Binocular Vision, Fusion, and Binocular Vision, Fusion, and AccommodationAccommodation

Fusion Development in the InfantFusion Development in the Infant

Birth – fixation reflex poor with random eye Birth – fixation reflex poor with random eye movementsmovements

2-3 weeks – follows light monocularly2-3 weeks – follows light monocularly 6 weeks to 6 months – follows light 6 weeks to 6 months – follows light

binocularlybinocularly 4 weeks to 6 months – convergence 4 weeks to 6 months – convergence

developingdeveloping By 6 months – accommodation developing – By 6 months – accommodation developing –

lags behind convergencelags behind convergence

FusionFusion

Sensory fusion – the cortical process of Sensory fusion – the cortical process of blending the images from each eye into a blending the images from each eye into a single binocular stereoscopic imagesingle binocular stereoscopic image

Motor fusion – the mechanism that allows Motor fusion – the mechanism that allows fine-tuning of eye position to maintain eye fine-tuning of eye position to maintain eye alignment – this is known as fusional alignment – this is known as fusional vergencevergence

Approximately 70% of the cells in the striate Approximately 70% of the cells in the striate cortex are binocular cellscortex are binocular cells

Retinal areas from each eye that project to Retinal areas from each eye that project to the same binocular cortical cells are called the same binocular cortical cells are called corresponding retinal points.corresponding retinal points.

Worth’s Three Degrees of FusionWorth’s Three Degrees of Fusion

Simultaneous perceptionSimultaneous perception

Flat fusionFlat fusion

StereopsisStereopsis

Simultaneous perceptionSimultaneous perception

Flat FusionFlat Fusion

Worth Four Dot TestWorth Four Dot Test

StereopsisStereopsis

Titmus Stereo TestTitmus Stereo Test

Binocular Single VisionBinocular Single Vision

Separate and slightly dissimilar Separate and slightly dissimilar images arising in each eye are images arising in each eye are

fused together as a single image.fused together as a single image.

Advantages of Binocular VisionAdvantages of Binocular Vision

Single VisionSingle Vision

StereopsisStereopsis

Enlargement of visual fieldEnlargement of visual field

Compensation for blind spot and other Compensation for blind spot and other differences in the field of visiondifferences in the field of vision

Normal Binocular Single Vision Normal Binocular Single Vision RequirementsRequirements

Clear visual axisClear visual axis

Sensory fusionSensory fusion

Motor fusionMotor fusion

Sensory ObstaclesSensory Obstacles

Dioptric obstacles – refractive errors, Dioptric obstacles – refractive errors, anisometropiaanisometropia

Prolonged monocular activity – severe Prolonged monocular activity – severe ptosis, media opacitiesptosis, media opacities

Retinoneural – lesions of retina, optic nerveRetinoneural – lesions of retina, optic nerve Proprioceptive Proprioceptive

Motor ObstaclesMotor Obstacles

Congenital craniofacial malformationsCongenital craniofacial malformations

Conditions affecting extraocular musclesConditions affecting extraocular muscles

CNS lesions – involving upper motor CNS lesions – involving upper motor neuronsneurons

The Perception of DepthThe Perception of Depth

StereopsisStereopsis

Monocular clues to depthMonocular clues to depth

Monocular Clues to DepthMonocular Clues to Depth

Relative sizeRelative size InterpositionInterposition Linear perspectiveLinear perspective Aerial perspectiveAerial perspective Light and shadeLight and shade Motion parallaxMotion parallax

Visual DirectionVisual Direction

Local sign – positional information Local sign – positional information transferred from the retina to the motor transferred from the retina to the motor system – the fovea has a retinomotor value system – the fovea has a retinomotor value of zeroof zero

Retinal correspondence = single visionRetinal correspondence = single vision Retinal disparity = diplopiaRetinal disparity = diplopia

Oculocentric Visual DirectionOculocentric Visual Direction

Egocentric Visual DirectionEgocentric Visual Direction

Cyclopean EyeCyclopean Eye

The Perception of SpaceThe Perception of Space

Retinal corresponding pointsRetinal corresponding points HoropterHoropter Retinal disparityRetinal disparity Panum’s fusional areaPanum’s fusional area Physiological diplopiaPhysiological diplopia

The HoropterThe Horopter

Vieth-Muller CircleVieth-Muller Circle

Empirical HoropterEmpirical Horopter

The HoropterThe Horopter

Normal binocular single vision – the images Normal binocular single vision – the images of the fixated object are bifoveal with no of the fixated object are bifoveal with no manifest deviation of the eyesmanifest deviation of the eyes

Anomalous binocular single vision – the Anomalous binocular single vision – the images of the fixated object are projected images of the fixated object are projected from the fovea of one eye and an from the fovea of one eye and an extrafoveal position in the other eye – there extrafoveal position in the other eye – there is a small manifest deviation of the eyesis a small manifest deviation of the eyes

Misalignment of the two eyes can lead to Misalignment of the two eyes can lead to diplopia and confusiondiplopia and confusion

Diplopia – occurs when one object is seen in Diplopia – occurs when one object is seen in two placestwo places

Confusion – occurs when two dissimilar Confusion – occurs when two dissimilar objects are seen in the same placeobjects are seen in the same place

Suppression and Retinal RivalrySuppression and Retinal Rivalry

SuppressionSuppression Normal – physiological diplopia – also Normal – physiological diplopia – also

known as suspensionknown as suspension Anomalous – pathological diplopia and Anomalous – pathological diplopia and

confusion – cortical inhibition of suppressed confusion – cortical inhibition of suppressed eyeeye

Retinal or binocular rivalry – rapid Retinal or binocular rivalry – rapid alternation of dissimilar imagesalternation of dissimilar images

Testing Retinal CorrespondenceTesting Retinal Correspondence

Bagolini lensesBagolini lenses Red filter testRed filter test Worth four dot testWorth four dot test Hering-Bielschowsky afterimage testHering-Bielschowsky afterimage test Foveo-foveal test of CuppersFoveo-foveal test of Cuppers

Worth Four Dot TestWorth Four Dot Test

Testing SuppressionTesting Suppression

Worth four dot testWorth four dot test Polaroid vis-à-vis testPolaroid vis-à-vis test Amsler gridAmsler grid 4 prism diopter base out test4 prism diopter base out test Red filter testRed filter test Bagolini lensesBagolini lenses

Polaroid TestsPolaroid Tests

Amsler GridAmsler Grid

Versions – conjunctive eye movements – Versions – conjunctive eye movements – the two eyes move in the same directionthe two eyes move in the same direction

PursuitsPursuits SaccadesSaccades

Vergences – disconjunctive eye movements Vergences – disconjunctive eye movements – the eyes move in opposite directions– the eyes move in opposite directions

ConvergenceConvergence DivergenceDivergence Vertical vergenceVertical vergence

VergenceVergence

TonicTonic ProximalProximal FusionalFusional AccommodativeAccommodative

AccommodationAccommodation

Tonic – in the absence of a visual stimulus, the Tonic – in the absence of a visual stimulus, the accommodation adopts an intermediate position of accommodation adopts an intermediate position of 0.5-1.0 D0.5-1.0 D

Proximal – resulting from apparent nearness of an Proximal – resulting from apparent nearness of an objectobject

Convergence – accommodation linked to Convergence – accommodation linked to convergenceconvergence

Reflex – involuntary response to blur to maintain a Reflex – involuntary response to blur to maintain a clear imageclear image

Voluntary – not dependent on a stimulusVoluntary – not dependent on a stimulus