Iridociliary apposition in plateau iris syndrome persists after cataract extraction☆

Methods 

Eyes with plateau iris syndrome scanned with UBM before and after cataract extraction between January 1994 and September 2001 were enrolled. All cataract surgeries were performed via phacoemulsification with posterior chamber intraocular lens implantation and were without complication. A clinical diagnosis of plateau iris syndrome required the presence of iridotrabecular apposition in the presence of a patent laser iridotomy during darkroom gonioscopy, an iris root angulating forward and then centrally, a flat or slightly convex iris contour, and a double hump sign on indentation gonioscopy.2 The UBM appearance consisted of iris apposition to the trabecular meshwork, a flat or slightly convex iris contour, and absent ciliary sulcus.3 Patients with ocular disease known to affect anterior segment anatomy, such as ciliary body or iris cysts or trauma, or use of topical drugs affecting iris configuration, were excluded, as were patients who had undergone prior incisional intraocular surgery.

The equipment and technique for UBM analysis have been described in detail elsewhere.10, 11 Scanning was performed with the commercially available unit (UBM, Paradigm Medical Industries, Salt Lake City, Utah, USA) with a 50 MHz transducer to assess the anterior chamber anatomy and surrounding structures. The iridociliary relationship was assessed before and after cataract extraction at the 3:00, 6:00, 9:00, and 12:00-o’clock positions. Anterior chamber depth was assessed on a line perpendicular to the anterior surface of the iris from a point 3 mm anterior to the scleral spur.

Results 

Six eyes of six patients were enrolled. Mean patient age was 74.2 ± 6.4 (standard deviation [SD]) years (range, 65–81 years). Mean refractive error was +1.0 ± 3.9 diopters [D] (range, −5.75–+ 5.50 D), and mean axial length was 21.85 ± 0.77 mm (range, 20.90–22.95 mm). Clinical examination confirmed the presence of plateau iris syndrome with patent laser iridotomy and prior argon laser peripheral iridoplasty in all study eyes. The fellow eye of each patient had plateau iris configuration or syndrome.

Ultrasound biomicroscopy examination revealed a narrow angle and absence of a ciliary body sulcus in all study eyes with focal areas of iridotrabecular apposition in three eyes (cases 1, 2, and 6). Following cataract extraction, the anterior chamber depth increased (P = .0006, paired t test), while the iridociliary contact remained unchanged. Postoperative indentation gonioscopy revealed the persistence of a double hump sign. The case data and characteristic UBM images are summarized in Table 1 and FIGURE 1, FIGURE 2.

TABLE 1. Summary Data for Each Case Report

	Case	Age [years]	Eye	RE	Axial Length (mm)	Gender	AC Depth*		Ciliary Sulcus
							B/CE	A/CE	B/CE	A/CE
	1	78	OS	5.5	20.9	M	0.98	1.78	absent	absent
	2	81	OD	−5.75	22.45	M	1.22	1.78	absent	absent
	3	72	OS	3.25	21.11	F	1.04	1.69	absent	absent
	4	69	OD	2.25	22.95	F	1.09	1.70	absent	absent
	5	80	OS	−1.00	21.86	F	0.82	1.49	absent	absent
	6	65	OD	1.75	21.86	F	1.10	1.34	absent	absent

A/CE = after cataract extraction; B/CE = before cataract extraction; F = female; M = male; RE = refractive error (diopters).

* AC depth = anterior chamber depth at 3 mm from the scleral spur (mm).

View Large Image Download to PowerPoint

FIGURE 1. Case 1. A 78-year-old man. (Left) Ultrasound biomicroscopy before cataract extraction shows an appositional angle-closure (black arrows), despite a patent laser iridotomy (asterisk). The ciliary sulcus is absent (white arrow), and the iris contour is flat. (Right) After cataract extraction the angle is slit-like (arrows), iridociliary apposition remains (asterisk), and the ciliary sulcus is absent.

View Large Image Download to PowerPoint

FIGURE 2. Plateau iris. (Left) The ciliary processes are visible through the patent laser iridotomy. (Right) Corresponding ultrasound biomicroscopy image, with the ciliary processes immediately posterior to the iridotomy.

Discussion 

Tornquist12 was the first to use the term plateau iris to describe the appearance of the iris of a 44-year-old man with angle-closure glaucoma, who had a normal anterior chamber depth, flat iris surface, and a sharp backward curvature to the peripheral iris. In 1977, Wand and associates6 differentiated plateau iris configuration from plateau iris syndrome. At the present time, plateau iris configuration refers to an angle appearance in which the iris root angulates sharply forward from its insertion point and then centrally but is not spontaneously or pharmacologically occludable after iridotomy. In both plateau iris configuration and plateau iris syndrome, the surface of the iris appears relatively flat, although in older patients with enlarged lenses, the contour may be somewhat convex, as the iris assumes the contour of the lens. On indentation gonioscopy, the ciliary processes prevent posterior movement of the peripheral iris, producing a double hump sign, in which the iris follows the curvature of the lens, reaches its deepest point at the lens equator, then rises again over the ciliary processes before dropping peripherally. Moderate pressure may need to be applied to the cornea with the gonioscopy lens to open the angle. This configuration may be seen in eyes with closed or occludable angles before iridotomy.

Plateau iris syndrome refers to a condition in which the angle in an eye with plateau iris configuration remains capable of closure either spontaneously or pharmacologically after iridotomy has eliminated any component of pupillary block.6, 7 Plateau iris syndrome has been divided into complete and incomplete forms, depending upon the presence or absence of an associated rise in intraocular pressure (IOP) upon occlusion of the angle.13 In the complete syndrome, which comprises the classic situation and is rare, IOP rises when the angle closes with pupillary dilation. Some patients may develop acute angle-closure glaucoma6, 7, 14, 15 In the far more common incomplete syndrome, IOP does not change. The complete and incomplete forms are differentiated by the “height” to which the plateau rises. If the angle closes to the upper trabecular meshwork or Schwalbe line, IOP rises, whereas if the angle closes only partially, IOP will not rise. Patients with incomplete plateau iris syndrome can develop peripheral anterior synechiae over time with continued appositional closure, and patients with plateau iris configuration can go on to develop plateau iris syndrome as the lens enlarges. The anterior location of the pars plicata leads to obliteration of the ciliary sulcus and a decrease in the size of the posterior chamber (Figure 2), while simultaneously maintaining the iris root in apposition to the angle wall.

The cause of the plateau iris configuration remains unknown. An anterior position of the pars plicata could be developmental or acquired. Ciliary processes develop at week 24 of embryogenesis.16, 17 The ciliary processes overlap the trabecular meshwork initially but later recede to a position behind the scleral spur.18 This repositioning is thought to be due to a differential growth rate of the various tissue elements.19 The absence of a ciliary sulcus in eyes with plateau iris might be due to failure of the ciliary processes to separate from the posterior iris surface. In a morphometric study of the ciliary sulcus, Orgül and associates20 proposed that the displacement of the pars plicata from the peripheral iris to the iris root during embryogenesis may be incomplete in eyes of shorter axial length. However, incomplete cleavage between the iris and ciliary body is unlikely. In eyes with plateau iris configuration and relative pupillary block, the ciliary sulcus is present and disappears after iridotomy so that the peripheral iris rests on the ciliary body.

The anomaly of the pars plicata position could be acquired. The distance between the zonular insertion and the lens equator increases with age, leading to an anterior shift of the zonular insertion on the anterior lens capsule.21, 22, 23 Therefore, forward positioning of the ciliary body may be secondary to traction and anterior displacement of the zonules by anterior movement of the zonular insertion and anterior movement of the lens capsule during cataractogenesis. Yet, this would not explain the occurrence of plateau iris in younger patients without cataract. An additional possibility is that a congenital variation leads to anterior zonular positioning with resultant displacement centrally of the pars plicata. Posterior zonular fibers originate at the pars plana, enter the dorsal part of the ciliary valleys, and then change direction toward the posterior face of the lens.24 Anterior zonular fibers originate mainly at the pars plana and occasionally at the ciliary valleys and, after running completely through the ciliary valleys in close contact with the lateral walls of the ciliary processes, change direction at the anterior endings of the pars plicata and reach the anterior lens capsule.24 On UBM, anterior zonular fibers often appear to extend directly to the lens from the anterior edge of the pars plicata. Zonular fibers intimately attached to the anterior ciliary processes might maintain the processes in a more central position, particularly in a hyperopic eye with a relatively smaller than normal anterior segment and perhaps shorter than average anterior zonules.

None of the six eyes with plateau iris syndrome in this study underwent a change of the configuration of the ciliary body after IOL implantation. However, the anterior chamber depth increased and the angle opened further after cataract surgery. It is possible that the zonular attachments to the capsular bag maintain apposition of the pars plicata to the iris. The persistent iridociliary apposition before and after cataract surgery suggests that the iris and pars plicata appear to move together, depending to some extent on the position of the lens capsule and the ciliary processes continue to support the peripheral iris.