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Editors Selection IGR 9-4

Surgical Treatment: SLT in NPG

Comment by Arthur Sit on:

55392 Comparison of Fluctuations of Intraocular Pressure Before and After Selective Laser Trabeculoplasty in Normal-tension Glaucoma Patients, Tojo N; Oka M; Miyakoshi A et al., Journal of Glaucoma, 2014; 23: e138-e143

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Therapies that improve outflow facility, such as laser trabeculoplasty, will generally result in smaller IOP fluctuations than those that reduce aqueous humor production

Intraocular pressure (IOP) fluctuation has been suggested as a possible risk factor for glaucoma pathogenesis. Therapies that improve outflow facility, such as laser trabeculoplasty,¹ will generally result in smaller IOP fluctuations than those that reduce aqueous humor production.² Consequently, the effect of laser trabeculoplasty on IOP fluctuations has been of significant interest. A prior study using a sleep laboratory demonstrated that the typical nocturnal rise in IOP could be reduced by argon laser trabeculoplasty (ALT) even when the diurnal IOP was unchanged compared to baseline in medically treated glaucoma patients.³

In contrast to ALT, selective laser trabeculoplasty (SLT) appears to have similar IOP reduction, but the histological damage caused to the trabecular meshwork is far less.⁴ In order to investigate the effect of SLT on IOP fluctuations, Tojo et al. utilized the Triggerfish contact lens sensor (CLS) to measure 24-hour IOP patterns in normal tension glaucoma (NTG) patients before and after treatment. They calculated IOP fluctuations, defined as the difference between the minimum and maximum signal from the CLS in millivolt equivalents (mVeq), for the 24-hour, diurnal and nocturnal periods. The nocturnal period was identified based on a characteristic decrease in blinks during as detected by the CLS.

The authors found that SLT reduced IOP fluctuation during the nocturnal period, but not during the diurnal period or the 24-hour period. However, the authors did not report on the magnitude of signal change from the diurnal to nocturnal period, so it is unclear if there was a reduction of the typical nocturnal rise in IOP after SLT. The authors also assessed the acrophase for the 24-hour curves, which indicates when the peak IOP occurs. Interestingly, only one of ten patients changed acrophase, while the remaining subjects maintained either a diurnal, nocturnal or no acrophase pattern. This suggests that NTG patients tend to maintain their overall 24-hour IOP patterns even after mean IOP has been reduced by SLT treatment. One potential limitation of the study is that the CLS reports a signal in mVEq and is not calibrated to mmHg. While this limits the ability of the study to determine the magnitude of IOP change, the overall effect on IOP patterns would presumably be valid. Another limitation was the small size of the study, which included only 10 patients. Further studies with larger populations and longer follow-up will be required to determine if the reported reduction in nocturnal IOP fluctuations has any benefit beyond the reduction in mean IOP in NTG patients.

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