Although early attempts by Krasnov1 and Kimbrough et al2 to modify the peripheral iris had some success, the outcomes were limited by technique and instrumentation. The current use of argon lasers has led to a refinement in technique that has increased both anatomical and clinical success.
Regardless of the technique, the success of laser iridoplasty relies on the proper application of energy along the peripheral iris to achieve contraction of the tissue. When the peripheral iris shrinks, it pulls away from the trabecular meshwork and opens the drainage angle.
During iridoplasty, the laser light is converted to heat that causes contraction of stromal collagen, which is primarily responsible for the immediate anatomical change.3 Later alterations include a proliferation of fibroblasts with the formation of a contraction membrane. Careful technique (see Step-by-Step Technique for Iridoplasty) is important, because overtreatment can lead to coagulative necrosis of the blood vessels.
INFORMED CONSENT
The preoperative discussion with patients should include a description of the moderate, transient discomfort they will experience with each laser application. Patients often describe the feeling as a pinprick or a sensation of pressure.
TECHNIQUE
Iridoplasty is most often performed with an argon laser and topical anesthesia in an outpatient setting. The surgeon applies one drop of 2% pilocarpine to stretch the iris and maximize access to the peripheral iris. Treatment should not begin until the pupil is maximally contracted, as evidenced by a lack of response to light. Applying one drop of brimonidine or apraclonidine decreases the chance of postoperative IOP spikes, and a topical anesthetic drop, such as proparacaine, enhances the patient's comfort.
There are basically two techniques for performing iridoplasty, direct and indirect. In the direct technique, which uses an Abraham lens (Ocular Instruments, Bellevue, WA) (Figure 1A), the surgeon applies laser energy perpendicular to the peripheral iris. With the indirect technique, which uses a single-mirror lens (Ocular Instruments) (Figure 1B), the ophthalmologist directs the beam at a low angle of incidence toward the peripheral iris and angle. The direct technique is easier to perform, but the indirect technique provides direct visualization of the angle during the procedure.
Figure 1. Iridoplasty may be performed with an Abraham lens (A, left) or a single-mirror lens (B, right).
It is important to note that, when using an Abraham lens, the surgeon should adjust the laser's settings to a lower energy and a larger spot size (for example, 200 to 300 mW and a 500-µm spot size). As opposed to the tangential application with a single-mirror lens, the direct laser application with the Abraham lens results in smaller spots and more concentrated burns. When using this lens, the surgeon should carefully overlap the limbus with the laser in order to treat the peripheral iris. Otherwise, the laser beam's application will be too central. When using the single-mirror lens, the treatment should be as peripheral as possible without encroaching on the trabecular meshwork.
Surgeons typically use a spot size of 300 to 500 µm with a duration of 0.3 to 0.5 seconds. The ophthalmologist varies the power between 300 and 500 mW to achieve a tissue response without the formation of air bubbles or dispersion of pigment into the anterior chamber. Contraction of the iris with a deepening of the peripheral chamber should be visible at the time of treatment (Figure 2).
Figure 2. A surgeon's view of laser burns with a single-mirror lens is shown. The burns cause the peripheral iris to contract away from the trabecular meshwork.
A lack of response is often due to an inadequate energy level, an improper application of laser energy away from the periphery, or the presence of multiple peripheral anterior synechiae. In these cases, the surgeon should adjust the laser's settings and location of the spots to achieve the desired tissue response.
Iridoplasty involves an estimated six to eight spots placed in each quadrant, depending on the spot size, with the spacing of one to two spot diameters between applications (Figure 3). Although some ophthalmologists advocate only treating 180º degrees at a time, we have found 360º treatment to be safe, without an increase in the frequency of IOP spikes.
Figure 3. The iris laser burns had this appearance after peripheral iridoplasty.
After the procedure, the eye receives a drop of a topical steroid or NSAID. The surgeon checks the IOP 1 hour after treatment. Our postlaser regimen usually consists of one drop of prednisolone acetate q.i.d. for 4 days. At the 1-week follow-up visit, we check the patient's IOP and perform gonioscopy to re-examine the anterior chamber angle. Retreatment may be indicated in some cases and will consist of either overlapping the spots or adding a row of applications to the initial treatment.
OUTCOMES
Laser iridoplasty effectively treats a wide range of anterior segment conditions. Plateau iris syndrome, the most common condition for which the procedure is indicated, is caused by large or anteriorly positioned ciliary processes that push the peripheral iris toward the trabecular meshwork. Diagnostically, the angle remains closed or occludable despite laser iridotomy, and iridoplasty is required to lower the IOP or prevent closure. A study by Ritch et al4 looked at the long-term effect of argon laser peripheral iridoplasty in eyes with plateau iris syndrome. The angle in 20 of 23 (87.0%) eyes remained open throughout the entire follow-up period (mean = 78.9 ± 8.0 months) after only one treatment, and the remaining three eyes required a single retreatment.
Studies have also shown that iridoplasty can be used as an initial treatment in acute angle closure.5,6 Early in the course of an acute angle-closure attack, the cornea is often edematous, and the view of the iris is poor. Performing laser peripheral iridotomy is not always possible, and medical management may not decrease the IOP.5 Lam et al6 performed a randomized, controlled trial to compare argon laser iridoplasty with medical therapy as the initial treatment of acute ACG not amenable to laser peripheral iridotomy. The iridoplasty group received immediate laser treatment, and the medical treatment group was given intravenous acetazolamide, followed by oral acetazolamide, until the subjects' IOP normalized. The laser group had a significantly lower IOP than the medically treated group throughout the first hour after the treatment's initiation. No serious, laser-related complications occurred. Once the IOP normalized, the corneal edema resolved, and the peripheral laser iridotomy was performed.
CONCLUSION
Argon laser iridoplasty is a safe and effective procedure for patients with narrow angles and/or plateau iris syndrome whose angles remain narrow after laser iridotomy. When properly performed, the procedure consistently delivers a long-term benefit to individuals with plateau iris syndrome. Patients with acute ACG may also profit from iridoplasty in cases where immediate peripheral iridotomy cannot be performed.
A precise technique and an attention to detail are key to successful iridoplasty, and ophthalmologists should be familiar with the finer points of performing this laser procedure.
The authors would like to acknowledge Kira L. Lathrop, MAMS, for her artistic contribution to Figures 2 and 3.
Malik Y. Kahook, MD, is Assistant Professor of Ophthalmology and Director of Clinical Research in the Department of Ophthalmology at the University of Colorado Health Sciences Center. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Kahook may be reached at (720) 848-5029; malik.kahook@gmail.com.
Robert J. Noecker, MD, MBA, is Director of the Glaucoma Service and Associate Professor/Vice Chair at the Department of Ophthalmology at the University of Pittsburgh. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Noecker may be reached at (412) 647-2152; noeckerrj@upmc.edu.
1. Krasnov MM. Q-switched laser iridectomy and Q-switched laser goniopuncture. Adv Ophthalmol. 1977;34:192-196.
2. Kimbrough RL, Trempe CS, Brockhurst RJ, et al. Angle-closure glaucoma in nanophthalmos. Am J Ophthalmol. 1979;88:572-579.
3. Sassani JW, Ritch R, McCormick S, et al. Histopathology of argon laser peripheral iridoplasty. Ophthalmic Surg. 1993;24:740-745.
4. Ritch R, Tham CC, Lam DS. Long term success of argon laser peripheral iridoplasty in the management of plateau iris syndrome. Ophthalmology. 2004;111:104-108.
5. Chew P, Chee C. Laser treatment of severe acute angle-closure glaucoma in dark Asian irides: the role of iridoplasty. Lasers and Light in Ophthalmology. 1991;4:129.
6. Lam DS, Lai JS, Tham CC, 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;109:1591-1596.
