What are the effects and complications of peripheral iridotomy in patients with angle-closure glaucoma?

Important Studies on Peripheral Iridotomy in Angle-Closure Glaucoma

Laser peripheral iridotomy (LPI) is indicated for primary angle closure (PAC) and primary angle-closure glaucoma (PACG), but its role in primary angle-closure suspects (PACS) remains controversial, with recent evidence showing it reduces progression risk by 50% but may not be justified given the low baseline progression rate of only 4%. 1

Key Evidence for Different Clinical Scenarios

Primary Angle-Closure Suspects (PACS)

The Zhongshan Angle Closure Prevention (ZAP) trial demonstrated that LPI reduced the risk of developing PAC by 50% over 6 years in PACS patients, but the absolute progression rate was only 4%, leading investigators to conclude that routine LPI may not be justified in similar populations. 1

• Observational studies consistently show that the majority of PACS patients will not progress to PAC or PACG without intervention 1
• The American Academy of Ophthalmology states that iridotomy may be considered to reduce angle closure risk, but observation is an acceptable alternative 1
• A 2023 Cochrane systematic review found no studies reporting on progressive visual field loss (the primary outcome), making it impossible to draw meaningful conclusions about LPI's effectiveness in preventing vision loss 2

Specific indications favoring prophylactic LPI in PACS include: 1

• Need for medications that may provoke pupillary block
• Symptoms suggesting prior intermittent acute angle-closure crisis (AACC)
• Limited access to immediate ophthalmic care (nursing home residents, frequent travelers to developing regions, merchant vessel workers)
• Poor compliance with follow-up
• Need for frequent dilated examinations (diabetic retinopathy, macular degeneration monitoring)

Primary Angle Closure and Primary Angle-Closure Glaucoma

Iridotomy is strongly indicated for all eyes with PAC or PACG, though eyes with advanced optic nerve damage and extensive peripheral anterior synechiae (PAS) >180 degrees may benefit less, particularly if lens extraction is being considered. 1

• A 1979 long-term study showed that peripheral iridectomy controlled acute angle-closure glaucoma without further therapy in 72% of cases 3
• A 2013 study found that 86.1% of patients with chronic PAC spectrum required additional medical, laser, or surgical treatment after PI, and 50.6% underwent lens extraction for reduced visual acuity 4
• The procedure can be performed using thermal or Nd:YAG laser 1

Gonioscopic and IOP Outcomes

Moderate certainty evidence from meta-analyses shows that iridotomy widens angles significantly (mean difference 4.93-5.07 Shaffer grading units) and reduces PAS formation at 5 years, but produces little to no difference in IOP or visual acuity compared to no treatment. 2

• At 1 year: IOP difference 0.04 mmHg (95% CI -0.17 to 0.24) 2
• At 5 years: IOP difference 0.12 mmHg (95% CI -0.11 to 0.35) 2
• Visual acuity (logMAR) difference at 1 year: 0.00 (95% CI -0.01 to 0.01) 2
• PAS reduction at 5 years: RR 0.41 (95% CI 0.24 to 0.67) 2

Complications and Adverse Events

Common complications include postoperative glare and diplopia (rare but bothersome), with other rare complications including cataract progression, posterior synechiae formation, increased IOP, corneal/lens/retinal burns, late-onset corneal edema, hyphema, and iritis. 1

• Horizontal placement of iridotomy is advocated to reduce dysphotopsia risk by avoiding the prismatic effect of the tear film at the eyelid margin 1
• Iridotomy remained patent in 96% of eyes in one study 5
• Low certainty evidence suggests little to no difference in acute angle-closure incidence (RR 0.29,95% CI 0.07 to 1.20) 2
• Ocular adverse events (eye pain, dry eye, redness, discomfort) were more common with iridotomy than controls, though rare 2

Critical Clinical Pitfalls

Careful follow-up within the first 4 postoperative months is essential, as rapid field loss can occur if pressure remains uncontrolled; further surgery should not be delayed if IOP control is inadequate. 3

• Some PACS patients develop elevated IOP requiring topical hypotensive agents despite successful LPI 1
• Extension of PAS can occur even after iridotomy in creeping angle-closure glaucoma 6
• Patients without iridotomy must be warned about AACC risk with anticholinergic medications (over-the-counter decongestants, cold/flu medications, allergy medications, sleeping aids, psychoactive drugs, motion-sickness medications) 1

Evidence Quality Assessment

The highest quality evidence comes from the 2021 American Academy of Ophthalmology Primary Angle-Closure Disease Preferred Practice Pattern guidelines, which incorporate the Zhongshan trial results and provide Level I++ evidence for iridotomy in PAC/PACG. 1

• The 2023 Cochrane review (moderate to low certainty evidence) found insufficient data on the primary outcome of visual field loss progression 2
• A 2021 systematic review overview noted that available studies directly comparing iridotomy to no iridotomy had not yet published results 1