Stereopsis Prof. Fred Kingdom Department Ophthalmology

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Stereopsis Prof. Fred Kingdom Department Ophthalmology Reading Chapter in Adler’s on binocular vision Lecture PPT on http://www.mcgill.ca/mvr/resident/ Seeing Depth Part I Cues to depth Part II Stereopsis Part III Clinical tests for stereopsis Part I. Cues to depth Position in field of view Occlusion/Interposition Object size Cues to depth Texture gradients Linear perspective Shading Texture gradients/Perspective Atmospheric: Occlusion/Interposition Blueing with distance What is the perceptual hypothesis here? Depth from shading Depth from occlusion Depth from shadows Depth from shadows Depth from shadows Blur is important for depth perception Tilt-shift photography Kurt Wenner Part II. Stereopsis -Definition - Retinal disparity - Horopters - Stereoacuity - Stereoscopes and anaglyphs - Form-from-stereopsis - Correspondence problem - Autostereograms definition……….. Stereopsis is the means by which we determine the relative depth of objects by virtue of the fact that our two eyes view the world from a slightly different angle. Retinal disparity more definitions……. Retinal disparity is the difference in angle subtended by the image of an object between the two eyes, relative to fixation. Stereoacuity is the minimal detectable stereoscopic depth in units of disparity. Normal = 5-15 secs of arc; best is 2 secs. Fusion limit is the largest disparity that can be fused Diplopia is the experience of double vision Stereoacuity: Normal: 5-15 arc secs of arc; best is 2 secs. Fusion Limit (Panum’s limit): 1.5 - 20 arc mins Development: Abrupt onset of stereopsis at 3-5 months Horopters Wheatstone stereoscope Perceived Principle of anaglyphs image F Screen F Perceived image filter Crossed disparity Uncrossed disparity Effect of disparity Random-dot stereogram Figural stereogram Random-dot Stereogram ‘global’ stereopsis Figural Stereogram ‘local’ stereopsis Figural stereogram Random-dot-stereogram ‘Local’ stereopsis ‘Global’ stereopsis ‘False-target’ or stereo-correspondence problem Autostereogram Autostereogram Clinical aspects Development: Abrupt onset of stereopsis at 3-5 months Critical periods: Infancy 6-10 months Childhood 10 months – 9 years Clinical aspects Stereoanomaly: Persons with a selective deficit in either crossed or uncrossed disparities (Richards, 1971), apparently unlinked to amblyopia Amblyopia: Strabismus and Anisometropia Tests for binocular vision and stereopsis Worth 4 dot: Test for binocular function Stereo Fly test: Test for ‘local’ stereopsis Stereo Butterfly: Test for ‘global’ stereopsis TNO: Test for ‘global’ stereopsis Randot E: Test for ‘global’ stereopsis.

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Interacting with Autostereograms
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