Observability of the spatial frequency doubled illusion, correlation with a multi-region perg

Purpose A glaucoma screening device based on the visibility of the spatial frequency doubled (FD) illusion will be marketed by Welch Allyn Ltd in the next year [ANU Patents (AUS) 611,585; (USA) 5,065,767 and application PL 3130J. An underlying assumption of the method is that retinal processes are being tested. To test this assumption we compare the visibility of the FD illusion over a range of conditions and in the same spatial locations as a multi-region pattern electroretinogram (PERG). Methods Psychometric functions describing the probability of seeing the FD illusion were obtained from 8 visual field regions for 35 spatial and temporal frequencies and 2 contrasts. Parallel measurement of a PERG having the same spatial test regions, and where all regions were tested simultaneously were also obtained Result Grating speed, and contrast where good predictors of the psychometric functions and PERG amplitude and phase (p < 0.0005). Of particular interest was the strong correlation between FD illusion visibility and PERG phase difference produced by increasing contrast. Correlated regional variation in the PERG and psychometric measures were also observed. Conclusions The visibility of the FD illusion, and PERG parameters related to the function of nonlinear retinal ganglion cells, covary suggesting a retinal origin for the illusion.