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

Contraction burn

This burn contracts the surrounding iris tissue towards, and compacts the stroma at the target site. Contraction burns are of low power, large spot size, and long duration. They (i) increase the density of iris stroma to facilitate laser energy absorption in blue or light brown irides, (ii) create a ‘hump’ on which penetrating burns are placed, and (iii) produce a peripheral iridoplasty or pupilloplasty effect. Settings are 500 µm spot size, 0.5–0.7 second duration, and 200–400 mW. If bubbles occur or pigment is released, reduce the power. Begin with 200 mW in brown irides and 300 mW in light ones, adjusting the power as necessary. In very light irides, a 200 µm spot size may be necessary.

There are two contraction burn techniques that we utilize: the linear incision and producing a contraction burn bed.

The linear incision technique involves placing a short line of circumferential burns instead of penetrating at a single spot (Fig. 44.2). When the stroma is fully incised in this manner, the iris dilator muscle assists in the separation of the iris pigment epithelium, reducing the amount of pigment epithelium which must be lasered and creating a larger opening.

Fig. 44.2 Laser application technique for peripheral iridotomy with linear incision placed within the area affected by one or more contraction burns.

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.

The contraction burn bed technique helps in lightly pigmented irides without crypts. One to three contraction burns are placed in a circumferential line, partially superimposed (see Fig. 44.2). Punch or penetrating burns are then placed using the contraction burns as a bed for the site of laser peripheral iridotomy. In very light irides, this method combined with linear incision usually results in larger iridotomies than attainable with other argon laser techniques. For light brown irides, we place a single contraction burn on either side of the selected penetration site (modified drumhead). The area between them is tautened and an iridotomy created with penetrating burns.

Penetrating burn

This is a higher power, small spot size burn designed to vaporize iris tissue and create an opening; use a 50 µm spot size. In the late 1970s and early 1980s, burns of 0.1 or 0.2 second duration were common. This introduces far too much power especially with dark brown irides. Shorter duration, lower power burns were shown to be more effective¹⁰, with less complications and less total energy for penetration. Burns of 0.01 or 0.02 second duration were formerly termed ‘punch burns’. The optimal power is between 600 and 1200 mW; it varies depending on burn duration and iris consistency and pigmentation.

Shorter duration (0.01 or 0.02 second) burns are optimal in dark irides, particularly in blacks and Asians, to avoid charring at the base of the iridotomy site. As they produce less thermal effect than longer duration burns, they are useful in all irides. Posterior synechiae may occur less frequently with short duration burns.

Our preferred approach is to perform linear incision using short duration penetrating burns for dark brown irides, a modified drumhead for medium brown irides, and penetration through contraction burns in combination with linear incision for light irides. Improvisation in technique and choice of laser settings for different types of irides is the key to success. The entire procedure may require anywhere from 1 to 300 burns.

For any iridotomy, the first burn often serves as an indicator for the ease of the procedure. The desired result is the appearance of a small hole with a dark brown base at the site of the burn and dispersion of debris into the anterior chamber. Bubble formation at the site of the burn indicates stromal vaporization. One then simply continues to deliver burns until the stroma has been penetrated.

In the absence of stromal pigmentation, bubble formation and pigment release may be minimal. One clue to the gradual deepening of the iridotomy is a gradual darkening of the base. An orange reflex at the time of beam impact, most commonly seen in irides with little stromal pigmentation, signifies that one is nearing the pigment epithelium.

When the iris pigment epithelium is reached, denser bursts of fine pigment (smoke signals) appear in the anterior chamber. A ‘mushroom cloud’ of pigment mixed with aqueous often slowly balloons into the anterior chamber. Simultaneously, the iris stroma floats backward and the peripheral anterior chamber deepens.

Cleanup burns

After penetration, the iridotomy may be enlarged and pigment epithelium removed with cleanup burns. Use either a low power penetrating burn (400–600 mW), or a longer, low power burn, such as 100 µm, 0.2 s duration, and 200 mW power. Occasionally, an impenetrable cord of stroma is present at the site of the iridotomy. One can create an opening on either side of this cord if it cannot be severed at its base.

At the completion of the iridotomy, the lens capsule should be visible through the opening (Fig. 44.3). If the opening is small and the capsule is not visible, one can often get a sense of depth behind the opening or note a green reflex off the lens capsule when the beam is applied to the opening. Gonioscopy should be performed to ensure that the angle is open.

Fig. 44.3 The lens capsule is visible through the iridotomy opening at the completion of laser peripheral iridotomy.

From Wise JB: Iris sphincterotomy, iridotomy, and synechiotomy by linear incision with the argon laser. Ophthalmology 1985;92:641.

Transillumination is not a reliable indicator of success in light irides. If too high a power is used in light irides, it is possible to destroy pigment epithelium without penetrating the stroma. Once this happens, the overlying stroma cannot be penetrated and the surgeon may be fooled into thinking the procedure has been successful.

Elevated IOP associated with LPI typically occurs in the first 1–2 hours postoperatively¹¹. One should monitor IOP during this time. Postoperative topical steroids for several days are recommended to control inflammation.

Neodymium:YAG laser peripheral iridotomy

The Nd:YAG laser creates a plasma of free ions and electrons at the site of optical breakdown. This photodisruption releases shock waves that mechanically cause tissue rupture, as opposed to the thermal effect of the argon laser¹². Iris color and density are much less important than with argon LPI.

Suggested settings for Nd:YAG LPI have varied from one to four pulses per burst and from 1 to 10 mJ per burst. One should begin with a single pulse at approximately 1.5–3 mJ to assess the response of both the patient and the iris to the laser application. An increase in laser energy to 4–6 mJ is often sufficient to create a patent iridotomy with one to three additional applications. We prefer a linear incision technique using lower power burns, of the order of 1 mJ. We also prefer a single pulse per burst. It is very important to focus on the anterior iris stroma to maximize photodisruption and to minimize the possibility of lens injury. Portable Nd:YAG systems may facilitate iridotomy in debilitated patients or in remote areas¹³.

Other wavelengths

Combining argon laser techniques to thin the iris stroma and coagulate blood vessels followed by Nd:YAG completion of the iridotomy has been advocated as an approach with few complications which takes advantage of the photothermal effects of the first and easier penetration of the latter¹⁴. This is particularly effective for light blue irides. The risk of operative hemorrhage is reduced. Laser iridotomies may also be created with the diode, krypton, and picosecond lasers.

Blurred vision

Blurred vision is transitory and occurs in the immediate post-laser period. Possible causes include retinal pigment bleaching by the argon laser, pigment dispersion, anterior segment inflammation, pilocarpine effects, or residual methylcellulose from the gonioscopy solution.

Pupillary abnormalities

The pupil may be peaked toward the iridotomy site. The extent of the peaking increases the closer the iridotomy is to the pupil, the lighter the iris, and the greater the total energy used. Pupillary distortion is more prominent with the argon laser than with the Nd:YAG laser. It is generally minor, transient, hardly noticeable, and not associated with visual difficulties.

Diplopia and glare

Diplopia and glare are uncommon given the small size of most laser iridotomies, but may develop or worsen if the iridotomy enlarges over time. Diplopia is particularly prone to occur if the iridotomy is placed nasally or temporally, but may occur anywhere if not covered by the upper lid. Younger patients are more likely to experience this problem. Placement superiorly so that it is covered by the upper lid and avoids the position of the tear meniscus reduces the frequency of these complaints.

A rather common finding and a not uncommon source of complaint is the sensation of a horizontal line in the upper visual field, occasionally accompanied by glare. This occurs when the iridotomy is partially covered by the lid margin and is relieved when completely covered or completely exposed¹⁵. There is also a ‘shutter effect’ created by the lid crossing the iridotomy site during blinking. Patients eventually become used to it and often no longer notice it after a few months. Tinted soft contact lenses may be used to ameliorate diplopia. Opaque contact lenses to cover the iridotomy site may be used to reduce the amount of stray light entering through it.

Corneal damage

All corneal complications were more common with high power (1500–2000 mW), long duration (0.1–0.2 second) laser applications in dark brown irides. They rarely occur with the much shorter duration, lower power burns described above. These include epithelial and endothelial thermal burns, and corneal edema, abrasions, and opacities. Epithelial coagulation and whitening are transient, but may interfere with the delivery of laser energy and impede the creation of a patent iridotomy. If epithelial coagulation occurs, an attempt can be made to angle the beam around the burn to complete the iridotomy. If this is impossible, it may be necessary to choose another location for the iridotomy, use a Nd:YAG laser, or postpone completion of the iridotomy until the epithelium has healed. Stromal edema and striate keratopathy may also occur.

Endothelial burns from the argon laser are generally dense white with sharp margins and result from the thermal effects of iris photocoagulation. They require more time for resolution and may result in focal endothelial cell loss. Although endothelial cell loss following LPI has not been statistically significant during follow-up of up to 1 year, an increase in mean endothelial cell size and endothelial cell loss with greater laser power have been reported¹⁶. Both epithelial and endothelial burns have been rare since 0.1–0.2-second duration pulses have been abandoned.

Although endothelial cell analysis after Nd:YAG iridotomy may be unchanged¹⁷, focal endothelial cell loss has been documented when photodisruption is less than 1 mm from the corneal endothelium and at the site of treatment¹⁷. The area of focal loss is reduced in size with the use of an Abraham lens. Damage to Descemet’s membrane occurs when this distance is reduced to 0.1 mm. Progressive corneal edema requiring penetrating keratoplasty has been reported following Nd:YAG or argon LPI. Risk factors include pre-existing guttata and excessive laser energy.

Anterior uveitis

Post-laser anterior segment inflammation is typical, usually mild and ceases within a few days. It may last longer than 1 month and may be worse in individuals with heavily pigmented irides¹⁸. Topical corticosteroids are routinely prescribed.

Posterior synechiae

Posterior synechiae may occur between the lens and either the pupil margin or the iridotomy site. They may be less common after Nd:YAG iridotomy. They can be minimized with post-laser topical steroids or they can be broken by post-laser dilatation.

Hemorrhage

Bleeding is rare with the argon laser, because the iris tissue undergoes thermal coagulation. However, hyphema may occur and may even occur days after the iridotomy, sometimes accompanied by increased IOP.

Nd:YAG photodisruption does not coagulate iris vessels, and a small hemorrhage at the iridotomy site may occur in up to 50% of patients. Gentle pressure on the eye with the contact lens may control the bleeding. Iridotomy in eyes with rubeosis or uveitis should be performed with the argon laser.

Elevations of IOP

Transient post-laser pressure elevations lasting less than 24 hours are common. These are usually mild and easily controlled. However, rapid elevation of IOP to high levels may occur immediately after both argon and Nd:YAG iridotomies.

Although the maximal elevation of IOP was reported to occur in the first hour in approximately 70% of patients, others found that as many as 40% of patients had a maximal pressure elevation during the second hour. A pressure rise greater than 6 mmHg occurred in up to 40% of patients and to over 30 mmHg in as many as 30% prior to the use of apraclonidine or brimonidine. Currently, such rises are rare.

No significant difference in postoperative pressure rises has been found between the two types of lasers. The elevation may be related to the amount of energy used, the degree of pigment dispersion, and the preoperative outflow facility. Eyes in which iridotomies are performed prophylactically may have a lower incidence of post-laser IOP elevations.

A pressure elevation may be treated with miotics, topical beta-blockers, carbonic anhydrase inhibitors, or oral hyperosmotic agents.

Lens opacities

Focal, anterior subcapsular opacities occur after both argon and Nd:YAG iridotomy. The incidence may be as high as 45% increasing with greater amounts of applied energy. Long-term follow-up has shown them to be stable.

The earlier widespread fear of acute onset of cataract after Nd:YAG iridotomy caused by inadvertent rupture of the lens capsule has not been substantiated.

Prophylactic LPI was reported to be associated with cataract progression in fellow eyes of patients with acute angle closure^19,20.

Closure of the iridotomy site

Closure of a previously patent iridotomy may be either delayed or immediate. Immediate closure is caused by occlusion of the opening by circulating debris or land-sliding of the surrounding pigment epithelium.

Delayed closure is usually caused by localized pigment proliferation occluding the opening. Pigment proliferation is more prominent after argon LPI and usually occurs within the first 6–12 weeks. Up to one-third of patients may require retreatment. The iris opening after Nd:YAG laser iridotomy is more irregular, with less pigment dispersion, but retreatment may be necessary in about 9% of patients. Closure is extremely common in patients with uveitis after either type of laser. Other causes of late failure include the development of a transparent, thin fibrous membrane occluding the opening, and regeneration of iris pigment epithelium from the margins of the iridotomy. This characteristically grows in evenly from the margins of the iridotomy toward the center and does not come forward to occlude the portion of the opening through the stroma. Functional closure may occur with the formation of posterior synechiae. Re-treatment to open the iridotomy is usually easy. Argon LPIs that repeatedly close may remain open after Nd:YAG treatment.

Retinal damage

Photocoagulation of the peripheral retina between the equator and the ora serrata during argon LPI usually occurs when an opening is being enlarged after iris penetration has been achieved. Inadvertent foveal photocoagulation can occur, and proper positioning of the laser beam is essential. Choroidal and retinal detachment and non-rhegmatogenous retinal detachment in nanophthalmic eyes have also been reported. Microperforations of the retina may occur with the Nd:YAG laser if the beam is inadvertently focused to within 2 to 3 mm of the retina. Decompression retinopathy has been reported after Nd:YAG LPI¹⁹.

Acute primary angle closure

ALPI can break an attack of acute primary angle closure which is unresponsive to medical therapy and where corneal edema, a shallow anterior chamber, or marked inflammation precludes immediate LPI. ALPI may also be useful for an attack which is unresponsive despite a patent iridotomy^1,4. Circumferential treatment of the iris is virtually 100% successful at opening the angle in those areas in which there are no PAS. The effect lasts sufficiently long for the cornea and anterior chamber to clear so that iridotomy can be performed.

ALPI may be used as primary therapy in eyes with acute primary angle closure, either with or without preliminary treatment with topical medications^21–24. It was shown to be more effective than conventional systemic medications in lowering IOP in acute primary angle closure in a randomized controlled study²³. Since ALPI does not eliminate pupillary block, LPI is still required in acute primary angle closure once IOP is controlled and the cornea has cleared sufficiently; otherwise the effect of ALPI may reverse.

Chronic angle closure

Eyes with chronic angle closure and a combination of PAS and appositional closure may respond to ALPI with opening of the appositionally closed portions of the angle, allowing filtration surgery to be avoided²⁵. If extensive PAS are present after ALPI, goniosynechialysis (GSL) may be performed to surgically strip PAS from the angle wall to restore aqueous access to the trabecular meshwork.

Plateau iris syndrome

A large or anteriorly positioned ciliary body can push the iris root onto the trabecular meshwork, creating a configuration known as plateau iris. In plateau iris syndrome, the angle remains appositionally closed or occludable following LPI. ALPI provides successful long-term control in eyes with plateau iris syndrome (Figs 44.5–44.7)²⁶.

Fig. 44.5 (A) Appropriate placement of laser burns for peripheral iridoplasty. (B) Burns placed too centrally are ineffective at opening the angle.

Fig. 44.6 Ultrasound biomicroscopy (UBM) image of an eye with plateau iris syndrome after LPI (A) and after ALPI (B).

Fig. 44.7 Ultrasound biomicroscopy (UBM) image of an eye with plateau iris in which the burns were placed (A) appropriately and (B) too centrally.

Angle closure related to the size or position of the lens

Angle closure caused by an enlarged lens (phacomorphic) or pressure posterior to the lens (‘malignant’ or ciliary block) often fails to respond to iridotomy, although a component of pupillary block may be present and must be eliminated first by iridotomy. In suspected cases of ciliary block in which the angle remains appositionally closed after LPI, the apposition can be reduced or eliminated by ALPI. After the angle has been opened and IOP reduced, cycloplegics may be given cautiously to ascertain the mechanism of the angle closure. ALPI is effective as a primary treatment to break attacks of acute phacomorphic angle closure^27,28. This may allow a week or more for the inflammation and Descemet’s folds to clear, facilitating cataract extraction. Any pupillary block can be treated subsequently with iridotomy as soon as possible (usually within 2–3 days).

Adjunct to laser trabeculoplasty

If the angle is narrow because of plateau iris configuration or angle crowding, ALPI can retract the iris away from the trabecular meshwork to facilitate laser trabeculoplasty.

Nanophthalmos

Patients with nanophthalmos are predisposed to angle closure owing to anterior chamber crowding. If appositional closure persists after LPI, ALPI is indicated.

Other applications of ALPI

ALPI has been successful to treat appositional angle closure secondary to ciliary body cysts²⁹, drugs (topiramate)³⁰, and uveitis³¹.

Corneal edema or opacification

In acute primary angle closure, moderate degrees of corneal edema are not a contraindication to ALPI, but severe edema may preclude a good enough view for iridoplasty.

Flat anterior chamber

Corneal endothelial burns result from aqueous heating at the site of the laser burn with aqueous reflux toward the corneal endothelium. If the iris is apposed to the cornea, any photocoagulation will damage the corneal endothelium. If the anterior chamber is very shallow, laser applications should be timed far enough apart so that heat generated can dissipate.

Synechial angle closure

ALPI relieves appositional closure but not synechial closure (e.g. in eyes with areas of PAS from chronic angle closure, uveitis, neovascular glaucoma, or iridocorneal–endothelial (ICE) syndrome).

Laser equipment

Preoperative preparation

ALPI is an outpatient procedure under topical anesthesia with an Abraham or Wise lens. Pre-treatment the pupil is constricted with pilocarpine. ALPI may be performed for any type of angle closure worsened by miotics, which increase lens axial thickness and further shallow the anterior chamber. Although miotics are contraindicated in maintenance therapy of these types of angle closure, their administration immediately before the iridoplasty facilitates the procedure. Miotics should not be continued following the procedure. Apraclonidine or brimonidine is administered about 30 minutes prior to treatment.

Procedure

The argon laser is set to produce contraction burns (500 µm spot size, 0.5–0.7 second duration, and, initially, 240 mW power). Occasionally, in light blue or gray irides, a 200 µm spot size may be more effective to achieve stromal contraction.

With the contact lens in place, the beam is aimed at the most peripheral portion of the iris possible. One of the most common errors resulting in procedure failure is spot placement in the mid- rather than extreme periphery of the iris. The contraction effect is immediate. A lack of visible contraction and deepening of the peripheral anterior chamber at any site are suggestive of too low a power, too short a laser pulse, or PAS. The power should be increased initially to improve contraction, particularly if the patient does not feel the burn. If bubble formation occurs, or if pigment is released into the anterior chamber, the power should be reduced.

Treatment consists of placing approximately 20–24 spots over 360°, leaving approximately two spot-diameters between each spot and avoiding large visible radial vessels if possible. Although rare, iris necrosis may occur if too many spots are placed too closely together. The presence of an arcus senilis should be ignored. An extremely shallow anterior chamber and corneal edema, which are relative contraindications to LPI, do not preclude ALPI.

Postoperative care

Immediately after the procedure, the patient is given a drop of topical steroid and apraclonidine or brimonidine. Patients are treated with topical steroids four to six times daily for 3–5 days. IOP is monitored post-laser as after any other anterior segment laser procedure, and patients are treated as necessary if a post-laser IOP rise occurs.