Purpose: To assess the frequency of visual field defects in frequency doubling technology (FDT) perimetry performed in healthy volunteers and the correlations between FDT and standard automated perimetry (SAP).
Method: A transversal study that included 57 healthy volunteers who were subject to visual field testing in both FDT and SAP (randomly effectuated in the same day). The studied parameters were: the frequency of visual field defects in the two techniques, the correlation of the quantitative parameters (MD, PSD) with the C/D ratio and also between techniques, the test reliability and the test duration. The subjects have been questioned about their preference for one test or another.
Results: The frequency of visual field defects was 47.35% in FDT and 22.8% in SAP. The MD values were significantly higher in FDT (MD FDT= -1.45+/-1.91, MD SITA= -0.77+/-1.58, p< 0.0001). Also the PSD values were higher in FDT (PSD FDT= 3.76+/-0.96, PSD SITA= 1.94+/-1.05). The correlation of quantitative parameters between the two techniques was low (r = 0.369 for MD and 0.206 for PSD). The correlation between the PSD value and the C/D ratio was extremely weak in both methods (because the subjects were healthy). The mean duration of a FDT test (4 '29") was significantly lower than that of a SITA test (5'18") - p < 0.00001. The reliability indices (fixation losses, false negative and false positive errors) were significantly better in FDT, and 3/4 of subjects declared that they preferred the FDT test.
Conclusions: In normal subjects the frequency of visual field defects was greater in FDT than in SAP. There was a low correlation of quantitative parameters (MD, PSD) between SAP and FDT, and also with the C/D ratio. Better reliability indices, shorter test duration and better patient compliance are arguments for using FDT as a screening test for glaucoma.