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Single-pass four-throw pupilloplasty an alternative for plateau iris
Laser peripheral iridotomy can fail in some eyes due to peripheral anterior synechiae and scarring.
The iris, which imparts the unique color of the human eye, is named after the Greek goddess Iris, meaning rainbow. In the embryology of the eye, iris development starts as early as the fourth week of gestation. The iris develops from both layers of the optic cup. The outer layer of the optic cup forms the pigmented layer of the iris, and the inner layer of the optic cup forms the non-pigmented layer of the iris. Neural crest cells give rise to the muscle layer of the iris. PAX6 is the key gene in eye development. The iris consists of an anterior limiting layer, a stromal layer, an anterior epithelial layer and a posterior pigmented epithelial layer. The anterior surface of the iris is divided into the pupillary zone and the ciliary zone by a zigzag line called the collarette.
Iris and angle
The anterior chamber angle is the anatomical recess formed between the corneosclera and the iris. Abnormal angle recess can lead to angle closure. Angle closure can be a block at the iris level, ciliary body level, lens or posterior segment. Abnormal iris configuration and position can induce various clinical disorders.
Plateau iris
Source: Dhivya Ashok Kumar, MD, FRCS, FAICO, FICO, and Amar Agarwal, MS, FRCS, FRCOphth
Plateau iris is called by that name because it simulates a plateau, which is a land significantly raised above the surrounding region. Plateau iris is a predisposition for angle closure in which the block is at the level of the ciliary body. During development, if the ciliary body is positioned anteriorly, a large or anteriorly positioned ciliary body can maintain the iris root in proximity to the trabecular meshwork, creating a configuration of plateau iris. In this anatomical variation, the root of the iris sharply angulates from the insertion, flat on the sagittal section, and is anteriorly inserted on the surface of the ciliary body (Figure 1). Plateau iris syndrome refers to the condition in which angle closure is still present, confirmed by gonioscopy, despite a patent peripheral iridotomy with normal central anterior chamber depth. The physical presence of the lens behind the iris plane holds the iris in position and tries to prevent posterior movement of the central iris. As a result, a sinuous configuration occurs, termed as “sigma sign.” The iris follows the curvature of the lens, reaches its deepest point at the lens equator and then rises again over the ciliary processes before dropping peripherally, forming a “double hump sign.” Thus, much more force is needed during gonioscopy to open the angle than in pupillary block because the ciliary processes must be displaced.
Plateau iris configuration has a risk for inducing high IOP and, when untreated, can lead to glaucomatous optic damage and irreversible visual loss. Hence, it has to be followed and managed appropriately.
Evaluation and treatment
Ultrasound biomicroscopy (UBM) and gonioscopy are the first-line tests for early assessment of plateau iris. With high-frequency, high-resolution UBM, we can image the structures surrounding the posterior chamber. UBM is ideally suited to the study of angle-closure glaucoma because of its ability to simultaneously image the ciliary body, posterior chamber, iris-lens relationship and angle structures. The extent, or the “height,” to which the plateau rises determines whether or not the angle will close completely or only partially. In complete plateau iris syndrome, the angle closes to the upper meshwork or Schwalbe’s line, blocking aqueous outflow and leading to a rise in IOP (Figure 2). This situation is far less common than the incomplete syndrome, in which the angle closes only partially, leaving the upper portion of the filtering meshwork open, so that the IOP will not rise. Provocative testing in eyes with plateau iris configuration may help in diagnosis after laser iridotomy. Under normal room illumination, the angle with a plateau configuration is narrow but open. During dark room provocation and ultrasound scanning, the peripheral iris dilates, and appositional angle closure develops. Nd:YAG laser peripheral iridotomy can be performed in initial cases. An argon laser iridoplasty, in which large spots are given for long duration and low power to the extreme iris periphery, can also help in some cases. Iridoplasty or pupilloplasty involves the mechanical pulling of the iris away from the angle and keeps the iris position using nonabsorbable sutures, thereby maintaining the angle open.
Single-pass four-throw pupilloplasty
Single-pass four-throw pupilloplasty (SFT) is a novel method of pupilloplasty in which a single anterior chamber pass through the cornea followed by four throws are performed to make a tight knot in the iris (Figure 3). This pulls the iris away from the angle and changes the vector. In a recent study of a few cases of angle-closure glaucoma, we have shown satisfactory IOP control and good functional outcomes. The technique provides an easy learning curve with minimal tissue manipulation and surgical complications. The surgical knot is strong enough, comparable to a timber hitch knot, providing good stability. In an OCT analysis, we noted no tissue damage or loss with maintenance of iris architecture. The knot region can show minimal changes with the Prolene suture end far away from the corneal endothelium, thereby preventing endothelial cell loss.
Postoperatively, pupil dilation can be performed to an extent to evaluate the fundus for screening. Postsurgical mydriasis has also been studied after SFT. Moreover, SFT can easily be combined with cataract surgery with IOL implantation. Because there are few treatment options and because no treatment is fully successful, SFT pupilloplasty can certainly be useful in such eyes with failed peripheral iridotomy in plateau iris glaucoma eyes. Figure 4 shows a preoperative plateau iris configuration that has been corrected by SFT, which can be seen by anterior segment OCT analysis.
Summary
Preoperative diagnosis of plateau iris by gonioscopy and UBM is necessary in such cases. A peripheral iridotomy trial can be performed to rule out primary angle closure simulating plateau iris. Laser peripheral iridotomy can fail in some patients due to peripheral anterior synechiae and scarring. SFT has a benefit of mechanical removal of the synechiae during surgery in such eyes. When peripheral iridotomy seems to not provide control of IOP and the gonioscopic features show plateau iris, one can proceed with SFT. Thus, with the added advantages of easy technique, less instrumentation, less surgical time and good functional outcome, SFT in plateau iris can be a good alternative.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: aehl19c@gmail.com; website: www.dragarwal.com.
Disclosures: The authors report no relevant financial disclosures.
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