Comparison of frequency doubling and flicker defined form perimetry in early glaucoma

To compare perimetric data based on the second-generation frequency doubling technology (FDT) and on flicker defined form (FDF) stimulation in early glaucoma patients.

Seventy-two experienced glaucoma patients and 50 healthy subjects of the Erlangen Glaucoma Registry participated in the study. The definition of glaucoma was solely based on optic disc appearance. All patients underwent FDF perimetry (HEP), FDT perimetry (Matrix), standard automated perimetry (SAP, Octopus), and peripapillar measurements of the RNFL thickness (Spectralis OCT). Exclusion criteria were: mean defect (MD) in SAP > 6 dB, eye diseases other than glaucoma, or non-reliable FDF or FDT measurements. Statistical analyses included comparison of the standard indices and correlations between methods. Venn-diagrams show the number of patients with abnormal results in HEP, Matrix, SAP, and mean RNFL thickness.

Mean defect data from FDT and FDF perimetry were strongly correlated (R = -0.85, P <0.001). In this cohort of early glaucoma patients, the MD values were 6.1 ± 5.0 dB (FDF) and 4.5 ± 4.1 dB (FDT). Sensitivity in this patient group was 65 % for FDF-MD, 60 % for FDT-MD, and 60 % for RNFL-thickness, all at a specificity of 95 %. The correlation analysis between local RNFL thickness and corresponding visual defects revealed significant Spearman correlation coefficients for the arcuate bundles of the visual field (FDF-inferior: R = -0.65, FDF-superior: R = -0.74, FDT-inferior: R = -0.55, FDT-superior: R = -0.72).

FDF and FDT stimulations can be used to detect patients with early glaucoma. Combined consideration of RNFL thickness and results from one of these perimetric tests can increase the total number of detected patients.