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    Laser Trabeculoplasty: Questions in Clinical Practice

    Glaucoma

    Author: Brian A. Francis, MD, MS

    Should trabeculoplasty or medications be used as a first-line treatment? What about as adjunctive or replacement treatment?

    There are two main considerations for using laser trabeculoplasty (LTP) versus medications as a first line or replacement treatment. The first consideration is disease related and the second consideration is economic.

    • Disease-related issues are efficacy, compliance, diurnal intraocular pressure (IOP) control, and side effects or risks. 
    • Economic issues are financial impact for the patient and medical-care costs for society.

    Efficacy

    Laser trabeculoplasty has been employed as an initial, adjunct or replacement therapy to lower IOP in patients with open-angle glaucoma (OAG).

    • The original procedure was described using argon laser (major peaks at 488 nm and 514 nm).
    • Large prospective studies have shown argon laser trabeculoplasty (ALT) to be a relatively safe and effective procedure
    • The Glaucoma Laser Trial showed that in patients with newly diagnosed OAG, ALT was at least as effective as initial treatment with timolol maleate 0.5%, even after 7 years.1, 2
    •  ALT, however, produces significant tissue disruption and coagulation damage to the trabecular meshwork (TM), possibly contributing to the limited effectiveness of retreatment.3, 4
    • If the angle is repeatedly treated with argon laser it will eventually lead to synechial angle closure and a decrease in outflow facility.
      • This, coupled with most patients ultimately using medications, lead to the failure of acceptance of ALT as primary glaucoma therapy.
      • Most physicians in the United States maintain the algorithm of medication first, possible LTP, then filtration surgery. 

    The FDA’s 2002 approval of selective laser trabeculoplasty (SLT) to treat OAG may change this treatment algorithm.

    • Using the 532-nm, frequency-doubled, Q-switched Nd:YAG laser, SLT results in the selective absorption of energy  by pigmented cells and spares adjacent cells and tissues from thermal energy.5
    • Compared to ALT, each SLT pulse delivers less than 0.1% total energy and is 8 orders of magnitude shorter in duration.
    • This results in milder tissue response and the potential for repeatable treatment, which has been shown only in some meeting abstracts.6
    • SLT is easier to perform since the area of the laser spot is 64 times larger than that of ALT and is large enough to cover the entire width of the TM.

    SLT was initially studied as a secondary modality in cases of failure of medical therapy or ALT.7-10 Recently, SLT has been proven effective as primary treatment in OAG with minimal side effects or complications.11-13  

    • Noncomparative trials showed an IOP reduction from an untreated baseline of approximately 30%, sustained for 3 to 5 years. 
    • Two randomized trials were conducted of SLT versus medication as primary therapy.
    • One trial showed an IOP reduction after SLT of 31% from baseline, which was comparable to the 30.6% reduction seen with a prostaglandin analog.
    • The second trial (SLT/MED) showed a reduction from baseline of 6.7 mm Hg with SLT and 7.6 mmHg with medical therapy.14

     When studied as adjunctive, or additive to medical therapy, the following was noted: 

    • Latina et al treated patients with IOP uncontrolled on maximal medical therapy or with prior failed ALT, and found 70% responding with a 3 mm Hg or more reduction in IOP at 6 months.9 
    • Replacement studies have focused on the ability to reduce glaucoma medications in patients with medically controlled OAG treated with SLT.
    • Francis et al found that glaucoma medications could be reduced by a mean of 2.1 at 6 months and 1.3 at 12 months when patients with medically controlled glaucoma were treated with SLT.15

    Compliance

    Compliance with medical treatment is a major problem, and glaucoma is no exception. 

    • A study by Nordstrom et al showed that most glaucoma patients have trouble complying with their glaucoma prescription regimens.16 
      • Over 90% were nonadherent, or failws to use medication at various time points. 
      • Nearly 50% were not persistent, defined as failure to maintain continuous treatment with prescribed medications.
    • Kass et al demonstrated the difficulties of compliance in a glaucoma population.17
      • The patients were using pilocarpine four times daily, and unknowingly, each received a bottle with an attached microchip sensor to monitor dosing.
      • Investigators found that 28% to 59% of patients were noncompliant, yet the patients’ perception was that they were compliant with 97% of their doses.
      • The treating physicians were not able to predict which patients had poor versus good compliance.

     LTP addresses the problem of compliance. 

    • While LTP may not be 100% effective, it has 100% compliance. 
    • The treating physician performs the procedure, and it either works or it does not work. 
    • The procedure has a role in poorly compliant patients, no matter the cause of noncompliance.
    • LTP alone will not completely control some patients, and these patients will still require medical therapy and hence continue to be at risk for noncompliance.
    • Simplifying a patient’s regimen and reducing the number of medications needed, may help with compliance.

    Diurnal IOP Control

    ALT’s effect on diurnal IOP was investigated by Greenidge et al, who measured patient IOP over a 24-hour-period every 2 to 4 hours, while the patient was in the sitting position.18  

    • This patient cohort was using maximal medical therapy, including combinations of pilocarpine, timolol, epinephrine and oral carbonic anhydrase inhibitors. 
    • Investigators found a significant reduction in the mean IOP, peak IOP, and range of IOP after laser.

     A similar, more recent study investigated diurnal IOP measurements in medically uncontrolled glaucoma patients before and after diode-pumped frequency doubled Nd:YAG laser trabeculoplasty.19

    • IOP measurements were taken sitting and supine during the day and supine at night. 
    • A significant reduction in nocturnal mean, peak, and range of IOP was found, but not in daytime IOP. 
    • They determined that LTP decreased the nocturnal IOP spike and therefore the mean 24-hour IOP in OAG patients on maximal medical therapy.

    It can be concluded that LTP can exert an effect on diurnal IOP, with a reduction in 24- hour IOP and nocturnal IOP spikes, even if it does not appear to change the daytime measured IOP. 

    • This has implications for normal tension glaucoma patients, or for those patients with IOP that seems to be controlled, but with signs of clinical progression.

    Side Effects/Risks

    The risks of LTP are minimal and primarily in the short-term postoperative period. 

    • A transient elevation of IOP (IOP spike) occurs in about 5% of patients and is successfully treated with medications, with reduction to near baseline by the first postoperative day.
    • Postoperative inflammation and discomfort can occur and last a few days.
    • This is treated with topical NSAIDs or steroids, or simply observation with or without an oral NSAID or analgesic. 

    The side effects of glaucoma medications are well-known and range from localized ocular and periocular effects to systemic effects, and in severity from mildly irritating to life-threatening. 

    • Medication risks last as long as the medications are used, but the risks are generally small, and therefore similar overall to LTP.

    Economic Issues

    Laser trabeculoplasty is usually covered by medical insurance, and is helpful for the personal finances for the patient. 

    • LTP as an initial, replacement, or adjunctive therapy, can save the patient some costs of chronic glaucoma medication use. 
    • The Canadian health care system studied the societal cost of treating glaucoma with medications versus LTP, and LTP had a favorable impact on cost.20,21

    Summary for the Clinician

    • LTP is effective for initial, replacement, and adjunctive therapy for OAG.
    • LTP is useful in addressing compliance problems with use of chronic glaucoma medications.
    • LTP is effective in flattening the diurnal IOP curve and decreasing nocturnal IOP spikes.
    • LTP may reduce patient medication costs.
    • LTP may reduce societal costs of treating glaucoma.


    Does ALT have a place given the availability of SLT? Should a practitioner invest in buying an SLT laser?

    There are several outcome measures that should be compared between ALT and SLT. 

    • Foremost is efficacy, reflected in IOP reduction and length of effect. 
    • Secondary is complications, which include IOP spike, scarring of the angle, inflammation, and patient discomfort. 
    • The two lasers can also be compared in terms of ability to re-treat and versatility of the laser platform.

    Efficacy

    Damji et al conducted a randomized trial comparing ALT with SLT.7, 8

    •  ALT was performed in 87 eyes and SLT was performed in 89 eyes with treatment to 180 degrees of the TM, and follow-up reported for 12 months. 
    • The baseline IOP was 23.48 mmHg in the ALT group and 23.84 in the SLT group. 
    • Both groups had a significant reduction in IOP at 12 months, with -6.04 in the ALT group and -5.86 in the SLT group.
    • There was no significant difference in IOP reduction at any time point between the 2 groups.
    • There were no differences in complications, although the SLT group noted a higher incidence of “cellular” reaction 1 hour after treatment.
    • “Cellular” reaction did not translate into a difference in complications, and the reaction was not present at 1 week after treatment.
    Juzych et al conducted a longer follow-up comparison.9
    •  They studied 154 eyes after ALT and 41 after SLT for up to 5 years with a mean follow-up of 37.4 months for the SLT group and 33.6 months for the SLT group. 
    • Both lasers were applied over 180 degrees of TM. 
    • Success was defined by two criteria: Criterion 1 was a decrease in IOP of 3 or more mmHg with no additional medications; and criterion 2 was a required reduction of 20% or more.
      • For criterion 1, success rates were similar between the 2 groups with 1-, 3-, and 5-year success of 68%, 46%, and 32% for SLT; and 54%, 30%, and 31% for ALT.
      • For criterion 2, success rates were 58%, 38%, and 31% for SLT; and 46%, 23%, and 13% for ALT. 
    • There was no significant difference in IOP reduction from baseline or glaucoma medications between groups.

    Complications

    Both ALT and SLT have a similar incidence of postoperative IOP spike, in the 3-5% range. 

    •  No randomized trials have found any difference in this occurrence. 
    • Most clinicians performing ALT, however, limit treatment to 180 degrees to avoid higher incidence of IOP spike.
    • Due to evidence that the incidence of IOP spike is similar between 180 and 360 degrees, most users perform initial SLT with 360-degree treatment.11

    Some in vitro studies have shown a difference in the amount of scar tissue and coagulative necrosis as a result of argon versus frequency doubled Nd:YAG laser applied to human trabecular tissue.  

    • This has been shown in eye bank eyes22 and in cultured human TM tissue.23 
    • This difference has to do with the selective nature of SLT, where only pigment containing cells within the TM take up the laser energy.
    • Because of the very short pulse duration (compared to thermal relaxation time of the tissue), the adjacent tissues do not take up the laser energy, and spread of heat damage is minimized.
    • Thus, SLT may cause less tissue damage and fewer anterior synechiae, which has implications for retreament.  

    Retreatment

    The accepted definition of retreatment with laser trabeculoplasty is applying laser to the same area that has been treated previously.  

    • This will usually be a 360-degree treatment followed by the same. 
    • Retreatment is usually applied when an initial treatment has been successful, but with the effect diminishing over time.
    • Retreatment, however, may be applied when the initial response is not enough to reach target IOP levels.
    • Treating 180 degrees followed by laser to the remaining 180 degrees should be termed augmentation of treatment.
    • SLT performed after ALT (or any LTP followed by treatment with a different laser) should be differentiated as sequential treatment with the two laser modalities identified. 

    Studies have demonstrated diminishing efficacy of retreatment with ALT.24-26   

    • The theory is that with repeat treatment greater coagulative necrosis of the TM occurs, thus decreasing the amount of surface area available for outflow. 
    • Because SLT has minimal tissue damage, it can theoretically be repeated without an appreciable decrease in efficacy. This has yet to be proven in published studies, however.

    Sequential treatment with SLT after ALT has documented success in several clinical studies. 

    • The initial clinical study by Latina et al10 included two SLT treatment arms: one group had uncontrolled IOP on maximal medical therapy, and the second had uncontrolled IOP with prior failed ALT.
    • A total of 101 patients completed the study, with 56 of those in the prior ALT group.
    • This group had a mean IOP reduction of 3.8 mmHg from a baseline of 25.3 mm Hg, which was comparable to the treatment naïve group.

    Versatility

    The final comparison between the 2 lasers is their versatility. 

    • Argon laser has many applications as a thermal laser, including LTP, iridoplasty or gonioplasty, pretreatment for iridotomy, pupilloplasty, and retinal laser. 
    • SLT is limited to laser trabeculoplasty, although one version of the instrument incorporates a 1064-nm wavelength Nd:YAG for use in procedures such as capsulotomy, membranotomy, lysis of vitreous strands, and anterior vitreolysis (of anterior hyaloid face). 

    Summary for the Clinician

    • Efficacy of ALT and SLT is equivalent.
    • Complications of ALT and SLT are equivalent.
    • SLT results in less scarring of the TM, and may have greater efficacy in retreatment (although this is not proven).
    • Argon laser platform is more versatile.
    • SLT can be performed after ALT failure, or loss of effect over time.


    When should SLT or ALT not be performed?

    Types of Glaucoma

    Laser trabeculoplasty enhances outflow facility through an intact trabecular outflow pathway.  Any form of glaucoma that has an intact TM and Schlemm’s canal, even though outflow facility may be reduced, is a candidate for ALT or SLT. 

    • Primary OAG and secondary OAG (exfoliation glaucoma, pigmentary glaucoma) are excellent candidates. 
    • Uveitic glaucoma and steroid-induced glaucoma are possible candidates, but the indication is not as strong. 
    • Any angle closure glaucoma, primary or secondary, is not a good candidate for LTP.
    • Neovascular glaucoma can actually be worsened with LTP and act as a stimulus for further neovascularization.

    IOP Reduction

    Laser trabeculoplasty is indicated as a primary or adjunctive glaucoma treatment, with the expectation of a 20% to 30% decrease in IOP. 

    • In cases of severe glaucoma damage or low-tension glaucoma where the target IOP is very low or the desired IOP reduction is very large, laser trabeculoplasty may not be indicated. 
    • If a large IOP reduction is desirable immediately, LTP is limited because of the delay of its effect.
    • In these cases, glaucoma filtration surgery may be a more appropriate choice.

    Maximal Medical Therapy

    Although ALT or SLT can be effective in addition to medications, the lowest success rate is seen when on maximum medical therapy. 

    • LTP can be considered in the same light as adding a medication. 
    • The more medications that are currently being used, the lower the efficacy of additional treatment.
    • Since LTP works by increasing trabecular aqueous outflow facility, its method of action is not redundant with any of the widely used glaucoma medications, and therefore is theoretically an additive to drugs acting on aqueous production or uveoscleral outflow.
    • The only drugs that act in a similar fashion to LTP are the miotic agents such as pilocarpine.

    Summary for the Clinician

    • LTP is most effective in open angle glaucomas.
    • IOP reduction is diminished with greater number of adjunctive medications.


    What are the laser settings and techniques for ALT and SLT?

    Argon Laser Trabeculoplasty

    The settings for ALT are 50-micron spot size, 0.1-second pulse duration, and power starting at 600 mW.  

    • The aiming beam is centered at the junction between the pigmented and nonpigmented TM (at the anterior edge of the pigmented TM), and spaced approximately 3 to 4 spot sizes apart so that 50 spots are used to cover 180 degrees of the angle. 
    • The power is titrated so that small bubble formation or slight blanching of the pigmented TM occurs.
    • If large bubble formation or charring of the TM occurs, the power is too high.
    • Most clinicians favor treating the inferior angle first, because of the greater pigmentation and to reduce any effect on possible future superior trabeculectomy.  

    Selective Laser Trabeculoplasty

    The settings for SLT are fixed except for power. The spot size is 400 microns, and the pulse duration is 3 nanoseconds. 

    • The starting power varies depending on the pigment in the angle. Power is started at 0.8 mJ in a normally pigmented eye; 0.6 mJ for a highly pigmented angle; and 1.0 mJ for a relatively nonpigmented angle. 
    • The aiming beam is centered on the TM, and effectively covers the entire TM with some overlap onto scleral spur and Schwalbe’s line. 
    • Because of the larger size, the margins of the aiming beam are not in sharp focus. 
    • The laser should be calibrated prior to use so that the aiming beam, slit lamp focus, and treating laser are confocal. This can be tested using any pigmented target, such as a piece of paper with dark ink on it. 
    • The power is titrated up or down until the treatment end point is reached. 
    • This consists of small cavitation energy bubbles seen in the aqueous proximal to the TM (not within the tissue such as in ALT). The power may need to be changed during the procedure if there is significant variation in trabecular pigment. 
      • Cavitation bubbles are commonly referred to as “champagne bubbles,” due to the resemblance and how they float superiorly after forming. 
      • The least amount of energy needed to see these bubbles for a majority of shots is recommended. 
    • In highly pigmented angles, such as pigmentary glaucoma or exfoliation glaucoma, care must be taken not to overtreat, with powers as low as 0.3 to 0.4 mJ are often adequate. In these cases, initially treating 180 degrees to prevent IOP spike can be considered.

     Summary for the Clinician

    • ALT settings are 50-micron spot size, 0.1-second duration, and power titrated to tissue effect (blanching of TM).
    • SLT settings are 400-micron spot size, 3-nanosecond duration, and power titrated to cavitation bubbles (champagne bubbles).


    What are the best approaches for each type of laser? 

    A mirrored goniolens without magnification is recommended for laser trabeculoplasty, because this ensures that the spot size and power delivered to the angle are not changed by the optics of the lens. 

    • Examples are the Goldmann 3 mirror lens (using the rounded angle mirror), or the Latina lens, or any mirrored goniolens applied with a coupling solution. 
    • The Ritch laser trabeculoplasty lens has four mirrors, two of which are magnified and two of which are nonmagnified. 
    • Methylcellulose (ie, Goniosol) is the most commonly used coupling agent, but it is sticky in some patients, and rarely it may result in a corneal abrasion as the lens is rotated.
    • An alternative is artificial tear gel (not ointment), which seems to be gentler on the corneal epithelium. 

     In cases of a narrow angle and poor visibility of the TM, there are several helpful measures. 

    • First is instillation of low dose pilocarpine (0.5% to 2%) 10 minutes prior to the procedure for pupillary miosis. 
    • This pulls the peripheral iris away from the angle and results in a better view. 
    • An easier alternative is to have an assistant shine a light into the contralateral eye, which will result in pupillary miosis via the consensual response and an improved view of the angle. 
    • Also helpful is to have the patient move their gaze towards the mirror being used for treatment. 
    • If the inferior angle is being treated, and the mirror of the goniolens is superior, instruct the patient to look up. This will rotate the eye such that more of the angle is visible in the goniolens. 
    • If the angle is so narrow that none of these procedures helps, then the patient probably requires a laser peripheral iridotomy for narrow angle. 
    • If the angle remains narrow after iridotomy, then an argon laser iridoplasty can be considered. 

     The highly anxious patient can cause problems with any laser procedure. 

    • These individuals can usually be identified during the initial exam and may have problems with tonometry and gonioscopy. 
    • Pretreatment with an oral sedative agent prior to attempting laser may be helpful.
    • Unless there are contraindications (eg, pregnancy, hypersensitivity, obstructive lung disease, depression, drug and alcohol addiction), alprazolam (Xanax) can be helpful.
      • A prescription for 0.5 mg tablets is written prior to the appointment, and the patient is instructed to take 1 tablet at the time of check-in, and may use an additional dose if anxiety is still present at the time of laser.
      • Precautions must be taken with the use of a psychoactive drug, and the responsibility for judgment rests with the treating physician.

     Summary for the Clinician

    • Mirrored goniolens without magnification
    • Pilocarpine or light in fellow eye can constrict pupil and open angle
    • Direct patient gaze towards treating mirror to get a better view of narrow angle
    • Topical anesthesia with rare oral sedation


    What are the expected complications and what should be done? How often is the patient checked postoperatively?

    Risks of LTP are minimal, and mostly centered around IOP spike.  

    • This can occur in up to 5% of individuals, and seems to be related to the type of laser used and the amount of energy delivered. 
    • IOP spikes are almost always transient, most occur within the first hour after laser, and the great majority resolved with treatment by the next day. 
    • Topical treatment with apraclonidine or brimonidine perioperatively effectively reduces the incidence of this complication. 
    • ALT is usually applied as a 180-degrees treatment to reduce the incidence of IOP spike, whereas SLT is increasingly being applied as a 360-degrees treatment initially to maximize the IOP reduction.
      • Nagar et aldid not show a significant increase in the incidence of IOP spike after SLT with this full treatment, but did show a dose response in IOP reduction related to the amount of angle treated.11 
      • The overall incidence of IOP spike may be lower with SLT than ALT, but both are generally in the 3% to 5% range.
      • Anecdotally, the amount of power used seems to be proportional to the frequency of IOP elevation. Thus, the minimum of power necessary to achieve the desired effect is recommended. 

    The recommended protocol is to check for IOP spike 1 hour after laser. An elevation of 8 mm Hg or more above baseline is considered significant, but the severity of disease must be taken into consideration.  

    • Treatment may include additional topical or oral glaucoma medications, depending on the amount of optic nerve damage and visual field loss. 
    • Sustained elevation of IOP after LTP is quite rare but has been seen.
      • If this occurs, filtration surgery is sometimes necessary.
      • If an IOP spike is seen, next-day follow up is recommended, otherwise, follow-up can be from 1 week to 1 month.
    • It is important to wait up to 3 months after therapy for lowering of IOP, as the biological response can take time to develop and exert its effect on outflow. 

    Pain and inflammation are possible and may be treated with observation, oral or topical NSAIDs, or topical steroids. 

    • Since the cascade to initiate the effect of IOP lowering is linked to initial tissue inflammation, many physicians avoid topical steroids so as to not blunt this response. 

    ALT can cause peripheral anterior synechiae (or goniosynechiae) and eventually lead to chronic angle closure. 

    • Because of the reduced amount of heat energy absorption, this is significantly less with SLT, but goniosynechiae can still be seen postoperatively. 

    Summary for the Clinician

    • Treat prophylactically for IOP spike
    • Check IOP at one hour
    • Pain and inflammation treated with topical or oral NSAID if needed


    What is the mechanism of action of ALT and SLT?

    The accepted method of IOP lowering with LTP is the increase in aqueous outflow facility through the TM outflow pathway, but there is some debate regarding how this occurs.

    Mechanical Theory

    This theory applies mainly to the argon laser as a result of its thermal effects on treated tissues. 

    • The electromagnetic energy of the laser is absorbed as heat energy when it contacts the TM, causing a contraction of tissue and shrinkage of collagen fibers. 
    • This results in a stretching of adjacent TM and widening of the spaces between trabecular beams and possible widening of Schlemm’s canal.
    • This can lead to an increase in aqueous outflow.

    Biologic Theory

    This theory can apply to all forms of lasers used for LTP, and suggests that the laser exerts its effects by the induction of a biological cascade of events as a response to tissue injury.  

    • ALT causes an increase in the macrophage recruitment to the treated site, which results in remodeling of the extracellular matrix and an increase in outflow.
    • ALT was shown to upregulate interleukin 1 (IL-1) and tumor necrosis factor (TNF) gene expression, which in turn upregulates matrix metalloproteinase (MMP) expression and remodeling of the extracellular matrix.27,28 
    • This remodeling results in lowering of aqueous outflow resistance.  

    Further support for the biologic theory comes from Alvarado et al, who irradiated cultured human trabecular meshwork endothelial (TME) cells with the SLT laser.29 

    • The TME cells were allowed to condition the culture medium, which was then added to Schlemm’s canal endothelial (SCE) cells. 
    • The response was observed both by measuring SCE permeability and gene expression.
      • The SCE cells exposed to TME cell-treated medium underwent a four-fold increase in fluid permeability and an increase in differential gene expression.
      • Among the upregulated genes are those for cytokines IL-8, IL-1α, IL-1β, and tumor necrosis factor (TNF-α).
      • Adding these cytokines to SCE cells significantly increased permeability.
    • This evidence shows that TME cells regulate SCE cell permeability and have a significant role of aqueous outflow regulation.
    • This regulatory capacity is stimulated by the application of laser energy and cytokine release. 

    Repopulation Theory

    Another proposed mechanism of action for ALT is that the laser energy stimulates increased cell division and repopulation of the TM. 

    • Studies have shown an increase in DNA replication and cell division after argon laser treatment.30-33 
    • This begins in the anterior nonfiltering tissue of the TM and eventually leads to repopulation of the burn sites.
    • This population of cells may serve as a source of pleuripotent stem cells that can repopulate the TM.

     Summary for the Clinician

    • Mechanical theory of ALT
    • Biologic theory of LTP (ALT and SLT)
    • Repopulation theory of ALT (may also apply to SLT)


    What are the newest laser trabeculoplasty modalities?

    Micropulse Laser Trabeculoplasty (MLT)

    Micropulse laser trabeculoplasty (MLT) is a newer technique using the 810-nm diode laser Iridex IQ810 (Iridex Corporation, Mountain View, CA). 

    • The goal is to use micropulsed emission mode with a short “on” time followed by a long “off” time to create a sublethal thermal insult to viable cells in the TM. 
    • This is thought to minimize heat absorption in the target tissue and reduce collateral thermal damage like that seen in ALT.
    • Micropulse settings are approximately 0.3 milliseconds on and 1.7 milliseconds off. The spot size is 300 microns, and 50 to 60 spots are delivered to cover 180 degrees of the angle. 
    • One advantage of the laser is that it has other applications, such as transscleral cyclophotocoagulation, retinal photocoagulation, iridotomy, and perhaps laser suture lysis.
    • The 1-year results of an Italian pilot study presented at the 2007 International Glaucoma Symposium and 2007 World Glaucoma Congress showed a mean IOP reduction of 22% in 24 out of 32 eyes with OAG.34

    Titanium Sapphire Laser Trabeculoplasty

    Another new modality in LTP is Titanium Sapphire laser using the SOLX 790 laser (Occulogix, Ontario, Canada).

    • Currently in phase III clinical trials, the efficacy of Titanium Sapphire laser trabeculoplasty (TLT) is being compared to ALT in patients having primary OAG with poorly controlled IOP on maximum-tolerated medical therapy and/or prior failed glaucoma surgery.
    • TLT emits flashlamp-pumped, near-infrared energy (790 nm) in pulses lasting 5 to 10 microseconds (duration between ALT and SLT).
    • TLT has been shown to provide deeper tissue penetration than the other lasers currently in use for LTP without causing damage to the TM, and may therefore be repeatable.
    • TLT results in a significant “opening” of the TM with statistically significant decrease in IOP (20 to 30%) and minimal complications.35 

    The 790-nm laser can ablate gold, and is being researched as a way to adjust the IOP lowering of the SOLX Gold Shunt in vivo, after implantation. 

    • This shunt is implanted with the anterior end in the anterior chamber, and the posterior plate in the suprachoroidal space, theoretically shunting fluid from the anterior chamber into this potential outflow pathway. 
    • The idea is to laser drainage channels in the shunt that are then capped with a thin layer of gold metal in order to open them and increase drainage through the shunt.

    Summary for the Clinician

    • Newer laser platforms are being studied for LTP, and include Micropulse Laser Trabeculoplasty and Titanium Sapphire Laser Trabeculoplasty.
    • There are no published data on trials with these newer lasers.

    Suggested Reading

    1. The Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial (GLT) and glaucoma laser trial follow-up study: 7. Results. Am J Ophthalmol. 1995;120(6):718-731.
    2. The Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial (GLT). 2. Results of argon laser trabeculoplasty versus topical medicines. Ophthalmology. 1990;97(11):1403-1413.
    3. Kramer TR, Noecker RJ. Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes. Ophthalmology. 2001;108(4):773-779.
    4. Rodrigues MM, Spaeth GL, Donohoo P. Electron microscopy of argon laser therapy in phakic open-angle glaucoma. Ophthalmology. 1982;89(3):198-210.
    5. Latina MA, Park C. Selective targeting of trabecular meshwork cells: in vitro studies of pulsed and CW laser interactions. Exp Eye Res. 1995;60(4):359-371.
    6. Barkana Y, Belkin M. Selective Laser Trabeculoplasty. Surv Ophthalmol. 2007;52(6):634-654.
    7. Damji KF, Shah KC, Rock WJ, Bains HS, Hodge WG. Selective laser trabeculoplasty v argon laser trabeculoplasty: a prospective randomised clinical trial. Br J Ophthalmol. 1999;83(6):718-722.
    8. Damji KF, Bovell AM, Hodge WG, et al. Selective laser trabeculoplasty versus argon laser trabeculoplasty: results from a 1-year randomized clinical trial. Br J Ophthalmol. 2006;90(12):1490-1494.
    9. Juzych MS, Chopra V, Banitt MR et al. Comparison of long-term outcomes of selective laser trabeculoplasty versus argon laser trabeculoplasty in open angle glaucoma. Ophthalmology. 2004;111(10):1853-1859.
    10. Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): A multi-center, pilot, clinical study. Ophthalmology. 1998;105:2082-2090.
    11. Nagar M, Ogunyomade A, O’Brart DP, et al. A randomized, prospective study comparing selective laser trabeculoplasty with latanoprost for the control of intraocular pressure in ocular hypertension and open angle glaucoma. Br J Ophthalmol. 2005;89(11):1413-1417.
    12. Melamed S, Simon B, Levkovitz-Verbin H. Selective laser trabeculoplasty as primary treatment for open-angle glaucoma: a prospective, non-randomized pilot study. Arch Ophthalmol. 2003;121(7):957-960.
    13. McIlraith I, Strasfeld M, Colev G, et al. Selective laser trabeculoplasty as initial and adjunctive treatment for open angle glaucoma. J Glaucoma. 2006;15(2):124-130.
    14. Katz LJ, Steinmann WC, Marcellino G, SLT/MED Study Group. Presented at the American Academy of Ophthalmology annual meeting. November 2006.
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