Plateau Iris Syndrome

Larissa Camejo, MD

Introduction

Primary angle-closure glaucoma occurs by pupillary block or plateau iris and is a common cause of angle-closure glaucoma in young people. Plateau iris configuration refers to anteriorly positioned ciliary body processes mechanically pushing the peripheral iris against the trabecular meshwork (Slide 1). Because, with rare exceptions, there is always some component of pupillary block, laser peripheral iridectomy (LPI) can open the angle to a certain extent. If the angle remains closed or is occludable in the presence of a patent iridectomy, the condition is called plateau iris syndrome (Slide 2).
Slide 1

Slide 1

Slide 2

Slide 2

Because plateau iris syndrome is a rare entity, its exact prevalence is unknown. However, plateau iris configuration should be suspected when angle closure occurs in a young myopic or less hyperopic patient.

Diagnostic Features

Clinical History
Patients with plateau iris configuration tend to be women in their 30s to 50s, with hyperopia, and with a family history of angle-closure glaucoma. The diagnosis may be an incidental finding of a routine eye examination or may be made after patients present with angle closure either spontaneously or after pupillary dilation. Plateau iris syndrome should be suspected when a patient with a history of narrow angles and a previous iridectomy develops angle closure. Two subtypes of plateau iris syndrome have been described - complete and incomplete.

In the complete syndrome, the angle is open only to the anterior trabecular meshwork, or Schwalbe's line, and the IOP is high. The incomplete syndrome occludes the angle partially, leaving the anterior portion of the trabecular meshwork open, and the IOP remains normal.

Examination
Slit lamp examination
Patients with plateau iris syndrome show a normal anterior chamber depth, and the iris can appear flat or slightly convex. This contrasts with the appearance of pupillary block, where the anterior chamber appears shallow, and the iris is convex or bowed forward.

Gonioscopy
Traditionally considered the gold standard in the diagnosis of plateau iris syndrome, gonioscopy reveals a narrowed or closed angle with a drop-off of the peripheral iris. On indentation gonioscopy, the double hump sign is seen. The first or central hump represents the iris draping the anterior lens surface, whereas the second or peripheral hump represents the iris draping the anteriorly positioned ciliary body. The depressed space between the first and second humps represents the lens equator, zonules and ciliary processes. Resistance to opening the angle by indentation is encountered.

Slide 3

Slide 3

Ultrasound biomicroscopy
Ultrasound biomicroscopy has helped in the understanding of plateau iris syndrome. It allows the visualization of the iris surface configuration, level of iris root insertion and location of the ciliary body, and can show differences in the angle under lighted conditions versus dark conditions. Ultrasound biomicroscopy also allows the visualization of the presence or absence of changes in the angle before and after procedures like LPI and argon laser peripheral iridoplasty (ALPI). A systematic approach to correctly study the angle images obtained with ultrasound biomicroscopy starts with locating the scleral spur. This should be at the union of the trabecular meshwork and the interface between the sclera and the ciliary body. The anterior chamber angle is then identified and described as either open or closed. The ciliary sulcus, present in normal eyes, is absent in cases of plateau iris (Slide 3). Optical coherence tomography has also been valuable in the evaluation of anterior segment dynamics in recent publications.

Differential Diagnosis

Slide 4A

Slide 4A

Slide 4B

Slide 4B

Slide 4C

Slide 4C

Treatment

  1. LPI should always be performed first. This allows resolution of any pupillary block component if present, opening the angle. If the angle remains closed or occludable, then the term plateau iris syndrome is used. A patient with plateau iris configuration whose angle opens after an LPI should not be considered cured because the angle may close in the future. The patient should be screened regularly by gonioscopy (Table 1).
  2. Iridoplasty thins out the peripheral iris stroma and, therefore, opens the angle in patients with plateau iris syndrome. Iridoplasty may be done by placing ~30 spots covering 360° of peripheral iris. The end point is contraction of tissue and opening of angle (Table 2).
  3. Medical treatments including pilocarpine might be used to open the angle but, if possible, should not be used long-term. Miotics can cause further anterior rotation of the ciliary body and worsening of the condition. If glaucoma develops, then use IOP lowering drops.
  4. When the angle remains closed after LPI and iridoplasty and chronic angle closure glaucoma develops, incisional surgical intervention is needed. If peripheral anterior synechiae are new, then a goniosynechiolysis might be tried. Trabeculectomy or tube shunt placement may be needed to avoid progression of disease.

Table 1

Nd:YAG LPI settings

Preoperative: brimonidine 0.15% and pilocarpine 2% every 5 minutes x 3

Spot size: Fixed

Duration: Fixed

Energy: 4 mJ to 6 mJ, single pulse mode

Lens: Abraham or Wise

Postoperative: IOP check 30 to 60 minutes after procedure is finished and prednisolone acetate 1% four times daily for 4 to 5 days.

Table 2

Iridoplasty settings. Gonioplasty is a different name for the same procedure.

Preoperative: brimonidine 0.15% and pilocarpine 2% every 5 minutes x 3

Spot size: 200 µm to 500 µm

Duration: 0.2 second to 0.5 second

Energy: 150 mW to 300 mWLens: Goldman three mirror or Abraham

Postoperative: IOP check and prednisolone acetate 1% drops four times daily for 4 to 5 days.

Summary

Bibliography