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.
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.
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.
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.
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.
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.
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