Sequential Laser Iridotomy Using Argon and Q-Switched 532 nm Frequency Doubled Neodymium Yag Laser: A Pilot Study

Laser iridotomy is an established procedure in the management of angle closure glaucoma (ACG) and for prophylaxis in the fellow eyes.

Sequential argon-YAG (SAY) laser iridotomy is the serial use of argon and Nd:YAG laser at the same treatment session to create an iridotomy. Argon laser is initially used to make a bore of about 500 μm in diameter to an estimated two-thirds iris thickness in depth. The 1064 nm Q-switched neodymium YAG laser is next used to complete the perforation1. Others aim the argon laser at the iris surface to create a crater, and the next shots at the base of the crater until the iris is penetrated as evidenced by a pigment plume. The Nd:YAG laser then creates a photodisruptive explosion to enlarge the opening.

This procedure was first described by Zborwski-Gutman in 1988. Sixteen eyes were treated with two argon stretch burns and up to 35 penetrating burns that produced an iridotomy that was either imperforate or inadequate. Nd:YAG laser was used to complete the iridotomy. In all the eyes, the iridotomy was achieved in one session, and two eyes had a moderate increase in pressure that was easily controlled. The authors found that the total energy levels for each laser modality were significantly lower than those previously reported using either laser alone. The authors concluded that the sequential technique is safe and effective, and is recommended for iridotomy in difficult iris types.

Lim et al in 1996 did a prospective study that compared argon laser iridotomy and SAY in dark irides. Twenty-four eyes of 17 patients were involved; and 13 underwent argon laser iridotomies, and 11 underwent SAY. The argon laser settings were standardized at 1.2 W, 50 μm spot size and 0.1 second duration. The Nd: YAG laser was set at 2.5 mJ and single-pulse shots were used. All the iridotomies were completed in a single session. The mean total energy used for argon laser iridotomy was 8.28 J; while for SAY, 3.12 J was used for the argon laser stage and 7.5 mJ for the Nd:YAG stage. The authors concluded that the total argon laser energy used can be reduced by 2.65 times using the SAY technique.

The SAY technique is ideal in Asian eyes because it avoids the disadvantages of argon and Nd-YAG laser, when they are used as separate methods.