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Mingjuan Lisa Zhang, Brian Chon, Jiangxia Wang, Gerard Smits, Shan C Lin, Tsontcho Ianchulev, Henry D Jampel; Single Versus Multiple Intraocular Pressure Measurements in Glaucoma Surgical Trials. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2166.
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Little is known about the necessity of multiple same-day intraocular pressure (IOP) measurements versus a single measurement in describing the effect of IOP-lowering surgical procedures, and such evidence could affect surgical trial recruitment and retention.
609 patients (609 eyes) with primary open-angle glaucoma and cataract from the pre-randomization phase of the COMPASS CyPass Micro-Stent randomized controlled trial underwent one IOP measurement while taking usual medications to lower IOP and three diurnal IOP measurements at 8am, 12pm, and 4pm after undergoing a 2-4 week washout of all IOP-lowering drops. The main outcome was the proportion of eyes in which the increase in IOP after washout, using the mean of the three measurements, differed by more than 0.5, 1, 1.5, or 2mmHg from the increase in IOP after washout using only one of the after-washout measurements. A proportion of ≤10% at the 1.5mmHg cutoff was considered clinically acceptable.
The mean IOP before washout was 18.5±4.0mmHg. The mean increase in IOP after washout using the mean of the three measurements was 5.3±4.2mmHg. The percentage of eyes in which the increase in IOP using a single after-washout IOP differed from the increase in IOP using the mean of three measurements by more than 1.5 mmHg was 35%, 26%, 34%, 30%, and 31% when the single measurement was made at 8am, 12pm, 4pm, a randomly chosen one of the three times, and the time closest to that of the before-washout IOP, respectively. By logistic regression, the 12pm after-washout IOP had the lowest proportion of eyes differing from the mean (p<0.001) and thus most closely approximated the mean diurnal IOP measurement.
Although eliminating multiple IOP measurements would simplify the conduct of surgical trials in glaucoma, our data show that using a single IOP measurement after washout does not adequately approximate the mean of multiple IOP measurements. Further evaluation is needed after the COMPASS trial is complete to determine whether single IOP measurements might have applicability for post-surgical IOP characterization.
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