Abstract
Abstract: :
Purpose: The visual system is capable of adapting to optical distortions caused by the ocular optics or by external lenses. Astigmatism is an optical error that distorts the visual input along one meridian of the image due to the cylindrical shape of the lens. We studied the time course of adaptation to cylindrically distorted visual inputs to one eye. Methods:Subjects wore on one eye a cylindrical lens of +1.00 D, to create an optical distortion which changed the perceived sharpness along one meridian and thus the directionality of the perceived pattern. The other eye was either covered (monoptic) with translucent lens or was open (dichoptic). We used a matrix of 10x10 dots as a target to test grouping by proximity. The subjects’ task was to distinguish between horizontal and vertical groupings without feedback. Perceived grouping before, after, and throughout the adaptation period was measured. Results: Perceived proximity with the cylindrical lens (N=12) showed a bias in accordance with the distortion meridian. After 2 hours with the cylindrical lens there was no sign for adaptation except for the after–effect when the lens was removed (reversed bias). After 4 hours, the monoptic group (N=6) showed reduced bias with the adapting eye while no effect was observed with the other eye. However, in the dichoptic group (N=3), the initial bias was increased during the adaptation period in the "astigmatic" eye while the other eye showed an opposite bias. In both groups, the magnitude of the effects was increased when the lens was re–applied the next day. Conclusions: The results suggest that the adaptation is affected by binocular interactions. The 1D difference between the eyes was sufficient to produce a conflict that prevented the development of a compensation for the distorting lens. The persistence of the effects across days shows that visual adaptation to astigmatic lens involves long term plasticity in the visual system.
Keywords: adaptation: blur • astigmatism • plasticity