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Plateau Iris

URGENT — Glaucoma

Symptoms

Presentation

  • Usually asymptomatic (detected on routine gonioscopy).
  • Intermittent "brow ache," halos around lights, or blurred vision.
  • Acute angle-closure: Sudden severe pain, nausea, and redness.
  • Classic: Angle closure symptoms that persist *even after* an LPI has been performed.

Clinical Findings

Core concept

  • Angle closure caused by an anatomical variant where the ciliary body is anteriorly rotated.
  • Unlike pupillary block, the central anterior chamber (AC) depth is often relatively deep.

The "unmasked" angle

  • Plateau iris syndrome: Angle closure that PERSISTS despite a patent laser peripheral iridotomy (LPI).
  • Distinguishes it from primary angle closure where LPI usually "fixes" the narrow angle.

Clinical signs

  • "Double-hump" sign: Seen on indentation gonioscopy; the iris rises over the lens, dips, then rises again over the ciliary processes.
  • Flat iris plane: The central iris appears flat rather than bowed forward (bombé).
  • Patent LPI: Essential to rule out pupillary block as the primary driver.

Etiology

Pathophysiology

  • Anteriorly positioned ciliary processes push the peripheral iris root forward into the trabecular meshwork.
  • This mechanical crowding prevents aqueous drainage even if a hole (LPI) exists in the iris.

Demographics

  • Typically younger patients (30s–50s) than standard angle closure.
  • Female predominance; usually hyperopic (farsighted) or emmetropic.

Red Flags

  • Persistent closure after LPI: Mandates UBM imaging to confirm plateau configuration.
  • Acute attack despite patent LPI: Diagnostic for plateau iris syndrome.
  • Mid-dilation closure: Phenylephrine or tropicamide can bunch the iris into the angle, triggering an attack.
  • Progressive PAS: Formation of peripheral anterior synechiae despite a patent LPI.

Investigations

Gold standard imaging

  • Ultrasound biomicroscopy (UBM): The only way to directly visualize the anteriorly rotated ciliary body pushing the iris.
  • Anterior segment OCT: Can show the crowded angle but less effective at seeing the ciliary body.

Gonioscopy

  • Indentation gonioscopy is mandatory to look for the "double-hump" sign and assess for PAS.

Clinical monitoring

  • Serial IOP checks and undilated optic nerve evaluation.

Treatment

Step 1: Laser Peripheral Iridotomy (LPI)

  • Mandatory first step to "unmask" the plateau and relieve any pupillary block.

Step 2: Argon Laser Peripheral Iridoplasty (ALPI)

  • Definitive treatment: Low-energy burns to the peripheral iris contract the tissue, pulling it away from the angle.

Step 3: Medical & Surgical Adjuncts

  • Low-dose pilocarpine (0.5–1%): Keeps the iris "stretched" and out of the angle.
  • Lens extraction (cataract surgery): Often curative as it creates more space in the anterior segment.
  • ECP (endoscopic cyclophotocoagulation): Can be used during surgery to shrink the ciliary processes.

Clinical Pearl

An angle that stays narrow after a patent iridotomy is plateau iris — UBM shows the anteriorly positioned ciliary processes, and argon laser iridoplasty opens the angle.

Differential Diagnosis

  • • Primary pupillary block (resolved by LPI).
  • • Lens-induced (phacomorphic) angle closure.
  • • Malignant glaucoma (aqueous misdirection).
  • • Ciliary body cysts (can push the iris forward in a similar pattern).

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