Abstract

Sloan letters, grating patterns, and bar offsets have been used to assess foveal spatial function. Because of the inherent redundancy of these stimuli and the "filling in" due to perceptual completion processes, these tests may not be sensitive enough to changes in the retinal sampling mosaic. An alternative to these stimuli is a spatially random block pattern which has been used to test symmetry discrimination.¹ These block patterns consist of elements of a constant size. The intensity of each element is randomly chosen to be either maximum or minimum, and the subsequent patterns range from those with a symmetrical distribution to those with an asymmetrical distribution (Figure 1). Due to the unpredictable location of each pattern element, and the lack of predictable redundancy, subjects cannot rely on perceptual completion processes to make accurate symmetry judgments. The present report tests whether a symmetry paradigm is useful to assess losses in the retinal sampling mosaic in patients in whom a loss of photoreceptors has been reported (e.g., retinitis pigmentosa [RP]^2,3)

© 1993 Optical Society of America