Abstract
Purpose: It is well known that visual acuity and contrast sensitivity in amblyopia are attenuated at high spatial frequencies. Amblyopes, however do not report that images appear blurred or lower in contrast as would be expected from these sensory deficits. Instead amblyopes report severe perceptual distortions, which extend beyond the restricted spatial range of the amblyopic eye. The purpose of this study is to identify and quantify such perceptual distortions in amblyopia. Methods: Perceptual distortions were measured with monocular forced choice discrimination tasks and inter-ocular matching tasks. Intrinsic blur was measured with blur increment and matching as a function of the standard deviation of Gaussian edges. Orientation, position and numerosity global distortions were measured in the same way with psuedo-random arrays of highly visible and resolvable Gabor patches whose local orientation and position were systemically varied. Results: Discrimination thresholds in the amblyopic eye were elevated for blur, orientation and spatial position but were within the normal range for numerosity discrimination. Interocular matching thresholds were also elevated for orientation and positional uncertainty, but were within the normal range for blur and numerosity discrimination. Conclusions: Blur and numerosity are veridically represented within the amblyopic visual system, but the representation of local orientation and spatial position shows greater variability compared to normal. It is this increased local spatial uncertainty that underlies the spatial deficit in amblyopia.
AJS is supported by a MRC Research Fellowship.