PLATEAU IRIS SYNDROME

Signs and Symptoms

Patients with plateau iris syndrome tend to be younger, typically ranging in age from 30 to 50 years, with a female predilection.1 In a series of 67 patients with angle closure developing at age 40 or younger, 52% had plateau iris syndrome.2 While pupil block angle closure glaucoma is associated with hyperopia, plateau iris configuration and syndrome can precipitate angle closure glaucoma even in myopic eyes.3

Patients are typically asymptomatic, not realizing they have this anatomic predisposition to angle closure unless diagnosed during an eye exam or having experienced an episode of angle closure (either spontaneously or following diagnostic mydriasis). Should this occur, the patient will then have the attendant signs and symptoms of ocular pain, redness, vision loss, headache and nausea. Plateau iris syndrome can, in other instances, instead result in asymptomatic chronic angle closure glaucoma with progressive disease in the absence of symptoms.4

Biomicroscopically and gonioscopically, there is a steep iris approach into the angle recess with a visible, large roll(s) of the iris prior to the angle recess. The iris does not exhibit the classic iris bombé associated with pupil block angle closure. Typically, the central anterior chamber is deep, differentiating this condition from the more common pupil block angle closure.5-7 The classic gonioscopic finding, in addition to a steep iris insertion, is a classic ‘double hump’ on indentation gonioscopy. The peripheral hump is created by the iris draping over an anteriorly located ciliary body and the central hump occurs from the iris curving over the anterior lens surface.8

Pathophysiology

Plateau iris configuration refers to the pre-iridotomy findings of a normal anterior chamber depth, flat iris plane and a narrow, or closed, angle. Plateau iris syndrome describes the post-iridotomy findings of either spontaneous or dilation-induced angle closure in patients with plateau iris configuration.5 Plateau iris syndrome is a less common condition than plateau iris configuration, which is itself an uncommon entity.5 Plateau iris syndrome can only be diagnosed following laser peripheral iridotomy (LPI) performed either in prophylaxis of an occludable angle or as part of therapy for angle closure glaucoma.9 Despite the presence of a patent LPI, the angle remains occludable or actually closed.10-12

In plateau iris configuration and syndrome, the ciliary processes are situated anteriorly compared to normal subjects and patients with angle closure caused by primary pupillary block.13 The ciliary processes provide structural support beneath the peripheral iris, preventing the iris root from falling away from the trabecular meshwork after iridotomy. An anatomical forward position of the ciliary processes keeps the peripheral iris root in apposition to the trabecular meshwork, consequently preventing the posterior repositioning of the iris following iridotomy, resulting in a persistent post-procedure narrow or closed angle.5,6,13-15

Plateau iris is an anatomic variant of iris structure in which the iris periphery angulates sharply forward from its insertion point. It then again angulates centrally backward, along with an anterior positioning of the ciliary processes which can be demonstrated with ultrasound biomicroscopy.16 While plateau iris configuration and syndrome is considered an anatomic anomaly existing independently of other findings, there have been cases where multiple iris cysts have caused anterior rotation of the iris root and a plateau iris configuration.17,18

Plateau iris syndrome is classified into a complete and incomplete form. In the incomplete form, intraocular pressure (IOP) does not elevate either spontaneously or following pharmacologic mydriasis. In contradistinction, the complete form will demonstrate an elevated IOP.19 However, the etiology of these distinctions remains unclear. It has been postulated that the lack of IOP elevation in the incomplete form is due to a difference in the extent or magnitude of circumferential angle closure.19

Another possibility is that the actual height of the plateau iris is the determining factor for IOP rise—that is, if only the posterior trabecular meshwork is blocked by the iris height, the IOP does not rise. However, if the plateau iris height is great enough to appose the anterior trabecular meshwork, a significant rise in IOP occurs.1

Management

In a gonioscopically-verified occludable or closed angle secondary to anatomical etiology, without inflammatory synechiae or neovascularization, an LPI is performed to remove any pupil block component. In the majority of cases of occludable or closed angles due to pupil block, the anterior chamber deepens and angle structures become visible following the procedure. However, in plateau iris configuration, there typically is no discernible response to LPI and the angle remains closed or occludable. Thus, the diagnosis of plateau iris syndrome is made.20,21

Optical coherence tomography can confirm a clinical suspicion of plateau iris configuration and syndrome. OCT can show a patent laser iridotomy and identify plateau iris syndrome after iridotomy.22

Most cases of plateau iris syndrome have been historically managed conservatively with pilocarpine 1% QD- BID. Low dosing of this medication is more for the miotic effect rather than IOP lowering. Pilocarpine causes iris stretching and thinning and is an effective means to open the anterior chamber angle and has historically been successful in managing plateau iris syndrome.14 However, this option is not ideal as it inhibits dilated fundus evaluations and many patient will not tolerate pilocarpine side effects. Additionally, future dilation can still put the patient into angle closure.

Recently, argon laser peripheral iridoplasty (ALPI) has been shown to be a successful management tool for plateau iris configuration and syndrome.1,15,18,20 ALPI is a thermal laser-induced iridoretraction procedure where burns are placed at all clock hours about the peripheral iris, effectively causing tissue contraction throughout the peripheral iris. This in turn pulls the peripheral iris away from the trabecular meshwork, relieving potentially occludable angles as well as actual angle closure. Thus, it is effective both in therapy for angle closure as well as in prophylaxis of potentially occludable angles. ALPI has become the treatment of choice both for plateau iris configuration and syndrome. This beneficial effect is maintained for years, though a small percentage of patients may eventually need retreatment.1 One controlled study demonstrated that ALPI is more effective than conventional medical therapy for acute angle closure glaucoma, especially from plateau iris sysndrome.23

Clinical Pearls

Plateau iris syndrome cannot be diagnosed without the performance of an LPI, wherein, after the procedure, the angle configuration remains unchanged. Prior to LPI, the patient with a steep iris and occludable angle is said to have plateau iris configuration.

Gonioscopy must be performed on patients—even those with patent LPIs. The presence of a patent LPI does not necessarily mean that the patient is safe to dilate or does not still have a risk of angle closure.

Plateau iris configuration is the condition most likely to respond to pharmacologic pupil dilation with closure of the angle.

Plateau iris syndrome is considered primary angle closure without pupil block.

Due to the anteriorly located ciliary processes, lens removal will not debulk the anterior chamber and open the angle as it would in primary pupil block angle closure. Therefore, cataract surgery is not a therapeutic option for plateau iris syndrome.

1. Ritch R, Tham CC, Lam DS. Long-term success of argon laser peripheral iridoplasty in the management of plateau iris syndrome. Ophthalmology. 2004;111(1):104-8.

2. Ritch R, Chang BM, Liebmann JM. Angle closure in younger patients. Ophthalmology. 2003;110(10): 1880-9.

3. Barkana Y, Shihadeh W, Oliveira C, et al. Angle closure in highly myopic eyes. Ophthalmology. 2006;113(2):247-54.

4. Besada E, Reynolds S. Evaluation and management of plateau iris syndrome: case report and review. Optometry. 2005;76(7):376-81.

5. Wand M, Grant WM, Simmons RJ, et al. Plateau iris syndrome. Trans Sect Ophthalmol Am Acad Ophthalmol Otolaryngol. 1977;83(1):122-30.

6. Mandell MA, Pavlin CJ, Weisbrod DJ, et al. Anterior chamber depth in plateau iris syndrome and pupillary block as measured by ultrasound biomicroscopy. Am J Ophthalmol. 2003;136(5):900-3.

7. Li PS, Lai JS, Lam DS. Anterior chamber depth in plateau iris syndrome and pupillary block as measured by ultrasound biomicroscopy. Am J Ophthalmol. 2004;137(6):1169.

8. Kiuchi Y, Kanamoto T, Nakamura T. Double hump sign in indentation gonioscopy is correlated with presence of plateau iris configuration regardless of patent iridotomy. J Glaucoma. 2009;18(2):161-4.

9. Hagadus R, Fabijanczyk B.Response to laser iridotomy in Hispanic and Caucasian patients with narrow, occludable filtration angles. Klin Oczna. 2005;107(1-3):39-42.

10. Ng WT, Morgan W. Mechanisms and treatment of primary angle closure: a review. Clin Experiment Ophthalmol. 2012;40(4):e218-28.

11. Razeghinejad MR, Kamali-Sarvestani E. The plateau iris component of primary angle closure glaucoma: developmental or acquired. Med Hypotheses. 2007;69(1):95-8.

12. Kumar RS, Tantisevi V, Wong MH, et al. Plateau iris in Asian subjects with primary angle closure glaucoma. Arch Ophthalmol. 2009;127(10):1269-72.

13. Pavlin CJ, Ritch R, Foster FS. Ultrasound biomicroscopy in plateau iris syndrome. Am J Ophthalmol. 1992;113(4):390-5.

14. Pavlin CJ, Foster FS. Plateau iris syndrome: changes in angle opening associated with dark, light, and pilocarpine administration. Am J Ophthalmol. 1999;128(3):288-91.

15. Leung CK, Chan WM, Ko CY, et al. Visualization of anterior chamber angle dynamics using optical coherence tomography. Ophthalmology. 2005;112(6):980-4.

16. Diniz Filho A, Cronemberger S, Mérula RV, Calixto N. Plateau iris. Arq Bras Oftalmol. 2008;71(5):752-8.

17. Azuara-Blanco A, Spaeth GL, Araujo SV, et al. Plateau iris syndrome associated with multiple ciliary body cysts. Report of three cases. Arch Ophthalmol. 1996;114(6):666-8.

18. Crowston JG, Medeiros FA, Mosaed S, et al. Argon laser iridoplasty in the treatment of plateau-like iris configuration as result of numerous ciliary body cysts. Am J Ophthalmol. 2005;139(2):381-3.

19. Sekhar GC, Onam KS, Kunjam V. Incomplete and complete plateau iris syndrome. Clin Experiment Ophthalmol. 2004;32(2):222-4.

20. Ouazzani BT, Berkani M, Ecoffet M, Lachkar Y. Argon laser iridoplasty in the treatment of angle closure glaucoma with plateau iris syndrome J Fr Ophtalmol. 2006;29(6):625-8.

21. Kumar RS, Baskaran M, Chew PT, et al. Prevalence of plateau iris in primary angle closure suspects an ultrasound biomicroscopy study. Ophthalmology. 2008;115(3):430-4.

22. Parc C, Laloum J, Bergès O. Comparison of optical coherence tomography and ultrasound biomicroscopy for detection of plateau iris. J Fr Ophtalmol. 2010;33(4):266.e1-3.

23. Lam DSC, Lai JSM, Tham CCY, et al. Argon laser peripheral iridoplasty versus conventional systemic medical therapy in treatment of acute primary angle-closure glaucoma: A prospective, randomized, controlled trial. Ophthalmology 2002; 109(9):1591-96.