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Editors Selection IGR 13-4

Laser and surgical treatment: SLT 180°, 360° versus ALT

Comment by Brian Francis on:

20977 Evaluation of a modified protocol for selective laser trabeculoplasty, George MK; Emerson JW; Cheema SA et al., Journal of Glaucoma, 2008; 17: 197-202

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Selective laser trabeculoplasty (SLT) has gained increasing use for lowering of intraocular pressure (IOP) in glaucoma and high risk ocular hypertensives as both a primary, adjunctive and replacement therapy. Initially, the protocol consisted of 180 degrees of treatment with approximately 50 applications of adjacently placed 400 micron spots centered on the trabecular meshwork. More recently, 360 degrees of treatment with approximately 100 applications has been employed with a greater reduction in IOP and minimal increase in complication rates (specifically IOP spike). Thus, it appears that there is a dose response with the amount of trabecular meshwork treated. George et al investigate a new protocol for SLT consisting of 100 overlapping spots over 180 degrees of trabecular meshwork and compare it to standard SLT treatment (360 degrees, 100 spots) and standard argon laser trabeculoplasty (ALT: 180 degrees, 50 spots). George et al. (848), in this retrospective case series of open-angle glaucoma patients (primary, pigmentary and pseudoexfoliative) compared 102 receiving the modified protocol (SLT-180°-100), with 89 undergoing standard SLT (SLT-360°-100), and 127 with standard ALT (ALT-180°-50). The main outcome measure was reduction in IOP compared to baseline with measurements at one hour, six weeks, four months and 14 months. To control for differences in baseline IOP, regression models were used to predict the fall in IOP in the three groups. They examined the effects of baseline characteristics such as preoperative IOP, glaucoma medications, central corneal thickness, lens status and prior ALT in predicting response to cur-rent laser treatment. Using a definition of success of a decrease in IOP of 3 mmHg and 20% decrease from baseline, they found the highest responder rate in standard SLT-360°-100, second in standard ALT-180°-50, and lowest in modified SLT-180°-100. The successes in the first two groups were statistically similar and both significantly higher than the modified SLT protocol. Standard SLT showed a significantly greater lowering of glaucoma medications than the other groups. The only significant predictive factor was baseline IOP in the standard SLT and ALT groups.

This study supports the current efficacy of SLT-360°-100, and ALT-180°-50, and demonstrates the inferiority of SLT delivered in overlapping spots over 180° (SLT- 180°-100)

In conclusion, this study supports the current efficacy of SLT-360°-100, and ALT-180°-50, and demonstrates the inferiority of SLT delivered in overlapping spots over 180 degrees (SLT-180°-100). The authors are to be commended for testing a novel protocol for SLT and including comparison groups of standard SLT and ALT. While comparison groups are preferable to a non-comparative case series, there are several limitations as a result of the non-randomized, retrospective nature of the study. The comparison groups are comparable in most ways except for the baseline IOP being higher in the ALT group. The two different SLT protocols were performed by different surgeons, and the postoperative treatment regimens differed in that the standard non-overlapping SLT group received diclofenac and the overlapping SLT group received prednisolone acetate 1%. In addition, the ALT procedures were all performed at an earlier date than SLT, presu-mably due to availability of this laser. Also, because of the design of the study, we do not know what power it contains to detect a difference between the treatment modalities. Clearly non-overlapping SLT is inferior and this is statistically significant. However, there is a trend for a greater responder rate for SLT-360°-100 compared with ALT-180°-50 at all time points (approximately 50% for the former and 40% for the latter) and given a larger number may have been statistically significant. The study did note a greater decrease in glaucoma medications with standard SLT versus ALT, however.

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