Iridoplasty

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Overview

Iridoplasty (the molding of the iris) is a procedure that can be performed using low energy argon laser to place circumferential burns to the iris to cause contracture of the iris away from the anterior chamber angle. This allows more access for aqueous outflow.

CPT code 66762

Introduction

In 1977, Krasnov was the first to pioneer the use of laser energy to reduce intraocular pressure (IOP). Though the initial procedure encompassed only 90 degrees of the angle, later developments by Kimbrough treated 360 degrees of the peripheral iris through a gonioscopy lens. Their work provided the basis for laser iridoplasty. Laser iridoplasty is done using an argon laser photocoagulation to contract peripheral iris tissue away from the trabecular meshwork, thereby opening the anterior chamber angle and lowering IOP. This results in widening of the anterior chamber, which improves aqueous humor outflow and decreases IOP.[1] Indications for Argon peripheral laser iridoplasty (ALPI) include acute primary angle closure, as well as angle closure associated with plateau iris syndrome, nanophthalmos, and iris and ciliary body cysts.

It has been suggested that the heat shrinkage of collagen may be responsible for the short‐term response to ALPI, and that contraction of the fibroblastic membrane may be responsible for its long-term effects.[2]

Indications

Acute Primary Angle Closure

Acute primary angle closure (APAC) is caused by pupillary block that disturbs the flow of aqueous from the posterior chamber to the anterior chamber, creating a pressure gradient that causes a forward bowing of the peripheral iris. This change in the iris configuration abruptly blocks the trabecular meshwork, leading to a sudden rise in IOP. Symptoms of APAC include sudden onset of headache, blurred vision, halos around lights, eye pain and redness. Signs of APAC include decreased visual acuity, elevated IOP, conjunctival injection, corneal edema, mid-dilated pupil and a closed angle on gonioscopy. [3]

For patients with APAC, laser iridotomy is indicated. Although iridotomy is initially done to decrease IOP in APAC, in many cases appositional angle closure persists after laser peripheral iridotomy. ALPI can be used both when angle closure persists after laser peripheral iridotomy and acute angle closure not secondary to pupillary block as well.[4] [5]

In the early stages of non-pupillary block acute angle closure, an edematous cornea may preclude an adequate view to safely perform laser peripheral iridotomy safely. If a patient has more than one quadrant of visible peripheral iris, an ALPI was found to be a safe option for immediate IOP lowering compared to medical management alone. Once IOP is normalized and corneal edema improves, definitive treatment can be performed using peripheral laser iridotomy.[5]

There is controversy about the effectiveness of ALPI in treating APAC long term. Although ALPI can mechanically open the angle and safely treat APAC there is insufficient evidence to support the use of ALPI in people with chronic angle closure glaucoma (Bayliss et al., 2021). [6] [7] [4] [8]

Although ALPI was shown to be significantly more effective in reducing IOP in APAC at 15 min, 30 min and 1 h after the start of treatment when compared to conventional systemic medication the follow-up study of the same group of patients showed that there was no statistically significant differences in IOP control between the treatment and control groups when comparing ALPI to the systemic medication at 15 months post-surgery. [5]Other studies show either increased incidence of angle closure post-ALPI at 12 months,, while others studies show a decreases in the incidence of angle closure but no reduction in IOP whether used as a primary or secondary procedure. [9][10] [11]

Despite the lack of significant differences in IOP control long term, ALPI is known to be useful in early-stage primary angle closure treatment because of its superior efficacy in lowering acute increases in IOP.[7]

Plateau iris syndrome

In plateau iris syndrome, anteriorly positioned ciliary processes push the peripheral iris toward the trabecular meshwork, thereby closing the angle and resulting in elevated IOP. Although iridotomy is the treatment of choice in acute angle closure, several studies report patients with persistent angle closure after iridotomy (58-80% of cases).[12][13] Residual areas of persistent narrowing can then widened with ALPI (Matai et al., 1987). [14][15]Studies have shown that ALPI can rapidly lower IOP and maintain pressures after 1 year.[16] In one retrospective cohort study, 87% of plateau iris eyes treated with ALPI had open angles at the end of long-term follow-up (mean 79 months) after a single treatment, with no need for future filtration surgery.[14]

While ALPI is known to both lower IOP and decrease the number of topical antiglaucoma medications by widening the iridocorneal angle, there is no current evidence of its long-term efficacy (Bourdon et al., 2019).

Although ALPI has been shown to lower IOP and widen the iridocorneal angle in chronic angle-closure due to plateau iris syndrome, long-term efficacy has been shown to be difficult to control IOP with ALPI alone.[17][14] It has been proposed that ALPI only thins the superficial iris tissue and has no impact on ciliary body anteposition, which might explain poor long-term outcomes. Thus, at present there is no robust evidence to support ALPI as a treatment for chronic angle-closure caused by plateau iris syndrome.[18]

Nanophthalmic eyes

Nanophthalmos is a developmental ocular disorder characterized by a normal but smaller eye with short axial length. Nanophthalmic eyes are prone to angle closure in adulthood due to an age-related increase in the anteroposterior diameter of the lens relative to the eye. If appositional closure persists after iridotomy, ALPI can effectively open the angle.[19][20]

Iris and ciliary body cysts

Iris and ciliary body cysts may cause appositional closure of the angle. ALPI can widen the angle as needed and has been shown to have long-term success.[21] [22]

Contraindications

ALPI causes inflammation and is contraindicated in cases of severe corneal edema and flat anterior chambers.[23] Other contraindications include uveitis, neovascular glaucoma or iridocorneal–endothelial (ICE) syndrome.

Surgical techniques

ALPI is most often performed with an argon laser following instillation of a topical anesthesia in an outpatient setting. Success of ALPI relies on proper application of energy along the peripheral iris to achieve contraction of the tissue, which pulls the trabecular meshwork and opens the drainage angle.[24]

The eye is first pretreated with pilocarpine to constrict the pupil and stretch the iris, increasing access to the peripheral iris. Brimonidine or apraclonidine is also administered to decrease the chance postoperative IOP spikes.[24]

ALPI can be performed using either a direct or indirect technique. In the direct technique, the laser energy is concentrated through an Abraham lens perpendicular to the peripheral iris. The contraction burns should be made at the most peripheral portion of the iris with a large spot size, long duration and low power Argon laser (e.g. 500 µm spot size, 0.5 s duration, start from a power of 240 mW). This laser power is gradually increased if iris stromal shrinkage is not observed.[1] Placing five to six spots per quadrant evenly spaced is appropriate.

In the indirect technique, the laser energy is directed through a single-mirror lens at a low angle of incidence toward the peripheral iris. The treatment should be as peripheral as possible while avoiding the trabecular meshwork. A spot size of 300 to 500 µm with a duration of 0.3 to 0.5 seconds is appropriate. The direct technique is easier to perform, but the indirect technique provides direct visualization of the angle during the procedure.[24]

Postoperatively, a drop of brimonidine is administered. In addition, a short course of topical steroids such as prednisolone acetate 1% dosed 4 to six times daily is prescribed to reduce inflammation. The postoperative IOP is monitored closely post-ALPI.[6][25][26]

Complications

Iridoplasty can cause Urrets-Zavalia syndrome, a rare phenomenon characterized by a fixed, dilated pupil unresponsive to miotic agents resulting in light sensitivity and cosmetic disturbance. This condition usually resolves itself over the course of a year without treatment.[27]

Other complications include corneal endothelial burns because of the proximity of peripheral iris and the cornea. Rare cases of iris necrosis have been described, usually related to crowded spot applications.[25][26]

Summary

Argon laser iridoplasty (ALPI) is currently used as a second-line treatment option in people with remaining appositional angle closure after peripheral iridotomy. Current indications of ALPI include acute primary angle closure, plateau iris syndrome with resultant angle closure, nanophthalmic eyes, and iris and ciliary body cysts. Although there is a low incidence of severe complications in ALPI, there is not provide enough evidence to suggest that ALPI can reduce IOP in the long-term.[28]

  1. 1.0 1.1 Ng WS, Ang GS, Azuara-Blanco A. Laser peripheral iridoplasty for angle-closure. Cochrane Database Syst Rev. 2012 Feb 15;2012(2):CD006746. doi: 10.1002/14651858.CD006746.pub3. Update in: Cochrane Database Syst Rev. 2021 Mar 23;3:CD006746. PMID: 22336823; PMCID: PMC7390262.
  2. Sassani JW, Ritch R, McCormick S, Liebmann JM, Eagle RC Jr, Lavery K, Koster HR. Histopathology of argon laser peripheral iridoplasty. Ophthalmic Surg. 1993 Nov;24(11):740-5. PMID: 8290212.
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  10. Lee JR, Choi JY, Kim YD, Choi J. Laser peripheral iridotomy with iridoplasty in primary angle closure suspect: anterior chamber analysis by pentacam. Korean Journal of Ophthalmology 2011;25(4):252-6.
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  18. Bourdon, H., Aragno, V., Baudouin, C., & Labbé, A. (2019). Iridoplasty for plateau iris syndrome: a systematic review. BMJ open ophthalmology, 4(1), e000340. https://doi.org/10.1136/bmjophth-2019-000340
  19. Tarongoy P, Ho CL, Walton DS. Angle-closure glaucoma: the role of the lens in the pathogenesis, prevention, and treatment. Surv Opthalmol. 2009;54(2):211-225
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  28. Bayliss JM, Ng WS, Waugh N, Azuara-Blanco A. Laser peripheral iridoplasty for chronic angle closure. Cochrane Database Syst Rev. 2021 Mar 23;3(3):CD006746. doi: 10.1002/14651858.CD006746.pub4. PMID: 33755197; PMCID: PMC8094583.
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