This document discusses various aspects of binocular vision including: - Sensory fusion which unifies visual excitations from corresponding retinal images. Motor fusion aligns the eyes to maintain sensory fusion. - Stereopsis is the perception of depth from retinal disparity between images on the left and right retina. It requires non-corresponding retinal stimulation. - Abnormal binocular vision can cause confusion, diplopia, suppression, or abnormal retinal correspondence as adaptations. - Binocular vision adaptations include sensory mechanisms like suppression and abnormal retinal correspondence, and motor mechanisms like fusion, head posture, and the blind spot mechanism.

1. Simi Afroz
Assistant Professor (ADHOC)
Department of Optometry
School of Allied Health Sciences and Research
Sharda University

2. We ‘‘see’’with our brain, not with our retina, but the first step in
elaboration of information received by the eye takes place in the retina.
Without the retina, there is no vision.

3. Sensory aspect
• Relative localisation
• Egocentric localization
• Each eye has a straight a head localization centred to
fovea.This straight a head localisation from fovea is the
primary visual direction.
• Common visual direction
• Cyclopean eye
• Any object imaged on the two primary visual direction are
perceived as superimposed and as if in the same line
through in reality they are separated in space.

4. Common subjective relative visual
directions
• If the two principal lines of direction intersect at the fixation
point, it is said that there is binocular fixation.
• If only one principal line of direction goes through the
fixation point, fixation is monocular.
• All object points that simultaneously stimulatethe two
foveae appear in one and the same subjective visual
direction.
• This direction belongs to both the right and left foveae and
therefore is called the common subjective visual direction of
the foveae.

5. Corresponding points and disparate
points
• Corresponding retinal elements are those elements of the two retinas that give rise
in binocular vision to the localization of sensations in one and the same subjective
visual direction.
• The existence of corresponding retinal elements with their common relative
subjective visual directions is the essence of binocular vision.
• All other retinal points in the two eyes, which have a localization relative to its own
fovea , will also have to relate to the over lapping points of the other eye.These
are called corresponding points. All the other points are called disparate points.
• Image on the corresponding point are perceived as binocularly single and image
on the disparate point are perceived as binocularly double.

7. Horopter
• In modern usage it is defined as the locus of all object points that are imaged on
corresponding retinal elements at a given fixation distance.
• Vieth-Muller circle.VMC, empirical horopter; EH, objective frontoparallel plane;OFPP,
fixation point; F,inset, law of inscribed circles. Object P on EH is seen singly, but object PO
onVMC elicits double vision because of discrepancies between the empirical and
theoreticalhoropter.

8. Panum’s area of Binocular Fusion
• The statement has been made that
object points lying on the horopter
are seen singly, whereas points off
the horopter are seen double.
• Not only is single vision possible in
Panum’s area but visual objects are
seen stereoscopically, that is, in
depth.

9. Retino motor value
• 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, also called saccade, is extraordinarily precise.
• Corresponding impulses are then sent to the extraocular muscles to perform the
necessary ocular rotation, mediated and controlled in a manner discussed.
• This function of the retinal elements may becharacterized by saying that they have a
retinomotor value.
• This retinomotor value of the retinal elements increases from the center toward
the periphery.
• The retinomotor value of the fovea itself is zero.

10. Sensory fusion
• The unification of visual excitations from corresponding retinal images into a
single visual percept, a single visual image.
• For sensory fusion to occur, the images not only must be located on
corresponding retinal areas but also must be sufficiently similar in size,
brightness, and sharpness.

11. Motor fusion
• The term motor fusion refers to the ability to align the eyesin such a manner that
sensory fusion can be maintained.
• Unlike sensory fusion, which occurs between corresponding retinal elements
in the fovea and the retinal periphery, motorfusion is the exclusive function
of the extra foveal retinal periphery.
• No stimulus for motor fusion exists when the images ofa fixated
visual object fall on the fovea of eacheye.

12. Physiological diplopia
• Points which are not lying on the
horopter curve are imaged disparately
and, with certain qualifications, are seen
double.
• Physiologic diplopia, a fundamental
property of binocular vision.
• Physiologic diplopia can be readily
demonstrated to anyone with normal
binocular vision.
• Crossed (heteronymous) diplopia of the
object p, closer than the fixation point F,
imaged in temporal disparity.
• Uncrossed (homonymous) diplopia of
the object P, more distant than the
fixation point F and imaged in nasal
disparity.

14. Grades of Binocular Vision
There are three grades of binocular vision as given by
Worth's classification:
Grade I : Simultaneous perception
Grade II : Fusion
Grade III : Stereopsis

17. • The normal fusional range is 35/40 PD base out
and 16 PD base in on near reading.
• 16PD base out and 8PD base in on distance
testing.

18. Contd...........
– Retinal disparity (Fixation disparity) is the basis
of 3 D perception
– Stereopsis occurs when
• Retinal disparity is large enough to simple
fusion but small enough to cause diplopia

20. The difference
stereopsis
• Non corresponding retinal elements are
stimulated
• Motor system is not required
• Without fusion it can not occur
• Stereopsis occurs only with horizontal
disparity
fusion
• Corresponding retinal elements are
stimulated
• Motor system is required
• Fusion can occur without stereopsis
• Fusion occurs horizontal or vertical
corresponding retinal points
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21. Stereopsis
• Stereopsis is defined as the relative ordering of visual objects in depth, that is, in
the third dimension.This extraordinarily intriguing quality of the visual system
requires a rather detailed analysis.
• Stereopsis is a response to disparate stimulation of the retinal elements.

22. Monocular clues for depth perception
• Relative size
• Interposition
• Linear perspective
• Aerial perspective
• Distribution of lights & shadows.
• Motion parallax

23. Relative size

24. Interposition

25. Linear perspective

26. Aerial perspective

27. Distribution of lights & shadows.

28. Motion parallax

29. Advantage and disadvatages of
BSV

30. Advantage of having BSV
• Stereopsis
• Binocular summation.
vision shaper, clearer & more sensitive
• Larger field of view.
• Spare eye
• To over come blind spot scotoma
• visual field

31. Abnormal binocular vision
Confusion AND
Diplopia
Suppression
Eccentric fixation and
Abnormal retinal
correspondence(ARC)
Amblyopia

32. 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.

34. Binocular vision Adaptation
Sensory adaptation
• Suppression
• ARC
Motor adaptation
• Fusion
• Head posture
• Blind spot mechanism

35. Suppression
• Cortical mechanism of ignoring the image of one eye from cognisance.
• Suppression requires for its development:
• Constant Large angle deviation
• Usually occurs in early childhood
• Types of suppression
Facultative
• Only under
binocular condition
• VA is not reduced
under binocular
condition
Obligatory
• It effects under
monocular
condition also.
• Results in decrease
in visual acuity.

36. ARC ( anomalous retinal correspondence)
• Establishment of new working relationship between fovea of one eye and extra
foveal point of other eye.
• The attempt to regain the advantage if binocular vision in spite of having anomaly
(squint).
• In monocular condition fixation is retained by the fovea.
Harmonious ARC
• Subjective angle is zero
• Objective angle is equal
to squint.
Unharmonious ARC
• Angle of deviation has
not been fully accounted
for subjective or sensory
adjustment.
• More physiological test
are required example
Bagolini’s glasses.

37. Fusion
Ability of the two eye to check a tendency for squint.
As log as the fusion is strong squint remains latent ( hetrophoria).
It requires binocular input and covering one eye breaks fusion.
Fusional convergence is stronger than fusional divergence.
If taxed more than its tolerance than it give rise to asthenopia.

38. Head posture
• To tackle manifest squint which has variable deviation in different gazes.
• It is that position of head by assuming which the eyes are in a position of no
deviation or such a small deviation that can be fused.
• Components of head posture:
• Chin elevation or depression
• Face turn to right or left side
• Head tilt to right or left shoulder

39. Blind spot mechanism
• In esotropia of 15degree (25 to 30 prism diopter) the image of that eye falls on the
blind spot of the other eye so it does not cause diplopia.
• Described by Swan.