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Measurements of therapeutic effect, IOP control unreliable over time
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Standard methods of estimating medication effectiveness and the number of measurements needed to control IOP in untreated glaucoma patients showed poor repeatability, according to a study.
“It is important to recognize that single estimates of therapeutic effect may be highly imprecise in an individual patient and we must be careful not to place too much confidence in such results when faced with this situation in the office,” the study authors said.
Thirty patients with a mean age of 64.4 years and primary open-angle glaucoma or ocular hypertension underwent Goldmann applanation tonometry at 8 a.m., 11 a.m. and 4 p.m. during a baseline visit and at three weekly visits before and three weekly visits after treatment initiation.
Study results showed a mean reduction in IOP of 7.5 mm Hg (29.9%). The coefficient of repeatability between visits was 7.8 mm Hg; a reduction in IOP of less than 7.8 mm Hg over one pair of measurements was indistinct from measurement error.
Mean therapeutic effect over the pre-treatment and post-treatment visits ranged from 6.7 mm Hg to 7.9 mm Hg, depending on time of measurement.
Results showed no change in treatment effect with duration of treatment, the authors said.
Perspective
Back to TopDouglas J. Rhee, MD
Rotchford and King’s study helps to further emphasize the limitations of our current methodology for measuring IOP during an office visit. The authors’ results demonstrate the potential pitfalls of relying solely on a single measurement, even if repeated measurements are taken at the same time of day as the prior measurement, to make management choices. At the time of this editorial, we still do not have the ability to continuously monitor IOP. Thus, these results by Rotchford and King lend further support to the clinical recommendation of trying to base important management decisions on more than one data point provided that the clinical situation allows for such flexibility.
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