The document outlines a seminar on the physiology of binocular vision presented by Dr. Roby D. in October 2022, covering its definitions, development theories, and physiological mechanisms. It discusses various grades of binocular vision, the importance of alignment and reflexes, as well as obstacles to its development and different theories explaining binocular functions. Additionally, it explains the concepts of visual direction, retinal correspondence, stereopsis, and aspects of depth perception that arise from the simultaneous use of both eyes.

1. Seminar on Physiology of
Binocular Vision
By Dr. Roby D.
October 2022
10/18/2022 1

2. Content
• Objective
• Introduction
• Theories of binocular vision
• Grades of binocular vision
• Visual directions
• Retinal correspondence
• Horopter and Panum’s fusional area
10/18/2022 2

3. • Suppression
• Abnormalities of binocular vision
• Summary
• References
10/18/2022 3

4. Objective
At the end of this seminar we should be able to discuss:
• the definition of binocular vision and its development
• different theories of binocular vision
• the definition and physiology of each grade of binocular vision
• horopter and panum’s fusional area
• definition and types of suppression
• definition of retinomotor value, binocular rivalry
• the difference between diplopia and confusion
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5. Binocular vision
• is the ability to use both eyes simultaneously so that each eye
contributes to a common single perception
• the state of simultaneous vision, which is achieved by the coordinated
use of both eyes, so that separate and slightly dissimilar images arising
in each eye are appreciated as a single image by the process of fusion
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6. • highly coordinated organization of series of sensory and motor
processes that culminate in perception of singleness and stereoscopic
depth enabling the eye to attain single vision from 2 retinal images
• normal binocular single vision results due to the presence of bifoveal
fixation and normal retinal correspondence and vice versa
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7. BV depends on normal functioning of underlying vision processes
including:
• central fixation with normal visual acuity in each eye
• accurate oculomotor control to obtain bifoveal fixation
• normal inter-retinal correspondence of visual directions
• sensory mechanisms to produce haplopia (single vision)
• neural mechanisms to extract selective depth signals from objects that
are nearer or farther than the plane of fixation
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8. Origin and Development of Binocular Vision
Theory of empiricism:
• describes that binocular vision depends on ontogenetic development
• describes that humans are born without binocularity or spatial
orientation and these functions are acquired as a result of experiences
from everyday life
• acquisition of this function is aided by all other sensations especially
kinesthetic sense
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9. Theory of nativistic teaching:
• states that simultaneous perception and binocular vision occur as result
of innate process i.e anatomicophysiological arrangement of
components of visual system
• binocular vision is acquired phylogenetically and not ontogenetically
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10. Development of binocular vision
• during the initial few years of life certain normal anatomical and
physiological conditions are required for the development of binocular
vision
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11. Anatomical factors:
• the eyes are spruced up in the orbit in such a way that the visual axis
of both eyes is aligned
• this occurs as a result of multiple anatomical factors:
i. architecture/shape of the orbit
ii. ligaments, muscles and connective tissue
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12. Physiological factors:
• normal physiological binocular reflexes determine the development of
binocular vision
• these physiologic reflexes can be either innate or acquired as a result
of appropriate environmental stimulation
Fixation reflex
Refixation reflex
Accomodation convergence reflex
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13. Fixation reflexes
a. compensatory fixation reflex (gravitational reflex) - the function of
this reflex is to keep the eyes in a fixed position i.e. looking in the
required direction compensating for the movement of the body,
head, limbs etc
b. orientation fixation reflex -it can be demonstrated by the eye
following a moving object or panorama, thus exhibiting a
comparatively slow movement of continued fixation and not a rapid
jerk fixation
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14. The refixation reflex
• the aim of this reflex is to bring the eye back to the original orientation
point or to the new orientation point
Accomodation convergence reflex
• it is aimed at correctly aligning the eyes and keeping them focused on
the object. It includes vergence fixation reflex, accommodation reflex
and fusional vergence reflex
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15. Development of BV in infant
First 2–3 weeks: follows light uniocularly
6 weeks to 6 months: follows light binocularly
1-6 months: convergence reflex develops
6 months: accommodation develops
• the sensitive period of development of binocular vision in human
beings begins at about 4 months of age, peaks at 2 years, it is well
developed by 4 years of age and slowly stops by 9 years of age
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17. • any obstacle in the reflex pathway is likely to hamper the development
of binocular vision and the obstacles can be in the form of:
Sensory obstacles
• dioptric obstacles – e.g. media opacities, uncorrected r/e
• prolonged uniocular activity- e.g. severe ptosis, anisometropia
• retinoneural obstacles – lesions of retina, optic nerve
• proprioceptive obstacle
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18. Motor obstacles
• congenital craniofacial malformations
• conditions effecting extra-ocular muscles
• CNS lesions- involving the nerve trunks, root of nuclei
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19. • the presence of these obstacles gives rise to various sensory
adaptations to binocular dysfunction especially if the disruptive factor
is present in the sensitive period
• this can be in the form of:
 ARC
suppression
amblyopia
10/18/2022 19

20. Theories of Binocular Vision
• Correspondence and disparity theory
• Neurophysiological theory
• Alteration theory
• Projection theory
• Motor theory
• Theory of isomorphism
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21. Correspondence and disparity theory
• most widely accepted theory
• according to this theory sensory binocular cooperation is based on
system of correspondence and disparity
• it assumes the presence of one to one retinocortical relationship
between the two eyes
• simultaneous stimulation of the corresponding points by one object
transmits single visual impression with no depth quality
• simultaneous stimulation by two objects points that differ in character
results in binocular rivalry
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22. • diplopia occurs when disparate elements are stimulated by one object
point
• however, BSV with stereopsis results when the horizontal disparity
remains within the limits of panums area
10/18/2022 22

23. Neurophysiological theory
• approximately 80% of the neurons in the striate cortex can be
stimulated from either eye in response to a visual stimulus, assuming
there is a precise and orderly arrangement of connections along the
retino-geniculate striate pathway
• of these 75% represented graded response from either left or right eye
while 25% are binocularly driven cells and are equally stimulated from
each eye
• these 75% cells that could be driven by stimulation of either eye had
receptive fields of nearly equal size and in corresponding positions of
visual field
10/18/2022 23

24. • retinal field disparity is detected by sensitive binocular neurons giving
rise to binocular vision and stereopsis which occurs as a result of the
difference in direction or distance of the fields in each retina, forms the
basis of Panum’s fusion area
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25. Alteration theory
• states that sensory fusion is perceptual unification of images perceived
in corresponding location in the two retinae
• this theory fails to explain many phenomena of binocular vision
particularly stereopsis
10/18/2022 25

26. Projection theory
• according to this theory visual stimuli are exteriorized(projected to
physical space) along the lines of direction
• this is an obsolete theory
• the basic reason for the failure of the projection theory is that the
distinction between physical and subjective space is disregarded and it
fails to explain physiologic diplopia
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27. Motor theory
• this theory conceptualizes that spatial orientation is obtained from the
movement of the head, conjugate movements of the eye and
convergence
• the eyes are made aware of their movements by muscle sense
• it is this awareness that produces spatial localization
• the sensations arising from the convergence effort determine whether
one object is nearer or further away than the others
• this theory fails to explain many sensory aspects of the binocular
vision especially stereopsis
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28. Theory of isomorphism
• states that there exists a one to one relationship between the retina and
cortex and strict conformity or isomorphism between the distribution
of objects in space and cortical events forms the basis of spatial
orientation
• based on a rigid retinocortical relationship
• there is no evidence of physiological rigidity of the retinocortical
relationship or the convergence of the pathways on which this theory
is based
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29. Grades of Binocular Vision
• binocular single vision can be classified into three grades according to
Worth’s classification
1. Simultaneous perception and superimposition
2. Fusion
3. Stereoscopic vision
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30. 10/18/2022 30

31. Simultaneous perception and superimposition
• simultaneous perception: the ability of both eyes to perceive
simultaneously two images, one formed on each retina
• superimposition: simultaneous perception of the two images formed
on corresponding areas, with the projection of these images to the
same position in space
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32. Fusion
• is the cortical unification of 2 images of an object, 1 from each eye,
into a single percept
• for fusion of macular images (central fusion) to occur, there can be
very little dissimilarity between the images in each eye, because of the
small receptive fields in the area near the fovea; otherwise, diplopia
results
• more image dissimilarity is tolerated in the periphery (peripheral
fusion), where the receptive fields are larger
10/18/2022 32

33. Sensory fusion
• the hallmark of retinal correspondence
• defined as the ability of both eyes to perceive two similar images, one
formed on each retina, when interpreted as one single visual image
• the images not only must be located on corresponding retinal areas but
also should be sufficiently similar with respect to size, brightness and
sharpness (prerequisites for sensory fusion)
• a severe obstacle to fusion are unequal images
10/18/2022 33

34. Motor fusion
• is the ability to align both the eyes in such a way that sensory
fusion can be maintained
• unlike sensory fusion, motor fusion is a function of the extrafoveal
retinal periphery
• fusion, whether sensory or motor, is always a central process, i.e., it
takes place in the visual cortex
10/18/2022 34

35. Stereopsis
• is a binocular sensation of relative depth caused by horizontal disparity
of retinal images
• is the ability of both eyes to fuse images that lie within Panum’s
fusional area resulting in three dimensional perception of the object
• is the highest form of binocular cooperation and adds a unique quality
to vision
• 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
10/18/2022 35

36. Stereoscopic acuity
• the smallest relative binocular disparity that can generate a sensation
of depth
• can be defined as the disparity beyond which no stereoscopic effect
can be produced
• is the smallest binocular disparity that can be readily detected
• stereopsis cannot work beyond critical distance of 125-200 meters
10/18/2022 36

37. 10/18/2022 37
In tests for
stereopsis the angle
c is expressed in
seconds of arc

38. • the stereo-acuity threshold for static targets is 2-10 arc sec; for targets
in motion towards and away from the observer the threshold increases
to about 40 arc sec
• stereo-acuity is maximal about 0.25 degrees off dead center in the
foveola, and diminishes exponentially with increasing eccentricity
along the x-axis
• stereopsis is nil beyond 15 degrees eccentricity
• stereo-acuity diminishes in similar exponential fashion when the target
is moved in front or behind the horopter along the y-axis
10/18/2022 38

39. Monocular cue for depth perception
• the brain can achieve depth perception with a single eye through
simulated stereopsis and the use of monocular cue including
texture variations and gradients
 linear perspective
 monocular movement parallax
shade and shadows
relative size which enable the cortex to estimate the distance and
depth of the object
10/18/2022 39

40. Advantages of binocular vision
• stereopsis
• binocular summation- vision sharper, clearer and more sensitive
• larger field of view
• single vision
• any image distortion due to optical or pathological defects in one eye
can be masked by a normal image in the other eye
10/18/2022 40

41. Visual direction
• is a two dimensional localization of an object and it is represented by a
straight line which connects any given point on the retina to points in
the physical space
Principal visual direction/ visual axis
Oculocenteric visual direction
Egocentric visual direction
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42. Principal visual direction
• visual direction of an object that can be represented by a line that joins
the fovea and the object of the regard
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43. Oculocenteric visual direction
• when eye fixes an object through principal visual axis the other objects
around the fixation point focus around the fovea; those visual
directions are called oculocenteric visual direction
10/18/2022 43

44. Egocenteric localization
• when we see with one eye the direction of the object is judged in
relationship to the visual axis of that eye but when we see with both
eyes we localize the objects in the visual space in relation to an
imaginary eye centered between the two eyes, the cyclopean eye- this
is called egocentric localization
10/18/2022 44

45. 10/18/2022 45

46. Sensory binocular correspondence
• the retinal receptors and subsequent local retinal neurones responding
to the visual stimulus are known as a retinal element
• for most of each retina, every retinal element or ‘retinal point’ shares a
common relative subjective visual direction with an associated retinal
point in the other eye
• there are some peripheral retinal elements that never actually share a
common visual direction because they receive images from objects in
the monocular visual field of each eye
10/18/2022 46

47. • retinal elements of each eye that do have the same common subjective
visual directions are called corresponding retinal points
• for a given retinal element in one eye, all retinal elements in the other
eye except the corresponding retinal point are non corresponding
points
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48. 10/18/2022 48

49. Types of retinal correspondence
• Normal retinal correspondence is defined when fovea of one eye
corresponds to the fovea of the other eye and they both share a
common visual direction
• points located nasal to the fovea in one eye correspond to the points
located temporal to the fovea of the other eye
10/18/2022 49

50. • Anamolous retinal correspondence is a type of sensory adaptation in
which fovea of one eye shares a common visual direction with the
extra foveal point of the other eye
• this is an adaptation in manifest squint resulting in BSV
• it is known as anomalous because extra foveal point of one eye
corresponds to foveal point of the other eye
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51. Theories on anomalous retinal correspondence
• the 1st theory states that, with anomalous correspondence the two eyes
perceive space independently. Each eye computes egocentric visual
direction from its own sense of eye position and oculocentric retinal
image location. In effect, there is a lack of correspondence
• the 2nd theory proposes that there is a shift in retinal correspondence so
that retinal points that are normally disparate are shifted to acquire an
anomalous coupling in the striate cortex
• the 3rd theory proposes that strabismics who have no suppression are
able to perceive space singly due to enlarged Panum’s fusional areas
10/18/2022 51

52. Horopter
• derived from Greek words, horos-boundary, opter-observer
• is a curved line formed when all the corresponding points are
projected in space at a particular distance from the observer
• hence it is the locus of all points in the space that stimulates the
corresponding points of the retina leading to a BSV
• it can be plotted by joining the points of intersection of the lines drawn
from the corresponding points through the nodal points
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53. Geometric horopter (Vieth Muller
circle)
• it is a geometrically constructed
circle which passes through the
corresponding points of the two
eyes; but actually it is not
spherical, it is flatter
• is a theoretical horopter
10/18/2022 53

54. Empirical or longitudinal horopter
• when the horopter is determined experimentally, the locus of points
that are seen singly falls not on a circle but on a curve called the
empirical horopter
• is slightly flatter than vieth muller circle i.e. it has a greater radius of
curvature
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56. • the difference between the geometric and the empirical horopter is
known as the Hering-Hillebrand deviation
• if the horopter includes all points in space that stimulate corresponding
retinal points, double vision would be expected when the target does
not lie on the horopter
• however, the visual system can combine slightly disparate points
within a limited area surrounding the horopter, called Panum’s area of
single binocular vision
10/18/2022 56

57. Panum’s area
• the field infront of and behind the horopter in which the expected
diplopia does not occur
• objects within Panum’s area do not result in diplopia
• objects outside Panum’s area stimulate widely disparate retinal points,
resulting in physiologic diplopia
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58. 10/18/2022 58

59. Physiologic diplopia
• when an object is located closer than the horopter it is imaged
temporal to the fovea in each eye resulting in crossed
diplopia/heteronymous
• when an object is located beyond the horopter it is imaged nasal to the
fovea in each eye resulting in uncrossed diplopia/homonymous
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61. Binocular disparity
• images of a single object that do not stimulate corresponding retinal
points in both eyes are said to be disparate; binocular disparity is
defined as the difference in position of corresponding points between
images in the two eyes
• the horizontal component of binocular disparity is the unique stimulus
for stereoscopic depth perception and is quantified by the difference in
the longitudinal visual angles, also called horizontal disparity angles
10/18/2022 61

62. Suppression
• is the alteration of visual sensation that occurs when an eye’s retinal
image is inhibited or prevented from reaching consciousness during
binocular visual activity
• physiologic suppression is the mechanism that prevents physiologic
diplopia (diplopia elicited by objects outside Panum’s area) from
reaching consciousness
• pathologic suppression may develop because of strabismic
misalignment of the visual axes or other conditions resulting in
discordant images in each eye, such as cataract or anisometropia
10/18/2022 62

63. • if a patient with strabismus and normal retinal correspondence (NRC)
does not have diplopia, suppression is present, provided the sensory
pathways are intact
• classification of suppression
central versus peripheral
nonalternating versus alternating
facultative versus constant
10/18/2022 63

64. Central suppression
• is the mechanism that keeps the foveal image of the deviating eye
from reaching consciousness, thereby preventing visual confusion
Peripheral suppression
• eliminates diplopia by preventing awareness of the image that falls on
the peripheral retina in the deviating eye, which corresponds to the
image falling on the fovea of the fixating eye
10/18/2022 64

65. Non-alternating suppression
• if suppression always causes the image from the dominant eye to be
predominant over the image from the deviating eye
• this may lead to amblyopia
Alternating suppression
• if the process switches between the 2 eyes
10/18/2022 65

66. Facultative suppression
• if the suppression is present only when the eyes are deviated and is
absent in all other states. Patients with intermittent exotropia, for
instance, often experience suppression when the eyes are divergent but
may experience high-grade stereopsis when the eyes are straight
Constant suppression
• denotes suppression that is always present, whether the eyes are
deviated or aligned. The suppression scotoma in the deviating eye may
be either relative (permitting some visual sensation) or absolute
(permitting no perception of light)
10/18/2022 66

67. Retinomotor values
• the appearance of an object in the periphery of the visual field attracts
attention, and the eye is turned toward the object so that it may be
imaged on the fovea
• the resulting eye movement is called a saccade and is extraordinarily
precise
• it is initiated by a signal from the retinal periphery that transmits to the
brain the visual direction, relative to the foveal visual direction, where
the peripherally seen object has appeared
10/18/2022 67

68. • corresponding impulses are then sent to the extraocular muscles to
perform the necessary ocular rotation
• this function of the retinal elements may be characterized by saying
that they have a retinomotor value
• retinomotor value of the retinal elements increases from the center
toward the periphery
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69. • the retinomotor value of the fovea itself is zero: once an image is on
the fovea, there is no incentive for ocular rotation.
• the fovea, then, in addition to its other functions, is also the
retinomotor center or retinomotor zero point
10/18/2022 69

70. Retinal rivalry/ Binocular rivalry
• when dissimilar contours are presented to corresponding retinal areas
fusion becomes impossible since two dissimilar objects localized in
the same place give rise to conflict and confusion
• the conflict which results when contradictory and incompatible signals
are transmitted from corresponding points to the visual cortex is
termed retinal rivalry
• the visual system responds to retinal rivalry by suppression
10/18/2022 70

71. Abnormalities of Binocular Vision
• when a manifest deviation of the eyes occurs, the corresponding
retinal elements of the eyes are no longer directed at the same object
• this places the patient at risk for 2 distinct visual phenomena: visual
confusion and diplopia
10/18/2022 71

72. Visual Confusion
• is the perception of a common visual direction for 2 separate objects
• the 2 foveal areas are physiologically incapable of simultaneous
perception of dissimilar objects
• the closest foveal equivalent is retinal rivalry, wherein there is rapid
alternation of the 2 perceived images
• clinically significant visual confusion is rare
10/18/2022 72

73. Diplopia
• usually results from an acquired misalignment of the visual axes that
causes an image to fall simultaneously on the fovea of one eye and on
a nonfoveal point in the other eye
• the same object is perceived as having 2 locations in subjective space,
and the foveal image is always clearer than the nonfoveal image of the
nonfixating eye
10/18/2022 73

74. • the loss of normal binocular fusion in an individual unable to suppress
disparate retinal images results in intractable diplopia, referred to as
central fusion disruption (horror fusionis)
• this condition is typically seen in adults or visually mature children
and can occur in a number of clinical settings, including prolonged
visual deprivation due to monocular occlusion or a mature cataract,
traumatic brain injury, or long-standing strabismus
• management is challenging
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75. 10/18/2022 75

76. Summary
• binocular vision is the ability to use both eyes simultaneously to bring
about single perception
• there is continued development of visual system during the initial few
years of life
• correspondence and disparity theory is the most accepted theory of BV
• there are 3 grades of BV
• retinal correspondence can be NRC and ARC
• horopter is a curved line formed with locus of all points in the space
that stimulates the corresponding points of the retina leading to a BSV
and the field in front and behind it is called panum’s area
10/18/2022 76

77. • suppression occurs when an eye’s retinal image is inhibited or
prevented from reaching consciousness during binocular visual
activity
• physiologic Vs pathologic diplopia
• confusion Vs diplopia
10/18/2022 77

78. References
• Adler’s physiology of the eye, 11th edition
• BCSC 2020-2021, Section 6: Pediatric ophthalmology and Strabismus
• Duane’s Ophthalmology 2012 edition
• Normal Binocular Vision Theory, Investigation and Practical Aspects,
Pdf
• Binocular Vision and Ocular Motility, Pdf
• Binocular Functions, Pdf
• Binocular Vision , Rahul Bhola, MD
• Different online videos
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