Converting to SITA-Standard from Full-Threshold Visual Field Testing in the Follow-up Phase of a Clinical Trial

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. 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. 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). 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.