Laser peripheral iridotomy

Laser iridotomy has, for the most part, replaced incisional surgical iridectomy. It is safer, achieves similar results, and is preferred by patients.1–3 Laser iridotomy is indicated for all forms of angleclosure glaucoma involving pupillary block and as a prophylactic measure for patients with occludable angles. A success rate of almost 100% can be achieved by experienced laser surgeons. Late failure is rare, especially in eyes treated with the neodymium: yttrium-aluminum-garnet (Nd:YAG) laser.4,5

Using light energy transmitted through the cornea instead of a blade incision to create an iridotomy was first demonstrated by Meyer-Schwickerath6 in 1956 with a xenon light source. Argon and Q-switched Nd:YAG lasers have enabled the creation of iridotomies more safely than by incisional surgical methods because the eye need not be opened.The laser procedure requires only topical anesthesia.7–12 In addition, the postoperative recovery period is shorter. This improvement in the risk:benefit ratio has changed the criteria for iridotomy. Surgical iridotomy is currently used only when laser iridotomy is not possible, such as when the cornea is opacified or the anterior chamber is very shallow.

Box 30-1  Indications for laser iridotomy

Firm indications

Acute angle-closure glaucoma

Chronic angle-closure glaucoma with peripheral anterior synechiae Intermittent angle-closure glaucoma with classic symptoms of angle

closure

Aphakic or pseudophakic pupillary block

Anatomically narrow angles and signs of previous attacks Narrow-angle eye with acute angle-closure glaucoma in the fellow eye Incomplete surgical iridectomy

Luxated or subluxated crystalline lens Anterior chamber lens implant Nanophthalmos

Pupillary block from silicone oil after vitrectomy13

Mixed-mechanism forms of glaucoma when filtering surgery might not be necessary for adequate pressure control

Relative indications

Critically narrow angles in asymptomatic patients

Younger patients, especially those who live some distance from medical care or who travel frequently

Narrow angles with positive provocative test

Iris–trabecular contact demonstrated by compression gonioscopy

Indications

A firm indication for laser iridotomy exists if the patient has pupillary block as evidenced by an anterior bowing of the peripheral iris with occludable angles accompanied by one or more conditions (Box 30-1). Certainly, laser iridotomy should be a strong consideration in any patient who has had symptoms of intermittent blurring of vision accompanied by rainbow-colored haloes around lights, occurring under circumstances that promote pupil dilation and whose examination shows bowing forward of the peripheral iris and very narrow or worse angles on gonioscopy.

Not all patients with narrow angles require iridotomy; most such patients never develop glaucoma. Relative indications for laser iridotomy exist because the procedure is not totally free of complications, and it is not always possible by gonioscopy alone to predict who will develop acute or chronic angle-closure glaucoma.

However, some asymptomatic patients in whom the angles are critically narrow are well served by laser iridotomy. In general, asymptomatic elderly patients who have access to adequate medical care can be counted on to report symptoms typical of angle closure and return for routine monitoring and can be observed safely. However, care must be taken to monitor these patients so that iridotomy can be instituted if progressive narrowing of the angle, formation of peripheral anterior synechiae, or elevated intraocular pressure (IOP) occurs.

Laser iridotomy should be considered in asymptomatic patients whose angles are narrow such that a portion is closed, in patients whose life expectancy will allow their lens to increase in size with subsequent angle narrowing and for whom cataract extraction is not anticipated in the immediate future, and in patients who do not have constant ready access to medical care such as frequent travelers or those who live in remote areas.This procedure is generally preferred over miotic therapy in such patients because, in many cases, miotic treatment does not prevent angle closure. If the choice is not clear and the two eyes are similar gonioscopically, iridotomy can be performed in one eye and the other eye can be observed.

In acute angle-closure glaucoma caused by pupillary block, treatment is initiated with medication to decrease IOP and help restore corneal clarity. Laser iridotomy, which is the definitive treatment, can then be performed more successfully.

Types of laser

Types of laser commonly used for iridotomy include the photodis-

ruptive Q-switched Nd:YAG laser, the photothermal argon lasers, or the solid state lasers.9,11,14–29 The Q-switched Nd:YAG laser is pre-

ferred by many surgeons because it perforates the iris easily.This is

particularly true in dark brown or light blue irides. It is more difficult to penetrate dark brown irides with photothermal argon or solid-state lasers because they have a tendency to char during treatment; light blue irides can be difficult because pale irides do not

absorb argon or solid-state laser energy very well. Moreover, Nd: YAG iridotomies may be less likely to close over time.24,26,30–32

Because the Nd:YAG laser (unlike photothermal argon or solid-state lasers) has no coagulative effect, bleeding occurs more frequently. Local hemorrhage is usually self-limited and rarely of consequence. Bleeding may be limited by pretreating the proposed iridotomy site with the coagulative energy from an argon laser or a 532-nm frequency-doubled solid-state Nd:YAG laser,33 but this is rarely performed. However, it may be indicated in those who have a coagulative disorder or who are using anticoagulative medications. In patients with severe coagulative disorders, pretreatment with intravenous blood derivatives to replace a missing factor(s) may help limit intraocular bleeding.The vast majority of the time, if bleeding does occur at the surgical site, it can be stopped by pressing on the contact lens and temporarily raising the IOP (Fig. 30-1).

Fig. 30-1  Small cascade of hemorrhage from the site of Nd:YAG iridotomy. Bleeding is effectively stopped by gentle pressure on the globe via the Abraham contact lens (see Fig. 30-2.)

General preparation

Miosis, which helps to tighten and thin the peripheral iris and pull it away from the cornea, can be accomplished with a drop of pilocarpine 1% or 2%.Topical anesthesia is achieved with proparacaine hydrochloride 0.5%.

An Abraham iridotomy lens (Fig. 30-2) greatly improves visualization, separates the lids, stabilizes the eye, minimizes epithelial burns because it acts as a heat sink, and increases the power density by concentrating the energy into a smaller spot size at the iris.The Wise lens modification34 provides a higher power density at the tissue site but causes greater image distortion as a result of the higher magnification. A variety of other lenses that are especially corrected for argon or Nd:YAG wavelengths have been developed for this purpose. One relatively recent one is the Pollack lens (Ocular Instruments, Bellevue, WA) which we have found to be useful for iridotomies, trabeculoplasty, and also for iridoplasty (see below).

The iridotomy should be placed in the periphery of the iris. Such placement reduces the likelihood of lens injury and possible subsequent sealing of the iridotomy by posterior synechiae to the lens. Furthermore, peripheral placement also reduces the likelihood of later ghost images through the iridotomy. If a dense arcus senilis is present, the iridotomy site must be central to it. A site between the 11 and 1 o’clock meridians is preferable because it will be covered by the upper lid. Iridotomies within the palpebral fissure can cause visual disturbances due to polycoria. The 12 o’clock meridian should be avoided because (1) with argon or solid-state laser iridotomy, gas bubbles rise to this area and may obscure the laser site before treatment can be completed, and (2) with Nd:YAG laser iridotomy, a small trickle of hemorrhage may cascade down from the treatment site and obscure the patient’s vision temporarily. Both of these problems will be avoided if the iridotomy is placed closer to the 11 or 1 o’clock positions.Wand (Personal Communication) has advocated placing the iridotomies in the temporal or nasal periphery and reports no visual problems or ghost images with this technique.

With careful examination, a relatively thin region in the iris can often be identified. This area may be located in the depths of a crypt or in an area evidenced by a rather lacy, translucent appearance of the superficial stroma. In blue irises, the dense white radial cords of the iris stroma should be avoided. Perforation of the iris is recognized by release of a pigment cloud billowing forward from

Fig. 30-2  Abraham iridotomy lens is a modified Goldmann fundus lens. A small 66D plano convex button is added to a flattened surface. This focussing effect increases the power density by a factor of 4.

the iridotomy site and the posterior movement of the iris deepening the anterior chamber. With Nd:YAG iridotomies a rapid gush of fluid is often indicated by small flecks of pigment racing through the opening. Transillumination through the iridotomy is a reasonably good sign of complete perforation in a brown iris but can be misleading in a light blue or grey iris. Clear evidence of perforation is direct observation of the anterior lens capsule through the iridotomy site.Another useful technique is to direct the aiming beam into the depths of the iridotomy. Be sure the main beam is inoperative. If the opening is through-and-through the iris, the aiming beam will disappear. The aiming beam is also helpful for coherent transillumination. A small but complete peripheral perforation is the ideal end point. It is important to have the patient gaze upward, both to clear a peripheral corneal arcus and to ensure that no laser light will be aimed toward the macula.

Nd:YAG laser iridotomy

Q-switched Nd:YAG lasers (1064 nm) are very useful for iridotomy (Figs 30-3 and 30-4). Power settings depend on the power