BINOCULAR VISION

BINOCULAR VISION

Moderator Dr. N. Kori

Presenter Dr. Isha Gupta

DEFINITIONState of simultaneous vision with two seeing eyes (neither of which needs necessarily be normal) that occurs when an individual fixes his visual attention on an object of regard.

Ref parson2

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.

Types of Vision1.Monocular Vision with single eye

2.Bi-ocular no co-ordination between two eyes

3.Binocular Co-ordinated vision from two eyes

Pre-requisites for development of BSV

Motor Mechanism:correct neuromuscular development so that the visual axes are directed at the objectoverlap of visual fields

Sensory Mechanism:approximately equal image clarity and size in the two eyescorresponding retinal areas so that the eyes are cyclopeannormal visual pathways

Mental Process:ability of visual cortex to promote binocular single vision

GRADES OF BINOCULAR VISIONSIMULTANEOUS PERCEPTIONFUSIONSTEREOPSIS

ADVANTAGES OF BINOCULAR VISIONMasking of optical defects and blind spot.Safety factorLarger field of viewConvergence helps in estimating absolute distanceStereopsis

Disorders of binocular vision produce diplopia / supression / amblyopia

MECHANISM OF BINOCULAR VISIONVisual directionRetinal correspondenceEgocentric localisationHoropterPannums fusional area

VISUAL AXIS

Visual space vs physical space Visual space is the subjective space that is based of anatomic and physiological systems,visual clues and on learning.

Physical space is the actual space of the object.

Anatomic distribution of retinal elements does not coincide with physiological distribution of spatial values Kundst- Munsterberg illusion

VISUAL DIRECTION OCULOCENTRIC MonocularLaws of oculocentric visual direction

EGOCENTRIC Cyclopean eyeHerings law of identical visual direction

EGOCENTRIC LOCALISATION

RETINAL CORRESPONDENCERetinal rceptors in both eyes that dictate a common visual direction under binocular conditions are called corrresponding retinal points.Corresponding retinal points are areas of zero disparity.

Normal retinal correspondenceAbnormal retinal correspondence(ARC) Harmonius arc Un harmonius arcHARMONIUS angle of anamoly= angle of strabismusUNHARMONIUS angle of anamoly< angle of strabismus

FOVEOLA

HOROPTER It is the sum total of all the points in the physical space that stimulate corresponding retinal elements of the two eyes.

Vieth muller horopter / theoritical / geometric horopterEmpirical horopter

HOROPTER

Empirical horopter

BINOCULAR FUSIONSensory fusion should be distinguished from the motor fusion.

Sensory fusion is the ability of visual cortex.

Motor fusion refers to the ability to align eyes in such a manner that sensory fusion can be maintained. It's the exclusive function of extrafoveal retinal periphery.

PANNUMS FUSIONAL AREARegion in front and back of the horopter in which single vision is present is known as Panums area of single binocular vision or Panums 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 Pannums fusional area

TypesA.Crossed (Heteronymous) Diplopia Temporal (crossed) disparity B.Uncrossed (homonymous) DiplopiaNasal (uncrossed) Disparity

Fixation Disparity It is the minute image displacement, rarely exceeding several minutes of arc of angle, occurs within Panums space while fusion is maintained.

Due to presence of pannums fusional area

A physiological variation in placement of retinal image displacement from corresponding retinal points Even Allow fusion

Displacement of retinal images in two eyesRetinal disparity

Theories of binocular fusionPhysiologic hypothesis most acceptedSynergy hypothesisLocal sign hypothesisEye movement hypothesisSuppression hypothesis

Physiologic basis of fusion

Dichoptic stimulation Refers to different stimulation in the two eyes which occurs when binocular stimuli fall on non corresponding points on the two retinae.Depending on the degree of non correspondence five classes of percepts are obtained.Depth with fusion Depth with diplopia Diplopia without depth Binocular rivalry and suppression Binocular lustre.

Retinal rivalry and suppression

When dissimilar contours are presented to the corresponding retinal areas fusion becomes impossible.

This conflict which results when such signals are transmitted to the visual cortex is termed as retinal rivalry.

When presented with such signals,signal presented from one eye is actively suppressed. This results on perception of single signal at a time. This is known as suppression

RETINAL RIVALRY

Binocular lustre The lustrous appearance of surfaces like a waxed surface,table top is due to binocular lustre.It results from the different position of partially reflected objects in the surface by virtue of the different positions of the two eyes.

STEREOPSIS3rd Grade of Binocular VisionVisual 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 diplopiaNot similar to depth perception.

PHYSIOLOGIC BASIS OF STEREOPSIS Horizontal disparity produces stereopsis.

Local stereopsis square by square matchingGlobal stereopsis - to resolve ambiguities

Fine stereopsis - specific pattern matching < 0.5 degreesCoarse stereopsis - act beyond the range of retinal rivalry , dissimilar images can be simultaneously perceived

Fusion is not absolutely required for stereopsis .But similar parts of stereogram reaching corresponding points must fuse to form reference points.

Stereoscopic acuity

Minimal disparity beyond which no stereoscopic effect is produced characterizes the persons stereoscopic acuity. normal = depth of 10 arc secClosest fixation of 10 inches = depth of thousandth of an inchBeyond 600 mts there is no true stereopsis.

PERCEPTION OF DEPTHPerception of distance of objects from each other or from the observer.Several clues contribute-A] BINOCULAR CLUE: Stereopsis. B] MONOCULAR CLUES:

Monocular./Non Stereoscopic CluesParallactic movementsLinear perspectiveOverlay of contoursSizeDistance from horizonDistribution of highlights & shadowsAerial perspective

PARALLACTIC MOVEMENTSMost 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 directionObjects closer move in opposite direction

LINEAR PERSPECTIVE

OVERLAY OF CONTOURS

DISTANCE FROM HORIZON

DISTRIBUTION of HIGHLIGHTS AND SHADOWS

THEORIES OF BINOCULAR VISIONTheory of correspondence and disparityNeurophsiological theory

Older theoriesAlternation theoryProjection theoryMotor theoryIsomorphism theory

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 Panums area.

Neurophysiology of binocular vision

Optic chiasma. First structure that contributes for BSV

Partial decussation at chiasmserves to project to same place in visual cortex2 neuronal pathways Parvocellular Magnocellular

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.

Development of horopter & vergence is also influenced by dramatic changes in eyeball size & orbital position during infancy.

Abnormal binocular visionConfusionDiplopia Suppresion Eccentric fixation Abnormal retinal correspondence(ARC)

Amblyopia

Anamolies of binocularityConfusion 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.

INVESTIGATIONSFor retinal correspondenceFor supression1.Red filter test2.Worth FDT3.Bagolinis striate glass test4.After image testing

Red glass test

WFDT

MONOFIXATION SYNDROME

BAGOLINIS GLASS TEST

BAGOLINIS GLASS TEST

Stereopsis testingStereo 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=