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 Depth from shading 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 betwen 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 largets 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