Acute primary angle closure

LPI should be performed after the acute attack has been terminated with medical therapy or ALPI and the eye is no longer actively inflamed, usually about 2 days later. Attacks of acute angle closure which do not respond to a brief period of medical treatment to lower IOP and to open the angle may be treated successfully with ALPI, although in some cases the media may be clear enough to perform an LPI. If LPI is to be attempted during an acute attack, the argon laser is preferred because of the greater incidence of iris bleeding in these inflamed eyes.

A recent randomized controlled trial reported that LPI may not be as effective as early phacoemulsification in reversing angle closure and preventing the subsequent IOP increase in acute angle closure eyes⁴. It was suggested that if LPI could be performed within 7 days after the onset of symptoms in acute angle closure the chance of successful post-iridotomy IOP control would be higher⁵. After LPI in acute angle closure eyes, up to 55.6% may still have appositionally closed angles⁶. It is therefore important to monitor both the drainage angle and IOP in acute angle closure patients following LPI.

Chronic angle closure

As well as an attack of acute angle closure, eyes with appositional angle closure with or without peripheral anterior synechiae (PAS) are at risk for progressive trabecular damage and chronically elevated IOP.

Iridotomy can eliminate the progression of synechial closure in patients with chronic angle closure caused by pupillary block. Even if the angle structures cannot be visualized by indentation gonioscopy prior to treatment, areas of functional meshwork may become apparent after LPI has been performed.

LPI alone may control IOP, or elevated IOP may persist as a result of prior trabecular damage, warranting continued medical treatment or filtration surgery. Failure of medications to control IOP, particularly if the angle is closed, does not mean necessarily that the IOP will be uncontrollable medically after iridotomy. It is often not possible to predict which eyes will respond favorably; in one series, LPI reduced the IOP in 44% of eyes in patients with chronic angle closure glaucoma⁷.

Aphakic or pseudophakic pupillary block

Aphakic and pseudophakic pupillary block may be relieved by LPI. In some cases, pockets of both aqueous and vitreous may be present posterior to the iris, or broad areas of vitreous may be adherent to the posterior iris. An iridotomy made over an area of vitreous–iris adhesion or apposition will not relieve the pupillary block. Multiple iridotomies may be required before a pocket of aqueous is located and the block relieved. Creating the iridotomy also helps differentiate pupillary block from malignant glaucoma (ciliary block, aqueous misdirection), which requires disruption of the anterior hyaloid face.

Malignant glaucoma

The classic presentation of malignant glaucoma was an eye with angle closure glaucoma which persisted after pupillary block was eliminated by a surgical iridectomy or other intraocular procedure, accompanied by a shallow or flat anterior chamber. When the condition is bilateral, prophylactic LPI usually protects the fellow eye against both acute angle closure and malignant glaucoma, which could be triggered by opening and decompressing the globe. However, after elimination of pupillary block other mechanisms of angle closure may continue to progress or additional ones may develop over time.

Prophylactic laser peripheral iridotomy

A prophylactic LPI should be performed in the fellow eye of a patient with either acute or chronic angle closure if the fellow eye also has a narrow angle. Eyes with spontaneous appositional closure on darkroom gonioscopy despite a normal IOP and eyes with narrow angles and positive provocative tests should also have a prophylactic iridotomy.

Other situations

Contact lenses for laser procedures

Firm control of the contact lens reduces saccades and extraneous eye movements that interfere with accurate superimposition of burns. The lens helps to separate the lids, to focus the laser beam, and to minimize loss of laser power from reflection. By absorbing heat delivered through the cornea, the gonioscopy solution decreases the incidence of corneal burns.

The Abraham lens (Fig. 44.1) consists of a fundus lens with an anterior +66 diopter planoconvex button. The button magnifies without loss of depth of focus. The effective size of a 50 µm spot is reduced to approximately 30 µm; this provides higher energy per unit area and permits the procedure to require a lower total energy. Posterior to the site of focus, the beam is more rapidly defocused, decreasing potential injury to structures behind.

Fig. 44.1 Abraham laser contact lens – useful for both laser peripheral iridotomy and laser peripheral iridoplasty.

From Ritch R, Solomon IS. Glaucoma Surgery. In: L’Esperance FA, editor. Ophthalmic Lasers. 3rd ed. St. Louis: CV Mosby Co; 1988. p. 650-748.

Preoperative treatment

Topical anesthesia suffices. If the pupil is not already maximally miotic, 1–2% pilocarpine is given topically. The smaller the pupil, the thinner is the iris stroma at any point, needing less laser energy to penetrate. Perioperative treatment with apraclonidine or brimonidine reduces the magnitude and frequency of post-laser IOP spikes. Patients require careful monitoring of IOP postoperatively.

Iris types

Irides vary in thickness, color, and number and size of iris crypts and freckles. These characteristics need to be considered to minimize potential technical difficulties and complications. Generally, medium brown irides are the easiest to penetrate with the argon laser, the energy of which is readily absorbed by the iris pigment. Light blue and dark brown irides are more difficult. Lighter irides are more easily penetrated with the Nd:YAG laser than are darker, thicker irides.

A site in the iris periphery should be selected for the iridotomy. The iridotomy is best placed between the 11 o’clock and 1 o’clock positions, where it will be covered by the upper lid to minimize glare and diplopia. When the Nd:YAG laser is used, choose a site beyond the lens equator to avoid damage to the lens capsule.

Performing the iridotomy in the base of an iris crypt, where the stroma is thinner, often facilitates penetration. Avoid a corneal arcus senilis because its density will drop laser power, and interfere with clear focusing of the beam. Aiming the laser beam away from the fovea is important to limit accidental retinal damage. The beam should be perpendicular to the contact lens surface to maximize energy delivery.

Argon laser peripheral iridotomy