Binocular vision and stereopsis

1. Binocular Vision
and
Stereopsis
Dr Sameeksha Agrawal

2. Binocular Single Vision
• It 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

3. Requirement of binocular single vision
1. Clear visual axis
2. Sensory fusion – the ability of retino-cortical element to
function in association of each other so that two disssimilar
object from either eye is fused to single image
3. Motor fusion - the precise co-ordination of the two eyes in
all direction of gazes, so that corresponding retino-cortical
element are placed in a position

4. Advantages of Binocular Single Vision
• 1. Single vision with two separate eyes
• 2. Stereopsis – depth perception
• 3. Wide visual field
• 4. Compensation of blind spot

5. Sensory aspect of BSV
The objects in space are localized by us in two ways –
A. Relative localization - relative to one another
B. Egocentric localization - in relation to ourselves.

6. Definition –Retinal element
• It is a retino-cerebral apparatus engaged in elaborating a
sensation in response to excitation of a unit area of retinal
surface.
• The retinal area, when stimulated, identifies the
brightness, colour and form and also the direction of the
object in visual space.
• This direction is relative to the visual direction of the fovea

7. Visual axis
• It is an imaginary line which connects the object to its
image formed on retinal surface
• If the line connects to the fovea – Principal visual axis
• If the principal visual axis from two eyes bisect each other
at the object point – binocular fixation

9. Common subjective visual direction
• It consists of all object points that stimulates
simultaneously to corresponding retinal elements in two
eyes ; example two foveas
• The common subjective visual direction for fovea forms a
plane which coincides with the median plane of head

10. Retinal correspondence
• Retinal elements of the two eyes that share a common
subjective visual direction are called corresponding retinal
points.
• Rest are non corresponding points or disparate points
• Existence of corresponding retinal elements with their
common relative subjective visual direction is the essence
of binocular vision

11. Relative position of two object

12. Retinal correspondence
Two types –
• Normal retinal correspondence – two foveas have common
subjective visual direction
• Abnormal retinal correspondence – the fovea of one eye
shares subjective visual direction with extra foveal point.
• Phenomenon helps to have some stereopsis
• Normal foveal fixation taken over as soon as other eye is
closed.

13. Sensory fusion
• Sensory fusion is the cortical process of blending the
images from each eye into a single binocular stereoscopic
image
• The striate cortex has binocular cells which are stimulated
by corresponding retinal area in each eye
• In humans, approximately 70% of the cells in the striate
cortex are binocular cells

14. Motor fusion
• Motor fusion is the mechanism that allows fine-tuning of
eye position to maintain eye alignment
• The correctional eye movements that maintain binocular
foveal alignment provided by motor fusion are termed
fusional vergence movements
• Unlike sensory fusion, motor fusion is the exclusive
function of the extrafoveal retinal periphery.

15. Diplopia
• The simultaneous stimulation of non-corresponding or
disparate retinal elements by an object point causes this
point to be localized in two different subjective visual
directions

16. True vertical diplopia

17. Retinal rivalry
• Simultaneous excitation of corresponding retinal areas by
dissimilar objects leads to confusion
• Suppression of one image occurs to prevent confusion
• The constant foveal suppression of one eye with cessation
of rivalry leads to complete sensory dominance of the
other eye

18. CONFUSION

19. Suppression
• It is a neuro-physiological active inhibitory mechanism in
which when corresponding retinal areas are stimulated by
dissimilar stimuli or
• When non-corresponding retinal areas are stimulated by
similar stimuli

20. Horopter
• Psychophysical experiments indicate that the locus of
points, which project to corresponding retinal points of
each eye takes the shape of an ellipse
• This ellipsoid plane is called Horopter
• Objects located in front of or behind the empirical
horopter will project to noncorresponding retinal points

21. Panum’s fusional area
• The finite area in front of and behind the horopter line
where objects stimulate noncorresponding retinal points,
yet are still fusible into a single binocular image, is called
Panum’s fusional area

22. HOROPTER AND PANUM’S FUSIONAL AREA

23. Panum’s fusional area
• Stimulation of noncorresponding retinal points within
Panum’s fusional area will produce three-dimensional
vision.
• This ability for the brain to determine that images are
falling on retinal points that are not exactly corresponding
produces stereoscopic vision

25. • The fovea has high spatial resolution
• As we move to the peripheral fields, the receptive field size
enlarges and the spatial resolution decreases
• The retinal architecture of high central resolution versus
low peripheral resolution explains the excellent
stereoacuity from central fields and progressively poorer
stereoacuity from peripheral binocular retinal fields
Panum’s fusional area

26. Panum’s fusional area
• The object outside the Panum’s area produces disparate
images that can’t be fused
• This causes diplopia – physiological diplopia
• Object closer to the panum’s area produces crossed
diplopia and outside the panum’s area produces uncrossed
diplopia.

27. Stereopsis
• It is the ability to fuse images that stimulate horizontally
disparate retinal elements within Panum’s fusional area
resulting in binocular appreciation of visual object in
depth
• An object confined to the horopter is seen as flat
• The sensory fusion of these horizontally disparate unequal
retinal images results in a three dimensional percept

28. Stereopsis
• Interpupillary distance also influences stereoacuity.
• Farther apart the two eyes, the greater the angle of visual
disparity and the greater the stereoscopic potential
• Closer an object is to the eyes, the greater the angle of
disparity; therefore, the better the stereoscopic view

29. Grades of Binocular Vision
• Grade I - Simultaneous macular perception
• Grade II – fusion of the images
• Grade III – stereopsis ; it involves a perceptual synthesis at
higher level

30. Before any test is undertaken it is essential to
assess the :
• Visual acuity
• Fixation in the squinting eye
• Direction and size of deviation

31. Test for retinal correspondence
• Bagolini’s striated glass test
• Red filter test
• Synaptophore test
• Worth 4 dot test

33. Test for suppression
• 1. Worth's four dot test
• 2. Synaptophore
• 3. Friend test
• 4. Amsler Grid
• 5. 4 Δ prism base out test
• 6. Red filter test
• 7. Bagolini’s striated glasses

34. Stereoacuity testing
• Stereoscopic perception can be created from two-
dimensional figures by presenting each eye with similar
figures that are horizontally offset
• Bitemporal retinal stimulation within Panum’s fusional
area gives the stereoscopic perception of an image coming
toward the observer

35. Stereoacuity testing
• Stereoacuity can be quantified by measuring the amount
of image disparity
• Minimum stereoscopic resolution is a disparity of
approximately 30 to 40 s of arc.
• Stereoscopic resolution depends upon visual acuity, as
poor vision in one or both eyes will decrease stereoacuity.

36. Contour stereoacuity tests
• It uses stereoscopic figures with a continuous contoured
edge; example Titmus test
• Measures disparities from 3000s arc (the big fly) to 40 s arc
(ninth circle)
• They have the disadvantage of having monocular clues

38. There is a set of monocular or experimental clues that play an
important role in our estimation of relative distance of visual
objects
• Apparent size
• Interposition
• Shading
• Geometric perspective – physically parallel lines converge
toward a vanishing point at the horizon, e.g. railroad
tracks.
Mono ocular clues

39. • Relative velocity – the image velocity of a moving target in
the distance is lower than the image velocity of the same
moving target when it is nearby
• Motion parallax – translocation of the head cause the
images of near objects to move opposite the head and the
images of far objects to move with the head, assuming the
fixation point is at an intermediate distance

40. Monocular clues

41. Monocular clues
• Patients with monocular vision can identify which figure is
supposed to be stereoscopic, because that figure will be
horizontally off center.
• “Image jump” patients alternate fixation between the two
horizontally displaced figures and identify the figure that
jumps back and forth

42. Monocular clues

43. Monocular clue

44. Monocular clues
• The patient has true stereoacuity is to retest with the
Titmus test book turned 90°
• The monocular clues still work. If the patient again
identifies the stereoscopic target, they are using
monocular clues

45. Random dot stereograms
• It consist of two fields of randomly scattered dots or
specks, with one field of dots projected to each eye
separately through a haploscopic device
• Each field of random dots is identical except for a group of
dots that is displaced nasally
• Random dot tests have almost no monocular clues, and a
positive response indicates true stereopsis

47. Thank You