Choice of Procedure and Common Principles
Common Indications
- Progressive glaucomatous optic neuropathy, or intraocular pressure above the individual target pressure despite maximally tolerated medical and/or laser therapy (SLT)
- Intolerance or insufficient adherence to topical therapy
- Target pressure set individually according to disease stage (optic disc findings, visual field defect, life expectancy) per EGS classification
Choice of Procedure (based on the EGS Terminology and Guidelines for Glaucoma)
- Trabeculectomy: the reference procedure when very low, single-digit target pressures (< 12 mmHg) are required, particularly with advanced damage or a high risk of blindness. Highest published pressure reduction, but the most intensive postoperative management (suture lysis, needling) and the highest risk of hypotony/choroidal effusion.
- Deep sclerectomy: a non-penetrating procedure with a more favourable safety profile (less early hypotony, shallow anterior chamber less common) for moderate target pressures (approx. 12–15 mmHg). Slightly lower complete success rate without adjunctive medication than trabeculectomy; secondary Nd:YAG goniopuncture is possible if pressure reduction is insufficient.
- PreserFlo MicroShunt: a standardised ab-externo microshunt, technically simpler and shorter than trabeculectomy (approx. 60 vs. 70 minutes), with comparable pressure reduction in mid-range targets, though bleb revision/needling is more frequent than with deep sclerectomy.
- All three procedures can be used as a primary intervention or in previously treated/scarred eyes (re-operation); with extensive conjunctival scarring, the probability of success of all procedures is reduced.
Common Contraindications
- Active ocular infection/blepharitis
- Insufficient possibility for postoperative follow-up
- Known mitomycin C intolerance
- Heavily scarred, poorly mobilisable conjunctiva in the planned surgical area (relative contraindication; choose the procedure individually)
Common Elements of Informed Consent
- Hypotony, shallow anterior chamber, choroidal effusion/haemorrhage
- Bleb leak, blebitis, and a lifelong (albeit low) risk of endophthalmitis
- Cataract progression, need for revision procedures/needling
- Fluctuating and blurred vision in the early phase; transient diplopia possible
- Success is not guaranteed; adjunctive therapy or re-operation may still be necessary
1. Deep Sclerectomy
Indication
- Primary or secondary open-angle glaucoma (including pseudoexfoliation and pigment dispersion glaucoma) with insufficient pressure reduction despite maximal therapy
- Moderate target pressure and/or increased risk of hypotony (e.g. high myopia, younger patients, single-eye patients)
- Preference for a non-penetrating procedure with faster visual rehabilitation
Differential Diagnosis / Contraindications
- Narrow-angle or angle-closure glaucoma (relative contraindication, as dissection is performed close to the angle)
- Neovascular glaucoma, active uveitis
- Previously operated, heavily scarred conjunctiva in the planned quadrant
Preoperative
- Work-up: gonioscopy, perimetry, OCT of the optic disc/RNFL, central corneal thickness, photo documentation
- Informed consent including signed consent form: intraoperative conversion to trabeculectomy if the trabeculo-Descemet membrane is perforated, possibility of postoperative Nd:YAG goniopuncture, risk of recurrence
- Anticoagulation: adjusted according to in-house standard, in consultation with the referring physician
Preparation
- Tetracaine SDU® 1% eye drops x3 (every 5 minutes)
- Disinfection of lids/lashes/conjunctival sac with Hibidil® solution
Surgical Equipment and Materials
Equipment
Reusable instruments
- Bangerter lid speculum
- Westcott scissors
- Crescent (hockey) knife
- Castroviejo needle holder
- Colibri forceps, McPherson tying forceps
Disposables
- Hibidil® solution, BSS solution
- Lidocaine 1% subconjunctival
- MMC 0.2% on sponges
- 10-0 monofilament suture (scleral flap), Vicryl® 8-0 (conjunctiva)
- Tobradex® eye ointment
Surgical Procedure
Topical anaesthesia with Tetracaine® eye drops. Disinfection of the lids and periocular skin with Hibidil® solution, sterile draping, insertion of the lid speculum. Disinfection and irrigation of the conjunctival sac with Hibidil® solution or BSS.
Subconjunctival anaesthesia in the superior quadrant with lidocaine 1%. Opening of the conjunctiva superiorly with Westcott scissors, dissection of a fornix-based conjunctival flap. Cautery of the superficial episcleral vessels. Marking of a scleral flap approximately 5×5 mm in size, cutting the flap with a limbal hinge. Dissection of the superficial flap to a depth of approximately 200 µm up to the limbus, lifting the flap.
Dissection of a smaller, deeper flap to a depth of approximately 400 µm into the corneal stroma; excision of this deep flap and preparation of a stromal spacer. Placement of MMC 0.2%-soaked sponges for 3 minutes, followed by extensive irrigation with BSS. Peeling of the anterior wall of Schlemm's canal until aqueous humour percolates through the remaining trabeculo-Descemet membrane into the wound bed.
Insertion of the stromal spacer perpendicular to the limbus to keep the intrascleral lake open. Loose, adapting closure of the superficial flap with 10-0 monofilament suture (deliberately loose to promote filtration). Closure of the conjunctiva with Vicryl® 8-0. Tobradex® eye ointment, removal of the lid speculum.
Postoperative
- Tobradex® eye drops 6x/day and ointment at night, tapered over time according to findings
- Analgesia as needed: Dafalgan® 500 mg max. 8x/day, Mefenacid® 500 mg max. 3x/day
Follow-up
- Day 1: visual acuity, IOP, anterior chamber depth, assessment of the bleb and wound
- Week 1: IOP, bleb morphology, adjust steroid therapy if needed
- Weeks 4–6: consider Nd:YAG laser goniopuncture of the trabeculo-Descemet membrane if pressure reduction is insufficient
- 3 months: IOP, visual field/OCT follow-up relative to baseline
- In case of shallow anterior chamber or pronounced hypotony: close follow-up, anterior chamber reformation if needed
2. Trabeculectomy
Indication
- Advanced glaucoma or high risk of blindness requiring very low, single-digit target pressures
- Insufficient pressure reduction after a non-penetrating procedure (e.g. deep sclerectomy) or MIGS
- Secondary glaucomas requiring maximal pressure reduction (provided a primary tube-shunt setting is not indicated)
Differential Diagnosis / Contraindications
- Active neovascular or inflammatory aetiology without prior treatment
- Extensively scarred conjunctiva (consider an alternative site or a tube shunt)
Preoperative
- Work-up: gonioscopy, perimetry, OCT of the optic disc/RNFL, central corneal thickness, photo documentation
- Informed consent including signed consent form: higher risk of hypotony/choroidal effusion than with non-penetrating procedures, need for close postoperative follow-up including possible laser suture lysis and needling, risk of cataract progression
- Anticoagulation: adjusted according to in-house standard, in consultation with the referring physician
Preparation
- Tetracaine SDU® 1% eye drops x3 (every 5 minutes)
- Disinfection of lids/lashes/conjunctival sac with Hibidil® solution
Surgical Equipment and Materials
Equipment
Reusable instruments
- Bangerter lid speculum
- Westcott scissors, Vannas scissors
- Crescent knife, Kelly punch (sclerostomy punch)
- Castroviejo needle holder
- Colibri forceps, McPherson tying forceps
Disposables
- Hibidil® solution, BSS solution
- Lidocaine 1% subconjunctival
- MMC 0.2–0.4 mg/ml on sponges
- 10-0 nylon suture (scleral flap, releasable sutures where applicable), Vicryl® 8-0/9-0 (conjunctiva)
- Tobradex® eye ointment
Surgical Procedure
Topical anaesthesia, disinfection and sterile draping as above. Subconjunctival anaesthesia superiorly with lidocaine 1%. Dissection of a fornix- or limbus-based conjunctiva-Tenon flap in the superior quadrant, with careful haemostasis.
Placement of MMC-soaked sponges over a wide area beneath the conjunctiva/Tenon's capsule and the planned scleral flap for the individually determined exposure time (typically 2–3 minutes depending on scarring risk), followed by extensive irrigation with BSS.
Marking and dissection of a limbus-based scleral flap approximately 4×4 mm in size (approx. 1/3 scleral thickness, rectangular or triangular), prepared into clear cornea. Opening of the anterior chamber beneath the scleral flap. Creation of the sclerostomy with a Kelly punch or scalpel/Vannas scissors. Peripheral iridectomy to prevent iris prolapse or occlusion of the sclerostomy.
Reapproximation of the scleral flap with 2–4 interrupted 10-0 nylon sutures, optionally as releasable sutures for postoperative suture lysis; flow across the flap is regulated by suture tension (tighter for higher risk of early hypotony, looser for insufficient filtration). Watertight closure of the conjunctiva with a running or interrupted suture (Vicryl® 8-0/9-0). Check for bleb formation and watertightness (negative Seidel test). Tobradex® eye ointment.
Postoperative
- Topical steroids initially at high frequency (e.g. 4–6x/day), tapered according to bleb findings
- Topical antibiotic for the first postoperative week
- Analgesia as needed: Dafalgan® 500 mg max. 8x/day, Mefenacid® 500 mg max. 3x/day
Follow-up
- Day 1: visual acuity, IOP, anterior chamber depth, bleb assessment, choroidal/retinal check in case of hypotony
- Week 1: IOP, laser suture lysis or removal of releasable sutures if needed for insufficient filtration; consider suture reinforcement/pressure patch if the pressure is too low
- Weeks 2–3: bleb morphology, needling if early scarring is noted
- 1–3 months: IOP, visual field/OCT follow-up, taper/discontinue pressure-lowering therapy once the target is reached
3. PreserFlo MicroShunt Implantation
Indication
- Primary open-angle glaucoma, pseudoexfoliation and pigment dispersion glaucoma with insufficient pressure reduction despite maximal therapy
- Preference for a standardised procedure that is shorter than trabeculectomy, for a mid-range target pressure
- Alternative for patients at increased risk of early hypotony with gel-stent procedures (non-expanding implant material)
Differential Diagnosis / Contraindications
- Shallow anterior chamber, narrow angle in the planned implantation area
- Insufficient postoperative compliance
- Known MMC intolerance
- Markedly scarred conjunctiva in the planned quadrant
Preoperative
- Work-up: gonioscopy, perimetry, OCT of the optic disc/RNFL, central corneal thickness, photo documentation
- Informed consent including signed consent form: risk of bleb needling (literature approx. 8–15%), early hypotony/choroidal effusion, need for conjunctival revision in case of erosion over the implant
- Anticoagulation: adjusted according to in-house standard, in consultation with the referring physician
Preparation
- Tetracaine SDU® 1% eye drops x3 (every 5 minutes)
- Disinfection of lids/lashes/conjunctival sac with Hibidil® solution
Surgical Equipment and Materials
Equipment
Reusable instruments
- Bangerter lid speculum
- Westcott scissors
- Non-toothed grasping forceps (shunt insertion)
- Castroviejo needle holder
Disposables
- Hibidil® solution, BSS solution
- Lidocaine 1% subconjunctival
- MMC 0.2–0.4 mg/ml on sponges
- PreserFlo MicroShunt implant with applicator/introducer needle
- 10-0 nylon suture (conjunctival/Tenon closure), fluorescein strips (Seidel test)
- Tobradex® eye ointment
Surgical Procedure
Topical anaesthesia, disinfection and sterile draping as above. Subconjunctival anaesthesia superonasally or superotemporally with lidocaine 1%. Creation of a fornix-based conjunctiva-Tenon peritomy approximately 3–4 clock-hours wide in the chosen quadrant, with careful disinsertion of Tenon's capsule and haemostasis.
Placement of MMC-soaked sponges on the episcleral wound bed for the individually determined exposure time, followed by extensive irrigation with BSS. Marking of the scleral entry point approximately 3 mm posterior to the limbus. Creation of a scleral tunnel following the curvature of the globe, with a change in needle direction at the level of the trabecular meshwork, then entry into the anterior chamber parallel to the iris plane using the supplied introducer needle.
Advancement of the MicroShunt implant (bevel oriented upward) along the tunnel until the fixation wings are seated just within the distal scleral tunnel; approximately 2–3 mm of the implant should lie intracamerally. Verification of aqueous flow at the distal end of the shaft; if flow is absent, priming via an anterior chamber cannula may be performed.
Repositioning of the conjunctiva and Tenon's capsule over the implant, avoiding distal obstruction, watertight closure (interrupted or mattress sutures with 10-0 nylon, or a running suture). Watertightness check with fluorescein strips (negative Seidel test). Tobradex® eye ointment.
Postoperative
- Topical steroids initially at high frequency, tapered according to bleb findings
- Topical antibiotic for the first postoperative week
- Analgesia as needed: Dafalgan® 500 mg max. 8x/day, Mefenacid® 500 mg max. 3x/day
Follow-up
- Day 1: visual acuity, IOP, anterior chamber depth, assessment of the bleb and implant position
- Week 1: IOP, bleb morphology; consider early needling if signs of encapsulation appear
- Weeks 2–4: bleb follow-up, needling with 5-FU if needed for insufficient filtration
- 1–3 months: IOP, visual field/OCT follow-up, taper/discontinue pressure-lowering therapy once the target is reached
Additional Notes
How do the three procedures differ in the published evidence?
In comparative cohorts, trabeculectomy achieves on average the lowest pressures (approx. 12 mmHg after 3–5 years, failure rate approx. 28% at 3 years), but with the most intensive follow-up. In 2-year data, PreserFlo achieves qualified success rates of around 79% (IOP approx. 20 → 12 mmHg), with a shorter operating time but more frequent bleb needling than deep sclerectomy. Direct comparative 1-year data for PreserFlo vs. deep sclerectomy show comparable pressure reduction, but a higher complete success rate (without adjunctive medication) for deep sclerectomy.
When should conversion or combination be considered?
If the trabeculo-Descemet membrane is perforated intraoperatively during deep sclerectomy, conversion to conventional trabeculectomy is possible. All three procedures can be combined with phacoemulsification (adjust sequence, target pressure and MMC dosage individually).
Sources
- European Glaucoma Society. Terminology and Guidelines for Glaucoma. 5th/6th Edition. eugs.org
- Jóhannesson G, et al. Guidelines for the management of open-angle glaucoma. Acta Ophthalmol. 2024.
- EyeWiki (American Academy of Ophthalmology). Trabeculectomy; PreserFlo Ab-Externo MicroShunt.
- Comparative study of PreserFlo MicroShunt vs. non-penetrating deep sclerectomy, 1-year follow-up. Clin Ophthalmol (Dove Medical Press).
- PRESERFLO MicroShunt implantation versus trabeculectomy for primary open-angle glaucoma: a two-year follow-up study. Eye and Vision, 2023.
- Review of Ophthalmology. Patient Selection: Trab, Xen or PreserFlo.
- Glaucoma Today. Evolutions in Patient Selection, Sept/Oct 2025.
- Internal surgical protocol ONO (deep sclerectomy), Augenzentrum ONO AG.
