ARGON LASER PERIPHERAL IRIDOPLASTY

Guest author

SEHRISH

Ajmal Khan Tibbiya College

Aligarh, India

INTRODUCTION

Iridoplasty, also known as gonioplasty, uses low-energy laser burns to the peripheral iris in order to widen the anterior chamber angle and/or break peripheral anterior synechiae. Patients requiring laser iridoplasty are most often diagnosed with plateau iris syndrome, either by ultrasound biomicroscopy or follow up gonioscopy that demonstrates a narrow angle after laser peripheral iridotomy.

During iridoplasty, the laser light is converted to heat that causes contraction of stromal collagen, which is primarily responsible for the immediate anatomical change. 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.

HISTORY

Krasnov and Kimbrough’s attempts to modify the peripheral iris had some success; however,the outcomes were limited by technique and instrumentation.

Kimbrough et al described a technique for direct treatment of 360° of the peripheral iris through a gonioscopy lens, and termed the procedure gonioplasty. 

The current use of argon lasers has led to a refinement in technique that has increased both anatomical and clinical success.

ARGON LASER PERIPHERAL IRIDOPLASTY (ALPI)

Argon laser peripheral iridoplasty is a useful procedure to eliminate appositional angle closure resulting from mechanisms other than pupillary block. For those eyes with angle closure originating at an anatomic level posterior to iris, such as- plateau Iris, lens-induced angle closure, malignant glaucoma, central retinal vein occlusion etc.

Argon laser peripheral iridoplasty is often useful in these cases to further open the angle. It can be used to break an acute attack of angle closure glaucoma and relieve appositional angle closure secondary to plateau iris syndrome, or lens-related angle closure, and to widen the angle prior to argon laser trabeculoplasty treated as necessary if a postlaser IOP rise occurs.

CHARACTERISTICS OF ARGON

Phocoagulative ( lower energy & longer exposure)

Iris color (Pigment density) is the most important factor.

   (a) Light brown colour: 600-1000mW with a spot size of 50ûm and a shutter speed of 0.02-0.05 second

   (b)  Dark brown colour: 400-1000mW, spot size of 50ûm and a shutter speed 0.01 second

    (c) Blue Iris colour: 200-400mW, spot size 200ûm, speed 0.1 second

INDICATIONS

1. Acute angle closure glaucoma
2. Chronic angle syndrome
3. Plateau iris syndrome
4. Angle closure due to size or position of lens
5. Iris bombe
6. Adjunct to laser trabeculoplasty
7. Malignant glaucoma
8. Fellow eye
9. Nanophthalmos
10. Aphakic or pseudophakic pupillary block 
11. Incomplete surgical iridectomy
12. Subluxated Crystalline lens
13. Aqueous misdirection syndrome
14. Pigmentary glaucoma
15. ACIOL implant 

CONTRAINDICATIONS

1. Severe and extensive corneal edema or opacity
2. Flat anterior chamber
3. Synechial angle closure

TECHNIQUE

STEP-BY-STEP TECHNIQUE FOR IRIDOPLASTY

STEP 1: The informed consent for iridoplasty includes an explanation of potential side effects such as:

• Pain/discomfort

• Inflammation

• Elevated IOP

• Changed pupillary shape/size

• Possible need for retreatment

STEP 2 :Pretreat the patient with:

• One drop of pilocarpine 2%

• One drop of brimonidine or apraclonidine

• One drop of proparacaine

STEP 3: Set up laser:

• Power—300 to 500 mW (higher if needed)

• Spot size—300 to 500 µm

• Duration—300 to 500 milliseconds

STEP 4

Place Genteal gel (Novartis Ophthalmics, Inc., Duluth,GA), Refresh Celluvisc (Allergan, Inc., Irvine, CA), or another clear lubricant on the single-mirror lens (or the Abraham lens, if you choose) and position the lens over the eye.

STEP 5

•Treat the peripheral iris without encroaching on the trabecular meshwork.

• Increase the laser power as needed to cause the tissue to contract without forming bubbles or releasing pigment.

• Treat 360º.

STEP 6

• Remove the lens and clean off the eye.

• Instill one drop of prednisolone acetate 1%.

• Recheck the IOP in 1 hour.

• Send the patient home with instructions to administer one drop of Prednisolone q.i.d. for 4 days

• Follow up in 1 week.

                                       

After the procedure, the eye receives a drop of a topical steroid or NSAID. The surgeon checks the IOP 1 hour after treatment. At the 1-week follow-up visit, 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.

POST-OPERATIVE TREATMENT

Immediately after the procedure, the patient is given a drop of topical steroid and apraclonidine or brimonidine. Gonioscopy should be performed to assess the effect of the procedure immediately if pilocarpine has not been used. If it has, it is better to evaluate the success of the procedure at a sub-sequent visit. Patients are treated with topical steroids 4--6 times daily for 3 to 5 days. Intraocular pressure is monitored postoperatively as after another anterior segment laser procedure and patients treated as necessary if a post-laser IOP rise occurs.

COMPLICATIONS

Mild postoperative iritis

Iris atrophy

Ocular irritation.

Iridoplasty is often performed on patients with extremely shallow peripheral anterior chambers, diffuse corneal endothelial burns may occur.

During laser iridotomy, endothelial burns seen during ALPI are larger and much less opaque.

Endothelial burns present a problem early in the procedure, they may be minimized by placing an initial contraction burn more centrally before placing the peripheral burn (kriss-kross iridoplasty).

          A transient rise in IOP can occur as with other anterior segment laser procedures.    

          Lenticular opacification has not been reported.

        When IOP is rapidly reduced in acute primary angle closure by ALPI, decompression     retinopathy can rarely occur. 

         Urrets-Zavalia syndrome.

         Recurrence of angle-closure.

NEED FOR RETREATMENT

Although ALPI is highly successful long-term in eyes with plateau iris, patients need to be followed closely for recurrence of appositional closure, and if this develops, may require retreatment.

Patients should be observed gonioscopically at regular intervals and further treatment given if necessary. 

This is most common in a patient in whom the mechanism of the glaucoma is lens-related or as the lens enlarges over time.

Retreatment is only occasionally needed in patients with plateau iris, whereas those with intumescent lenses usually undergo cataract extraction.

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 iridoplasty/dotomy cannot be performed. 

A precise technique and an attention to detail are keys to successful iridoplasty, and ophthalmologists should be familiar with the finer points of performing this laser procedure.