Given the lower energy used in SLT as compared to ALT, the majority of anterior uveitis after SLT settles within 3 to 5 days (Lee et al. 2014a). Koucheki et al. reported an inflammatory rate of 42.6 % in OAG eyes (Koucheki and Hashemi 2012). Jinapriya et al. compared the use of artificial tears, prednisolone acetate 1 %, or ketorolac tromethamine 0.5 % eye drops four times per day for 5 days following SLT and found that the use of an anti-inflammatory medication for a short period of time after SLT did not affect the IOP-lowering efficacy of the laser (Jinapriya et al. 2014).
Similar to ALT, IOP spikes can occur within 1 to 2 hours of the procedure with spikes >5 mmHg in about 10 % of patients and spikes >10 mmHg in 3 % following SLT (Barkana and Belkin 2007). Similar to ALT, a topical alpha-adrenergic agent may be used as prophylaxis before or immediately after the procedure. However, it should be noted that increased trabecular meshwork pigment has been associated with significant IOP spikes necessitating urgent filtration surgery, thus, lower energies or perhaps less invasive laser trabeculoplasties like MicroPulse Laser Trabeculoplasty (MLT) may be considered in these cases (Koucheki and Hashemi 2012).
1.2.4.3 Late Postoperative Complications
Given the close proximity of the cornea to the trabecular meshwork, potential damage to the cornea following SLT needs to be considered. Moubayed et al. were the first to report a case of permanent corneal edema progressing into bullous keratopathy following SLT (Moubayed et al. 2009).
Knickelbein et al. reported four cases that developed corneal edema and subsequent corneal thinning and hyperopic shift, with two cases requiring contact lens wear. Although the cause of this rare complication remains unknown, it may be associated with myopia (Knickelbein et al. 2014).
Figure 1.2 from Ong and Ong illustrates a marked increase in dark spots/patches on specular microscopy following SLT reported in two patients with pre-SLT corneal pigment. Thus, the corneal endothelium should be examined for pigment deposition, corneal guttatae, or evidence of compromise prior to SLT (Ong and Ong 2013). Lee et al. (2014a) from Hong Kong investigated 111 eyes of 66 Chinese OAG subjects treated with SLT. They measured the endothelial cell count using a specular microscopy, central corneal thickness (CCT) videokeratography, and the spherical equivalent using a kerato-refractometer. Readings were taken before and at 1 month after SLT. The intraclass correlation coefficient (0.997) among these investigations was high, signifying excellent reproducibility of these measurements. The mean endothelial cell count was reduced by 4.5 % from baseline (2465.0 ± 334.0 cells/mm2) at 1 week (2355.0±387.0 cells/mm2) after SLT (p = 0.0004). At 1 month (2424.0 ± 379.4 cells/mm2, p = 0.3), the endothelial cell count returned to baseline levels. The authors attributed inflammatory cell attachment and microscopic endothelial cell edema as the causes of the apparent reduction in endothelial cell count as both of these conditions can affect the accuracy of cell counts with specular microscopy. On slit-lamp examination, none of the subjects had any clinically visible corneal edema. In a recent randomized controlled trial that compared SLT versus prostaglandin analogs in the treatment of primary angle closure glaucoma in subjects that had at least 180° of angle opening, the 6-month endothelial cell loss was 4.8 % from baseline (p = 0.001) (Narayanaswamy et al. 2014). This was in contrast to the 4.5 % transient reduction in the study by Lee et al. (2014a). The differences in angle opening among the two study populations could have accounted for the permanent damages documented by Narayanaswamy et al. (2014) since a narrower angle can predispose the corneal endothelium to absorb a greater amount of dissipated laser heat.
Fig. 1.2
The corneal endothelium of a patient before and after SLT showing a marked increase in dark spots/patches on specular microscopy (Taken from a case report by Ong and Ong (2013))
In Lee et al.’s study (Lee et al. 2014a), CCT decreased 1.1 % from 549.4 ± 37.6 μm at baseline to 543.9 ± 40.2 μm at 1 week (p = 0.02). By 1 month, CCT was back to baseline level (p = 0.2). Laser heat dissipation could have led to a thermal-induced corneal stromal contraction in the collagen fibers. When the keratocytes get replenished, the CCT returns to its original thickness. There was no evidence of clinically visible scarring on the cornea in the 111 OAG eyes that received SLT treatment. There were also no statistically significant changes in the spherical equivalent following SLT. Thus, in cases with angle closure elements, the potential risks of corneal damage should be discussed with patients prior to treatment.
The rate of peripheral anterior synechia formation following SLT is around 2.86 % or less which is significantly less than that reported after ALT (Wong et al. 2015). Damji et al. published the only randomized controlled trial comparing the safety of ALT versus SLT (Damji et al. 2006). A comparison in the side effects of these two lasers is summarized in Table 1.1. Table 1.2 summarizes complications of SLT reported in a recent meta-analysis (Wong et al. 2015).
Table 1.1
Comparison of complications between ALT and SLT from a randomized controlled by study by Damji et al. (2006)
Complications | ALT (n = 87) (%) | SLT (n = 89) (%) |
|---|---|---|
IOP spike > 6 mmHg | 3.4 | 4.5 |
PAS formation | 1.2 | 1.1 |
ALT retreatment within 1 year | 5.7 | 3.4 |
SLT retreatment within 1 year | 4.6 | 6.7 |
Trabeculectomy within 1 year | 8.0 | 9.0 |
Glaucoma drainage device within 1 year | 0.0 | 1.1 |
Cyclophotocoagulation within 1 year | 0.0 | 1.1 |
Table 1.2
Frequencies of SLT complications
Complications | Percentage or number of cases |
|---|---|
Side effects reported by case series: | |
Transient IOP rise | 0–62 % |
With prophylactic/empirical treatment | 0–28.8 % |
Anterior chamber inflammation | 0–89.3 % |
Eye pain/discomfort | 0–58 % (up to 65.7 % if redness included) |
Peripheral anterior synechiae | 0–2.86 % |
Headache | 4 % |
Photophobia | 3–96.7 % |
Hyphema | 0 % |
Pigment dispersion | 0 % |
Conjunctival hyperemia | 9–64 % |
Corneal haze | 0–0.2 % |
Corneal abrasion | 0.65 % |
Corneal endothelial dark/white spots | 50 % |
Cystoid macular edema | 0 % |
Side effects from case reports: | |
High IOP spikes (IOP 26–65 mmHg) | 4 cases |
Bilateral anterior uveitis following single eye SLT | 1 case |
Hyphema | 2 cases |
Corneal edema/haze/thinning | 4 cases |
Diffuse lamellar keratitis | 1 case |
Cystoid macular edema | 3 cases |
Severe iritis with choroidal effusion | 1 case |
Key Points
Intraocular pressure spikes can occur 1 to 2 hour after the procedure. Topical alpha-adrenergic agent may be used as prophylaxis before or after the procedure.
Increased trabecular meshwork pigment has been associated with extreme intraocular pressure spikes. Therefore, lower energy with close monitoring is recommended in these patients.
1.3 Lasers That Increase Aqueous Outflow: Micropulse Laser Trabeculoplasty and Titanium-Sapphire Laser Trabeculoplasty
1.3.1 Introduction
MicroPulse Laser Trabeculoplasty (MLT) can be delivered using a diode (810 nm) or a 532 nm/577 nm laser. The MLT technology makes use of a 15 % on and 85 % off duty cycle to minimize the thermal damage to the surrounding tissues. Although ALT causes damage and scarring to the trabecular meshwork and SLT destroys melanocytes through heat, MLT neither destroys nor scars the trabecular meshwork (Fudemberg et al. 2008).
Titanium-sapphire laser trabeculoplasty (TLT) is an emerging subtype of laser trabeculoplasty that uses a 790 nm laser (SOLX, Inc., Waltham, Massachusetts, USA) to emit near-infrared energy in pulses ranging from 5 to 10 ms.
1.3.2 Procedure
Similar to ALT and SLT, MLT is performed under topical anesthesia. However, the gonioscopic lens of MLT has a built-in, visible, inner reference guide that allows the surgeon to deliver exactly 10 confluent laser shots per clock hour for a total of 120 shots over 360°. The spot size is 300 μm, treatment duration 300 ms, and an initial power of 1000 mW. There are no visible endpoints in MLT, hence, the energy is only titrated down if the patient experiences pain during the procedure. No anti-inflammatory medications are required after MLT.
For TLT, the wavelength is 690 nm with energies of 30–80 mJ at pulse duration of 7 ms. The spot size is smaller than SLT or ALT at 200 μm. The laser is aimed at the pigmented trabecular meshwork and 50 nonoverlapping shots may be applied to 180° of the pigmented trabecular meshwork. The endpoint is the formation of bubbles or the visible bursting of pigments from the trabecular meshwork.
1.3.3 Efficacy and Outcomes
Gossage reported the 2-year data after treatment of 532 nm MLT in 18 POAG eyes. Three laser energies of 300 mW, 700 mW, and 1000 mW were used and at 4 months, those receiving 1000 mW had the greatest amount of IOP reduction of 30 %. At 24 months, the amount of IOP reduction in the group receiving 1000 mW treatment was 24 % (Gossage 2015).
There are very few studies reporting the efficacy of TLT. A 15-month pilot study with 37 subjects, reported that TLT-treated eyes had a mean IOP reduction of 32 % as compared to 25 % in the ALT group (Goldenfeld et al. 2009).
1.3.4 Complications
1.3.4.1 Intraoperative Complications
There are no reported intraoperative complications from MLT in the literature. In theory, the risk of intraoperative bleeding and pain should be less than in ALT and SLT due to the shorter duration of laser action from the duty cycle technology.
1.3.4.2 Early Postoperative Complications
Fea et al. (2008) reported on the safety of the 810 nm MLT in 32 eyes of 20 patients with OAG. The inferior 180° of the trabecular meshwork was treated and a Kowa FM 500 flare-meter was used to measure anterior chamber reaction at baseline and at 3 h, 1 day, 1 week, and 12 months after MLT. Only one patient (5 %) was found to have an increase in flare after MLT. The same patient, who had a history of pigmentary glaucoma, developed an IOP spike of 34 mmHg requiring oral acetazolamide treatment for 2 days. Otherwise, MLT was well tolerated apart from burning or heat sensation that was reported in four (20 %) of the patients.
In a prospective series in Hong Kong by Lee et al. using a 577 nm MLT in the treatment of OAG, only 7.5 % of treated OAG eyes had a mild and self-limiting anterior uveitis that resolved without medication. There was no corneal edema detected on slit-lamp examination and no recorded IOP spikes at day 1, 1 week, or 1 month after MLT (data pending publication). As MLT is still a relatively new technology; only gaining popularity in the early 2010s, larger-scale, randomized studies are warranted before its long-term safety in comparison with its predecessors can be determined.
For TLT, the IOP spike rate has been reported to be around 11 %.
1.3.4.3 Late Postoperative Complications
At present, the longest study involving the use of MLT in OAG is 2 years. There are no reported late postoperative complications in the literature (Fudemberg et al. 2008).
In a study of 18 patients with OAG treated with TLT, none of the patients developed PAS nor were there any reported long-term complications over a 2-year period.
1.4 Lasers That Increase Angle Width: Laser Peripheral Iridotomy
1.4.1 Introduction
Angle closure glaucoma is an optic neuropathy secondary to raised intraocular pressure (IOP) due to closure of the drainage angle. A number of different factors contribute to primary angle closure, including pupillary block, thickened iris root, cataract, and plateau iris configuration. Peripheral iridotomy removes the pupillary block mechanism by allowing aqueous to flow from the posterior chamber to the anterior chamber, by-passing the pupil. Laser peripheral iridotomy (LPI) has now essentially replaced the surgical iridectomy.
LPI is indicated for acute primary angle closure, the fellow eye in acute primary angle closure glaucoma if the angle is felt to be occludable, primary angle closure (angle closure with evidence of peripheral anterior synechia or raised IOP, but no glaucomatous optic neuropathy), primary angle closure glaucoma (primary angle closure with glaucomatous optic neuropathy) and primary angle closure suspects (angle closure in at least two quadrants of trabecular meshwork without any of the above findings). There is some evidence that LPI can be helpful in phacomorphic glaucoma and pigment dispersion syndrome.
1.4.2 Procedure
Table 1.3 summarizes the technique of LPI. The iridotomy needs to be of sufficient size to allow aqueous flow and pressure equalization between the anterior and posterior chambers. Mathematical modeling using Navier–Stokes equations suggests that a peripherial iridotomy length of 50 μm would reduce the pressure differential to under 1 mmHg (Silver and Quigley 2004). It has been proposed that a minimum diameter of at least 150 μm is necessary to add in a safety margin to account for posttreatment iris edema, fibrosis, pigment epithelial proliferation, or pupil dilatation (Fleck 1990).
Table 1.3
Recommendations on technique of performing laser peripheral iridotomy (LPI) at different stages
Stage of procedure | Recommendations on technique of performing LPI |
|---|---|
Pretreatment | Constrict pupil with 1–4 % pilocarpine 3 drops over 10–30 min Topical anesthesia such as tetracaine or alcaine |
Treatment | Use iridotomy contact lens such as Abraham (+66D button) or Wise (+103D button) Placement of iridotomy at either side of 12 o’Clock or just above or below 3 or 9 o’clock |
Optional pretreatment – argon laser for dark iris | Stage 1: spot size 50um, duration 0.1 s, power 100–200 mW around 15–25 shots Stage 2: spot size 50um, duration 0.1 s, power 500–700 mW around 15–25 shots |
Nd:YAG settings | Power: 1–5 mJ Spot size and duration is fixed |
Posttreatment | A single dose of topical Brimonidine 0.2 % and steroid may be administered to reduce postlaser pressure spike and inflammation Topical steroids can be prescribed 4 times a day for 1 week IOP should be checked 1 h after LPI Iridotomy should be checked for size and patency Gonioscopy should be repeated to document change in angle post iridotomy |
1.4.3 Complications
1.4.3.1 During Laser Iridotomy Procedure
Bubbles may form during the laser and may obstruct the visualization of the iridotomy site. The size and likelihood of bubbles is related to the argon laser power. Therefore, starting with a lower power, then increasing the power in stage 2 is recommended (see Table 1.3) (de Silva et al. 2007). The 12 o’clock position for LPI placement should be avoided as this is where bubbles congregate. If bubbles form they are absorbed rapidly and are of no consequence.
Argon laser corneal epithelium burns manifest as milky white spots, whereas corneal endothelial burns appear as opacities. Nd:YAG laser injury to the cornea appears as star-shaped bursts. These corneal injuries occur due to poor focusing. A mobile eye, shallow anterior chamber, or cloudy cornea can increase the risk of corneal injury. In the event of an injury, the procedure may need to be abandoned or a new LPI location chosen where the anterior chamber is deeper and there is less corneal clouding. Corneal epithelial burns recover after 1–2 days. Direct endothelial cell damage is not reversible but usually remains localized. Routine LPI for primary angle closure suspects does not appear to increase the risk of endothelial cell loss. A Singaporean study comparing the endothelial cell count after LPI to the fellow untreated eye found that both groups had a reduced endothelial cell count (3.6 % and 3.2 %, respectively) at 3 years, but the difference between both groups was not statistically significant (Kumar et al. 2013). There have been reports of focal and generalized corneal edema, Descemet’s membrane detachment, and even delayed corneal decompensation.
Anterior chamber bleeding is a common complication of LPI. Up to 36 % of patients develop this complication. Fortunately, it is often self-limiting and stops with gentle pressure on the eye applied with the contact lens (Jiang et al. 2012; Golan et al. 2013). If bleeding continues the iris vessel can be cauterized with the argon laser. The view may be compromised by the blood clot. The surgeon may wish to choose an alternative LPI site or wait for the blood to resolve, usually after 20–30 min. Anterior chamber bleeding can cause blurred vision for several days, elevation of IOP, and corneal endothelial blood staining. The risk of bleeding can be reduced by avoiding iris vessels and using pretreatment with argon laser (de Silva et al. 2012). Stopping antiplatelet therapy does not reduce the incidence of bleeding (Golan et al. 2013).
1.4.3.2 Postlaser Iridotomy Complications
The most common complication after LPI is postlaser IOP elevation, the incidence of which varies from 5.7 %–40 % depending on the definition of an IOP spike. A pressure spike usually occurs within the first 1 hour after LPI. The largest prospective study of primary angle closure suspects receiving LPI was from China. Of the 734 eyes, 9.8 % had an IOP spike of >8 mmHg, and only 0.54 % had an IOP >30 mmHg after 1 h. 0.82 % continued to have raised IOP at 2 weeks (Jiang et al. 2012). In another study that included both primary angle closure and angle closure suspects (therefore patients with angle pathology), the incidence of a postlaser IOP spike of more than 30 mmHg was higher at 7.2 % (Lee et al. 2014b). Some studies suggest that the energy used correlates to IOP spikes (Jiang et al. 2012), although other studies did not confirm this correlation (Lee et al. 2014b; Golan et al. 2013). A higher starting IOP is a risk factor for IOP spikes. Pre- and/or posttreatment with brimonidine 0.2 % or apraclonidine 0.5 % is helpful in preventing IOP spikes (Yuen et al. 2005). If the IOP is over 30 mmHg at 30–60 min after LPI medical management should be initiated. Topical beta blocker or oral acetazolamide can be considered. In rare cases, the IOP may not be controlled medically and filtration surgery may be required.
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