Understanding the basics of binocular vision

1. Basics of Binocular Vision
An approach to understand the complexity
Indra P Sharma
Optometrist

2. Objective
1.To understand the basic concept and terminologies used in
binocular vision
2. To understand the physiology of binocular vision.

3. Contents
1. Why to study binocular vision?
2. Historical perspective
3. Introduction to vision
4. Binocular vision
5. Mechanisms and terminologies in BSV
6.Grades of Binocular vision
7.Clues for monocular depth perception
8.Advantages and disadvantages of BSV
9.Conclusion
10.Glossary
11.Reference

4. 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.

5. Historical Perspective
Most of the concepts and terms used today were introduced
since the 19th century.
1. Johannes 2. Hermann 3. Ewald Hering
Mu¨ller von Helmholtz
Considered among the fathers of modern visual Physiology.

6. Vision
Vision:
Anatomic, physiologic, biophysical, & biochemical
arrangements & mechanisms within the retina give rise to
excitations that goes to our brain & ultimately result in vision.
Eye is a biological camera
We see from the brain ,not from the retina.

7. 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

8. Binocular Vision

9. Defination
Binocular vision may be defined
as the state simultaneous vision
with two seeing eyes that occurs
when an individual fixes his
visual attention on an object of
regard
The coordinated use of the
two eyes to produce a single
mental impression.

10. 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

11. 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.
6 month- 60 arc sec.
Development of horopter & vergence is also influenced by
dramatic changes in eyeball size & orbital position during
infancy.

12. 1. Theory of correspondence and disparity
(most widely accepted theory)
2. Neurophysiological basis
4. Alternation theory of Binocular Vision
5. Projection theory of Binocular Vision
6. Motor theory
7. Theory of isomorphism
Theories of BSV
Older theories

13. 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.

14. Neurophysiology of binocular
vision
Optic chiasm.
•First structure that
contributes for BSV
•Partial decussation at chiasm
•serves to project to same
place in visual cortex

15. Mechanisms and terminologies in
BSV

16. Visual Directions
A visual direction is defined as a line that connects an object
point with its image on the retina.
Types
Principal
Fovea – area of highest VA
-carries principal visual
direction.
Secondary
Other retinal elements-
secondary VD

17. Corresponding retinal Points
Retinal elements of two eyes that
share a common subjective visual
direction
– Example
• Fovea of two eyes
• Temporal retinal points of a eye –
Nasal retinal points of the fellow
eye & vice versa

18. Contd.....
Rest other retinal points
– Non corresponding /disparate
Significance:
– Corresponding retinal elements are principal
elements of the two retinas that give rise in
binocular vision
– Single vision is the hallmark of retinal
correspondence

19. Horopter
1613 Aguilonius
Horopter is defined as the
locus of all object points that
are imaged on corresponding
retinal elements at a given
fixing distance.
Horizon of vision

20. Contd....
Object points lying on the
horopter
- seen single
Object points off the horopter
- Seen double
Feature
2 Dimensional plane
Shape
Fronto-parallel plane :
Longitudinal curve

21. Theoretical horopter curve
Veith-Muller Circle
If corresponding retinal
points have a regular
horizontal distance from
the fovea of each eye
Shape of Horopter
-Circle passing through the
centre of rotation of two
eyes and the fixation
point

22. Empirical Horopter Curve
Hering and Hillebrand - showed Vieth-Mu¨ller circle does not
describe the longitudinal horopter.
Empirical horpter :
- Flatter than thoeritical horopter
- Distribution of the corresponding retinal elements are not the
same in the nasal & temporal parts of retinas
- Shape varies from person to person

23. Hering-Hillebrand Horopter deviation
The discrepancy (difference) between theoretical horopter
and the empirical horopter .
- Can be attributed to disturbing optical properties of the
ocular media.

24. Panum’s fusional area & space
In reality a retinal point of a eye is not only
corresponding to a point but to a retinal area of other eye
Panums area- the retinal area surrounding the
corresponding retinal points within which BSV can be
maintained.
Panums space: A narrow band around the horopter
within which objects gives rise to BSV
So objects located slightly off the horopter can remain
single
• Object stimulates slightly non-corresponding points

25. Size of Panum’s Fusional area
Increases with
Retinal Eccentricity-
– At fovea
• 6-10’ of arc
– 120
eccentricity
• 30-40’ of arc

26. 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

27. 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

28. Fixation disparity

29. Grades of Binocular Vision

30. 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

31. 1.Simultaneous Macular Perception
 Simultaneous perception exists when signals transmitted from
the two eyes to the visual cortex are perceived at the same time.
 It consists of the ability to see two dissimilar objects
simultaneously.

33. 2. Fusion
Defined as the cortical unification of visual objects into a single
percept that is made possible by the simultaneous
stimulation of corresponding retinal areas.
In simple words,
It is the ability of the two eyes to produce a composite picture
from two similar pictures each of which is incomplete in one
small detail

35. Components of fusion
Sensory Fusion
-the unification of visual excitations from corresponding retinal images into a
single visual percept, a single visual image
-The ability to unify images falling on corresponding retinal areas.
Motor Fusion
- It is a vergence movement that causes similar retinal images to fall and be
maintained on corresponding retinal areas.
• Ability to align the eyes in such a manner that sensory fusion can be
maintained
• Diplopia preventing mechanism

36. • 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.
Source: Rowe Fiona. Clinical Orthoptics 2nd Ed, Blackwell Publishing,2004 2: 23

37. 3. 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 i.e. in 3D

38. 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

40. Contd....
 Stereopsis & depth perception are not
synonymous.
 Not a form of simple fusion.
• Normal stereoacuity is considered to be
40 sec of arc

41. The difference
Fusion
 Corresponding retinal
elements are stimulated
 Motor system is required
 Fusion can occur without
streopsis
 Fusion occurs horizontal or
vertical corresponding retinal
points
Stereopsis
 Non corresponding retinal
elements are stimulated
 Motor system is not
required
 Without fusion it can not
occur
 Stereopsis occurs only
with horizontal disparity

42. Monocular clues for depth
perception

43. • Relative size
• Interposition
• Linear perspective
• Aerial perspective
• Distribution of lights & shadows.
• Motion parallax

44. Relative size

45. Interposition

46. Linear perspective

47. Aerial perspective

48. Distribution of lights & shadows.

49. Motion parallax

50. Advantage and disadvatages of
BSV

51. Advantage of having BSV
• Stereopsis
• Binocular summation.
– vision shaper, clearer &
more sensitive
• Larger field of view.
• Spare eye
visual field

52. Abnormal binocular vision
Confusion
Diplopia
Suppresion
Eccentric fixation
Abnormal retinal correspondence(ARC)
Amblyopia

53. 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.

55. Conclusion
• Without the basic concepts of BSV it is
almost impossible to understand strabismus
and treat it.
• The advantage of BSV outweights the
disadvantage.
• BSV – Every optometrist must know

56. Glossary
 BSV : binocular single vision
 EH: Emperical horopter
 F: Fovea
 LE: left eye
 PD: prism dioptre
 RE: right eye
 VMC : Veith-Muller Circle

57. Reference
Books
1. Gunter K. von Noorden: Binocular Vision and Ocular Motility, Theory and
Management of strabismus, Sixth ed ,2.
2. Kenneth Wright.W: Pediatric Ophthalmology and Strabismus, ed 95: 11:163.
3. Rowe Fiona. Clinical Orthoptics 2nd Ed, Blackwell Publishing,2004 2: 23
4. Khurana A. K.: Theory and Practise of Squint and Orthoptics; first ed .4:61-
89.
Websites
1.webeye.ophth.uiowa.edu/eyeforum/tutorials/BINOCULAR-VISION.pdf
2. www.authorstream.com/Presentation/admounion-1133268-binocular-visi...
3. www.google.com