TAG PI (Laser Peripheral Iridotomy) and TAG Capsulotomy (Nd:YAG Posterior Capsulotomy)

TAG PI - Laser Peripheral Iridotomy (LPI)

What it is

Indications

• Primary angle closure (PAC/PACG) - the main indication
• Primary angle closure suspect (PACS) - selectively; the ZAP trial showed LPI has only a small prophylactic effect over 6 years, so it should be offered only to those at highest risk
• Secondary angle closure with pupillary block
• Pigment dispersion syndrome (effectiveness under ongoing investigation)
• Prophylactic indications that may influence the decision:
  • Symptoms of previous intermittent angle closure
  • Systemic medication with atropine-like structure (risk of pharmacologic pupillary block)
  • Need for frequent dilated fundal examination (e.g., diabetes, AMD)
  • Occupational/geographic difficulty accessing urgent ophthalmic care

Technique

1. Pre-procedure: Topical anaesthetic + apraclonidine (or brimonidine) prophylactically. Pupil constricted with topical pilocarpine 2% (one drop).
2. Lens: Special iridotomy contact lens - Abraham lens or Volk MagPlus lens.

Fig. 11.67A - Abraham contact lens used for LPI:

1. Site: Between 11-1 o'clock (under upper eyelid) is standard. Some prefer 3 or 9 o'clock. The iridotomy should be in the outer third radially (to reduce lens damage risk). Targeting an iris crypt makes penetration easier.
   • Highest risk of monocular dysphotopsia occurs when the iridotomy is half-covered by the lid margin.
2. Energy: Nd:YAG laser at 4-5 mJ (2-4 mJ for thin blue iris). Risk of lens damage increases above 5 mJ. Single or up to 3-pulse shots.
   • Thick dark irides: pre-treat with argon/diode laser (600-900 mW, 50 µm spot, 0.03-0.05 s) before YAG application.
3. Endpoint: Gush of pigment debris confirms full-thickness penetration. Optimal size = 150-200 µm.

Fig. 11.67C - Temporal iridotomy (arrow showing patent PI):

1. Post-procedure: Second drop of apraclonidine. IOP check at 1-2 hours. Topical steroid (e.g., dexamethasone 0.1%) every 10 min x 30 min, then hourly x 6-8 hours, then QID x 1 week. Review at 1-2 weeks.

Complications

TAG Capsulotomy - Nd:YAG Posterior Capsulotomy

What it is

Background

• Pearl-type: Proliferation of equatorial lens epithelial cells (Elschnig pearls)
• Fibrosis-type: Fibroblastic metaplasia of epithelial cells with contractile qualities
• Soemmering ring: Whitish annular peripheral proliferation

Indications

• Reduced visual acuity or glare from PCO (primary indication)
• Inadequate fundus view impeding assessment/treatment of posterior segment pathology (e.g., diabetic retinopathy, AMD)

Technique

1. Energy: Start at 1 mJ/pulse; increase only if necessary.
2. Pattern: Cruciate or circumferential series of punctures using single-pulse shots.
3. Size: Opening should approximate the physiologically dilated pupil under scotopic conditions - average 4-5 mm in the pseudophakic eye.
   • Larger opening may be needed for persistent glare or retinal examination/treatment.
   • Do not extend beyond the optic edge - vitreous may prolapse around the edge.
4. Caution in high-risk eyes: Adopt higher threshold and minimize extent in:
   • High myopia (risk of retinal detachment)
   • History of uveitis (risk of CME)
   • Pseudoexfoliation (risk of lens displacement)
5. Energy limit: Total energy should be < 80 mJ to reduce risk of IOP spike.
6. Timing: Delay at least 6 months after cataract surgery to reduce risk of CMO.

Complications

Anterior capsulotomy (bonus point)