The Impact of Baseline Intraocular Pressure on Initial Treatment Response in the LiGHT Trial Selective Laser Trabeculoplasty versus Medication

Purpose: The Laser in Glaucoma and Ocular Hypertension Trial demonstrated the efficacy and safety of selective laser trabeculoplasty (SLT) compared with topical hypotensive medication as first-line therapy for ocular hypertension and open-angle glaucoma. This substudy explored the impact of pretreatment (baseline) intraocular pressure (IOP) on treatment response. Design: Post hoc analysis of randomized control trial data. Participants: A total of 1146 eyes from 662 patients were included in this analysis: 559 eyes in the SLT group and 587 in the medication group. Methods: Intraocular pressure reduction at 8 weeks after treatment with either SLT or prostaglandin analog (PGA) eye drops was assessed at different levels of baseline IOP, and the groups were compared. Differences in absolute and percentage IOP lowering between SLT and PGA groups were tested with a linear mixed-effects model. Differences in the probability of achieving >= 20% IOP lowering between SLT and PGA groups, at different levels of baseline IOP, were estimated using a logistic mixed-effects model. Main Outcome Measure: Intraocular pressure-lowering response to SLT versus PGA eye drops. Results: Mean IOP was not significantly different between the groups at baseline or 8 weeks after treatment initiation. Both treatments showed greater IOP lowering at higher baseline IOP and less IOP lowering at lower baseline IOP. Selective laser trabeculoplasty tended to achieve more IOP lowering than PGA drops at higher baseline IOP. Prostaglandin analog drops performed better at lower baseline IOP, and the difference compared with SLT, in terms of percentage IOP reduction, was significant at baseline IOP of <= 17 mmHg. A significant difference was found in the relationship between baseline IOP and probability of >= 20% IOP lowering between the two treatments (P = 0.01), with SLT being more successful than PGA at baseline IOP of more than 22.5 mmHg. Conclusions: We confirm previous reports of greater IOP lowering with higher baseline IOP for both SLT and PGA drops. In treatment-na & iuml;ve eyes, at higher baseline IOP, SLT was more successful at achieving >= 20% IOP lowering than PGA drops. At lower baseline IOP, a statistically greater percentage, but not absolute, IOP lowering was seen with PGA drops compared with SLT, although the clinical significance of this is uncertain.