- •There are 3 main approaches to glaucoma surgery: subconjunctival, Schlemm canal–based, and suprachoroidal/ciliary body.
- •Subconjunctival glaucoma surgery is ideal for patients with advanced disease, low target pressures, and prior failed surgery.
- •Although transscleral cyclophotocoagulation has classically been reserved for patients with refractory glaucoma, micropulse technology might become an indispensable tool used earlier during the disease process, sparing the higher frequency of serious complications of the older technology.
- •Although Schlemm canal–based procedures are usually considered in mild to moderate glaucoma cases with controlled or slightly above-target intraocular pressure and are often combined with cataract surgery, suprachoroidal shunts are still struggling to find their role and currently undergoing further trials to validate their efficacy and safety.
- •Preliminary evidence implies a possible role for some of the newer microinvasive glaucoma surgery in treating patients with prior failed incisional surgery.
- •Age and life expectancy
- •General health status, type of work, comorbid eye disease, and so forth
- •Type of glaucoma
- •Angle status (narrow, closed, open)
- •Lens status (phakic, cataract, pseudophakia, aphakia)
- •Level of glaucoma damage
- •Preoperative IOP
- •Target IOP
- •Refractive status (myopia, presbyopia)
- •Past ocular surgeries and ocular comorbidities
- •Resource availability
- •Reimbursement issues
When not to opt for subconjunctival surgery?
Nonpenetrating glaucoma surgery
- •Microperforations and macroperforations intraoperatively with possible iris incarceration. In the latter case, there is need to convert to a classic trabeculectomy procedure.
- •Insufficient deep flap dissection causing high pressures postoperatively.
- •Postoperative hyphema, which usually absorbs within a few days without complications.
- •Neovascular glaucoma (NVG)
- •Iridocorneal endothelial (ICE) syndrome
- •Chronic angle-closure glaucoma (relative)
- •Posttraumatic angle recession with extensive damage to the trabecular meshwork (TM)
- •Aphakic glaucoma
- •Active ocular inflammation
- •Thin sclera
XEN Gel Implant (Allergan Inc, Irvine, CA, USA)
Preserflo Microshunt (Santen Pharmaceutical Co Ltd, Osaka, Japan)
- 1Patients with previous ocular surgeries, including failed glaucoma surgery. The Tube versus Trabeculectomy study (TVT) was a multicenter randomized controlled trial (RCT) that compared the safety and efficacy of these 2 procedures in eyes with previous ocular surgeries. The trabeculectomy group had a higher rate of failure at 5 years, with higher rates of early postoperative complications.
- 2High risk for trabeculectomy failure, such as in NVG, chronic or recurrent uveitis, ICE syndrome, and pediatric glaucoma.
- 3Patients with scarred conjunctiva owing to ocular cicatricial pemphigoid, Stevens Johnson syndrome, and so forth.
Schlemm canal–based procedures
Selective laser trabeculoplasty
- 1Ocular hypertension
- 2POAG and normal-tension glaucoma
- 3PXE glaucoma
- 4Pigmentary glaucoma
- 5Primary angle closure (PAC)/PACG with patent iridectomy and visible angle at least 180°
- 6Steroid-induced glaucoma
- 1Uncontrolled uveitic glaucoma
- 3Poor visualization of the TM
Schlemm canal–based microinvasive glaucoma surgery
- 1Removal of the TM and inner wall of Schlemm canal
- 2Disruption of the TM and inner wall of Schlemm canal
- 3Implantation of a microstent to bypass the TM
- 4Dilation of Schlemm canal via an internal approach
|Removal of the trabecular meshwork and inner wall of Schlemm canal (ab interno trabeculectomy)|
|Device||Manufacturer||Design and technique||Efficacy|
|Trabectome||NeoMedix, Tustin, CA, USA||Single-use electrocautery handpiece with irrigation and aspiration unit, for removal of 60°–120° of the trabecular meshwork||Inconclusive results regarding efficacy|
Seventy-eight percent of patients achieve IOP between 6 and 15 mm Hg and at least 20% IOP reduction without medications when combined with phaco at 2 y according to 1 report [
|Kahook Dual Blade||New World Medical, Rancho Cucamonga, CA, USA||Single-use disposable blade with a sharp tip, which is used to pierce the trabecular meshwork, a ramp which stretches the trabecular meshwork, and dual parallel blades, which create paired parallel incisions in the trabecular meshwork||Phaco combined Kahook Dual Blade might be at least as effective as phaco-iStent for reducing IOP and medication burden [|
|Bent AbInterno Needle Goniectomy||Trabeculotomy using the bent tip of a 25-gauge needle||No long-term data available|
|Disruption of the trabecular meshwork and inner wall of Schlemm canal (ab interno trabeculotomy)|
|Device||Manufacturer||Design and technique|
|Gonioscopy-assisted transluminal goniotomy (GATT)||Ellex iScience, Fremont, CA, USA||Trabeculotomy 180°–360° using a 250-μm iTrack microcatheter with a fiberoptic tip advanced through the canal|
Trabeculotomy 360° using a Prolene 5-0 suture
|Efficacy reported in primary, secondary, and juvenile open-angle glaucoma and prior incisional glaucoma surgery [|
Younger age may be predictive of success [
|Trab360/OMNI||Sight Sciences, Menlo Park, CA, USA||Single-use handpiece with a microcatheter advancing from the tip allowing 2 opposite 180 trabeculotomies|
|Implantation of a microstent to bypass the trabecular meshwork|
|Device||Manufacturer||Design and technique|
|iStent G1||Glaukos Corporation, San Clemente, CA, USA||Snorkel-shaped heparin-coated, nonferromagnetic titanium stent|
Central inlet: 120 μm
|At 48 mo follow-up, a 14.2% between-group difference in favor of the combined iStent-phaco group vs phaco-only group was statistically significant for mean IOP reduction, compared with the phaco-only group, with a significant reduction in number of medications in both arms [|
|iStent inject-W||Glaukos Corporation, San Clemente, CA, USA||Bullet-shaped heparin-coated, nonferromagnetic titanium stent|
Inject: 0.36 width × 0.23 height
Central inlet: 80 μm
Inject: W: 0.36 mm width × 0.36 height
Central inlet: 80 μm
|At 24 mo, 75.8% of phaco-iStent inject eyes vs 61.9% of control phaco only eyes experienced ≥20% reduction from baseline in unmedicated IOP, while 83% of treatment arm achieving target unmedicated [|
|Hydrus||Ivantis Inc, Irvine, CA, USA||Biocompatible nitinol 8-mm-long trabecular bypass device with 3 openings|
Increases trabecular outflow and scaffolds the Schlemm canal
|At 24 mo, 77% of open-angle glaucoma patients achieved 20% or more decrease in unmedicated IOP after phaco-Hydrus compared with 57.8% in the phaco-alone group, with 1.4/1 medication reduction, respectively [|
|Dilation of Schlemm canal via an internal approach|
|Device||Manufacturer||Design and technique|
|Ab Interno Canaloplasty||iTrack microcatheter inserted through a small goniotomy and passed 360° with viscodilation on retraction||When compared with Hydrus, both implants allowed significant IOP reductions, with comparable rate of clinical success and safety profile [|
|VISCO360/OMNI||Sight Sciences, Menlo Park, CA, USA||OMNI system combines the TRAB360 with the VISCO360|
- 1Patients well controlled or slightly above target under medical treatment presenting for cataract surgery
- 2Patients with OAG mainly owing to trabecular dysfunction, including patients with PXE and pigment-dispersion glaucoma, and select cases of angle-closure glaucoma
- 3Patients willing to reduce burden of medical treatment owing to cost, comfort, or tolerance issues
- 4Patients with uncontrolled pressures found inapt to undergo subconjunctival surgery
- 1Patients with high EVP, such as Sturge-Weber syndrome
- 2Patients who perform Valsalva maneuver very often, such as heavy weight-lifters, because of the increased risk of recurrent hyphemas mainly after excisional procedures
- 3Patients with active ocular inflammation
- 4Phakic patients with angle closure as a standalone procedure
- 5Patients requiring low target IOPs
- 6Multiple drug allergies precluding possible additional glaucoma medications postoperatively
- 1Phaco-MIGS procedures in general achieved higher mean reduction of IOP and postoperative medications relative to control.
- 2iStent as a standalone procedure is more effective than medication alone and reduces postoperative medication use.
- 3Implanting a second iStent adds to the IOP reduction, while implanting a third has a less pronounced additive effect.
- 4Hydrus standalone procedure performs better when compared with iStent or ABiC.
- 5Data regarding other Schlemm canal–based surgeries were less conclusive, and some did not meet the quality criteria set by the researchers.
CyPass (Alcon, Fort Worth, TX, USA)
MINIject (iSTAR Medical, Isnes, Belgium)
iStent Supra (Glaukos, San Clemente, CA, USA)
Patients with very advanced disease
Patients with very high intraocular pressure
Patients with angle-closure glaucoma
- •Primary angle-closure suspect (PACS)
- •Patients with symptoms characteristic of intermittent or impending episode of AAC
- •Patients with low compliance to treatment and follow-up
- •Patients with AAC in the fellow eye
- •Patients with family history of angle-closure glaucoma
- •Patients with retinal disease necessitating frequent fundus examinations
Primary angle closure
Primary angle-closure glaucoma
Patients with neovascular glaucoma
Reoperation after failed glaucoma surgery
- 1Failed conjunctival surgery:
- •If the first surgery is salvageable, it might be wise to save the resting conjunctiva for later options and try to perform needling or revision of the bleb with injection of antifibrotics to increase the chances of success. Reports about revision of trabeculectomy surgery have yielded good long-term results [].
- •If the first operation is not salvageable, as in the case of high risk for postoperative leak because of an ischemic bleb or very scarred conjunctiva, then one should think about performing another type of conjunctival surgery if the condition of the conjunctiva allows, and in any case, performing a tube surgery should be strongly advised, as the chances of success might be higher with this type of surgery, as reported in earlier studies.
- •Angle surgery also might be an option to be considered. Gonioscopy-assisted transluminal trabeculotomy (GATT) was shown to be safe and successful in treating 60% to 70% of open-angle patients with prior incisional glaucoma surgery, including trabeculectomy and tube shunts in 1 retrospective study [].
- 2Failed angle surgery:
- Early failure of a Schlemm canal–based surgery might indicate a diseased distal outflow rendering a second-angle surgery less plausible. In the case of a later failure, another angle-based operation might be not feasible, as in the case of removal of large portions of the TM in GATT surgery.
- Similarly, after trabectome surgery in which only part of the TM is excised, treating the rest of available TM with SLT, has shown a very limited duration of significant IOP-lowering effects with low success rates []. A histopathologic study comparing changes after iStent, which spans a very limited area of the TM, when compared with specimens from normal and glaucoma human TM tissues showed histopathologic changes adjacent to the location of implants consistent with inflammation and scarring [], a fact that might preclude a second-angle surgery spanning the nasal angle. In this case, one might opt directly for the subconjunctival route or ciliary body procedures, as they have a higher chance of success.
- 3Failed tube surgery:
- In this case, there are several options to consider:
- •If the tube is thought to be functioning, but to a limited extent, one might try flushing the tube with saline or viscoelastic using a 30-cc syringe via an ab interno or externo approach
- •Revision of the bleb over the tube with excision of the capsule restricting flow
- •Replacement of valved implant to a nonvalved implant
- •Insertion of a second tube in an opposite quadrant
- •Performing CPC laser. One study comparing this technique to insertion of a second tube has shown a superior long-term efficacy for CPC with more VA conservation at 12 months, but with more secondary interventions needed []. The American Glaucoma Society (AGS) is sponsoring a trial to compare a second Baerveldt shunt to diode cyclophotocoagulation (the ASSISTs trial [AGS Second aqueous Shunt Implant vs TransScleral Treatment Study]).
- •Performing Schlemm canal procedures. One study reported a success rate of 84% at 12 months after trabectome surgery for a failed tube surgery []. Similar success rates have been described as mentioned earlier with the GATT procedure after incisional surgery.
- •Limited reports have described the use of a retrobulbar shunt device connecting the anterior chamber into the retrobulbar space, although it is not yet commercially available and is undergoing further studies [].
- Failed subconjunctival
- •Bleb revision
- •Schlemm canal–based
- •Ciliary body/suprachoroidal
- Failed angle
- •Ciliary body/ suprachoroidal
- Failed GDD
- •Tube revision
- •Implant replacement
- •Second GDD
- •Ciliary body/suprachoroidal
- •Schlemm canal–based
- •Retrobulbar shunt
Current relevance and future avenues
Clinics care points
- •In patients requiring low target pressure postoperatively, one should opt for subconjunctival surgery.
- •Avoid doing Schlemm canal–based procedures, especially excisional procedures, in patients who perform Valsalva or those with high episcleral venous pressure.
- •One must make all efforts to prevent hypotony in patients undergoing subconjunctival surgery, especially in older patients with very high preoperative pressures and advanced disease.
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