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Editors Selection IGR 18-2

Clinical Examination Methods: IOP and Ocular Perfusion Variability

Comment by Tony Realini on:

70027 Short-term reproducibility of intraocular pressure and ocular perfusion pressure measurements in Chinese volunteers and glaucoma patients, Gao Y; Wan B; Li P et al., BMC Ophthalmology, 2016; 16: 145

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Gao and colleagues have conducted an interesting study to evaluate the next-day repeatability of both intraocular pressure (IOP) and ocular perfusion pressure (OPP) parameters in samples of healthy volunteers and subjects with both normal-tension (LT-OAG) and high-tension openangle glaucoma (HT-OAG). IOP was measured in the sitting position with Goldmann tonometry every three hours from 6AM to 12 midnight on two consecutive days; blood pressure was also measured at the same time points. The investigators reported that IOP repeatability at individual time points was generally fair to excellent in all three groups, while OPP repeatability was generally excellent across the groups. More global summary parameters of IOP and OPP were also assessed. Mean IOP and OPP were generally highly repeatable from day to day, while peak and trough IOP and OPP were somewhat less so, and IOP and OPP variability (peak minus trough) were poorly repeatable. The study design had a few important issues. Firstly, it appears that at each time point, only a single IOP and blood pressure measurement were taken, rather than several to be averaged. Secondly, IOP was measured by a different person on each of the two consecutive days - making this a study of both inter-day and inter-observer variability. These two issues are likely minor in importance as they would have biased study results toward poorer repeatability, when in truth the results obtained in this study suggest good next-day repeatability of the various parameters in these three groups.

Short-term (single-day) assessment of IOP (and likely OPP) is unlikely to robustly characterize long-term variability of these parameters

The results are better than have been reported by other groups - including our own - which may be attributable to the short timeframe (consecutive days rather than days farther apart). One wonders if IOP rhythms may be more conserved in the short term than the long term. As continuous tonometry gets closer to reality, the lesson to be drawn from this body of work is that short-term (single-day) assessment of IOP (and likely OPP) is unlikely to robustly characterize long-term variability of these parameters. The optimal frequency and timing of assessments for robust characterization of IOP and OPP have not yet been established.

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