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Ocular System

Plateau iris syndrome (PIS)

Relatively uncommon form of primary angle closure glaucoma characterized by persistently narrow angle capable of closure in spite of a patent iridotomy.

Contents

Relatively uncommon form of primary angle closure glaucoma characterized by persistently narrow angle capable of closure in spite of a patent iridotomy.

  • Plateau iris configuration (PIC): Preoperative condition with a gonioscopically confirmed narrow-angle and a flat iris.
  • Plateau iris syndrome (PIS): Postoperative diagnosis where angle closure is observed with PIC, despite eliminating the pupillary block mechanism with patent peripheral iridectomies.
Schematic illustration of the (a) normal eye, (b) plateau iris eye, and (c) pupillary block eye | a) Normal eye. The blue arrow demonstrates the direction of aqueous outflow and the black arrowhead represents the structure of anterior chamber angle. b) Plateau iris eye. It shows convex iris contour and the structure of angle was occluded by the peripheral iris. c) Pupillary block eye. It shows the anterior positioning of the ciliary process and a narrow angle. | Chen, Y. Y., Chu, D., & Chou, P. (2015). Enhancing the early differential diagnosis of plateau iris and pupillary block using a-scan ultrasonography. PloS one, 10(2), e0118811. https://doi.org/10.1371/journal.pone.0118811

History:

The term plateau iris was first coined by Tornquist in 1958 to describe the iris configuration of a young female with high intraocular pressure (IOP) and flat iris surface. Wand et al. in 1977 classified plateau iris into plateau iris configuration (PIC), a preoperative diagnosis, in which the iris is anteriorly displaced compromising the iridocorneal angle resulting in angle closure glaucoma, but often resolves with peripheral iridectomy and plateau iris syndrome (PIS), a postoperative diagnosis where angle closure is observed with PIC, despite eliminating the pupillary block mechanism with patent peripheral iridectomies. Wand et al confirmed and illustrated their observations in 1993 with histological and ultrasound biomicroscopy (UBM) exploration, showing an anteriorly displaced ciliary body that may secondarily rotate and push forward the peripheral iris root into the trabecular meshwork, causing angle narrowing or closure with a flat iris. As a consequence, PIS is now regarded as one of the mechanisms of angle-closure glaucoma.

In 1982, after observing angle widening in front of an iridotomy site, Ritch proposed repeated non-transfixing spots on the iris periphery, describing the first argon laser peripheral iridoplasty (ALPI). ALPI contracts the peripheral iris tissues, pulling the iris away from the trabecular meshwork and reducing the area of iris–trabecular contact. Although ALPI is still considered as a laser treatment for PIS management, since 1982 and the first ALPI description, only a few studies have been conducted on this technique for PIS management.


Diagnosis

Gonioscopy:

  • Iridotrabecular apposition in the presence of patent iridotomy in a dark room
  • Anteriorly and centrally angled peripheral iris
  • Flat or slightly convex iris
  • Double hump sign on indentation (caused by the anterior concavity of the iris at the lens equator level)

Ultrasound biomicroscopy (UBM):

Ultrasound biomicroscopy image showing anteriorly directed ciliary processes, a steep rise of the iris from the root, followed by downward angulation and iridotrabecular contact | Kumar, G., Bali, S. J., Panda, A., Sobti, A., & Dada, T. (2012). Prevalence of plateau iris configuration in primary angle closure glaucoma using ultrasound biomicroscopy in the Indian population. Indian journal of ophthalmology, 60(3), 175–178. https://doi.org/10.4103/0301-4738.95865
  • UBM diagnostic criteria (presence of all the following findings in ≥ 2 quadrants):
    1. Anteriorly directed ciliary process supporting the peripheral iris, steep rise of the iris root from its point of insertion, followed by a downward angulation from the corneoscleral wall
    2. Central flat iris plane
    3. Absent ciliary sulcus
    4. Iridoangle contact in the same quadrant

A-scan ultrasonography:

Measure important structural parameters, such as anterior chamber depth, lens thickness, and axial length in normal eyes, plateau iris eyes, and pupillary block eyes.
A-scan ultrasonography image along the optical axis of an eye: Peaks correspond to cornea (C), anterior lens (AL) surface, posterior lens (PL) surface, and retina (R). Anterior chamber depth (ACD), lens thickness (LT) and axial length can be derived from A-scan ultrasonography. | Chen, Y. Y., Chu, D., & Chou, P. (2015). Enhancing the early differential diagnosis of plateau iris and pupillary block using a-scan ultrasonography. PloS one, 10(2), e0118811. https://doi.org/10.1371/journal.pone.0118811

Management

Therapeutic options in plateau iris | Feraru, C., Bâlha, A., Aursulesei, V., Filip, A., & Pantalon, A. (2017). Plateau Iris – Therapeutic options and functional results after treatment. Romanian journal of ophthalmology, 61(2), 117–122. https://doi.org/10.22336/rjo.2017.22

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