Converting to SITA-standard from full-threshold visual field testing in the follow-up phase of a clinical trial

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 243 patients in the Collaborative Initial Glaucoma Treatment Study (CIGTS) who had follow-up visits in 2004. FT and SS VF tests were performed in random order on the same day. RESULTS. The average duration of the SS test (6.3 minutes) was shorter ( P < 0.0001, paired t-test) than the FT test (11.8 minutes). The mean deviation did not differ between SS and FT testing. A small difference was found in the pattern SD (PSD) ( P = 0.02). The mean CIGTS score from the FT test (4.5) was significantly lower ( P < 0.0001) than the mean CIGTS score from the SS test (6.0). Although the two tests yielded identical Glaucoma Hemifield Test (GHT) results in 179 patients (76%), 16 patients had a normal GHT result on FT testing and an SS test result that was outside normal limits. Six patients had the reverse finding. The most significant factor associated with an increased ( positive) difference between the CIGTS VF score generated from SS and FT testing was conducting the FT test first ( P < 0.0001). CONCLUSIONS. Although SS and FT testing yielded very similar mean deviation results, the CIGTS VF score and GHT differed between SS and FT tests. Changing the approach used to measuring a study's primary VF outcome should be accompanied by a critical evaluation of the change's impact.