Eyes with pre-laser IOP greater than 15mm Hg saw a 2.6±3.1mm Hg at one month and 1.7±2.8mm Hg at 48 months. Photo: Nate Lighthizer, OD. Click image to enlarge.

Previously, the Glaucoma Intensive Treatment Study (GITS) demonstrated that laser trabeculoplasty (LTP) was beneficial in multi-treated eyes if the IOP before laser was ≥15mm Hg and if it was maintained up to a year. This was not the case for eyes with IOP lower than 15mm Hg. Both the older argon laser procedure and the now-standard selective laser trabeculoplasty (SLT) were used in GITS.

The same researchers investigated if the IOP-lowering effect was sustained beyond one year of follow-up in eyes with pre-laser IOP ≥15mm Hg by studying the long-term effect of LTP based on data from the GITS five-year follow-up. They found that the chance of success is small if the pre-laser IOP is lower than 15mm Hg.

Patients with untreated, newly diagnosed open-angle glaucoma were treated with three glaucoma drugs for one week, after which 360° argon or selective LTP was performed. IOP was measured just before LTP and repeatedly during the 60-month study period.

Before the laser procedure, mean IOP in all 152 study eyes of 122 multi-treated patients was 14.0±3.5mm Hg. After exclusion of eyes that were lost to follow-up or received increased therapy during follow-up, IOP was significantly reduced at all visits up to 48 months in eyes with pre-treatment IOP ≥15mm Hg, measured at 2.6±3.1mm Hg at one month and 1.7±2.8mm Hg at 48 months (n=56 and 48, respectively).

No significant IOP reduction was seen in eyes with pre-treatment IOP <15mm Hg. Seven eyes (<13%) above 15mm Hg at baseline required increased IOP-lowering therapy at 48 months.

The pressure-lowering effect of laser trabeculoplasty and its duration was highly dependent on the IOP level before the laser treatment. A sustainable IOP reduction lasted for up to four years in the group of eyes where pre-LTP IOP was ≥15mm Hg. The authors noted this was particularly interesting since eyes with reduced IOP-lowering treatment during follow-up were included, and this may have affected the IOP-lowering effect negatively.

“Consequently, the IOP-lowering effect of LTP in this group might be better than reported. However, the LTP had no significant IOP-lowering effect in eyes with pre-LTP IOP <15mm Hg on a group level, where the IOP on the contrary increased over time,” the authors explained in their paper. “A possible explanation to this result was that treatment was reduced during follow-up in 12% of these eyes which may have contributed to the increase. Furthermore, the vast majority (82%) of the group with pre-LTP IOP ≥15mm Hg did not receive any enhancement of therapy during the five years of follow-up.”

Although laser trabeculoplasty, particularly SLT, is considered a safe procedure and in some cases delays the need of glaucoma surgery, these results show that it is not likely to provide additional IOP reduction if pressure is lower than 15mm Hg, prompting some practitioners to offer clinical guidance not to consider the intervention in these cases, according to the authors. This is in line with previous studies, with some showing that patients who received selective LTP and had pre-laser IOP below 14mm Hg may not benefit from laser treatment at all.

“In the Early Manifest Glaucoma Trial, eyes with newly-diagnosed glaucoma were treated with argon LTP one week after initiation of betaxolol treatment,” the authors wrote. “Their mean baseline IOP was, as expected, higher than in our study group—18mm Hg vs. 14mm Hg—and the authors concluded, similar to the current study, that argon LTP had no pressure-lowering effect when IOP was lower than 15mm Hg.”

“LTP performed in multi-treated patients may provide a useful IOP reduction that is maintained over several years,” the authors concluded. “This is true on a group level when the initial IOP is ≥15mm Hg, but if the pre-laser IOP is lower than that, the chance of LTP success is small.”