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L.-J. Hwang, R. Varma, J. W. Grunden; Long-Term Intraocular Pressure (IOP) Fluctuation - An Alternative Parameter for Assessing IOP Control in Clinical Trials. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1264.
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Mean diurnal IOP is generally used as the primary measure of IOP control. However, recent evidence suggests long-term IOP fluctuation may be important in the development of optic nerve damage. We evaluated whether long-term IOP fluctuation provides additional information on IOP control from data collected in the XLT (Xalatan Lumigan Travatan) study.
The XLT study was a masked-evaluator, randomized, parallel-group comparison of the efficacy of X, L, and T after 12 weeks of treatment in patients with open-angle glaucoma or ocular hypertension (OHT). Pre-treatment IOP was measured once at screening (-4 weeks), once (-2 weeks) during a 4-week washout period as a safety check, and 4 times (8:00 AM, 12 noon, 4:00 PM, 8:00 PM) at baseline. Post-treatment IOP was assessed once at Week 2 and 4 times (time points as above) at Weeks 6 and 12. IOP fluctuation was defined as the IOP range (Highest - Lowest IOPs) during the specified period (pre- or post-treatment).
Included in the analyses were 410 patients (X: 136, L: 136, T: 138). Reductions in mean IOP were similar among the treatment groups.1 Pre-treatment mean IOP fluctuations were similar across the groups (range, 7.5-7.8 mmHg). Treatment with X, L, and T resulted in significant within-treatment-group reductions in mean IOP fluctuation during 12 weeks (X: -2.69, L: -2.41, T: -1.90 mmHg; p< 0.01). When IOP fluctuation was dichotomized as ≤6 (low) or > 6 mmHg (high), percentages of patients with high IOP fluctuation in each group were comparable before treatment (63%-64%). After 12 weeks of treatment, percentages of patients with high fluctuation were reduced to 21%, 28%, and 36% in the X, L, and T groups, respectively; the overall comparison among groups was significant (p=0.016) as was the pair-wise comparison between X and T (p=0.005).
In the XLT study, there were no statistically significant differences at Week 12 between therapies in mean IOP reductions at 8:00 AM (peak) or 8:00 PM (trough). However, when assessing long-term IOP fluctuation, our analysis noted differences between treatment groups. Thus, determining only mean IOP reduction may not provide a complete assessment of IOP control. IOP fluctuation may be another useful method of evaluating IOP control particularly in trials on patients with glaucoma or OHT.1. Parrish RK et al. Am J Ophthalmol 2003;135:688-703.
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