What is reverse pupillary block, particularly in eyes that have undergone scleral‑fixed intraocular lens implantation after pars plana vitrectomy?

Reverse Pupillary Block

Reverse pupillary block is a condition where the iris bows posteriorly (backward) rather than anteriorly, creating a concave iris configuration with an abnormally deep anterior chamber, caused by aqueous humor becoming trapped in the anterior chamber due to a valve-like mechanism between the iris and intraocular lens. 1, 2

Mechanism and Pathophysiology

• The fundamental mechanism involves aqueous humor flowing forward through the pupil but becoming unable to flow backward, creating higher pressure in the anterior chamber than the posterior chamber—the opposite of traditional pupillary block 1, 2

• A flap-valve-like mechanism develops between the posterior iris surface and the IOL optic, particularly when there is close iridolenticular contact at the pupillary margin 1, 3

• The iris assumes a concave configuration with posterior bowing, resulting in an extremely deep anterior chamber (typically >4.4 mm) and abnormally wide anterior chamber angles (often >60-90 degrees) 2, 4

Clinical Context and Risk Factors

High-Risk Surgical Scenarios

• Scleral-fixated IOLs (both sutured and sutureless techniques) carry the highest risk, with approximately 27% (11 of 41 eyes) developing reverse pupillary block in one series 1

• The Yamane technique for scleral fixation is particularly associated with this complication due to loss of the normal 5-degree posterior angulation of 3-piece IOLs when haptics are stretched 3

• Concomitant vitrectomy (pars plana or anterior) appears to be a significant risk factor, as all cases in one series had undergone vitrectomy 2

Patient-Specific Risk Factors

• Iris flaccidity manifesting as iridodonesis or floppy iris syndrome predisposes to reverse pupillary block 1, 2

• Use of α1A-adrenoceptor antagonists for benign prostatic hyperplasia causes latent iris flaccidity and increases risk 2, 5

• High axial myopia may be an additional risk factor, possibly due to altered ocular anatomy 5, 4

• Angle pigmentation noted preoperatively was present in all cases in one series and may indicate predisposition 2

Clinical Presentation

Ocular Findings

• Extremely deep anterior chamber with posterior concavity of the iris is the hallmark finding on slit-lamp examination 2, 3, 4

• Contact between the IOL optic and iris at the pupillary margin creates the valve mechanism 2

• Marked pigment dispersion in the anterior chamber results from iris chafing against the IOL 5, 3

• Pupil capture may occur in some cases 2

• Gonioscopy reveals extremely wide angles (Spaeth classification E 60c or wider) in all quadrants 4

Intraocular Pressure

• IOP elevation is common but not universal—mean pretreatment IOP was approximately 19.8 mmHg in one series 2

• The condition can exist without elevated IOP initially but may lead to complications over time 1

Complications and Long-Term Sequelae

• Iris chafing from constant contact with the IOL optic causes mechanical trauma 3

• Pigment dispersion glaucoma develops from chronic pigment release into the trabecular meshwork 1, 3

• Uveitis-glaucoma-hyphema syndrome can occur from persistent inflammation and iris trauma 1

• Persistent anterior chamber inflammation compromises trabecular outflow and contributes to IOP elevation 3

Diagnostic Evaluation

• Ultrasound biomicroscopy (UBM) or anterior segment OCT definitively demonstrates the posterior iris bowing, iridolenticular contact, and deep anterior chamber 2, 3, 4

• Anterior chamber depth measurement typically exceeds 4.4 mm (mean 4.42 mm in one series) 2

• Anterior chamber angle measurement shows abnormally wide angles (mean 89.91 degrees before treatment) 2

Treatment Approach

Immediate Management

• Laser peripheral iridotomy (LPI) is the definitive treatment when the iris can be adequately visualized 1, 2, 3

• The iris immediately flattens after successful LPI, with documented reduction in anterior chamber depth (from 4.42 mm to 4.14 mm) and angle width (from 89.91° to 51.70°) 2

• IOP typically decreases significantly after LPI (from mean 19.75 mmHg to 15.63 mmHg) 2

• Pharmacological pupil dilation may provide temporary relief by reducing iridolenticular contact, but is not definitive treatment 5

Surgical Alternatives

• Surgical iridectomy is required when anterior chamber hemorrhage obscures visualization for laser treatment 1

• Intraoperative surgical iridectomy should be performed prophylactically in high-risk patients undergoing scleral-fixated IOL implantation 1, 3

Prevention Strategies

• Prophylactic laser peripheral iridotomy or surgical iridectomy is recommended for patients with flaccid iris, iridodonesis, or floppy iris syndrome undergoing scleral-fixated IOL procedures 1, 3

• Consider prophylactic iridotomy in patients taking α1A-adrenoceptor antagonists who require secondary IOL implantation 2, 5

• Maintain awareness of the risk in eyes with high myopia undergoing IOL procedures 5, 4

Important Clinical Distinctions

• Reverse pupillary block is fundamentally different from traditional pupillary block: in traditional pupillary block (as seen in acute angle-closure crisis), the iris bows anteriorly with a shallow anterior chamber and narrow angles 6, whereas reverse pupillary block features posterior iris bowing with a deep anterior chamber and wide angles 2, 4

• Unlike acute angle-closure crisis where mydriatics worsen the condition, in reverse pupillary block, mydriatics may temporarily improve the situation by reducing iridolenticular contact 6, 5

• The mechanism differs from aqueous misdirection (malignant glaucoma), which is listed as a separate entity in differential diagnoses of angle closure 6