Test-retest variability in glaucoma patients tested with C-20-1 screening-mode frequency doubling technology perimetry

Purpose: To investigate test-retest variability in glaucoma patients tested with C-20-1 (screening) Frequency Doubling Technology (FDT) perimetry. Methods: Thirty-one glaucoma patients with a range of visual field defects (17 with mild, 11 with moderate, and 3 with severe defects by AGIS classification) and experienced in standard automated perimetry but not FDT perimetry were prospectively recruited. The C-20-1 screening mode of FDT was consecutively administered three times. Concordance between tests for each patient was measured by presence and severity of defects for each test location. Learning and/or fatigue effects were also evaluated using FDT test scores in which number and severity of defects was graded. Results: Agreement between FDT test locations averaged 88% for any defect, but only 51% for severity of defect. Although the mean test score increased slightly over the three tests, subjects did not demonstrate a statistically significant change in test score across the three testings (P = 0.975). Among 17 patients with early glaucoma (AGIS score 1-5), two returned a normal initial FDT test, and four returned a normal second FDT test. Conclusions: Using C-20-1 FDT, concordance between tests at a given test location was high for the presence of any defect, which would be important in glaucoma screening, but was only fair for severity of defect. Six of 17 patients with early glaucoma returned normal tests during testing. This group of glaucoma patients with perimetric experience did not demonstrate a significant learning or fatigue effect with FDT screening perimetry.