Binocular Single Vision

Binocular single vision (BSV) is the ability to use both eyes together to achieve a single fused percept, even in the presence of disparity of the image seen by each eye. It is divided into five grades: simultaneous perception, superimposition, sensory fusion, motor fusion, and stereopsis.
The current study aimed to examine the contribution that motor fusion and stereoacuity make to visuomotor task performance, while addressing some of these confounding factors. Individual differences in task performance and adaptation to BSV deficits were minimized using a repeated measures design, in which participants with normal BSV and no amblyopia or strabismus had their fine visuomotor task performance assessed as their BSV was progressively degraded.

2. Course: Strabismus
Course code: OD-130
MZ
Department of Optometry
KEMU

3. BSV
Learning Objectives
Students will learn about
•What is BSV
•Grades of BSV
•Mechanism of Binocular single vision
•Evaluating different grades of BSV

4. BSV
CONTENTS
•BSV & components of BSV
•Requirements for BSV
•Fixation disparity
•Horopter & Panum’s area
•References

5. Basics of Binocular Vision
.

6. Types of Vision
1.Monocular
Vision with single eye
2.Bi-ocular
no co-ordination between
two eyes
3.Binocular
Co-ordinated vision from
both eyes

7. Definition
Binocular vision may be
defined as the state of
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.

8. Pre-requisites fordevelopment 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

9. Cont,,,
•Corresponding retinal areas so that the eyes
are cyclopean
•Normal visual pathways
Mental Process:
•Ability of visual cortex to promote binocular
single vision

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

11. Mechanisms and terminologies in
BSV

12. VisualDirections
A visual directionis 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

14. 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

15. Contd.....
Rest other retinal points
–Noncorresponding /disparate
Significance:
–Corresponding retinal elements are principal
elements of the two retinas that give rise in
binocular vision
–Single vision is mainly because ofretinal
correspondence

16. 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

17. Contd....
Object points lying on
the horopter
-seen single
Object points off the
horopter
-Seen double

18. 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
another eye
Panums area-the retinal area surrounding the
corresponding retinal points within which BSV
can be maintained.

19. Cont,,,
Panums space: A narrow band around the
horopter within which objects gives rise to
BSV
So objectslocated slightly off the horopter
can remain single
•Object stimulates slightly non-
corresponding points

20. Size of Panum’s Fusional area
Increases with Retinal
Eccentricity-
–At fovea
•6-10’ of arc
–12
0
eccentricity
•30-40’ of arc

21. Physiological Diplopia
The Diplopia elicited by an object point off the
Panum’s fusional area
Types
A.Crossed (Heteronymous) Diplopia
Temporal (crossed) disparity
B.Uncrossed (homonymous) Diplopia
Nasal (uncrossed) Disparity

23. Fixation Disparity
It is theminute image displacement, rarely
exceeding several minutes of arc of angle,
occurswithin Panum’sspacewhile fusion is
maintained.
•Due to presence of pannum’sfusionalarea

24. Cont,,,
–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

25. Fixation disparity

26. Grades of Binocular Vision
There are three grades of binocular vision as given
by Worth'sclassification:
Grade I : Simultaneousperception
Grade II :Fusion
Grade III : Stereopsis

27. 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.

29. 2. Fusion
Defined as the cortical unification of visual objects
into a single percept thatis made possibleby the
simultaneous stimulation ofcorresponding retinal
areas.
In simple words,
It is the ability of the two eyes to produce a
composite picture from two similar pictures each of
whichis incomplete in one small detail

30. Cont,,,

31. Components of fusion
Sensory Fusion
unification of visual excitations from
correspondingretinal images into a single
visual percept,a single visual image
Ability to unify images falling on
corresponding retinal areas.

32. Cont,,,
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

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

34. 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

35. Cont,,,
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
Normal stereoacuity is considered to be
40 sec of arc

37. The difference
Corresponding
retinal elements are
stimulated
Motor system is
required
Fusion can occur
withoutstreopsis
Stereopsis
Non corresponding
retinalelements are
stimulated
Motor system is not
required
Without fusion it can
not occur
Fusion

38. References
•Clinical Orthopticsby FionaJ. Rowe
•Diagnosis & management of ocular motility
disorders
•Google

39. Learning Outcomes
Students have learnt
BSV & its grades
•Tests used for BSV