![PERCEPTION OF DEPTH
Perception of distance of objects from each other
or from the observer.
Several clues contribute-
A] BINOCULAR CLUE: Stereopsis.
B] MONOCULAR CLUES:](https://image.slidesharecdn.com/binocularvisionisha-161111155239/85/Binocular-vision-basics-34-320.jpg)
Binocular vision basics
- 1. BINOCULAR VISION Moderator – Dr. N. Kori Presenter – Dr. IshaGupta
- 2. DEFINITION State of simultaneous vision with two seeing eyes (neither of which needs necessarily be normal) that occurs when an individual fixes his visual attention on an object of regard.
- 3. Why to study binocular vision? The basic laws of binocular vision forms the very foundation on which our current understanding of strabismus and its symptoms and sensory consequences is based. Knowledge on BSV forms basis to orthoptic treatments and many physiological processes in the eye.
- 4. Types of Vision 1.Monocular Vision with single eye 2.Bi-ocular no co-ordination between two eyes 3.Binocular Co-ordinated vision from two eyes
- 5. Pre-requisites for development of BSV Motor Mechanism: •correct neuromuscular development so that the visual axes are directed at the object •overlap of visual fields Sensory Mechanism: •approximately equal image clarity and size in the two eyes •corresponding retinal areas so that the eyes are cyclopean •normal visual pathways Mental Process: •ability of visual cortex to promote binocular single vision
- 6. GRADES OF BINOCULAR VISION SIMULTANEOUS PERCEPTION FUSION STEREOPSIS
- 7. ADVANTAGES OF BINOCULAR VISION Masking of optical defects and blind spot. Safety factor Larger field of view Convergence helps in estimating absolute distance Stereopsis Disorders of binocular vision produce diplopia / supression / amblyopia
- 8. MECHANISM OF BINOCULAR VISION Visual direction Retinal correspondence Egocentric localisation Horopter Pannums fusional area
- 9. VISUAL AXIS
- 10. Visual space vs physical space Visual space is the subjective space that is based of anatomic and physiological systems,visual clues and on learning. Physical space is the actual space of the object. Anatomic distribution of retinal elements does not coincide with physiological distribution of spatial values – Kundst- Munsterberg illusion
- 11. VISUAL DIRECTION 1. OCULOCENTRIC – - Monocular - Laws of oculocentric visual direction 2. EGOCENTRIC – - Cyclopean eye - Hering’s law of identical visual direction
- 13. RETINAL CORRESPONDENCE Retinal rceptors in both eyes that dictate a common visual direction under binocular conditions are called corrresponding retinal points. Corresponding retinal points are areas of zero disparity. Normal retinal correspondence Abnormal retinal correspondence(ARC) Harmonius arc Un harmonius arc HARMONIUS angle of anamoly= angle of strabismus UNHARMONIUS angle of anamoly< angle of
- 14. FOVEOLA
- 15. HOROPTER It is the sum total of all the points in the physical space that stimulate corresponding retinal elements of the two eyes. 1. Vieth muller horopter / theoritical / geometric horopter 2. Empirical horopter
- 16. HOROPTER
- 18. BINOCULAR FUSION Sensory fusion should be distinguished from the motor fusion. Sensory fusion is the ability of visual cortex. Motor fusion refers to the ability to align eyes in such a manner that sensory fusion can be maintained. It's the exclusive function of extra– foveal retinal periphery.
- 19. PANNUMS FUSIONAL AREA Region in front and back of the horopter in which single vision is present is known as Panum’s area of single binocular vision or Panum’s fusional area Horizontal extent of these areas is small at the center (6 to 10 minutes near the fovea) Increases toward the periphery (around 30 to 40 minutes at 12° from the fovea)
- 21. Physiological Diplopia The Diplopia elicited by an object point off the Pannum’s fusional area Types A.Crossed (Heteronymous) Diplopia Temporal (crossed) disparity B.Uncrossed (homonymous) Diplopia Nasal (uncrossed) Disparity
- 22. Fixation Disparity It is the minute image displacement, rarely exceeding several minutes of arc of angle, occurs within Panum’s space while fusion is maintained. • Due to presence of pannum’s fusional area – A physiological variation in placement of retinal image displacement from corresponding retinal points • Even Allow fusion • Displacement of retinal images in two eyes – Retinal disparity
- 24. Theories of binocular fusion 1. Physiologic hypothesis – most accepted 2. Synergy hypothesis 3. Local sign hypothesis 4. Eye movement hypothesis 5. Suppression hypothesis
- 25. Physiologic basis of fusion
- 26. Dichoptic stimulation • Refers to different stimulation in the two eyes which occurs when binocular stimuli fall on non corresponding points on the two retinae. • Depending on the degree of non correspondence five classes of percepts are obtained. • Depth with fusion • Depth with diplopia • Diplopia without depth • Binocular rivalry and suppression • Binocular lustre.
- 27. Retinal rivalry and suppression • When dissimilar contours are presented to the corresponding retinal areas fusion becomes impossible. • This conflict which results when such signals are transmitted to the visual cortex is termed as retinal rivalry. • When presented with such signals,signal presented from one eye is actively suppressed. This results on perception of single signal at a time. This is known as suppression
- 28. RETINAL RIVALRY
- 29. Binocular lustre • The lustrous appearance of surfaces like a waxed surface,table top is due to binocular lustre. • It results from the different position of partially reflected objects in the surface by virtue of the different positions of the two eyes.
- 30. STEREOPSIS 3rd Grade of Binocular Vision Visual appreciation of three dimensions Ability to obtain impression of depth by superimposition of two images of the same object, seen from 2 slightly different angle. Retinal disparity (Fixation disparity) is the basis of 3 D perception Stereopsis occurs when Retinal disparity is not large enough for simple fusion but small enough to cause diplopiaNot similar to depth perception.
- 32. PHYSIOLOGIC BASIS OF STEREOPSIS • Horizontal disparity produces stereopsis. •Local stereopsis – square by square matching •Global stereopsis - to resolve ambiguities •Fine stereopsis - specific pattern matching < 0.5 degrees •Coarse stereopsis - act beyond the range of retinal rivalry , dissimilar images can be simultaneously perceived -Fusion is not absolutely required for stereopsis . -But similar parts of stereogram reaching corresponding points must fuse to form reference points.
- 33. •Stereoscopic acuity -Minimal disparity beyond which no stereoscopic effect is produced characterizes the person’s stereoscopic acuity. - normal = depth of 10 arc sec -Closest fixation of 10 inches = depth of thousandth of an inch -Beyond 600 mts there is no true stereopsis.
- 34. PERCEPTION OF DEPTH Perception of distance of objects from each other or from the observer. Several clues contribute- A] BINOCULAR CLUE: Stereopsis. B] MONOCULAR CLUES:
- 35. Monocular./Non Stereoscopic Clues a) Parallactic movements b) Linear perspective c) Overlay of contours d) Size e) Distance from horizon f) Distribution of highlights & shadows g) Aerial perspective
- 36. PARALLACTIC MOVEMENTS Most important in depth perception next to stereopsis Slight shift of head while fixation is maintained results in change of relative position of objects in gaze Objects beyond fixation point – move in same direction Objects closer – move in opposite direction
- 37. LINEAR PERSPECTIVE OVERLAY OF CONTOURS
- 38. DISTANCE FROM HORIZON DISTRIBUTION of HIGHLIGHTS AND SHADOWS
- 39. THEORIES OF BINOCULAR VISION Theory of correspondence and disparity Neurophsiological theory Older theories Alternation theory Projection theory Motor theory Isomorphism theory
- 40. Theory of correspondence and disparity Salient features are : -Simultaneous stimulation of the corresponding points by one object transmits single visual impression with no depth quality. -Simultaneous stimulation by two objects points that difference in character results in binocular rivalry. -Diplopia occurs when disparate elements are stimulated by one object. - Binocular single vision with stereopsis results when the horizontal disparity remains within the limits of Panum’s area.
- 41. Neurophysiology of binocular vision Optic chiasma. •First structure that contributes for BSV •Partial decussation at chiasm •serves to project to same place in visual cortex 2 neuronal pathways 1. Parvocellular 2. Magnocellular
- 42. Milestone of BSV Development 2 to 3 weeks – the infant turns his head to fixate an object. 4 to 5 weeks - infant can sustain monocular fixation of large near objects First 1 to 3 months -superimpose images. 3 months- binocular fusion. 3 to 6 months – stereopsis. Development of horopter & vergence is also influenced by dramatic changes in eyeball size & orbital position during
- 43. Abnormal binocular vision Confusion Diplopia Suppresion Eccentric fixation Abnormal retinal correspondence(ARC) Amblyopia
- 44. Anamolies of binocularity Confusion When squinting occurs the two foveas view two different objects that are physically separated in objective space, and send two different images to a single cortical perceptual area. This leads to confusion. Diplopia When squinting occurs an object in space is perceived by the fovea of one eye and some other extra-foveal point of the other eye, which has a different projection or localization value in space. Thus an object would be localized twice in space causing diplopia.
- 46. INVESTIGATIONS For retinal correspondence For supression 1.Red filter test 2.Worth FDT 3.Bagolinis striate glass test 4.After image testing
- 47. Red glass test
- 51. Stereopsis testing Stereo acuity is a quantitative measure of stereopsis, it represents the smallest horizontal retinal image disparity that give rise to a sensation of depth. Stereopsis is measured in seconds of arc. 1degree=60minutes of arc, 1minute=60seconds of arc. Normal stereoacuity= <60seconds of arc.
- 52. Tests for stereopsis Qualitative - Random dot stereograms - Synaptophore Quantitative -Titmus fly test -TNO test -Lang test
- 57. MACULAR BV EXTRAMACULAR BV BEGINS AT 2-3 MONTHS MATURE AT BIRTH IF DEPRIVED NEVER DEVELOPS WILL NOT DEPRIVE POOR VN AND NYSTAGMUS -- SEVERES FIXATION --- ONCE DEVELOPED REINFORCEMENT REQUIRE TILL 9 YRS AGE --- OTHERWISE AMBLYOPIA DEVELOPS --- CONES AND PARVOCELLULAR GANGLION CELLS RODS AND MAGNOCELLULAR ANGLION CELLS 14’ OF ARC OF STEREOPSIS 200’ ARC OF STEREOPSIS
- 58. BV MACULAR EXTRAMACULAR SIMULTANEOUS PERCEPTION NONE EXCELLENT FUSION EXCELLENT LIMITED STEREOPSIS EXCELLENT LIMITED SO THERE ARE NO ADAPTATIONS IF MACULAR BINOCULAR VISION IS IMPAIRED AND THERE WILL BE LIMITED FUSION AND STEREOPSIS IF EXTRAMACULAR BV IS IMPAIRED- SUPPRESSION AND ARC TAKES PLACE
- 59. SUMMARY BSV is not inborn,but develops in the first decade of life Abnormal visual experience results in poor or no BSV Reversible only if intervened in the plastic period of development A good understanding of mechanism of BSV is fundamental in successive treatment of its anamolies
- 60. THANK YOU
Editor's Notes
- #3: Ref parson