Single post-washout IOP measurement inadequate

This analysis of data from a large prospective study found that a single IOP measurement after washout does not adequately approximate the mean of multiple IOP measurements.

Using data from the prospective, multicenter CyPass Micro-Stent COMPASS trial, investigators evaluated whether a single post-washout IOP measurement could be used to approximate the mean of post-washout IOP measurements taken at 8 a.m., 12 p.m. and 4 p.m. in 609 patients with primary open-angle glaucoma.

The percentage of eyes in which a single measurement differed from the mean by more than 1.5 mm Hg (defined as the clinically acceptable cutoff) was about 30%. By logistic regression, the 12 p.m. pressure reading was the closest to the mean IOP.

In examining risk factors contributing to a larger disparity between single IOP measurements and the mean post-washout IOP, they found that for every 1-mm Hg increase in mean post-washout IOP, an eye was 1.1 times more likely to deviate more than 1.5 mm Hg from an increase in IOP after washout using the mean post-washout IOP. These results support the idea that IOP fluctuation increases with increased mean IOP.

They note that because the COMPASS study was ongoing at the time of this analysis, they were limited to the pre-randomization data. It may be possible that only a single IOP measurement is needed after surgery if the operation results in decreased IOP fluctuation.

Further research is needed to determine whether single IOP measurements might have applicability for postsurgical IOP characterization, as well as to address the clinical usefulness of single-day multiple diurnal IOP measurements.