SLT on Open-Angle Glaucoma Patients

Selective Laser Trabeculoplasty can be used several times for a modest IOP reduction.

Thomas E. Bournias, MD, Chicago
12/30/2005

Today surgeons can utilize selective laser trabeculoplasty as adjunctive therapy to help open-angle glaucoma patients continue to lower intraocular pressure. The procedure, which causes less inflammation and is gentler than argon laser trabeculoplasty, can be performed on patients previously treated with ALT and can be repeated with subsequent success over several years.

I have been performing SLT in my practice for many years and have performed many cases on a wide array of glaucoma patients. Laser trabeculoplasty is an excellent procedure that lowers IOP in many patients.

 

SLT, the Technique

The SLT technique, which uses the Lumenis laser, was developed by Mark Latina, MD,1 and differs from ALT, which uses a continuous wave laser. For SLT, the parameters of the procedure are modified, and utilize very short pulses (about 3 nanoseconds) with a large spot size (400 µm) to give minimal fluence to the targeted tissue. This allows for selective photothermolysis, whereby the heat generated by the short pulses is confined to the pigmented, melanin-containing cells. Therefore, there is a minimal thermal effect on the trabecular meshwork and fewer side effects.

One of the major benefits of the SLT procedure is this minimal destruction of the TM, which preserves the architecture of the meshwork and decreasing inflammation. Subsequently, this also increases the potential repeatability of the procedure.

 

Patient Selection

SLT can be used on most patients with glaucoma or ocular hypertension who need pressure reduction where there is access to the TM and no inflammation is present. I use SLT on all types of open-angle glaucoma, including pseudoexfoliation and pigmentary dispersion. I also utilize SLT on patients who have had sub-acute angle closure or in cases where peripheral anterior sy­ne­ch­­iae (PAS) are present. Surgeons can easily treat in between the PAS and mi­nimize further PAS formation as this modality causes minimal resultant PAS. Some patients are currently on glaucoma medication, while others are not (See Figures 1-3).

The procedure can also be performed on people who have had previous SLT, ALT, or previous diode laser trabeculoplasty. DLT, which had a very minimal success rate of 10 to 20 percent in both blacks and whites, is not a very common procedure today. However, we have performed SLT on patients with previous DLT—both successful and unsuccessful—and have had a good response.

 

IOP Reduction

Generally, I do not use SLT as a first- line therapy. For a surgeon like me, it is a technique that I employ when I need to get another 3 to 5 points of IOP re­duction on a fair number of patients.


In my practice, the 360-degree treatment with approximately 90 to 100 non-overlapping spots is preferred; 360-degree treatment appears to be more successful than 180 degree. Evidence presented at meetings such as ARVO and the American Academy of Oph­thal­mo­logy has demonstrated that 360-de­gree treatment works better than 180.

Although the manufacturer recommends starting at 0.6 mJ or 0.7 mJ, in general, I have found that it is more ef­fective to begin treatment at closer to about 0.8 mJ (if the TM has 1 to 2-plus pigment) and titrate by 0.1 mJ increments. The energy level is titrated to the targeted response looking for bubbles forming in the anterior chamber. Once bubbles are visualized, titration is not decreased. For more heavily pigmented TM, such as in pigment dispersion or pseudoexfoliation, I start off in the 0.4-0.6 mJ range to avoid an IOP spike.

Pressure reduction is usually seen within a day or two if SLT has been effective. However, I usually allow for a full six weeks or up to three months (unless it is very advanced glaucoma) to see if the pressure will drop before I declare the procedure a failure. Then, I would decide on repeating SLT or consider another modality or medication.

 

Repeatability

Currently, there are no formal studies in the literature with data that show SLT performed on a person who has had previous 360-degree SLT actually re­sults in a sustained pressure reduction. A colleague and I presented a poster at the ARVO 2005 meeting with data that illustrates that this can in fact be done. (J. Lai and T.E. Bournias. Repeatability of Selective Laser Trabeculoplasty (SLT). Invest. Ophthalmol. Vis. Sci. 2005 46: E-Abstract 119.)

We conducted a study to determine the repeatability of SLT in OAG pa­tients successfully treated previously with SLT who had subsequently lost efficacy after one year of initial treatment.

The study included 30 eyes of 30 patients who had been treated with the Lumenis Selecta 7000 frequency doubling Q-switched 532-nm neodymiun (Nd):YAG laser (from Lumenis Santa Clara, Calif.,) from November 2001 through April 2002.



The patients experienced a suc­cessful re­duction of IOP (≥ 3 mmHg), which was sustained for at least one year, but they had a resultant loss of efficacy, and therefore, were retreated. Re­treat­ment consisted of approximately 90 to 100 non-overlapping spots over 360 de­grees of the TM at energy levels ranging from 0.7 to 1.2 mJ per pulse.

After treatment, patients were maintained on the identical drug regimen to be­­fore treatment. IOP was recorded for at least one year post retreatment.

The average IOP of the 30 eyes pretreatment was 21.3 mmHg. The average IOP reduction at one year was 4.3 mmHg (p<0.03). All eyes had ≥ 3 mmHg IOP reduction. All of the eyes lost efficacy by 18 months post-treatment with the whole group averaging 20.8 mmHg. Retreatment resulted in 26 of 30 eyes attaining ≥ 3 mmHg IOP reduction with an average drop in IOP of 3.9 mmHg (p<0.05). None of five eyes that underwent a third SLT procedure attained a successful result (See Figure 4).

We concluded that SLT appears to be repeatable in eyes with OAG that have previously been successfully treated, with subsequent loss of efficacy. Long-term prospective studies need to be performed, however, to determine how many times SLT can be successfully performed in one eye.

 

Switching to SLT

Some surgeons may be hesitant to per­form SLT because they are underwhelmed with the amount of reported pressure reduction.

Traditionally, trabeculoplasty is successful in approximately two-thirds of patients. From my experience, I have found that there is a modest pressure re­duction more frequently than a huge drop (at least when the IOP averages in the low 20s and the patient is already on antiglaucoma medication, as is usually the case in most of my patients. SLT, however, appears not to last as long as ALT. But it is very well-tolerated in pa­tients, and it appears to be repeatable. In addition, the procedure works whether patients have had previous ALT or not.

Because we perform many cases in which we treat one eye and compare the difference between the two eyes, we actually see the real efficacy of trabeculoplasty. In general, these cases show that SLT gives a reduction, but it is typically not as dramatic as medications such as topical hypotensive lipids. In­flam­mation is definitely much less with SLT, and often no drops are needed after the procedure. In addition, pa­tients also seem to tolerate SLT better.

It is up to the surgeon to determine whether a patient should receive SLT or ALT first. Some physicians may feel that, because they do not have the state-of-the-art SLT technology, and ALT does coagulate the TM, they shouldn't be doing trabeculoplasty at all. But that should not necessarily be the case.

Because SLT sometimes actually works better on patients who have had previous ALT,3 I tell physicians if all you have is ALT, go ahead and use it when you feel it is indicated. Both modalities appear to activate the biological responses that increase outflow. In my practice, I have had patients in which ALT worked and SLT did not, and vice versa. There is something a little different about the two procedures and each pa­tient responds differently.

I have had patients who were retreated a third time with SLT, and failed, but responded to subsequent ALT. Un­fortunately there is little data on this in the literature.

 

Case Study

Normally, trabeculoplasty is not thought to work in steroid-responder glaucoma. However, I have had good re­sults with numerous patients. For example, a 16-year-old female patient presented to me with IOP in the 50s OU from chronic topical steroid use. Medication reduced her IOP to the 30s OU. With SLT, she had further reduction to a pressure of 12 mmHg in both eyes.

She sustained this low IOP for almost one year, then lost efficacy with her IOP returning to the upper 20s. After SLT retreatment, her IOP was again lowered to the 12 to 13 mmHg OU range. Al­most one year later, her IOP increased back to the mid-20 mmHg range. A third treatment was done, however it was not effective. This helped a young girl avoid a trebeculectomy with its associated complications for two years.

Baseline intraocular pressure in patients treated in this study was 21.3 mmHg. Post-SLT IOP was 17.0 mmHg, a 4.3-mmHg reduction (p<0.05). Baseline IOP for retreatment was 20.8 mmHg. Post-repeat SLT IOP was 16.9 mmHg, a 3.9-mmHg reduction (p<0.05).

This was not surprising, because in cases in which I have performed SLT three times, there has not been a large response. For many people, there ap­pears to be an endpoint with SLT, and a third time is usually it. SLT does still have a repeatability advantage over ALT, in which the 360-degree treatment can only be done once in general.

 

SLT Outlook

Although anecdotal data is available for SLT and other trabeculoplasty procedures such as ALT, long-term pro­spective studies are needed to determine the endpoint of repeatability for SLT in one eye. My colleagues and I continue to study laser trabeculoplasty and its success in patients for additional pressure reduction. 

 

Dr. Bournias is an assistant professor of clinical ophthalmology at North­western University Feinberg School of Medicine, in Chicago. He has no financial interest in any products mentioned in the article.

 

1. Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532nm Nd:YAG laser trabeculoplasty (Selective laser Trabeculoplasty). Ophthalmology 1998; 105: 2082-2090.

2. Damji KF, Shah KC, Rock WJ, et al. Selective laser trabeculoplasty vs argon laser trabeculoplasty: A prospective randomized clinical trial. Br J Ophthalmol 1999; 83:718-722.

Another View on Tips for Success with SLT
Robert J. Noecker, MD, MBA
Pittsburgh

Selective laser trabeculoplasty works like a good medication, and that's where it fits into my treatment algorithm. For some glaucoma patients, I will begin treatment with a prostaglandin analog, and if intraocular pressure is not lowered, I will quickly move to SLT. As with other therapies, SLT works best when used earlier in the treatment algorithm.

Higher IOP, Greater Effect

Patients can typically expect a 3- to 6-mmHg IOP drop. Approximately 80 percent of patients experience this type of IOP decrease after SLT. The higher the pa­tient's pressure, the better SLT works. (continued on page 118)

My expectations for success are very high when a patient comes in with a pressure of 30 mmHg and a normal angle, because SLT improves outflow. It does not work as well in normal-tension glaucoma patients, who tend to get a pressure decrease of only about 2 mmHg. If the pressure is 15 mmHg, it is not realistic to expect it to come down to 8 mmHg with anything short of surgery.

Some have questioned whether SLT works as well in patients who have been on drugs that target outflow, i.e., prostaglandins. In my opinion, prior pro­sta­glan­din use doesn't have any effect on SLT. The fact that patients on beta-blockers get a better response is due to the relative inefficacy of beta blockers. Those patients begin with higher IOP and, thus, get a bigger drop in pressure from SLT.

Patient Selection

For SLT to be successful, it is im­portant for patients to have an open angle, so that the trabecular meshwork can be visualized and treated. In patients with chronic angle closure, there is simply not enough access to the TM. SLT has worked successfully in patients who have pigmentary, pseudoexfoliation, juvenile and angle-recession glaucomas.

It also works well in patients who are not compliant with medical therapy. In my inner-city practice, I often use SLT as first-line therapy for patients I know will not be compliant with medical therapy. Patients who are intolerant of or unresponsive to medical therapy are good candidates for this procedure. Other good candidates are patients who have undergone argon laser trabeculoplasty with good results, but the effect has started to drift.

Initially, in patients who had previously undergone 180-degree ALT, we would attempt to treat the other 180 degrees with SLT. Today, I treat 360 degrees in all patients, absent a mitigating factor. The more aggressive approach of 360-degree treatment results in larger and longer-lasting pressure drops compared to 180-degree treatment.

Treatment Protocol

Pretreatment, I use one drop of Alphagan P as prophylaxis against IOP spikes, and one drop of proparacaine. I also use Refresh Celluvisc, a thick artificial tear, to keep patients comfortable and decrease the incidence of corneal abrasion.

Then, the lens is placed. I prefer a Goldmann 3-mirror lens, but there is a variety of acceptable lenses. It is important not to use a magnifying lens because changes in magnification will alter the laser's beam diameter and energy. I try to center the lens over the trabecular meshwork.

The duration of treatment is preset at 3 nanoseconds. The spot size is also preset at 400 µm, much smaller than the ALT burns some might be accustomed to. The clinician controls the energy per pulse. I typically start at 1 mJ per pulse, with the ex­pectation that I will adjust the energy level after a few spots. The highest energy I ever use—in a lightly pigmented angle, for example—is 1.4 or 1.5 mJ/pulse. The appearance of champagne-like bubbles slowly and consistently wafting into the anterior chamber indicates that you are operating at the desired threshold. Blanch­ing or large bubbles alert you to adjust the energy level up or down accordingly.

I usually plan to treat 360 degrees of the trabecular meshwork with 100 applications per eye or 25 per quadrant and to cover the angle without hitting the iris. Hitting the iris won't cause peripheral anterior synechiae, as it did with ALT, but it can be uncomfortable for the patient.

Treat patients with pigmentary glaucoma cautiously. Because there is so much pigment outside and in front of the trabecular meshwork, it is advisable to begin with half the usual energy to avoid a pressure spike. In such patients, I also often plan to only treat 180 degrees. If an IOP spike is going to happen, it typically occurs within an hour after treatment.

Post-treatment Protocol

Post-treatment, I instill a drop of Alphagan P and one drop of Acular LS. I check the pressure at one hour postop and then send the patient home, unless there is a pressure spike. I prescribe Acular LS q.i.d. for four days, and follow up in 10 to 14 days. Steroids should be avoided because they may impair the mac­rophage recruitment that is important for long-term success of SLT.

At the two-week visit, there may or may not be an IOP response. While some decrease in pressure early on is favorable, it's not conclusive. The more crucial visit is at six to eight weeks. If no effect is seen at that time, I deem the treatment a failure and the prognosis for retreatment poor. However, in patients who have a good initial response that fades with time, retreatments can be effective.

Dr. Noecker is vice chair and director of the Glaucoma Service for the University of Pittsburgh Medical Center Eye Center, and an associate professor of ophthalmology there. Contact him at (412) 647-2200 or noeckerrj@upmc.edu.