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S BINOCULAR SINGLE VISION Presented by: Dr. Shrey Maheshwari
Transcript
Page 1: binocular single vision

S

BINOCULAR SINGLE

VISION

Presented by: Dr. Shrey Maheshwari

Page 2: binocular single vision

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.

Page 3: binocular single vision

GRADES OF BINOCULAR

VISION

1. Simultaneous perception

2. Fusion

3. Stereopsis

Page 4: binocular single vision

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.

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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

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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.

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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.

Page 10: binocular single vision

PHYLOGENETIC

BACKGROUND AND

EVOLUTION

Present only in higher animals.

Frontally placed eyes

Binocular co-ordination of eye movements

Semidecussation of optic tract

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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

Page 12: binocular single vision

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.

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Discrepancies of Objective

and Subjective Metrics

S Hering’s experiment.

S Kundt and Münsterberg experiment.

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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

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HERING’S EXPT.

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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.

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VISUAL DIRECTIONS

S OCULOCENTRIC (MONOCULAR)

S EGOCENTRIC (BINOCULAR)

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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

Page 19: binocular single vision

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.

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CYCLOPEAN EYE

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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

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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

Page 23: binocular single vision

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

Page 24: binocular single vision

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

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HOROPTER CURVE

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PHYSIOLOGIC

DIPLOPIA

All points on the horopter curve are seen singly

Diplopia elicited by object points off the horopter is called

physiologic diplopia.

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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.

Page 28: binocular single vision

PHYSIOLOGIC

DIPLOPIA

CROSSED DIPLOPIA UNCROSSED DIPLOPIA

Page 29: binocular single vision

CLINICAL SIGNIFICANCE

In diagnosing binocular cooperation

In orthoptic treatment of comitant strabismus

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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

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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

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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.

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PANUM’S AREA

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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

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FIXATION DISPARITY

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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

Page 37: binocular single vision

PHYSIOLOGICAL BASIS

OF FUSION

4 classes of neurons identified by HUBEL & WIESEL

① Binocular Corresponding

② Binocular Desperate

③ Monocular Right

④ Monocular left

Page 38: binocular single vision

PHYSIOLOGICAL BASIS OF

FUSION

Page 39: binocular single vision

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

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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

Page 41: binocular single vision

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.

Page 42: binocular single vision

RETINAL RIVALRY AND

SUPPRESSION

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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.

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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

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STEREOPSIS

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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.

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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.

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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

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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

Page 50: binocular single vision

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

Page 51: binocular single vision

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

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LINEAR PERSPECTIVE OVERLAY OF CONTOURS

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DISTANCE FROM HORIZON DISTRIBUTION of HIGHLIGHTS AND SHADOWS

Page 54: binocular single vision

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.

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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.

Page 56: binocular single vision

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.

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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.

Page 58: binocular single vision

BINOCULAR VISION TESTS

1. Simultaneous perception

2. Fusion

3. Stereopsis

Most useful instrument for the testing is the

Synaptophore.

Page 59: binocular single vision

SIMULTANEOUS PERCEPTION

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FUSION

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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

Page 62: binocular single vision

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

Page 63: binocular single vision

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

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FLY TEST

• USEFUL IN YOUNG CHILDREN

• TEST GROSS STEREOPSIS

• THRESHOLD 3000 SEC OF ARC

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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 .

Page 66: binocular single vision

ANIMAL & FLY TEST

Page 67: binocular single vision

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.

Page 68: binocular single vision

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.

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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

Page 71: binocular single vision

LANG TEST

Page 72: binocular single vision

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

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MOTOR TESTS

Page 75: binocular single vision

TWO PENCIL

TEST

S Popularised by Lang in 1975

S Effective to test gross stereopsis

S Threshold value 3000-5000 sec of arc

Page 76: binocular single vision

TWO PENCIL TEST

Page 77: binocular single vision

THANK YOU


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