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S
BINOCULAR SINGLE
VISION
Presented by: Dr. Shrey Maheshwari
DEFINITION
Acc. to ROMANO & ROMANO
State of simultaneous vision with two seeing eyes
that occurs when an individual fixes his visual
attention on an object of regard.
GRADES OF BINOCULAR
VISION
1. Simultaneous perception
2. Fusion
3. Stereopsis
SIMULTANEOUS
PERCEPTION
S Does not imply that both eyes see same object.
S Does not imply superimposition of both objects.
“Power to see 2 dissimilar objects simultaneously”
Ceases only when we suppress the image from
one eye at will.
FUSION
S 2nd Grade of Binocular Vision
S Ability of the eyes to produce a composite picture from two similar pictures, each of which is incomplete in a small detail.
S It is not superimposition of dissimilar pictures
STEREOPSIS
S 3rd Grade of Binocular Vision
S Visual appreciation of three dimensions
S Ability to obtain impression of depth by superimposition of two images of the same object, seen from 2 slightly different angle.
Not similar to depth perception.
ADVANTAGES
1. Optical defects in one eye are made less obvious by the normal image in the other eye
2. Defective vision in one part of the visual field is masked because the same image falls on the functioning area of the other retina.
3. Field of vision is definitely larger.
4. Allow the individual to converge the line of sight and obtain a reading as to the absolute distance of objects.
5. Presence of stereopsis.
PHYLOGENETIC
BACKGROUND AND
EVOLUTION
Present only in higher animals.
Frontally placed eyes
Binocular co-ordination of eye movements
Semidecussation of optic tract
PSYCHOPHYSICS AND
SENSORY ASPECTS
1. Visual direction and horopter
2. Binocular fusion
3. Dichoptic stimulation
4. Stereopsis
5. Depth perception
6. Integration of motor and sensory systems
VISUAL DIRECTION AND
HOROPTER
S Location of an object is its Physical space.
The (objective) lines of direction determine which retinal area will be
stimulated
S Localisation of an object is its Visual/ Subjective
space.
The (subjective) counterpart, the visual directions, determine thedirection in
which the object will be seen in visual space.
Discrepancies of Objective
and Subjective Metrics
S Hering’s experiment.
S Kundt and Münsterberg experiment.
HERING’S EXPT.
Demonstrated that objects that may be widely separated in physical space may have a common direction in subjective space.
Anatomic distribution of retinal elements and physiological distributuion of spatial values do not coincide
Demonstrated that spatial values of retinal receptors defer above and below horizontal midline
HERING’S EXPT.
KUNDT AND
MÜNSTERBERG
EXPERIMENT
S If one attempts to bisect a monocularly fixated line in an arrangement that excludes other visual clues from the field, a constant error is detected.
S If placed horizontally, the line segment imaged on the nasal side of the retina, that is, the one appearing in the temporal half of the field, is larger than the temporally imaged retinonasal line segment.
S In general, the discrepancies in the two eyes are symmetrical. They compensate each other, and the partition of a line into two equal segments is more nearly correct in binocular fixation.
VISUAL DIRECTIONS
S OCULOCENTRIC (MONOCULAR)
S EGOCENTRIC (BINOCULAR)
OCULOCENTRIC
(MONOCULAR)
S When an object is viewed, its image falls on the foveola. The visual direction is represented by a line joining the two points, known as the principle visual line or axis
S Each point on retina can have its own visual axis
S Therefore, for a given eye position , objects having superimposed retinal images will be seen in a line but at different distances
EGOCENTRIC
(BINOCULAR)
S Frame of reference is head (egocentric) not eyes.
S Visual space is seen with imaginary single eye(cyclopean
eye)
S Herring’s law of identical visual direction – foveae have a
common subjective visual direction.
CYCLOPEAN EYE
RETINAL
CORRESPONDENCE
S Fovea determines the principle visual direction.
S Both fovea has same space value i.e. ‘ZERO’
S Each receptor under monocular condition dictates visual direction in relation to fovea.
S Images falling on corresponding locations in each eye creates single mental impression.
S Acc. To BAGOLINI it’s area to area relationship not point to point relationship
HOROPTER
Introduced in 1613 by Aguilonius
Approached mathematically by Helmholt
Means ‘Horizon of vision’
Locus of all object points that are imaged on
corresponding retinal elements at a given fixation
distance.
Different horopter for each fixation distance
VIETH-MÜLLER
CIRCLE
o Theoretical or mathematical horopter curve
o If corresponding points have a geometrically regular
horizontal distance from the two retinas, the longitudinal
horopter curve would be a circle passing through the
center of rotation of the two eyes and the fixation point
EMPIRICAL HOROPTER
CURVE
• Hering and his pupil Hillebrand could show that the Vieth-Müller
circle does not describe the longitudinal horopter.
• Empirical horopter curve is flatter than the Vieth-MÜller circle
• Distribution of the elements that correspond to each other is not
the same in the nasal and temporal parts of the two retinas
HOROPTER CURVE
PHYSIOLOGIC
DIPLOPIA
All points on the horopter curve are seen singly
Diplopia elicited by object points off the horopter is called
physiologic diplopia.
PHYSIOLOGIC
DIPLOPIA
S When fixating a distant object, a nearer object is seen in
crossed (heteronymous) diplopia.
S When fixating a near object, a distant object is seen
in uncrossed (homonymous) diplopia.
PHYSIOLOGIC
DIPLOPIA
CROSSED DIPLOPIA UNCROSSED DIPLOPIA
CLINICAL SIGNIFICANCE
In diagnosing binocular cooperation
In orthoptic treatment of comitant strabismus
BINOCULAR
FUSION
SENSORY FUSION
MOTOR FUSION
When images of an object fall on corresponding retinal
points, they seem fused into a single mental impression
• The ability to align the eyes in such a fashion that sensory fusion
can be maintained is Motor fusion.
• The stimulus for these fusional eye movements is retinal
disparity.
• It is the exclusive function of the extra foveal retinal periphery
PANUM’S AREA
Panum, the Danish physiologist, first reported this
phenomenon.
Region in front and back of the horopter in which single
vision is present is known as Panum’s area of single
binocular vision or Panum’s fusional area
PANUM’S AREA
• Horizontal extent of these areas is small at the
center (6 to 10 minutes near the fovea)
• Increases toward the periphery (around 30 to 40
minutes at 12° from the fovea)
• If the fixation distance is 20m, objects behind the
horopter always appear single since the
disparity of their images is always smaller than
panum’s area.
PANUM’S AREA
FIXATION DISPARITY
Ogle and coworkers coined this term.
A physiologic variant of normal binocular vision exists when a
minute image displacement, rarely exceeding several minutes
of arc of angle, occurs within Panum’s area while fusion is
maintained.
May arise from small foveal scotoma or oculomotor imbalance
used to measure the accommodative convergence–
accommodation (AC/A) ratio
FIXATION DISPARITY
THEORIES OF BINOCULAR
FUSION
4 Different Theories
1. Synergy hypothesis of panum
2. Local sign hypothesis of hering
3. Eye movement hypothesis of helmholtz
4. Suppression hypothesis of du tour and verhoff
O
B
S
O
L
E
T
E
PHYSIOLOGICAL BASIS
OF FUSION
4 classes of neurons identified by HUBEL & WIESEL
① Binocular Corresponding
② Binocular Desperate
③ Monocular Right
④ Monocular left
PHYSIOLOGICAL BASIS OF
FUSION
DICHOPTIC
STIMULATION
Different stimulation in two eyes when binocular stimuli fall on non-corresponding points of the two retinae. 5 classes of percepts are obtained :-
a) Depth with fusion
b) Depth with diplopia
c) Diplopia without depth
d) Binocular rivalry and suppression
e) Binocular lustre
DIPLOPIA WITHOUT DEPTH
S Diplopia can be crossed or uncrossed
S Sensory adaptation to reduce diplopia :-
a. Supression
b. Amblyopia
c. Abnormal Retinal Correspondence
Motor adaptation to reduce diplopia :-
a. Abnormal head posture
b. EOM changes
RETINAL RIVALRY AND
SUPPRESSION
S When dissimilar contours presented to corresponding retinal areas,
does not fuse it’s k/a Retinal Rivalry; eg. Uniform surfaces of different colour,
unequal luminances of two targets
S Response – Suppression (innate involuntary process) whereby the signals
coming from certain retinal elements are ignored in favor of those
coming from another part
S 1st line of defense in against pathological interruption; e.g. Marked
refractive error in one eye, strabismus.
RETINAL RIVALRY AND
SUPPRESSION
STEREOPSIS
S Wheatstone invented stereoscope in 1838
S Visual appreciation of three dimensions during binocular
vision, occurring through fusion of signals from disparate
retinal elements.
S Vertical displacement produces no stereoscopic effect.
STEREOPSIS
S A solid object placed in the median plane of the head
produces unequal images in the two eyes.
S The sensory fusion of the two unequal retinal images
results in a three-dimensional percept.
S A stereoscopic effect can also be produced by two-
dimensional pictures
STEREOPSIS
STEREOPSIS
o An object placed in front of fixation, but within panum’sfusional space will stimulate disparate retinal elements.
o Each image will be temporal to the point corresponding to location of image in the other eye.
o Although both images are fused, the perception has the added quality of nearness relative to the fixation point.
o Conversely an object behind the fixation point will cause nasal disparity and give the perception of farness.
STEREOPSIS
Stereopsis is a unique cognition, a distinct perceptional quality.
If one does not have it, one cannot learn it even in the presence of all requirements such as bifoveal fixation, fusion, and good visual acuity.
It is all or none phenomenon
Beyond 600mts there is no true stereopsis. At this distance monocular clues take over for the perception of depth.
PHYSIOLOGICAL BASIS OF
STEREOPSIS
o Stereopsis a fucntion of spatial disparity
o Local and global stereopsis
o Fine v/s coarse stereopsis
o Stereopsis and fusion
DEPTH PERCEPTION
• Perception of distances from object from each other or from observer.
• It is independent of the appreciation of 3-D and depends on various factors:
Stereopsis
Non Stereoscopic Clue – Retinal Disparity
Monocular./Non Stereoscopic Clues
Accomodation And Convergence
Monocular./Non
Stereoscopic Clues
a) Parallactic movements
b) Linear perspective
c) Overlay of contours
d) Distance from horizon
e) Distribution of highlights & shadows
f) Aerial perspective
PARALLACTIC
MOVEMENTS
Most important in depth perception next to stereopsis
Slight shift of head while fixation is maintained results in
change of relative position of objects in gaze
Objects beyond fixation point – move in same direction
Objects closer – move in opposite direction
LINEAR PERSPECTIVE OVERLAY OF CONTOURS
DISTANCE FROM HORIZON DISTRIBUTION of HIGHLIGHTS AND SHADOWS
DEVELOPMENT OF
BINOCULAR VISION
S Basic visual functions are innate and therefore
present at birth.
S Their coordination, maturation and refinement
take place during early postnatal period.
MILESTONES
At birth : no bifoveal fixation.
Monocular fixation is present at birth, but poor.
2-3wks : infant begins to make movements of regard, turning his eyes to fixate an object
4-5wks : can sustain monocular fixation of large near objects
6wks : fixation alternates rapidly b/w two eyes & child begins to fixate binocularly with conjugate pursuit movements which are saccadic initially but become smooth and gliding by 3-5mts of age.
3-6mts : conjugate movements and disjugate vergence movements.
1yr : fusional movements are firmly established.
2-3yrs : adult level of visual acuity is reached.
MATURATION OF
BINOCULAR FUNCTION
At birth- eyes act as 2 independent sense organs.
Foveas are not formed until the 3rd month.
By trial and error the child learns that, when the
image of an object is brought on to the 2 foveae
simultaneously, the image is most detailed.
Hence visual axes are oriented in such a way that
each fovea is directed at the object of regard.
NEUROPHYSIOLOGY OF
DEVELOPMENT
2 different visual pathways from different population of retinal ganglion cells.
Parvo and Magno cells- in lateral geniculate body.
P cells- colour, fine 2 point discrimination (what) and project to the areas of fovea
M cells- direction, motion, speed, flicker, gross binocular disparities(where). Project to the areas of Parafoveal and peripheral retina
In striate cortex- p & m-recipient lamellae are segregated. M cells go predominantly to parieto-occipital areas, P cells to temporo-occipital areas. But there are inter-connecting pathways, so information overlaps.
BINOCULAR VISION TESTS
1. Simultaneous perception
2. Fusion
3. Stereopsis
Most useful instrument for the testing is the
Synaptophore.
SIMULTANEOUS PERCEPTION
FUSION
TEST FOR
STEREOPSISa) SYNAPTOPHORE/STEREOSCOPE TEST
b) VECTOGRAPH TEST - TITMUS STEREO TEST
Fly test
Animal test
Circles test
c) RANDOM DOT STEREOGRAM TEST
RD ‘E’ test
TNO RDT
Lang test
d) MOTOR TASK
FEATURES FOR STEREOPSIS
TEST
S EYES MUST BE DISSOCIATED
S MUST BE PRESENTED WITH SEPERATE FIELD OF
VIEW
S EACH FIELD MUST CONTAIN ELEMENTS IMAGED ON
CORRESPONDING RETINAL AREAS
VECTOGRAPH TEST -
TITMUS STEREO TEST
It consists of Polaroid material on which the two targets are imprinted
Each target is polarized at 90 degree with respect to the other.
Use of polaroid spectacles.
It is a 3D Polaroid vectograph which is made up of two plates in a form of
booklet.
Advantages : simple and easy to perform.
Disadvantages : unreliability in differentiating patients with amblyopia and
heterotropia
FLY TEST
• USEFUL IN YOUNG CHILDREN
• TEST GROSS STEREOPSIS
• THRESHOLD 3000 SEC OF ARC
ANIMAL TEST
It is performed if the gross stereopsis is present
3 rows of 5 animals
One animal from each row is imaged disparately(threshold of 10, 200 and 400 sec of arc respectively).
In each row one of the animals correspondingly imaged in two eyes is printed heavily black which serves as a misleading clue.
The subject is asked which one of the animals stands out.
A subject without stereopsis will name the animal printed heavily while in the presence of stereopsis he will name the disparately imaged animal .
ANIMAL & FLY TEST
CIRCLE TEST
Only one of the circles in each square is imaged disparately at random with threshold from 800 to 40 sec of arc.
If the subject has passed other two tests, he is asked to push down the circle that stands out, beginning with the first set.
Circle no. 5 (100sec of arc) is considered lowest limit of fine central stereoacuity & designated as the lowest limit of good stereoacuity.
RANDOM DOT TESTS
RDT ‘E’ Test
S All three cards should be viewed with Polaroid glasses.
S Card A : bas relief model of the stereotest figure and is used to show the patient for what he should look.
S Card B : it contains the ‘E’ stereo figure with a random dot background.
S Card C : it is stereoblank with an identical random dot background.
S Card b and c are held at distance of 50cm and pt is asked to indicate which card contains the letter ‘E’.
S The stereoacuity when present can be quantitated by increasing the testing distance from the patient.
LANG TEST
S Random dot stereogram with panographic presentation.
S Seen through cylindrical lenses not polaroid glasses.
S Test card held at a distance of 40cms
S Disparity of car and star 600secs and cat 1200secs
LANG TEST
TNO RANDOM DOT
TEST
It is to provide retinal disparities ranging from 15 to 480 sec of arc.
Advantage of testing quantitative responses without changing the testing distance.
It consists of seven plates.
Each plate consists of stereogram in which various shapes have been created by random dots in complementary colours.
First 3 stereograms of the test booklet are used to establish the presence of gross stereopsis while remaining four to test fine stereopsis
MOTOR TESTS
TWO PENCIL
TEST
S Popularised by Lang in 1975
S Effective to test gross stereopsis
S Threshold value 3000-5000 sec of arc
TWO PENCIL TEST
THANK YOU