Testing for glaucoma with the spatial frequency doubling illusion

We examined the performance of tests for glaucoma based on the spatial freq uency doubling (FD) illusion. Contrast thresholds for seeing the FD illusio n in four large visual field regions were measured from 340 subjects who we re tested up to seven times over 2 years. Median sensitivities of 91% at sp ecificities of 95% were obtained. Test-retest variability for the worst hem ifield thresholds averaged 2.22 db +/- 0.09 S.E. for all tested groups, and significant progression was observed for glaucoma suspects over the seven visits, indicating that tests based on the FD illusion can detect diffuse e arly glaucomatous loss. (C) 1999 Elsevier Science Ltd. All rights reserved.