Ophthalmologists have used laser trabeculoplasty for several decades to enhance aqueous outflow and reduce IOP. Although the procedure can use a number of different visible or near-infrared lasers, it is most commonly performed as argon laser trabeculoplasty (ALT) or selective laser trabeculoplasty (SLT). The efficacy is similar among the different types of trabeculoplasty. This article will concentrate on SLT, due to the focus of the reader's question and relative newness of the technique, in an effort to highlight the similarities and differences between the procedures.
SLT is performed using a double-frequency, Q-switched Nd:YAG laser. SLT was developed as an alternative to laser trabeculoplasty techniques such as ALT.1 SLT's use of very low levels of energy over a large surface area (400 µm) results in low fluence (energy/area) to targeted tissue. By employing extremely short pulses (3 nanoseconds) that minimize the amount of heat generated, the laser selectively treats only melanin-containing cells with minimal, if any, effect on adjacent tissues.2
The theoretical advantages of using SLT versus ALT include (1) greater comfort for patients during laser treatment, (2) no coagulative damage to the trabecular meshwork, (3) potential repeatability, (4) easier performance, and (5) less dependence on the degree of trabecular pigmentation. To date, there are no data to show that SLT (with or without retreatment) results in greater clinical success compared with ALT, and more research is needed regarding SLT's long-term efficacy and repeatability.
WHOM DO WE TREAT WITH SLT?
Patient selection for SLT is similar to that for ALT, although the former modality's nature allows its earlier use in the treatment algorithm than ALT. Most glaucoma patients with open angles and a clearly visible trabecular meshwork are candidates for SLT. Patients with a previous or current history of anterior segment inflammation, those who have extensive anterior synechiae, and those who had a traumatic injury to the trabecular meshwork, however, may not benefit as much from this treatment modality.
SLT lowers the IOP to a similar degree as first-line medical therapies when used in that position in the treatment algorithm.3 We therefore might choose SLT as a primary therapy in patients who are unable to tolerate medical therapy (eg, due to allergies) or in those who are unlikely to adhere to prescribed therapeutic regimens (eg, individuals with physical or economic limitations). Alternatively, SLT can be used as adjunctive therapy when monotherapy with topical drops fails to achieve the targeted IOP. If at all possible, we try to hold patients to a single medication due to proven decreases in adherence when a second medication is added.4
Although ALT can be used as primary therapy, the procedure is more frequently considered after maximum medical therapy. In contrast, many surgeons perform or at least offer SLT early in the treatment algorithm. Typically, it is thought that the efficacy of SLT is equivalent to that of a first- or second-line glaucoma medication without the burden on patients of taking an additional drug. Likewise, surgeons sometimes perform SLT in order to decrease the number of required medications in patients whose IOPs are well controlled but for whom the drug regimen is a burden.
TECHNIQUE
We favor a 360º treatment of the trabecular meshwork with 100 spots that do not overlap, based on our own experience and published data illustrating the poor long-term efficacy of 180º treatments.5 We begin at 0.8 mJ per pulse, depending on the degree of the angle's pigmentation. Angles with pigment greater than +2 (as seen with pigmentary and pseudoexfoliative glaucoma) may benefit from lower initial applications of energy (0.4 mJ), which can be titrated to achieve the desired effect. The goal is the occasional, visible formation of champagne bubbles upon laser applications (Figure 1); they signify the proper absorption of energy by the melanin-rich cells of the trabecular meshwork.
Figure 1. Gonioscopy during SLT treatment reveals the formation of champagne bubbles (white arrow).
Our posttreatment regimen consists of a topical nonsteroidal anti-inflammatory drop q.i.d. for 4 days and a follow-up examination in 1 to 2 weeks to check the patient's IOP. There are no definitive data available to guide post-SLT therapy with topical drops or even to indicate if such therapy is needed. Theoretically, tempering the eye's inflammatory response with a topical steroid drop after SLT may decrease the laser therapy's efficacy due to an adverse effect on the migration of macrophages that occurs with the application of laser energy. More studies are needed to elucidate the mechanism of action for SLT and the appropriate posttreatment management to achieve desired results.
EFFICACY
Patients who undergo SLT can expect a drop in IOP of 3 to 6 mm Hg. Individuals with a high pretreatment IOP may experience a more dramatic decrease. Approximately 60% to 80% of individuals treated with a 360º application of laser energy will achieve a significant decrease in IOP (20% to 30%).3 Many patients on previous medical therapy will be able to stop using one or more medications. It is important to note that there is no proven advantage to using SLT versus ALT in terms of clinical efficacy. Again, additional prospective research is needed to determine SLT's efficacy in the long term and its repeatability.
Section editors Malik Y. Kahook, MD, and Robert J. Noecker, MD, MBA, are in academic glaucoma practice. Dr. Kahook is Assistant Professor of Ophthalmology and Director of Clinical Research in the Department of Ophthalmology at the University of Colorado at Denver & Health Sciences Center. Dr. Noecker is Director of the Glaucoma Service and Associate Professor/Vice Chair at the Department of Ophthalmology at the University of Pittsburgh. The authors acknowledged no financial interest in the technologies mentioned herein.
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. Kramer TR, Noecker RJ. Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes. Ophthalmology. 2001;108:773-779.
3. Nagar M, Ogunyomade A, O'Brart DP, et al. A randomised, 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;89:1413-1417.
4. Robin AL, Covert D. Does adjunctive glaucoma therapy affect adherence to the initial primary therapy? Ophthalmology. 2005;112:863-868.
5. Song J, Lee PP, Epstein DL, et al. High failure rate associated with 180 degrees selective laser trabeculoplasty. J Glaucoma. 2005;14:400-408.
SEND US YOUR QUESTIONS!
Fellows and residents are encouraged to submit their questions for consideration. Interested parties should send a question, their name, and their academic affiliation to Dr. Kahook at malik.kahook@uchsc.edu.
