Prof. Fred Kingdom Department Ophthalmology Reading

Chapter in Adler’s on

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 Tilt-shift photography

Kurt Wenner

Part II. Stereopsis

-Definition - Retinal disparity - Horopters - Stereoacuity - and anaglyphs - Form-from-stereopsis - - 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 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: 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