothelial cell density was not found to change up to 36 months after Trabectome with or without cataract surgery in a retrospective study of 159 eyes.[14]

In a chart review of 600 eyes that underwent trabeculectomy, tube shunt surgery, cyclophotocoagulation, or Trabectome, none of the Trabectome eyes required reoperation for complications within 90 days.[15] However, vision-threatening complications have rarely been reported following Trabectome, including aqueous misdirection (four cases), endophthalmitis (one case), and suprachoroidal hemorrhage (one case).[7] Although hypotony following Trabectome is generally transient and without visual sequelae (1.5% of 1127 cases),[16] inadvertent cyclodialysis cleft creation may result in prolonged hypotony[17,18] and require surgical repair.[18]

Kahook Dual Blade

The Kahook Dual Blade (KDB; New World Medical, Inc., Rancho Cucamonga, CA, USA) is a disposable goniotomy knife used to excise and remove a strip of trabecular meshwork. KDB goniotomy may be performed as a stand-alone procedure or with concurrent cataract surgery. Retrospective studies have identified transient hyphema (up to 17%) and IOP spikes (up to 17%) as the most common early postoperative complications associated with KDB and/or phaco-KDB.[19–25] In a prospective randomized trial comparing phaco-KDB (n = 82) to phaco-iStent (n = 82; Glaukos Corp., San Clemente, CA, USA), 26 (31.7%) phaco-KDB eyes developed IOP spikes responsive to medical therapy, and three (3.7%) phaco-KDB eyes had hyphema persisting beyond the first postoperative week.[26] Descemet's membrane injury during KDB goniotomy is rare, occurring in two of 42 (3.8%) eyes in one retrospective study.[21] Cyclodialysis cleft is also infrequent (up to 1.2%),[23,26] and cases refractory to conservative management may require treatment with argon laser photocoagulation.[27]

Gonioscopy-assisted Transluminal Trabeculotomy

Gonioscopy-assisted transluminal trabeculotomy (GATT) involves circumferential cannulation and subsequent cleavage of Schlemm's canal using a suture or illuminated microcatheter (iTrack, Ellex, Mawson Lakes, Australia). A metaanalysis of 537 eyes by Guo et al.[28] found hyphema (12.5–80.6%), IOP spike (1.9–32.3%), and transient hypotony (4.5–6.5%) to be the most frequent complications following GATT. Descemet's detachment (0.5%), iridodialysis (0.5%), and vitreous hemorrhage (2.9%) occurred less commonly.[28] Choroidal effusions have been detected using anterior segment optical coherence tomography (AS-OCT) in up to 47.7% of patients undergoing GATT,[29,30] and are thought to result from cyclodialysis cleft formation, relative hypotony, inflammation, or a combination of mechanisms. Although choroidal effusions following GATT are typically asymptomatic and self-limited, Aktas et al.[31] observed two cases of associated myopic shift (−4.5 and −6.0 diopters) in the absence of hypotony or cyclodialysis cleft. Both resolved spontaneously within the first postoperative week. Yalinbas et al.[32] reported intracapsular hemorrhage posterior to the intraocular lens implant following phaco-GATT in two patients with pseudoexfoliation glaucoma. One patient underwent successful yttrium-aluminum-garnet (YAG) capsulotomy to clear the hematoma, and the other required intraocular lens exchange and anterior vitrectomy due to capsular phimosis and intraocular lens subluxation. A case report by Aktas et al.[33] described panscleritis with serous retinal detachment developing after GATT in a patient with active idiopathic anterior uveitis at the time of surgery. Although the panscleritis responded well to systemic steroids, the serous retinal detachment remained refractory to treatment at three months.

Ab Interno Canaloplasty

Ab interno canaloplasty (ABiC) employs an illuminated microcatheter to circumferentially dilate Schlemm's canal with cohesive viscoelastic, thereby extracting compressed trabecular meshwork from within the ostia of collector channels. Published data are limited to retrospective series, in which transient postoperative microhyphema/hyphema have been reported.[34,35] Microhyphema limiting the visual acuity was observed in 19 of 36 (52.8%) eyes in one series, and cleared over one to two days.[34] Izquierdo Villavicencio et al.[36] described a hemorrhagic Descemet's membrane detachment thought to result from forceful viscoelastic injection during ABiC, which resolved after three months of observation.

iStent and iStent Inject

The first-generation iStent and second-generation iStent Inject (Glaukos Corp., San Clemente, CA, USA) are heparin-coated titanium microstents that are inserted into Schlemm's canal using preloaded injectors. Both devices are Food and Drug Administration (FDA)-approved for implantation during concomitant cataract surgery. A metaanalysis of patients undergoing iStent or iStent Inject with or without phacoemulsification reported adverse events in 261 of 1159 (22.5%) eyes but did not provide rates of specific complications.[37] Adverse events reported in randomized clinical trials evaluating the iStent and/or iStent Inject included hyphema (1.2–1.9%), IOP spike (1–33.3%), corneal injury (3.1%), PAS formation (1.8%), and cyclodialysis cleft (1.2%).[26,38–46] Stent-related complications included obstruction (1–13.2%) and malposition (3–18%).[26,38–46] Persistent loss of best-corrected visual acuity (BCVA) has been reported in 0.9–2.6% of patients undergoing iStent or iStent Inject.[26,38–46] Case reports have described recurrent hyphema following iStent implantation.[47,48] Sandhu et al.[48] reported two episodes of spontaneous delayed-onset hyphema 13 and 19 months after uncomplicated phaco-iStent in a patient who slept on the affected side, both of which resolved with conservative management.

Hydrus Microstent

The Hydrus microstent (Ivantis Inc., Irvine, CA, USA) is an 8-mm nitinol scaffold that is inserted into Schlemm's canal using a preloaded injector to improve aqueous access to collector channels across a three-clock hour arc. The microstent is FDA-approved for implantation during cataract surgery. Most complications of the Hydrus microstent tend to be self-limited, including hyphema (0.5–36.0%), IOP spike (0.5–20%), and corneal edema (1.4–28.0%).[49,50] Adverse events relating to the microstent itself include focal PAS (8.7–20.0%), device obstruction (1.1–12.2%), and device malposition (1.1%).[50] Loss of BCVA of two or more Snellen lines following Hydrus microstent implantation occurred in one of 369 (0.3%) patients in a pivotal randomized study[51] comparing phaco-Hydrus to phaco alone, and in two of 75 (2.7%) patients in a randomized clinical trial comparing the Hydrus microstent versus two iStents.[38]