Test-retest variability of multifocal visual evoked potential and SITA standard perimetry in glaucoma

PURPOSE. To investigate the test-retest variability of multifocal visual evoked potential (mfVEP) and threshold perimetry in glaucoma, and to examine the relationship between the two techniques. METHODS. Data were recorded using the AccuMap mfVEP and SITA standard program of the Humphrey Field Analyzer. Data were obtained twice within a 4-week period from both eyes of 74 patients with varying amounts of glaucomatous visual field loss. The number of defective test locations (those falling beyond a given probability value of being normal) were calculated for mfVEP and SITA, using databases incorporated within the instruments software. Reliability measures and test times were recorded along with patient test preference. RESULTS. Both tests showed a large degree of test-retest variability in the number of defective test locations (95% limits of agreement for mfVEP and SITA being 13-39 and 9.88, respectively). A "fair to moderate" degree of spatial agreement was found between mfVEP and SITA. The number of mfVEP defective locations was dependent on the signal amplitude. No relationship was found between test-retest variability and the reliability indices for either test. The mean time taken to perform mfVEP and SITA standard was 33 and 20 minutes, respectively, and 73 of the 74 patients preferred the mfVEP test. CONCLUSIONS. Test-retest variability was found to be slightly greater for mfVEP. The processing of mfVEP signals needs to be changed to remove the relationship between the number of defective locations and signal amplitude. The majority of patients preferred mfVEP to conventional perimetry although mfVEP takes longer to perform.