binocular single vision

binocular single vision

1. BINOCULAR SINGLE VISION Presented by: Dr. Shrey Maheshwari

2. DEFINITION Acc. to ROMANO & ROMANO State of simultaneous vision with two seeing eyes that occurs when an individual fixes his visual attention on an object of regard.

3. GRADES OF BINOCULAR VISION Simultaneous perception Fusion Stereopsis

4. SIMULTANEOUS PERCEPTION Does not imply that both eyes see same object. Does not imply superimposition of both objects . “Power to see 2 dissimilar objects simultaneously” Ceases only when we suppress the image from one eye at will.

5. FUSION 2 nd Grade of Binocular Vision Ability of the eyes to produce a composite picture from two similar pictures, each of which is incomplete in a small detail . It is not superimposition of dissimilar pictures

6. 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. Not similar to depth perception.

7. ADVANTAGES Optical defects in one eye are made less obvious by the normal image in the other eye Defective vision in one part of the visual field is masked because the same image falls on the functioning area of the other retina. Field of vision is definitely larger. Allow the individual to converge the line of sight and obtain a reading as to the absolute distance of objects. Presence of stereopsis.

8. PHYLOGENETIC BACKGROUND AND EVOLUTION Present only in higher animals. Frontally placed eyes Binocular co-ordination of eye movements Semidecussation of optic tract

9. PSYCHOPHYSICS AND SENSORY ASPECTS Visual direction and horopter Binocular fusion Dichoptic stimulation Stereopsis Depth perception Integration of motor and sensory systems

10. VISUAL DIRECTION AND HOROPTER Location of an object is its Physical space . The (objective) lines of direction determine which retinal area will be stimulated Localisation of an object is its Visual/ Subjective space . The (subjective) counterpart, the visual directions, determine the direction in which the object will be seen in visual space.

11. Discrepancies of Objective and Subjective Metrics Hering’s experiment. Kundt and Münsterberg experiment.

12. HERING’S EXPT. Demonstrated that objects that may be widely separated in physical space may have a common direction in subjective space. Anatomic distribution of retinal elements and physiological distributuion of spatial values do not coincide Demonstrated that spatial values of retinal receptors defer above and below horizontal midline

13. HERING’S EXPT.

14. KUNDT AND MÜNSTERBERG EXPERIMENT If one attempts to bisect a monocularly fixated line in an arrangement that excludes other visual clues from the field, a constant error is detected . If placed horizontally, the line segment imaged on the nasal side of the retina, that is, the one appearing in the temporal half of the field, is larger than the temporally imaged retinonasal line segment . In general, the discrepancies in the two eyes are symmetrical. They compensate each other, and the partition of a line into two equal segments is more nearly correct in binocular fixation.

15. VISUAL DIRECTIONS OCULOCENTRIC (MONOCULAR) EGOCENTRIC (BINOCULAR)

16. OCULOCENTRIC (MONOCULAR) When an object is viewed, its image falls on the foveola . The visual direction is represented by a line joining the two points, known as the principle visual line or axis Each point on retina can have its own visual axis Therefore, for a given eye position , objects having superimposed retinal images will be seen in a line but at different distances

17. EGOCENTRIC (BINOCULAR) Frame of reference is head (egocentric) not eyes. Visual space is seen with imaginary single eye (cyclopean eye) Herring’s law of identical visual direction – foveae have a common subjective visual direction .

18. CYCLOPEAN EYE

19. RETINAL CORRESPONDENCE Fovea determines the principle visual direction. Both fovea has same space value i.e. ‘ZERO’ Each receptor under monocular condition dictates visual direction in relation to fovea. Images falling on corresponding locations in each eye creates single mental impression. Acc. To BAGOLINI it’s area to area relationship not point to point relationship

20. HOROPTER I ntroduced in 1613 by Aguilonius Approached mathematically by Helmholt Means ‘Horizon of vision’ Locus of all object points that are imaged on corresponding retinal elements at a given fixation distance . Different horopter for each fixation distance

21. VIETH-MÜLLER CIRCLE T heoretical or mathematical horopter curve If corresponding points have a geometrically regular horizontal distance from the two retinas, the longitudinal horopter curve would be a circle passing through the center of rotation of the two eyes and the fixation point

22. EMPIRICAL HOROPTER CURVE Hering and his pupil Hillebrand could show that the Vieth -Müller circle does not describe the longitudinal horopter . E mpirical horopter curve is flatter than the Vieth- MÜller circle D istribution of the elements that correspond to each other is not the same in the nasal and temporal parts of the two retinas

23. HOROPTER CURVE

24. PHYSIOLOGIC DIPLOPIA A ll points on the horopter curve are seen singly D iplopia elicited by object points off the horopter is called physiologic diplopia.

25. PHYSIOLOGIC DIPLOPIA W hen fixating a distant object, a nearer object is seen in crossed (heteronymous) diplopia . When fixating a near object, a distant object is seen in uncrossed ( homonymous ) diplopia.

26. PHYSIOLOGIC DIPLOPIA CROSSED DIPLOPIA UNCROSSED DIPLOPIA

27. CLINICAL SIGNIFICANCE In diagnosing binocular cooperation In orthoptic treatment of comitant strabismus

28. BINOCULAR FUSION SENSORY FUSION MOTOR FUSION When images of an object fall on corresponding retinal points, they seem fused into a single mental impression The ability to align the eyes in such a fashion that sensory fusion can be maintained is Motor fusion. The stimulus for these fusional eye movements is retinal disparity. It is the exclusive function of the extra foveal retinal periphery

29. PANUM’S AREA Panum , the Danish physiologist, first reported this phenomenon. 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

30. PANUM’S AREA H orizontal extent of these areas is small at the center (6 to 10 minutes near the fovea) I ncreases toward the periphery (around 30 to 40 minutes at 12° from the fovea ) If the fixation distance is 20m, objects behind the horopter always appear single since the disparity of their images is always smaller than panum’s area.

31. PANUM’S AREA

32. FIXATION DISPARITY Ogle and coworkers coined this term. A physiologic variant of normal binocular vision exists when a minute image displacement, rarely exceeding several minutes of arc of angle, occurs within Panum’s area while fusion is maintained. May arise from small foveal scotoma or oculomotor imbalance used to measure the accommodative convergence–accommodation (AC/A) ratio

33. FIXATION DISPARITY

34. THEORIES OF BINOCULAR FUSION 4 Different Theories Synergy hypothesis of panum Local sign hypothesis of hering Eye movement hypothesis of helmholtz Suppression hypothesis of du tour and verhoff O B S O L E T E

35. PHYSIOLOGICAL BASIS OF FUSION 4 classes of neurons identified by HUBEL & WIESEL Binocular Corresponding Binocular Desperate Monocular Right Monocular left

36. PHYSIOLOGICAL BASIS OF FUSION

37. DICHOPTIC STIMULATION Different stimulation in two eyes when binocular stimuli fall on non-corresponding points of the two retinae. 5 classes of percepts are obtained :- Depth with fusion Depth with diplopia Diplopia without depth Binocular rivalry and suppression Binocular lustre

38. DIPLOPIA WITHOUT DEPTH Diplopia can be crossed or uncrossed Sensory adaptation to reduce diplopia :- Supression Amblyopia Abnormal Retinal Correspondence Motor adaptation to reduce diplopia : - Abnormal head posture EOM changes

39. RETINAL RIVALRY AND SUPPRESSION When dissimilar contours presented to corresponding retinal areas, does not fuse it’s k/a Retinal Rivalry ; eg . Uniform surfaces of different colour , unequal luminances of two targets Response – Suppression (innate involuntary process) whereby the signals coming from certain retinal elements are ignored in favor of those coming from another part 1 st line of defense in against pathological interruption; e.g. Marked refractive error in one eye, strabismus.

40. RETINAL RIVALRY AND SUPPRESSION

41. STEREOPSIS Wheatstone invented stereoscope in 1838 Visual appreciation of three dimensions during binocular vision, occurring through fusion of signals from disparate retinal elements. Vertical displacement produces no stereoscopic effect.

42. STEREOPSIS A solid object placed in the median plane of the head produces unequal images in the two eyes. The sensory fusion of the two unequal retinal images results in a three-dimensional percept . A stereoscopic effect can also be produced by two-dimensional pictures

43. STEREOPSIS

44. STEREOPSIS An object placed in front of fixation, but within panum’s fusional space will stimulate disparate retinal elements . Each image will be temporal to the point corresponding to location of image in the other eye. Although both images are fused, the perception has the added quality of nearness relative to the fixation point. Conversely an object behind the fixation point will cause nasal disparity and give the perception of farness.

45. STEREOPSIS Stereopsis is a unique cognition, a distinct perceptional quality . If one does not have it, one cannot learn it even in the presence of all requirements such as bifoveal fixation, fusion, and good visual acuity . It is all or none phenomenon Beyond 600mts there is no true stereopsis. At this distance monocular clues take over for the perception of depth.

46. PHYSIOLOGICAL BASIS OF STEREOPSIS Stereopsis a fucntion of spatial disparity Local and global stereopsis Fine v/s coarse stereopsis Stereopsis and fusion

47. DEPTH PERCEPTION Perception of distances from object from each other or from observer. It is independent of the appreciation of 3-D and depends on various factors: Stereopsis Non Stereoscopic Clue – Retinal Disparity Monocular./Non Stereoscopic Clues Accomodation And Convergence

48. Monocular./Non Stereoscopic Clues Parallactic movements Linear perspective Overlay of contours Distance from horizon Distribution of highlights & shadows Aerial perspective

49. 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

50. LINEAR PERSPECTIVE OVERLAY OF CONTOURS

51. DISTANCE FROM HORIZON DISTRIBUTION of HIGHLIGHTS AND SHADOWS

52. DEVELOPMENT OF BINOCULAR VISION Basic visual functions are innate and therefore present at birth. Their coordination, maturation and refinement take place during early postnatal period.

53. MILESTONES At birth : no bifoveal fixation. M onocular fixation is present at birth, but poor. 2-3wks : infant begins to make movements of regard, turning his eyes to fixate an object 4-5wks : can sustain monocular fixation of large near objects 6wks : fixation alternates rapidly b/w two eyes & child begins to fixate binocularly with conjugate pursuit movements which are saccadic initially but become smooth and gliding by 3-5mts of age. 3-6mts : conjugate movements and disjugate vergence movements. 1yr : fusional movements are firmly established. 2-3yrs : adult level of visual acuity is reached.

54. MATURATION OF BINOCULAR FUNCTION At birth- eyes act as 2 independent sense organs. Foveas are not formed until the 3rd month. By trial and error the child learns that, when the image of an object is brought on to the 2 foveae simultaneously, the image is most detailed. Hence visual axes are oriented in such a way that each fovea is directed at the object of regard.

55. NEUROPHYSIOLOGY OF DEVELOPMENT 2 different visual pathways from different population of retinal ganglion cells. Parvo and Magno cells- in lateral geniculate body. P cells- colour , fine 2 point discrimination (what) and project to the areas of fovea M cells- direction, motion, speed, flicker, gross binocular disparities(where). Project to the areas of Parafoveal and peripheral retina In striate cortex- p & m-recipient lamellae are segregated. M cells go predominantly to parieto -occipital areas, P cells to temporo -occipital areas. But there are inter-connecting pathways, so information overlaps.

56. BINOCULAR VISION TESTS Simultaneous perception Fusion Stereopsis Most useful instrument for the testing is the Synaptophore .

57. SIMULTANEOUS PERCEPTION

58. FUSION

59. TEST FOR STEREOPSIS SYNAPTOPHORE/STEREOSCOPE TEST VECTOGRAPH TEST - TITMUS STEREO TEST Fly test Animal test Circles test RANDOM DOT STEREOGRAM TEST RD ‘ E ’ test TNO RDT Lang test MOTOR TASK

60. FEATURES FOR STEREOPSIS TEST EYES MUST BE DISSOCIATED MUST BE PRESENTED WITH SEPERATE FIELD OF VIEW EACH FIELD MUST CONTAIN ELEMENTS IMAGED ON CORRESPONDING RETINAL AREAS

61. VECTOGRAPH TEST - TITMUS STEREO TEST It consists of Polaroid material on which the two targets are imprinted E ach target is polarized at 90 degree with respect to the other. Use of polaroid spectacles. It is a 3D Polaroid vectograph which is made up of two plates in a form of booklet . Advantages : simple and easy to perform. Disadvantages : unreliability in differentiating patients with amblyopia and heterotropia

62. FLY TEST USEFUL IN YOUNG CHILDREN TEST GROSS STEREOPSIS THRESHOLD 3000 SEC OF ARC

63. ANIMAL TEST It is performed if the gross stereopsis is present 3 rows of 5 animals One animal from each row is imaged disparately ( threshold of 10, 200 and 400 sec of arc respectively). In each row one of the animals correspondingly imaged in two eyes is printed heavily black which serves as a misleading clue. The subject is asked which one of the animals stands out. A subject without stereopsis will name the animal printed heavily while in the presence of stereopsis he will name the disparately imaged animal .

64. ANIMAL & FLY TEST

65. CIRCLE TEST Only one of the circles in each square is imaged disparately at random with threshold from 800 to 40 sec of arc. If the subject has passed other two tests, he is asked to push down the circle that stands out, beginning with the first set. Circle no. 5 (100sec of arc) is considered lowest limit of fine central stereoacuity & designated as the lowest limit of good stereoacuity .

66. RANDOM DOT TESTS RDT ‘ E ’ Test All three cards should be viewed with Polaroid glasses. Card A : bas relief model of the stereotest figure and is used to show the patient for what he should look. Card B : it contains the ‘ E ’ stereo figure with a random dot background. Card C : it is stereoblank with an identical random dot background.  Card b and c are held at distance of 50cm and pt is asked to indicate which card contains the letter ‘ E ’ . The stereoacuity when present can be quantitated by increasing the testing distance from the patient.

67. LANG TEST Random dot stereogram with panographic presentation. Seen through cylindrical lenses not polaroid glasses. Test card held at a distance of 40cms Disparity of car and star 600secs and cat 1200secs

68. LANG TEST

69. TNO RANDOM DOT TEST It is to provide retinal disparities ranging from 15 to 480 sec of arc. Advantage of testing quantitative responses without changing the testing distance. It consists of seven plates. Each plate consists of stereogram in which various shapes have been created by random dots in complementary colours . First 3 stereograms of the test booklet are used to establish the presence of gross stereopsis while remaining four to test fine stereopsis

70. MOTOR TESTS

71. TWO PENCIL TEST Popularised by Lang in 1975 Effective to test gross stereopsis Threshold value 3000-5000 sec of arc

72. TWO PENCIL TEST

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