Purpose: The frequency doubling (FD) illusion is the basis for new diagnostic methods for glaucoma. The FD illusion is seen when low spatial frequency grating patterns are contrast modulated at high rates. The present experiments examined which spatial frequencies might be optimal and whether high flicker rates are required.
Methods: We determined contrast thresholds for the following: W1, a wide-field 0.25 c/deg grating at 27 Hz contrast reversal; W2, as W1 but no flicker; MAC, 27 Hz, 4 c/deg grating presented to the central 4 degrees; and E1 to E7, seven spatial frequencies in the range 0.063-0.813 c/deg, 27 Hz, presented in a 5 degrees aperture at 15 degrees (nasal) eccentricity.
Results: W1 was the best predictor of glaucoma. Of the eccentrically presented stimuli, E6 (0.688 c/deg) was the best predictor of glaucoma while the lower spatial frequencies performed less well. Only MAC was significantly age-dependent.