How is aqueous misdirection syndrome (malignant glaucoma) diagnosed in a middle‑aged or older adult after intraocular surgery or with pre‑existing angle‑closure glaucoma?

Diagnosis of Aqueous Misdirection Syndrome

Diagnose aqueous misdirection syndrome by identifying the triad of elevated intraocular pressure, shallow or flat anterior chamber, and a patent peripheral iridotomy, particularly in the postoperative setting or in eyes with pre-existing angle-closure disease. 1, 2

Clinical Presentation and Key Diagnostic Features

The diagnosis is primarily clinical, based on characteristic examination findings:

Essential Diagnostic Criteria

• Shallow or flat anterior chamber with axial flattening of the entire chamber (both central and peripheral), distinguishing it from pupillary block where only central shallowing occurs 2, 3
• Patent peripheral iridotomy must be present and confirmed—this is critical because it excludes pupillary block as the mechanism 2, 3
• Elevated intraocular pressure in most cases, though IOP may occasionally be normal, making the diagnosis more challenging 2
• Absence of suprachoroidal effusion or hemorrhage on examination, which helps differentiate from other causes of anterior chamber shallowing 3

Clinical Context

Aqueous misdirection typically occurs:

• After intraocular surgery, most commonly following glaucoma filtration surgery in eyes with prior chronic angle closure 1, 2
• After phacoemulsification, particularly in hyperopic eyes with narrow angles 3, 4
• After pars plana vitrectomy, even in eyes without prior angle closure history 5
• Spontaneously in rare cases, though this is uncommon 2

Differential Diagnosis to Exclude

Because the presentation overlaps with other causes of anterior chamber shallowing and elevated IOP, systematically exclude:

Pupillary Block Mechanisms

• Secondary pupillary block from uveitis, lens malposition, or vitreous prolapse—check for patent iridotomy and iris bombé configuration 1
• Lens-related disorders including ectopia lentis or malpositioned intraocular lens that can cause mechanical pupillary block 1, 6

Posterior Pushing Mechanisms

• Choroidal detachment or effusion—perform careful fundoscopic examination and consider B-scan ultrasonography 1
• Suprachoroidal hemorrhage—typically presents with severe pain and may show dark choroidal elevation 1
• Ciliary body edema from medications (topiramate, sulfonamides), panretinal photocoagulation, or scleral buckle placement 1
• Intraocular gas or silicone oil causing forward lens-iris displacement 1

Anterior Pulling Mechanisms

• Neovascularization, epithelial ingrowth, or inflammatory membranes—perform careful gonioscopy when possible 1

Imaging Modalities for Confirmation

Ultrasound Biomicroscopy (UBM)

• Superior for visualizing posterior iris and ciliary body position, which is essential for understanding the mechanism of aqueous misdirection 1
• Can identify anteriorly rotated ciliary processes and absence of ciliary sulcus that contribute to the condition 1
• More operator-dependent but provides better posterior segment detail than anterior segment OCT 1

Anterior Segment Optical Coherence Tomography (AS-OCT)

• Useful for documenting anterior chamber depth and configuration quantitatively 1
• Less effective than UBM for evaluating ciliary body abnormalities but easier to perform 1
• Can track changes over time with treatment 1

B-Scan Ultrasonography

• Essential for excluding choroidal detachment or hemorrhage when fundus view is limited 3

Special Diagnostic Considerations

Nanophthalmos Recognition

• Measure axial length preoperatively—eyes with axial length <20.0 mm are at high risk 1
• Look for small horizontal corneal diameter (<11.0 mm) and high hyperopia 1
• Diagnosing nanophthalmos before surgery is critical to prevent aqueous misdirection complications 1

Delayed Presentation

• Aqueous misdirection can occur weeks to years after uncomplicated surgery, not just in the immediate postoperative period 2, 4
• Myopic surprise (unexpected myopic refractive outcome) may be the only initial presenting sign, with elevated IOP developing later 4
• Maintain high index of suspicion in at-risk patients even with delayed presentation 4

Common Diagnostic Pitfalls

• Assuming pupillary block without confirming iridotomy patency—always verify the iridotomy is patent and functional before diagnosing aqueous misdirection 2, 3
• Missing the diagnosis when IOP is normal—a subset of patients present with normal IOP, so rely on anterior chamber configuration and patent iridotomy 2
• Failing to consider aqueous misdirection after vitrectomy—it can occur even in previously vitrectomized eyes without prior angle closure 5
• Overlooking subtle presentations—myopic surprise or gradual anterior chamber shallowing may be the only early signs 4