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Editors Selection IGR 15-2

Laser Treatment: Latanoprost, SLT and Circadian IOP

Comment by Andrew Tatham on:

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Intraocular pressure (IOP) fluctuates considerably, and though it remains uncertain whether variation in IOP increases the risk of glaucoma progression, treatments that provide sustained IOP control are appealing.¹ Selective laser trabeculoplasty (SLT) is an effective initial treatment for open-angle glaucoma (OAG) and ocular hypertension (OHT), with the Laser in Glaucoma and Ocula Hypertension (LiGHT) Trial showing almost 70% of eyes treated with SLT first remained at or below target IOP without medical or surgical treatment at six years.² Sleep laboratory studies have shown some medical therapies (e.g., topical beta-blockers) have limited effect on nocturnal IOP.³ Combined with the likely effect of poor adherence on IOP fluctuation with topical treatments, it is conceivable that SLT may offer superior 24-hour IOP control, however, few studies have examined this topic.⁴

In this prospective randomized study, Shi and colleagues compared the 24-hour efficacy of 360-degree SLT and 0.005% latanoprost eye drops as first-line in treatment naïve Chinese patients with POAG or OHT followed over a 12-week period. Patients were hospitalized for 24-hour IOP measurements (taken at 7 am, 10 am, 2 pm, 6 pm, 10 pm, 2 am, 5 am) using Goldmann applanation tonometry at baseline and at four- and 12-weeks following SLT or initiation of medical treatment. Twenty-three participants were randomized to SLT and 22 to latanoprost.

Both SLT and latanoprost significantly reduced IOP at all time points through to 12 weeks, however, the IOP reduction with latanoprost was greater. There was a significantly greater reduction in mean IOP and peak IOP in the latanoprost compared to SLT groups at four and 12 weeks and diurnal and nocturnal IOP reduction was greater with latanoprost at the same time points. Latanoprost was more effective than SLT in reducing 24-hour IOP fluctuation, with the effect of SLT on circadian IOP fluctuation short lived, returning to the pre-procedure level at just four weeks.

The study, however, was limited by its single site, small sample size, short follow-up and focus on IOP endpoints only. In addition, patients were woken for IOP measurements, which were taken in the sitting position, perhaps not reflecting actual IOP variation

The lack of sustained effect of SLT on 24-hour IOP fluctuation was surprising, particularly given the performance of SLT in the LiGHT study. The efficacy of SLT does wear off over time, but the duration of Shi and colleagues' study was only 12 weeks. Six-year results from the LiGHT study have shown better long-term disease control with SLT-first, with fewer SLT eyes progressing (19.6% versus 26.8%) and fewer undergoing trabeculectomy.^2,5 In the LiGHT study both groups were treated to target IOP, with the protocol allowing target IOP to revised up or down. The reason for better long-term disease control with SLT-first despite treating to target IOP might have been due to poor adherence in the drop-first arm or due to SLT providing 'better quality' IOP reduction, lessening IOP fluctuations. The results of Shi and colleagues suggest contrary, with latanoprost performing better than SLT. The study, however, was limited by its single site, small sample size, short follow-up and focus on IOP endpoints only. In addition, patients were woken for IOP measurements, which were taken in the sitting position, perhaps not reflecting actual IOP variation. There was also a fairly high 11% dropout rate even with the short study duration. The controversy of the importance or otherwise of IOP fluctuation continues.

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