Influence of Selective Laser Trabeculoplasty on the 24-Hour Diurnal Intraocular Pressure Fluctuation in Primary Open-Angle Glaucoma: A Pilot Study

Abstract

Purpose:: To investigate the influence of selective laser trabeculoplasty (SLT) on mean diurnal intraocular pressure (IOP) and diurnal IOP fluctuation in primary open-angle glaucoma (POAG).

Methods:: Both eyes of 13 Caucasian POAG patients underwent a 4-week washout period before the baseline diurnal IOP curve was obtained. No eyes had previuos laser trabeculoplasty or incisional eye surgery. IOP measurements were performed at 12.00 am, 4.00 pm, 8.00 pm, 12.00 pm, 4.00 am, 8.00 am. SLT with 0.4 to 0.9 mJ energy per pulse was performed in 360^o. The IOP curve was repeated for eyes requiring no medication (n=10) at month 3 and 6. IOP lowering medication was introduced for safety reason if mean diurnal IOP was higher than 22 mmHg or any single IOP value exceeded 26 mm Hg at any visit in the follow-up period. The unpaired t-test and ANOVA with the Duncan test were used in the statistical analysis.

Results:: IOP elevation >5 mmHg was found in 16 of the 26 eyes (62%) within two hours after SLT. An at least 20% decrease of the mean diurnal IOP was not seen for any eye in the 6-month follow-up period, but office-time IOP decreased with at least 20% in 5 eyes. Topical IOP lowering medication was introduced in 11 eyes before and in 5 eyes after the month 3 visit. Baseline mean IOP and diurnal IOP fluctuation (mean±SD) were higher for the 11 eyes requiring medication before the month 3 visit than for the other eyes (mean IOP: 28.8±5.2 mmHg vs. 20.8±3.1 mmHg, unpaired t-test, p<0.0001; IOP fluctuation: 9.5±3.7 mmHg vs. 6.8±1.9 mmHg, p=0.0423). Mean diurnal IOP changed from 19.3 ± 1.4 mmHg (baseline) to 18.6 ± 1.4 mmHg (month 3, Duncan test, p=0.090) and to 18.2 ± 2.0 mmHg (month 6, p=0.017). Diurnal IOP fluctuation decreased from 7.2 ± 2.3 mmHg (baseline) to 4.3 ± 1.7 mmHg (month 3, p=0.0004) and to 5.1 ± 1.7 mmHg (month 6, p=0.004).

Conclusions:: Office time IOP decrease does not characterize sufficiently the SLT-induced IOP decrease. Though no eyes showed a 20% reduction of the mean diurnal IOP after treatment, SLT resulted in a clinically and statistically significant decrease of the diurnal IOP fluctuation. Poor IOP control was seen on eyes with high mean diurnal IOP and diurnal IOP fluctuation before SLT. IOP elevation immediately after SLT was frequent.

Keywords: laser • intraocular pressure