What are evidence-based management strategies for early postoperative hypotony after glaucoma surgery, including trabeculectomy, tube shunts, and subconjunctival (Minimally Invasive Glaucoma Surgery) MIGS (XEN)?

Management of Early Postoperative Hypotony After Glaucoma Surgery

The management of early postoperative hypotony after glaucoma surgery depends critically on identifying the underlying mechanism—whether from overfiltration, wound leak, or cyclodialysis—and then applying targeted interventions ranging from conservative observation with cycloplegia to surgical revision, with the specific approach varying by procedure type (trabeculectomy, tube shunt, or XEN). 1

Initial Assessment and Monitoring

Define the Clinical Problem

• Hypotony is defined as IOP ≤5 mmHg with potential for vision-threatening complications including hypotony maculopathy, choroidal effusions, and flat anterior chamber 1
• Examine within 12-36 hours postoperatively to assess IOP, anterior chamber depth, and bleb morphology 2
• Perform slit-lamp examination to identify wound leaks (positive Seidel test), overfiltration, or shallow/flat anterior chamber 2
• Use gonioscopy once corneal clarity permits to assess for cyclodialysis cleft 3

Risk Stratification by Procedure Type

• Trabeculectomy with antimetabolites (MMC/5-FU) carries the highest risk of early hypotony due to enhanced filtration and reduced wound healing 1
• Ex-PRESS shunts show higher early hypotony rates compared to standard trabeculectomy in some studies 1
• Nonvalved tube shunts (Baerveldt, Molteno) have higher hypotony risk than valved devices (Ahmed) unless properly restricted during implantation 1
• XEN gel stents demonstrate hypotony rates up to 21.5% in the early postoperative period 4

Conservative Management Strategies

Medical Management for Mild Hypotony (IOP 3-5 mmHg, formed anterior chamber)

• Prescribe topical cycloplegics (atropine 1% or cyclopentolate 1%) to reduce ciliary body inflammation and promote aqueous production 5
• Continue topical corticosteroids at higher frequency (every 2-4 hours) to control inflammation that may reduce aqueous production 2, 5
• Discontinue all aqueous suppressants immediately 5
• Monitor IOP every 2-4 hours initially, then daily until stabilization above 5 mmHg 3, 2

Observation Protocol

• Transient hypotony (lasting <2 weeks) without maculopathy or significant choroidal effusion can be observed as it often resolves spontaneously 6
• However, prolonged hypotony beyond 2 weeks increases risk of permanent visual acuity loss and requires intervention 6
• Examine for hypotony maculopathy (chorioretinal folds) which mandates more aggressive management 1

Procedure-Specific Interventions

Trabeculectomy and Ex-PRESS Management

For Overfiltration:

• Increase aqueous viscosity with intracameral injection of viscoelastic or gas (SF6, C3F8) to temporarily reduce flow 5
• Apply pressure patching or bandage contact lens if shallow but formed anterior chamber 5
• Perform surgical bleb revision if hypotony persists beyond 2-4 weeks: excise excessive conjunctiva, advance Tenon's capsule, or place compression sutures 5

For Wound Leak:

• Apply cyanoacrylate tissue adhesive with bandage contact lens for small conjunctival buttonholes 5
• Perform surgical conjunctival advancement or resuturing for larger leaks that fail conservative management 5
• Aqueous suppression is contraindicated as it worsens hypotony 5

For Flat Anterior Chamber:

• Immediate reformation with viscoelastic or balanced salt solution if lens-cornea touch or significant choroidal effusion present 5
• Drain choroidal effusions surgically if kissing choroids or persistent flat chamber despite medical management 5

Tube Shunt Management

Preventive Strategies (Preferred Approach):

• For nonvalved shunts, use complete intraluminal occlusion with stent plus external ligature at time of implantation to prevent early hypotony while capsule forms 7
• This protocol reduces transient hypotony to <1% and persistent hypotony to 0% compared to historical rates of 10-30% 7
• Perform staged tube opening: laser suture lysis at 4-6 weeks, then partial stent removal, then complete removal based on IOP response 7

Treatment of Established Hypotony:

• Insert 3-0 Supramid multifilament suture into tube lumen via intracameral approach to increase flow resistance without conjunctival dissection 8
• Add external ligature if intraluminal stent alone insufficient 8
• This achieves hypotony resolution in 100% of cases with overall success (IOP 6-21 mmHg) in 78% at mean 33-month follow-up 8
• May require subsequent laser suture lysis or stent adjustment in 44% of cases 8

Alternative Surgical Options:

• Tube ligation with 7-0 or 8-0 absorbable suture if intraluminal approach unavailable 5
• Tube repositioning if malpositioned causing cyclodialysis 5

XEN Gel Stent Management

Early Hypotony Occurs in 21.5% of Cases:

• Perform needling revision with injection of viscoelastic around stent to compress bleb and reduce filtration 4
• Consider intraluminal injection of viscoelastic through the stent lumen 4
• Surgical revision with conjunctival advancement or stent removal if conservative measures fail 4
• Most hypotony cases resolve within first postoperative month with conservative treatment 4

Surgical Intervention Thresholds

Indications for Urgent Surgical Intervention

• IOP ≤5 mmHg persisting beyond 2-4 weeks despite maximal medical management 6
• Flat anterior chamber with lens-cornea touch 5
• Progressive hypotony maculopathy with vision loss 1
• Kissing choroidal effusions not responding to drainage 5
• Persistent wound leak failing tissue adhesive 5

Timing Considerations

• Earlier intervention (within 1-2 weeks) warranted if hypotony maculopathy develops as delayed treatment may result in permanent visual loss 1, 6
• Prolonged hypotony beyond 2 weeks associated with worse final visual acuity outcomes 6

Follow-Up Protocol

Intensive Monitoring Phase (First 2 Weeks)

• Daily visits if IOP ≤5 mmHg or flat/shallow anterior chamber 2
• Check IOP, anterior chamber depth, bleb appearance, and fundus for choroidal effusions 2
• More frequent visits mandatory if complications develop 2

Stabilization Phase (Weeks 2-12)

• Weekly visits until IOP stabilizes above 5 mmHg 2
• Assess for late complications including encapsulated blebs or tube malposition 2
• Taper corticosteroids cautiously while monitoring for rebound inflammation 3, 2

Long-Term Monitoring

• Monthly visits for 3 months, then every 3 months for first year 3, 2
• Assess for permanent glaucomatous damage requiring ongoing treatment 3

Critical Pitfalls to Avoid

• Never continue aqueous suppressants in hypotonic eyes—this worsens the condition 5
• Do not delay intervention beyond 2 weeks if hypotony persists, as prolonged hypotony increases risk of permanent vision loss 6
• Avoid excessive MMC concentration/exposure time as this increases hypotony risk; trend toward lower concentrations (0.2 mg/mL for 2 minutes) 1
• For nonvalved tube shunts, always use flow restriction at implantation rather than treating hypotony after it develops 7
• Do not assume all hypotony is benign—examine carefully for maculopathy even with IOP 3-5 mmHg 1, 6