Glaucoma Drainage Devices

Glaucoma Drainage Devices

Glaucoma Drainage Devices

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GDD Basics - Tube Time Intro

  • Glaucoma Drainage Devices (GDDs): Implantable shunts creating an alternative pathway for aqueous humor outflow from anterior chamber to a subconjunctival bleb, bypassing diseased trabecular meshwork.
  • Goal: Achieve target intraocular pressure (IOP) & prevent further optic nerve damage.
  • Main Indications:
    • Refractory glaucomas
    • Previous failed trabeculectomy
    • Neovascular glaucoma
    • Uveitic glaucoma
    • Traumatic glaucoma
    • Congenital/Juvenile glaucoma

Glaucoma Drainage Device Mechanism

⭐ GDDs are preferred in eyes with extensive conjunctival scarring or high risk of trabeculectomy failure due to their ability to shunt aqueous to a posterior location, avoiding scarred anterior conjunctiva.

Device Roster - The Valve Lineup

Glaucoma Drainage Devices (GDDs) are classified as Valved or Non-Valved:

FeatureValved (e.g., Ahmed - AGV)Non-Valved (e.g., Baerveldt - BGI, Molteno)
MechanismFlow-restrictive valve (opens ~8-12 mmHg)No valve; requires temporary ligation/stent (e.g., 5-0 nylon)
MaterialSilicone / PolypropyleneSilicone / Polypropylene
Advantages↓ Early hypotony riskPotentially lower long-term IOP
DisadvantagesHypertensive phase common↑ Risk of early hypotony if ligation fails
Plate Sizes (mm²)AGV: S2 (184), FP7 (184)BGI: 250, 350; Molteno: 130, 270
Mnemonic 📌Ahmed is Always ready (valved)Baerveldt is Bigger & Blocked initially (non-valved)

Surgical Snippets - Implant Insights

  • Anesthesia: Peribulbar, retrobulbar, or general.
  • Conjunctival Flap: Fornix or limbus-based created.
  • Plate Placement: Typically superotemporal quadrant. Positioned 8-10 mm posterior to the limbus.
  • Tube Insertion:
    • Into anterior chamber (AC) via scleral tunnel or needle track.
    • Bevel up (common), 1-3 mm into AC.
    • Parallel to iris, avoiding cornea/lens.
  • Patch Graft: Scleral, pericardial, or donor corneal tissue covers scleral portion of tube.
  • Priming/Ligation: Valved devices (e.g., Ahmed) primed. Non-valved (e.g., Baerveldt) often ligated with a releasable suture.
  • Closure: Meticulous conjunctival and Tenon's closure.

⭐ A patch graft (scleral, pericardial) over the scleral portion of the GDD tube is crucial to prevent tube erosion through the conjunctiva.

Trouble Shooters - Complication Control

  • Key Goal: Maintain IOP control & minimize GDD-related morbidity.
Complication TypeExamplesKey Features/Management Hints
EarlyHypotony, Choroidal effusion/hemorrhage, Shallow AC, Tube-cornea touch, Diplopia, Hypertensive phase, Tube obstruction (blood/iris)Hypotony: Observe, cycloplegics, steroids; may need AC reformation. Hypertensive phase (📌 Healing Plateau): Aqueous suppressants, steroids.
LateTube erosion/exposure, Plate encapsulation (Tenon's cyst → ↑IOP), Tube blockage/migration, Corneal decompensation, Strabismus, EndophthalmitisTube erosion: Graft patch. Encapsulation: Needling, antifibrotics, or revision. Endophthalmitis: Intravitreal antibiotics.

⭐ The "hypertensive phase" is a common occurrence 4-8 weeks post-operatively, particularly with non-valved GDDs, due to fibrosis around the plate before a stable capsule forms, leading to a temporary ↑IOP.

  • Management Principles: Identify cause, medical therapy first, surgical intervention if needed. Regular follow-up is crucial for early detection and management of complications to preserve vision and device function long-term. Corneal endothelial cell count monitoring is important if tube is near cornea.

High‑Yield Points - ⚡ Biggest Takeaways

  • GDDs (Glaucoma Drainage Devices) treat refractory glaucoma after failed trabeculectomy or medical/laser therapy.
  • Key types: Ahmed Glaucoma Valve (AGV) and Baerveldt Glaucoma Implant (BGI).
  • AGV (valved) offers immediate IOP control but carries a higher encapsulation (Tenon's cyst) risk.
  • BGI (non-valved) has a larger plate, often achieves lower long-term IOP, but needs temporary ligature.
  • Mechanism: Aqueous humor diversion from anterior chamber to a posterior subconjunctival bleb via a tube and plate.
  • Major complications include hypotony, choroidal effusion, tube erosion/migration, bleb encapsulation, and diplopia.
  • Plate surface area and material significantly influence final IOP and complication rates for GDDs.

Practice Questions: Glaucoma Drainage Devices

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Which of the following is NOT an approach followed in revised NPCB cataract surgeries?

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Flashcards: Glaucoma Drainage Devices

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Molteno implant is a _____ based episcleral implant used as a glaucoma drainage device

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Molteno implant is a _____ based episcleral implant used as a glaucoma drainage device

silicone and polypropelene

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