Long-term SLT results promise ‘valuable’ primary treatment

By Cheryl Guttman

ORLANDO, FL — Selective laser trabeculoplasty (SLT) provides effective and sustained intraocular pressure (IOP)-lowering in eyes with primary open-angle glaucoma (POAG) or ocular hypertension (OHT), both as first-line intervention or as a treatment in medication-refractory eyes.

Madhu Nagar MBBS, MS Ophth, FRCS Ophth presented results from a prospective series of 398 eyes treated with SLT at Clayton Eye Centre, Wakefield, UK.
The initial protocol was designed to evaluate the safety and efficacy of SLT among POAG and OHT eyes with medically uncontrolled IOP.
That study was later expanded to enroll treatment-naïve patients and includes 102 eyes with a minimum of two years of follow-up, Dr Nagar told the annual meeting of the American Academy of Ophthalmology.

Overall, clinically significant reductions in IOP were obtained in all patient subgroups without clinically significant side effects.
However, various pair-wise comparisons showed the IOP-lowering effect of SLT was greater in eyes with OHT when the laser treatment was applied as first-line therapy.

“In view of the excellent results and lack of long-term side effects observed in this study, we believe SLT will become more valuable and acceptable as primary treatment, particularly in younger patients with ocular hypertension or glaucoma where compliance and quality of life are major issues,” Dr Nagar said. She added that SLT will also prove a valuable treatment in older individuals where medication compliance may be complicated by physical and mental disability.

The data also suggests the need for larger and more long-term studies to define the critical area which needs to be treated when performing SLT, she said. SLT was performed with a Q-switched, frequency-doubled, Nd:YAG laser (Selecta 7000TM, Lumenis) with a 400-micron spot size and three-nanosecond pulse duration. Energy levels titrated between 0.6 mJ and 1.2 mJ, depending on the degree of pigmentation.

In the initial study, all patients received 180o treatment with SLT. That protocol enrolled 186 eyes with IOP control refractory to medication, including 149 eyes with POAG and 37 eyes with OHT. In addition, 120 eyes were enrolled to receive SLT as first-line treatment.

Of those, 59 eyes had POAG and 61 eyes had OHT. Mean baseline IOP values for the uncontrolled POAG, uncontrolled OHT, newly diagnosed POAG and newly diagnosed OHT groups were 23.8, 27.0, 25.4 and 28.9 mm Hg, respectively.

Follow-up over two years showed mean IOP was reduced by about 40% on the first day after surgery, rose slightly over the first week but was generally sustained thereafter at about 27% below the pre-SLT baseline level.
Subgroup analyses of the IOP-lowering effect showed more favourable results were obtained when SLT was performed as primary versus secondary treatment.

At last follow-up, the mean reduction from baseline IOP was 32% in newly diagnosed OHT patients and 35% in treatment-naïve POAG patients versus 25% and 28% in patients with treatment-refractory OHT or POAG.
The same pattern was observed when the data was analysed with patients categorised as responders (IOP lowering of 20% or greater) and non-responders (IOP lowering less than 20%),

A difference favouring better efficacy in OHT versus POAG eyes was also noted using that end point. For the latter analysis, responder rates were 94% for the OHT group and 90% for the POAG eyes.
About 15 to 18 months into the study, the researchers observed that about 4% of patients achieved an initial good response to SLT, albeit not enough to achieve target IOP.

In addition, there was another subgroup of patients, comprising about 5% of the population, who achieved a very good response despite receiving 180o of treatment with just 30 to 35 shots rather than the usual 50 spots.

Fewer treatment spots were delivered in those eyes either because of the presence of a narrow angle or of peripheral anterior synechiae after argon laser trabeculoplasty.
“Reviewing the features of these patients, we identified that those who did not achieve target IOP generally entered the study with a very high IOP of 30 mm Hg or more and we wondered if such individuals might do better with 360o of treatment.
“The experience of the second subgroup made us question whether in some eyes we might be doing more than is actually required,” Dr Nagar said.

To investigate those issues, a second phase of the study was initiated with random allocation of patients to 90o, 180o or 360o of treatment.
Follow-up of about six months was available for 31 eyes in each group and showed a direct relationship between IOP-lowering effect and treatment area.

Mean baseline IOP values for the three treatment groups ranged from 25.5 mm Hg to 27.2 mm Hg. Mean reductions achieved from baseline IOP were 24% in eyes treated across 90, 33% for those receiving the 180 treatment and 38% for the 360 group.
Corroborating those results, the failure rate was inversely related to the treatment area, decreasing from 20% in eyes receiving 90o of treatment to 11% for the 360o treatment group.

While adverse event incidence increased as the treatment area increased, safety did not limit treatment since all adverse events tended to be mild, transient and clinically insignificant, Dr Nagar said.

“The most common adverse reaction occurring in our studies is mild discomfort during the laser treatment. Otherwise, we observed some increase in anterior chamber reactions on the first day after SLT but that resolved in all cases by the one-week visit.

“There were also some IOP spikes but none of the increases exceeded 10 mm Hg and all responded to topical treatment with apraclonidine (Iopidine) drops and a single dose of oral acetazolamide. No eyes have developed peripheral anterior synechia,” she explained.

Dr Nagar’s study results are some of the first long-term data reported for SLT. The treatment is being promoted as an alternative to argon laser trabeculoplasty (ALT).
Proponents of SLT point to its apparent high efficacy, low side effects and re-treatment capability. Those backing ALT have expressed concern about short-term IOP spikes seen after SLT and advocate waiting for more data from randomised clinical trials before spending money on a new laser.

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