Why is a peripheral iridectomy required when performing scleral‑fixed intraocular lens implantation?

Peripheral Iridectomy in Scleral-Fixed IOL Surgery

Peripheral iridectomy is performed during scleral-fixed IOL implantation to prevent reverse pupillary block (RPB), a potentially serious complication where aqueous humor becomes trapped behind the iris, causing anterior chamber shallowing, angle closure, and elevated intraocular pressure.

Primary Mechanism and Rationale

The fundamental reason for performing iridectomy during scleral IOL fixation relates to altered aqueous dynamics:

• Reverse pupillary block occurs when aqueous humor accumulates in the posterior chamber behind the iris, unable to flow forward through the pupil, pushing the iris-lens diaphragm anteriorly 1
• In scleral-fixated IOL surgery combined with pars plana vitrectomy, RPB developed in 25% of eyes without prophylactic iridectomy, compared to 0% in eyes that received intraoperative peripheral iridectomy 1
• The mechanism differs from traditional pupillary block seen with phakic IOLs, where aqueous is trapped anterior to the lens; in RPB, the posterior chamber becomes pressurized 1

Clinical Evidence Supporting Mandatory Iridectomy

A 2025 study provides the strongest evidence for this practice:

• Eyes without peripheral iridectomy had significantly deeper anterior chambers postoperatively (4.11 ± 0.75 mm vs 3.79 ± 0.67 mm), indicating anterior displacement from RPB 1
• Postoperative IOP was significantly higher without iridectomy (18.20 ± 4.51 mm Hg vs 15.51 ± 2.48 mm Hg) 1
• Anterior chamber angles were dangerously shallower without iridectomy (52.45 ± 17.93 degrees vs 41.72 ± 3.47 degrees), creating risk for angle-closure glaucoma 1
• Pupillary capture occurred in 10% of eyes without iridectomy, requiring additional intervention 1

Surgical Technique and Timing

The iridectomy should be performed intraoperatively:

• Peripheral iridectomy is created at the time of scleral fixation surgery, typically as part of the combined procedure with pars plana vitrectomy 1
• The iridectomy can be performed via the clear cornea tunnel incision using a bent-tip needle inserted behind the iris, with scissors to enlarge the opening 2
• Size should be approximately 0.2 to 0.5 mm, placed superiorly to avoid visual symptoms, though this guideline derives from phakic IOL literature 3

Management When Iridectomy Is Omitted

If RPB develops postoperatively without prophylactic iridectomy:

• Laser peripheral iridotomy (LPI) effectively treats established RPB, with significant reduction in IOP, ACA normalization, and ACD decrease after intervention 1
• However, prevention is superior to treatment, as 25% of patients will require this secondary intervention 1
• Surgical peripheral iridectomy via existing phacoemulsification incisions can be performed if laser is unavailable or ineffective, particularly useful in brown irides 2

Critical Distinction from Phakic IOL Guidelines

The evidence provided primarily addresses phakic IOLs, which have different indications:

• Phakic IOLs require iridectomy to prevent traditional pupillary block where aqueous is trapped between the crystalline lens and the phakic IOL 3
• Newer phakic IOLs with central holes eliminate this need for iridectomy 3
• Scleral-fixed IOLs in aphakic/pseudophakic eyes face the opposite problem (RPB), but the solution—creating an iris opening—remains the same 1

Common Pitfalls to Avoid

• Do not assume that absence of a crystalline lens eliminates pupillary block risk—RPB is a distinct entity in vitrectomized eyes with scleral IOLs 1
• Do not rely on postoperative laser iridotomy as primary management—intraoperative surgical iridectomy prevents 25% of patients from requiring secondary intervention 1
• Monitor for PAS formation postoperatively, as anterior segment surgery can lead to secondary angle closure mechanisms 4
• Perform gonioscopy postoperatively to assess for angle compromise 4