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BINOCULAR VISION

Presenter- Dr Saransh Jain

DEFINITION

NORMAL BINOCULAR VISION

DEVELOPMENT OF BINOCULAR VISION

THEORIES OF BINOCULAR VISION

MECHANISM OF BINOCULAR VISION

GRADES OF BINOCULAR VISION

ABNORMALITIES OF BSV

CLINICAL TESTS FOR BSV

TO THE SEMINAR

DEFINITION

• State of simultaneous vision with two seeing eyes that occurs when an individual fixes his visual attention on an object of regard.

• It is the co-ordinated use of both eyes to produce a single mental impression.

Pre-requisites for development of BSV

Motor Mechanism:• Correct neuromuscular development so that the visual axes are

directed at the object (FIXATION)• Overlap of visual fields

Sensory Mechanism:• Approximately equal image clarity and size in the two eyes• Corresponding retinal areas (cyclopean eye)• Normal visual pathways

Mental Process:• Ability of visual cortex to promote binocular single vision

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 & many physiological processes in the eye.

DEVELOPMENT OF BINOCULAR VISION

2 to 3 weeks turning head to fixate an object

4 to 5 weeks sustain monocular fixation of large near objects

3 months binocular fusion

3 to 6 months stereopsis

1 YR Fusional movements firmly established

2-3 yr Adult level visual acuity reached

1. Theory of correspondence and disparity (most widely accepted theory)

2. Neurophysiological basis

3. Alternation theory of Binocular Vision

4. Projection theory of Binocular Vision

5. Motor theory

6. Theory of isomorphism

Theories of BSV

Older theories

Theory of correspondence and disparity

-Simultaneous stimulation of the corresponding points by one object transmits single visual impression with no depth quality.

-Simultaneous stimulation by two object points that differ 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.

NEUROPHYSIOLOGY OF DEVELOPMENT

2 different visual pathways from different population of retinal ganglion cells.

Parvo and Magno cellular pathway- lateral geniculate body.P cells- colour, fine 2 point discrimination and project to the

areas of foveaM cells- direction, motion, speed, flicker, gross binocular

disparities. 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.

MECHANISM OF BINOCULAR VISION

• Visual axis

• Retinal correspondence

• Egocentric localisation

• Horopter

• Pannums fusional area

VISUAL AXIS

VISUAL DIRECTIONS• OCULOCENTRIC (MONOCULAR)

• EGOCENTRIC (BINOCULAR)

OCULOCENTRIC (MONOCULAR)

• When an object is viewed, its image falls on the foveola. visual direction -represented by principle visual line or axis

• Each point on retina can have its own visual axis

• For a given eye position , objects having superimposed retinal images will be seen in as being in alignment in visual field (law of OC visual direction)

EGOCENTRIC (BINOCULAR)

• Frame of reference(single system of VD) is head (egocentric) rather than 2 eyes.

• Visual space is seen with imaginary single eye(cyclopean eye)

• Herring’s law of identical visual direction – fovea have a common subjective visual direction.

RETINAL CORRESPONDENCE• Correspondence- relative localisation of objects in space to each other

under binocular conditions.

• Fovea determines the principle visual direction

• Both fovea has same space value i.e. ‘ZERO’ (principal VD)

• Each receptor under monocular condition dictates visual direction in relation to fovea

• Images falling on corresponding locations in each eye creates single mental impression.

• 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 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

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

• 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)

PANNUMS FUSIONAL AREA

Physiological Diplopia

The Diplopia elicited by an object point off the Pannum’s fusional area

TypesA.Crossed (Heteronymous) Diplopia

Temporal (crossed) disparity

B.Uncrossed (homonymous) Diplopia

Nasal (uncrossed) Disparity

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

GRADES OF BINOCULAR VISION

• SIMULTANEOUS PERCEPTION• FUSION• STEREOPSIS

SIMULTANEOUS 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. • Does not imply that both eyes see same object.

• 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• 2nd Grade of Binocular Vision

• Ability of the eyes to produce a composite picture from two similar pictures, each of which is incomplete in a small detail.

• It is not superimposition of dissimilar pictures

Components of fusionSensory 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

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.

STEREOPSIS• 3rd Grade of Binocular Vision• Visual appreciation of three dimensions

• Ability to obtain impression of depth by superimposition of two images of the same object, seen from 2 slightly different angle.

• Retinal disparity (Fixation disparity) is the basis of 3 D perception

• Stereopsis occurs when Retinal disparity is not large enough for simple fusion but small enough to cause diplopia

Not similar to depth perception.

ADVANTAGES1. 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.

PERCEPTION OF DEPTH

• Perception of distance of objects from each other or from the observer.

• Several clues contribute-A] BINOCULAR CLUE: Stereopsis. B] MONO OCULAR CLUES:

Monocular./Non Stereoscopic Clues

a) Parallactic movementsb) Linear perspectivec) Overlay of contoursd) Sizee) Distance from horizonf) Distribution of highlights & shadowsg) 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

Advantage of having BSV

• Stereopsis

• Binocular summation.– vision shaper, clearer &

more sensitive

• Larger field of view.

• Spare eye

visual field

Abnormal binocular vision

ConfusionDiplopia

Suppresion Eccentric fixation

Abnormal retinal correspondence(ARC)

Amblyopia

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.

Conclusion

• Without the basic concepts of BSV it is almost impossible to understand strabismus and treat it.

• The advantage of BSV outweights the disadvantage.

CLINICAL TESTS

• For retinal correspondence• For supression1.Red filter test2.Worth FDT3.Bagolinis striate glass test4.After image testing

• Tests for stereopsisQualitativeRandom dot stereogramsSynaptophore

QuantitativeTitmus fly testTNO testLang test

WFDT

MONOFIXATION SYNDROME

BAGOLINIS GLASS TEST

AFTER IMAGE TESTING

Stereopsis testing

• Stereo acuity is a quantitative measure of stereopsis, it represents the smallest horizontal retinal image disparity that give rise to a sensation of depth.

• Stereopsis is measured in seconds of arc.• 1degree=60minutes of arc, 1minute=60seconds of arc.• Normal stereoacuity= <60seconds of arc.

FEATURES FOR STEREOPSIS TEST

• EYES MUST BE DISSOCIATED

• MUST BE PRESENTED WITH SEPERATE FIELD OF VIEW

• 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

ANIMAL & FLY TEST

TNO RANDOM DOT TEST

THANK YOU !!