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June 2004

The Benefit of Repeated Intraocular Pressure Measurements in ClinicalTrials

Arch Ophthalmol. 2004;122(6):936-937. doi:10.1001/archopht.122.6.936-b

When evaluating a new ocular hypotensive agent the intraocular pressure(IOP), as measured by the Goldmann applanation tonometer, is used as the primaryefficacy variable. Although Goldmann applanation tonometry is the standardfor measuring IOP, there is an intraobserver variability.1 Dielemanset al2 noted that both the average intraobserverand interobserver variation in IOP was 1.6 mm Hg. Accordingly, to limit intraobservervariation, Kass3 has suggested measuringthe IOP at least twice, and a third time if the first 2 measurements differedby more than 2 mm Hg. Further, some designers of pharmaceuticals have specifiedthat the IOP should be measured 3 successive times at each time point to increasethe reliability of the primary efficacy variable. However, performing repeatedIOP measurements consumes extra time for the technician, may potentially increaseiatrogenic adverse events due to repeated corneal contact by the tonometer,and falsely reduces the IOP after the first measurement.3 Unfortunately,little information exists that indicates whether repeated measurements influencethe IOP reading beyond the first measurement.