Repeatability of Frequency Doubling Technology Perimetry (20-1 Screening Program) and the Effect of Pupillary Dilatation on Interpretation

Abstract

Purpose: To evaluate the repeatability of frequency doubling technology perimetry (FDT, screening-20-1 program) and the effect of pupillary dilatation on its interpretation. Methods: Group I comprised 85 eyes (85 glaucoma patients) with field defects on automated perimetry classified on the basis of severity. Group II comprised 41 normal eyes (41 subjects). At baseline all subjects underwent conventional automated perimetry using the Swedish Interactive Testing Algorithm program (SITA standard). On two subsequent visits both groups underwent FDT (C20-1 FDT). At the final (third after baseline) visit, all patients underwent C 20-1 test before and after pupillary dilatation. Sensitivity and specificity was calculated for each test. Mean number of defective points for 20-1 test at each test was noted; differences between the repeat 20-1 tests were calculated. Reproducibility of repeated FDT was tested by the limits of agreement plot. Results: The sensitivity and specificity of the first test was 85% and 95% and did not vary much between visits; sensitivity and specificity were 77.6% and 97.7% for the “dilated” test. The mean difference (with 95% CI) in number of defective points per patient between tests 1 and 2 and between test 1 and the “dilated” test for both glaucoma group and normal group was not significant. On the limits of agreement plot more than 95% points lay between 2 SD. Conclusions: FDT has a clinically acceptable repeatability. Dilatation decreases sensitivity but not specificity.