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Shaban Demirel, Genichiro Takahashi, Chris A. Johnson; A comparison of visual field indices for standard FDT and a spatially finer testing pattern. Journal of Vision 2002;2(10):96. doi: https://doi.org/10.1167/2.10.96.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare visual field indices generated by standard Frequency Doubling Technology perimetry (FDT) to those generated using stimuli arranged with spatially finer resolution, equivalent to the Humphrey 24-2 pattern.
Methods: Fine resolution FDT perimetry was conducted using a custom display system consisting of four high-resolution (1280 × 1600 pixels) 21-inch monochrome monitors combined with front surface mirrors to cover the central 30 degrees radius of the visual field. A 24-2 stimulus pattern (6 degree grid bracketing the horizontal and vertical meridians), consisting of 54 locations throughout the central 24 degrees radius, was employed for FDT testing. Testing was also conducted with the commercially available FDT perimeter using standard N30 test parameters (10 degree diameter square targets, 0.25 cycles/degree sinusoidal gratings undergoing 25Hz counterphase flicker). The 24-2 targets were 4-degree diameter squares, which displayed 0.5 cycle/degree sinusoidal gratings undergoing 18 Hz counterphase flicker. Background luminance was 50 cd/m2. Thresholds were obtained by means of a Modified Binary Staircase (MOBS) procedure. 119 eyes of 89 glaucoma suspects (with normal SAP visual fields at baseline) were evaluated annually over a four-year period.
Results: Mean Defect, an index of generalized visual field sensitivity loss, was statistically significantly correlated (p<0.001) between the two FDT procedures (r between 0.51 and 0.63 depending on year). Pattern Standard Deviation (PSD), an index of localized visual field sensitivity loss, was also statistically significantly correlated (p<0.005) between the two FDT procedures (r between 0.27 and 0.34 depending on year). However agreement for PSD was lower than for MD.
Conclusions: There is a strong correlation between visual field indices for FDT perimetry using different spatial arrangements of test locations. Correlation is higher for indices of overall sensitivity loss than for indices of local loss. This difference is probably related to the different spatial resolution characteristics of the two tests.
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