Dr. Sajjan SangaiDept. of Ophthalmology

MGM Medical College and Hospital, Aurangabad

Binocular Vision

Development of Binocular VisionGrades of Binocular VisionTests for Binocular VisionSome important terminology

Binocular VisionIt is the vision achieved by the coordinated

use of both eyes so that the images arise in each eye separately are appreciated as Single Mental Impression in visual part of cerebral cortex.

Prerequisites for development of binocular vision:

Proper Fixation with each eye.

Reflex activities which produce fusional movements must be present.

Image formed on each retina must be approximately similar.

Visual fields of the two eyes must overlap to a large extent.

Common visual direction must be there of two eyes

Development of Binocular VisionMechanisms: A. Sensory Mechanism: Concerned

essentially with visual apparatus and proprioceptive receptors of extrinsic ocular muscles.

B. Motor Mechanism: Concerned essentially with the maintenance of two eyes in a correct positional relationship at rest and in motion.

C. Central Mechanism: Concerned with act of fusion (Sensory) and cortical control of ocular movements (Motor).

Sensory Mechanism

Depends on:1) Visual acuity value of retinal receptors of each

eye.2) Normal Correspondence of retinal receptors of

the two eyes.3) At hemidecussation of the optic nerve fibre at

Optic Chaisma and integrity of apparent visual pathway.

4) Proprioceptive impulses from the extrinsic ocular muscles.

A. Factor of Visual acuity value of retinal receptors of each eye.

1. It depends on adequate degree of central vision (Fovea and Macula) and of the refracting media of the eye ( Cornea, Aqueous , Lens , Vitreous).

2. A certain degree of comparability of the two eyes with regard to their refraction ( i.e. the size difference of two retinal images is not too great to prevent their fusion, Anisekonia)

B. Factor of Normal Correspondence of retinal receptors of the eyes:Extreme temporal part of

the peripheral visual field is UNIOCULAR but the whole of rest of total visual field is binocular due to almost complete overlap of separate visual fields.

Stimulation of Corres. Retinal Points results in formation of SINGLE MENTAL IMPRESSION despite the existence of two separate patterns of stimulation one from each eye.

Retinal CorrespondenceCorresponding retinal elements are those

elements of the two retinae, the stimulation of which in binocular vision, gives rise to localization in one and same visual direction .

The retinal receptors in both eyes that dictate a common visual direction under binocular conditions are called corresponding points or elements.

HoropterIntroduced by Anguilonius c.1613

Meaning Horizon Of Vision

Imaginary surface passing through the point of intersection of the two visual axes.

Sum of the points in space , the image of which fall on corresponding retinal areas is termed as Horopter.

When an image is viewed binocularly it is viewed by a median eye- Binoculus / Cyclopean Eye.

Any point on the horopter is seen by corresponding retinal areas of each eye and this is appreciated by the fovea of binoculus.

Conversely any object which does not lie on the horopter forms image on non- corresponding retinal points and if attention is drawn , the object appears double known as PHYSIOLOGICAL DIPLOPIA or Introspective diplopia

A

Physiological Diplopia

Away from Fixation Object ‘A’

Homonymous or uncrossed Diplopia

Near from Fixation Object ‘A’Heteronymous or crossed

diplopia

Veith-Muller CircleTheoretical or mathematical horopter curve

If corresponding points have a geometrically regular horizontal distances from the two retinas, the longitudinal horopter curve would be a circle passing through the centre of rotation of two eyes and the fixation point.

Veith Muller circle and Empirical Horopter

Empirical Horopter CurveHerring and Hillebrand could show that the

veith muller circle does not describe the longitudinal horopter.

Empirical horopter curve is flatter than the veith muller circle

Distribution of the elements that correspond to each other is not the same in nasal and temporal part of the two retinas.

Pannum’s Fusional AreaThe field in front of and behind the horopter

in which the expected diplopia does not occur is known as Pannum’s fusional space.

Smallest at fixation point, towards the periphery it gains increasingly in depth so that objects located peripherally may be farther from horopter without producing diplopia than objects located more centrally.

C. Factors at hemidecussation of the optic nerve fibre at Optic Chaisma and integrity of apparent visual pathway.

It is dependent on hemidecussation because this enables nerve fibres from corresponding retinal areas of the two eyes to become associated with one another ultimately in the visual area of the occipital cortex

Are relayed in the optic radiation to the striate areas of the visual cortex in occipital lobe.

D. The factor of Proprioceptive impulses from the extrinsic ocular muscles.

Extrinsic ocular muscles provide the brain with sensory information of a proprioceptive nature .

Motor MechanismsMaintenance of correct positional

relationship at rest and in motion

Anatomical Factors

Structure of bony orbit/ contents

Physiological FactorA. Postural Reflex:Maintenance of the two eyes in their correct

relative positions within the orbits so that the visual axes are aligned correctly to one another despite changes in the movement of head relative to the body or of the body relative to space in the absence of any visual stimulus .

They are entirely unconditioned reflexes.

Two types:a) Static postural reflex: Changes in the

position of head relative to body. Controlled by part of labyrinth: utricle and saccule and proprioceptive impulses from neck muscles. e.g. proprioceptive head turning reflex or “the dolls head phenomenon”

b) Stato-kinetic reflex: Changes in the position of head relative to space, in response to movements of acceleration and deceleration. Controlled by semi-circular canals.

B. Fixation reflex (Psycho-optical):Maintenance of two eyes in their correct

positions within the orbits so that visual axes are aligned correctly with one another despite changes in movement of the head relative to the body or of the body relative to space as a result of visual stimuli which reach the visual cortex by afferent visual pathway.

They are conditioned reflexes.

Types 1.Fixation reflex: Ability of each eye to fix a definite object. Dependent on presence of adequate field

of vision and functioning fovea. This reflex is present at birth but only to a

feeble extent. It is initiated with afferent visual stimuli.

2. Re-fixation reflex:

Development of re-fixation reflex follows shortly after the development of fixation reflex.

Passive re-fixation

•Ability of eye to retain fixation of a moving object

Active re-fixation

•Change fixation from one object to another object

3. Conjugate-Fixation reflex:

Application of fixation reflexes to both eyes at same time so that they retain fixation during the conduct of conjugate movements.

Well established at age of 6 months.

4. Disjunctive or Vergence fixation reflex:

Application of fixation reflex to both eyes at the same time so that the eyes retain fixation movements during the conduct of a disjunctive movement.

Reflex is later in development than the conjugate fixation reflex but it is well established by the age of 6 months.

5. Corrective-Fusion reflex:Elaboration of the conjugate and

disjunctive fixation reflexes which permits the eyes to function binocularly even under condition of stress.

It functions to some extent in the first year but is fully developed after the age of about 5 years.

C. Kinetic Reflex:

Maintenance of two eyes in their correct relative position within the orbits as a result of controlled accommodation-convergence relationship.

Central Mechanisms

Central Mechanism

Act of fusion( Sensory

Phenomenon)

Cortical control of ocular movement

(Motor Phenomenon)

A. Factor of fusion:The function of visual cortex to perceive a

single mental impression of an object despite the fact that the object is viewed separately by the two eyes.

The image of an object is build up on two separate halves with the object divided vertically.

Right half of the object is viewed by :1. Nasal hemi retina of right eye.2.Nasal hemi fovea.3. Temporal hemi retina of left eye.4.Temporal hemi fovea of left eye.Image is perceived by the left half of visual cortex.

Left half of the object is viewed by :1. Temporal hemi retina of right eye.2. Temporal hemi fovea.3. Nasal hemi retina of left eye.4. Nasal hemi fovea of left eye.Image is perceived by the right half of cortex.

B. Factor of cortical motor control:Centres in frontal and occipital parts of

cerebral hemispheres control the intermediate centres and cranial nuclei concerned in final efferent impulses to extrinsic ocular muscles.

Development of Binocular VisionTime Action Developed

2 to 3 Weeks Turning head to fixate at an object

4 to 5 Weeks Sustain monocular fixation of large near objects

3 months Binocular fusion

3 to 6 months Stereopsis

1 Year Fusional movements firmly established

2 to 3 year Adult level visual acuity reached

Theories of Binocular VisionSynergy Hypothesis of Panum

Local Sign Hypothesis of Herring

Eye Movement Hypothesis of Helmholtz

OBSOLETE

Physiologic Basis of Fusion

By Hubel and Weisel.Classified neurophysiologically, 4 Classes of

neurons1. Binocular Corresponding BC2. Binocular Disparate BD3. Monocular Right MR4. Monocular Left ML

Binocular Single Vision

Fused Stimulus up to certain range

Monocular response is associated with a different

visual direction and therefore two separate stimuli are

perceived in diplopia

BD

Grades of Binocular VisionThree grades of Binocular Vision (Claude Worth c.1901)

A. Simultaneous perception

B. Fusion

C. Stereoscopic vision

A. Simultaneous PerceptionSignals transmitted from two eyes to the

visual cortex are perceived at same time.

It is the power to see two dissimilar objects simultaneously.

B. FusionAbility of the two eyes to produce a

composite picture from two similar pictures, each of which is incomplete in one small detail.

C. Stereoscopic VisionAbility to obtain the impression of depth by

superimposition of two pictures of the same object which have been taken from slightly different angles.

It refers to visual appreciation of three dimensions during binocular vision.

Monocular (non-stereoscopic) Clues to spatial orientation

Stereopsis is restricted relatively to short visual distances.

Hence a second set of clues, the MONOCULAR clues are important in our estimation of the relative distance of visual objects and are active in monocular as well as binocular vision.

Monocular clues are result of EXPERIENCE.

Monocular CluesMotion parallax

Linear perspective

Overlay of contours

Distribution of highlights and shadow

Size of known objects

Aerial perspective

Motion Parallax:When one looks at two objects , one of which

is closer than the other and moves either the eyes or head in a plane parallel to the plane of one of these objects, movement of the objects becomes apparent.

The farther object appears to make a larger excursion than the near object.

E.g. Depression /elevation in the fundus , one can observe the apparent movement of retinal vessels by moving the head from side to side.

Linear Perspective:Objects having a constant size appears to

subtend smaller angle as they recede from the subject.

Foreshortening of horizontal and vertical lines is one of the most powerful tool for creation of 3D impression on a 2D surface.

Overlay of Contours:Shapes in which contours are interposed on

the contours of other shapes providing impelling distance clues.

1. An Object that interrupts the contour of another object is generally seen as being in front of the object with incomplete contours.

2. Farther object is also higher than the first one.

Distribution of Highlights and Shadows:The positioning of shadows is helpful in

determining the elevations and depressions. i.e. Relative depth of objects.

Size of known objects:If size of two objects is known one can judge the relative distance of these objects by their apparent size.If an object known to be smaller appears to be larger than the other, we judge it to be near.

Aerial Perspective:Influence of atmosphere on contrast condition and colours of more distant objects.

SynoptophoreUses: 1. Measurement of angle of deviation (Angle of squint) 2. Assessment of Patients Binocular Function

Synoptophore

Parts of Synoptophore1. Base: Electric components and control of

operations. ( Voltage selector)2. Columns: Support for optical tubes and

conduit for electrical housing of lamps.3. Optical Tubes4. Slide carrier5. Reflecting mirror6. Eyepiece lens of +6.5 D sph.7. Scale for recording of the movements.

Tests for Binocular Vision1.Test for Simultaneous macular perception:

It can be demonstrated by presenting separate stimuli to two eyes, such as picture of cage (one eye) and lion ( other eye).

2. Tests for fusion:It can be demonstrated by producing two

similar pictures each of which incomplete in one small detail.

E.g. Rabbit with a missing tail and bunch of flowers.

3. Tests for Stereopsis:Pre-requisites for testing stereopsis:

Dissociated Eyes

• Presented with separate field of vision

Retinal Correspondence

• Each of the two fields of targets must contain elements imaged on corresponding retinal areas.

Stereoscopic VisionSynoptophore / Stereoscope test

Vectograph test

Random dot stereogram test.

Stereoscopic contours induced optokinetic nystagmus test and television random dot stereo test

A. Synoptophore / Stereoscope test:

Demonstrated by two pictures of same object taken from slight different angles.

e.g. Bucket pictures from two different angle is appreciated in three dimension.

B. Vectograph test:Vectograph consists of a polaroid material on

which two targets are imprinted so that each target is polarized at 90˚ with respect to other.

Vectograph dissociates the eyes optically.Used with polarized spectacles.e.g. Titmus stereo testAdvantage: Easy to performDisadvantage: Unreliable in different

patients with amblyopia and heterotropia from those with normal vision.

Titmus Stereo Test:It is made up of two plates in form of a booklet and to test the plates are reviewed by the polaroid glasses.

The Fly

Test

•Large house fly to test gross stereopsis (threshold 3000 sec of arc)•The subject is asked to pick up one of the wings of fly.

The Animal Test

•3 rows of 5 animals each.•1 animal from each row is imaged disparately and another animal is printed heavily black.

The

Circles

Test

•Nine squares each containing four circles.•Only one circle in each square is disparately imaged at random with threshold 800 to 40 sec of arc.

C. Random Dot Stereogram Test:These tests are devoid of MONOCULAR CLUES,

hence the patient cannot guess what the stereo figure is and where it is located on the plate.

Truer measurement of stereopsis than Titmus test.

1. Random dot E- test2. TNO random dot test 3. Lang test4. Frisby test5. Stereoscopic contours induced optokinetic

nystagmus test and television random dot stereo test.

1.Random dot E-Test: •3 cards to be viewed with polaroid spectacles ,kept 50 cms away.

•One card is the base relief model of the stereo test figure and is used to show what to look for.

•Second card contains “E” stereo figure with random dot background.

•Third card is stereo blank with an identical random dot background.

Random Dot “E” TestThe patient gives a pass/ fail response. The stereo acuity, when present, can be quantified by increasing the testing distance from the patient.

2. TNO random dot test:It provides retinal disparities ranging from 15 to

480 sec of arc.Has the advantage of eliciting quantitative

responses without changing the testing distance.Contains a booklet with 7 plates in which various

shapes (square , dot, crosses) have been created by random dots in complementary colours.

Plate contains two types of figures , the one which can be perceived binocularly with RG Glasses.

Second set which can be seen with or without the glasses even in absence of stereopsis.

Plates 1,2,3- Gross stereopsisPlates 4,5,6,7- Quantitative level of stereopsis

Figures in TNO testCross is seen with and without red green glasses, hidden shapes which can be seen with red green glasses in the presence of stereopsis.

3. LANG Test:Tests consist of random dot stereogram with

panographic presentation.The stereoscopic images of car, star ,cat

embedded in random dots on the test card are seen disparately by each eye through the cylindrical lenses imprinted on the surface lamination of the test.

Test card is held at 40 cms in front of the subject, asked to name or point to the shapes on the test card.

Disparity of the car and star is 600 sec and of the cat is 1200 sec of arc.

Lang Stereo test

4. Frisby Test:Stereo test consists of plastic cards each

containing four squares of small random shapes, one of the square contains in each plate contains a hidden circle which is seen disparately.

The disparity is created by displacement of random shapes by the thickness of the plate.

Frisby Stereo Test

5. Stereoscopic contours induced optokinetic nystagmus test / Television random dot stereo test.

Important Terminologies1.Primary Position:Two eyes are directed straight ahead with head held vertically erect and with vertical meridians of the cornea vertical and parallel.

2. Nodal Point: Optical centre of the eye. Lies on the optical axis slightly in front of the centre of eyeball and is adjacent to post surface of lens

3. Anterior Pole:Central point of corneal curvature

4. Posterior Pole: Central point of Post. Scleral curvature

5. Geometric Axis: Line joining the anterior pole and posterior pole . Also known as Sagittal Diameter.

6. Optic Axis: Line on which main optical components are centred and passing through the nodal point.

7. Central Pupillary Line:Line perpendicular to the cornea, passing through centre of pupil to reach nodal points of eye.

8. Visual Axis: Line passing from the object of fixation to fovea.

9. Centre of rotation:Point around which eyeball rotates

10. Fixation Axis:Line passing from fixation object to centre of rotation.

References1. Gunter K. Von Noorden: Binocular Vision

and Ocular Motility , theory and management of strabismus, Sixth ed .

2. Lyle And Jackson’s : Practical Orthoptics in the Treatment of Squint, Fifth ed.

3. webeye.ophth.uiowa.edu/eyeforum/tutorials/BINOCULAR-VISION.pdf