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D.C. Musch, B.W. Gillespie, B.M. Motyka, R.P. Mills, P.R. Lichter, CIGTS Study Group; Converting to the SITA–Standard Visual Field Test Strategy in the Follow–up Phase of a Clinical Trial: Agreement With the Full Threshold Visual Field Test Strategy . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3730.
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Purpose: To evaluate the impact of converting from Humphrey 24–2 full threshold (FT) visual field (VF) testing to SITA–Standard (SS) VF testing during the follow–up phase of a clinical trial. Methods: VF data were obtained from the first 135 Collaborative Initial Glaucoma Treatment Study (CIGTS) patients who had follow–up visits in 2004. FT and SS VF tests were obtained in random order, with recovery time allowed between testing. Both test results were scored according to the CIGTS scoring algorithm, which assigns weights to points on the VF test’s total deviation probability plot. Other Humphrey VF test parameters that are common to both tests were recorded. SAS 9.0 software was used for data analyses. Results: Average duration of the SS test (6.4 min) was significantly shorter (P<0.0001, paired t–test) than the FT test (11.9 min). Mean deviation and pattern standard deviation values did not differ between SS and FT testing, whereas the CIGTS score differed substantially (P<0.0001). The mean CIGTS score from the FT test (4.6) was lower than the mean CIGTS score computed from the SS test (6.0). While the two tests yielded identical Glaucoma Hemifield Test (GHT) results on 95 patients (72%), 12 patients had a normal GHT result on FT testing and a SS test result which was outside normal limits. Five patients had the reverse finding. Upon modeling the difference in results between tests on subject factors (e.g., age, sex, race, smoking status) and eye–specific factors (pupil diameter, test sequence, severity of visual field loss), only one factor was significantly associated with an increased (positive) difference between the CIGTS VF score generated from SS and FT testing: conducting the FT test first (P=0.01). When the FT test was done first, the resulting CIGTS VF score from the SS test was 2.1 units higher than the FT test result. When the SS test was done first, the resulting CIGTS VF score was 0.9 units higher than the FT test result. Conclusions: Although SS and FT testing yielded very similar mean deviation results, the CIGTS VF score and GHT differed between SS and FT tests. If the approach used to measuring a study’s primary VF outcome is changed, a critical evaluation of the change’s impact must be conducted, and may lead to the need to establish a new reference baseline value.
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