Laser Therapy in Glaucoma

Laser Principles & Types - Beam Me Up!

• Core Principle: Selective absorption of laser energy by target tissue.
  • Photocoagulation: Thermal effect (e.g., Argon laser for ALT, Diode for cyclophotocoagulation).
  • Photodisruption: Optical breakdown (e.g., Nd:YAG for iridotomy, capsulotomy).
  • Selective Photothermolysis: Targets pigmented cells with minimal collateral damage (e.g., SLT).
• Common Lasers in Glaucoma:
  • Argon Laser (thermal)
  • Nd:YAG Laser (photodisruptive)
  • Selective Laser Trabeculoplasty (SLT) Laser (selective photothermolysis)
  • Diode Laser (thermal, transscleral cyclophotocoagulation - TCPC)

⭐ Nd:YAG laser creates a shockwave and plasma formation for tissue disruption, crucial for peripheral iridotomy in angle-closure glaucoma to create an alternative aqueous outflow pathway. Its wavelength is typically 1064 nm (infrared).

Laser Trabeculoplasty - Drain Game Changer

• Enhances aqueous outflow via trabecular meshwork (TM); lowers Intraocular Pressure (IOP).
• Argon Laser Trabeculoplasty (ALT):
  • Thermal effect (Argon laser); coagulative burns → mechanical TM stretching.
  • Spot size: 50 µm; Duration: 0.1 sec; Power: 300-1000 mW.
  • Typically ~50 spots applied over 180°; can treat up to 360°.
  • Risks: Transient IOP spike, peripheral anterior synechiae (PAS); scarring limits repeatability.
• Selective Laser Trabeculoplasty (SLT):
  • Q-switched, frequency-doubled Nd:YAG laser (532 nm).
  • Selectively targets pigmented TM cells (photothermolysis) with minimal thermal spread.
  • Spot size: 400 µm (fixed); Duration: 3 ns; Energy: 0.4-1.2 mJ.
  • Typically ~100-120 non-overlapping spots over 360°.
  • Mechanism: Induces biological response (cytokine release, macrophage recruitment) → TM remodeling.
  • Repeatable; less inflammation and structural damage than ALT.
• Indications: Primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), pigmentary glaucoma, pseudoexfoliation glaucoma. Can be primary or adjunctive therapy.

⭐ SLT is often considered a first-line laser option for open-angle glaucoma due to its favorable safety profile, non-destructive nature, and repeatability compared to ALT.

Mnemonic: "SLT is Selective & Safe & Superiorly repeatable."

Laser Iridotomy & Iridoplasty - Angle Attackers

• Laser Iridotomy (LI): Full-thickness iris opening.
  • Mechanism: Relieves pupillary block, equalizing pressure between anterior & posterior chambers.
  • Indications: Primary Angle Closure Glaucoma (PACG), Primary Angle Closure (PAC), high-risk Primary Angle Closure Suspect (PACS), secondary pupillary block.
  • Laser: Nd:YAG. Site: Superior (e.g., 11/1 o'clock), mid-peripheral iris, often at a crypt.
  • Key: Patentcy vital. Target size ~150-200 µm.
  • Complications: IOP spike (commonest), hyphema, iritis, dysphotopsia, corneal burn.
• Laser Peripheral Iridoplasty (LPI / ALPI): Contracts peripheral iris stroma.
  • Mechanism: Mechanically pulls peripheral iris from Trabecular Meshwork (TM); for non-pupillary block mechanisms (e.g., Plateau Iris).
  • Indications: Plateau Iris Syndrome/Configuration, persistent appositional closure post-patent LI.
  • Laser: Argon.
  • Complications: Iris atrophy, pigment dispersion, transient IOP ↑, iritis.

⭐ Prophylactic LI in the fellow eye of a patient experiencing acute angle closure glaucoma (AACG) dramatically reduces the risk of an AACG attack in that fellow eye by over 90% within 5 years compared to no treatment.

Cyclodestructive Lasers - Ciliary Crushers

• Principle: Ablate ciliary body epithelium → ↓ aqueous humor production.
• Indications:
  • Refractory glaucoma (failed medical/surgical treatments).
  • Painful blind eye (e.g., neovascular glaucoma, absolute glaucoma).
  • Glaucoma with poor visual prognosis.
• Types & Techniques:
  • Transscleral Cyclophotocoagulation (TSCPC):
    • External application (Diode, Nd:YAG laser).
    • Targets ciliary body through sclera.
    • Common: Diode laser (810 nm).
    • Risks: Hypotony, Inflammation, Pain, Phthisis bulbi, Sympathetic ophthalmia (rare) (📌 HIPPS).
  • Endoscopic Cyclophotocoagulation (ECP):
    • Internal approach via endoscope (Diode laser).
    • Direct visualization & treatment of ciliary processes.
    • Often combined with phacoemulsification.
    • More targeted, potentially less collateral damage.
• Primary Goal: Significant IOP ↓.

⭐ ECP allows direct visualization of ciliary processes, offering more precise ablation compared to the "blind" approach of TSCPC.

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High‑Yield Points - ⚡ Biggest Takeaways

• ALT and SLT improve trabecular outflow in OAG; SLT is selective, repeatable, and often preferred.
• Laser Peripheral Iridotomy (LPI) is crucial for angle-closure glaucoma (ACG), bypassing pupillary block.
• Cyclophotocoagulation (CPC), including TSCPC and ECP, reduces aqueous production in refractory glaucoma.
• A transient IOP spike is a common early complication after trabeculoplasty (ALT/SLT).
• LPI is first-line for acute angle-closure crisis and prophylactic in narrow angles (occludable angles).