binocular-vision-fusion-and-accommodationluchansky-1937-1937.ppt

Binocular Vision, Fusion, and
Accommodation

Fusion Development in the Infant
 Birth – fixation reflex poor with random eye
movements
 2-3 weeks – follows light monocularly
 6 weeks to 6 months – follows light
binocularly
 4 weeks to 6 months – convergence
developing
 By 6 months – accommodation developing –
lags behind convergence

Fusion
 Sensory fusion – the cortical process of
blending the images from each eye into a
single binocular stereoscopic image
 Motor fusion – the mechanism that allows
fine-tuning of eye position to maintain eye
alignment – this is known as fusional
vergence

 Approximately 70% of the cells in the striate
cortex are binocular cells
 Retinal areas from each eye that project to
the same binocular cortical cells are called
corresponding retinal points.

Worth’s Three Degrees of Fusion
 Simultaneous perception
 Flat fusion
 Stereopsis

Flat Fusion
 Worth Four Dot Test

Stereopsis
 Titmus Stereo Test

Binocular Single Vision
Separate and slightly dissimilar
images arising in each eye are
fused together as a single image.

Advantages of Binocular Vision
 Single Vision
 Stereopsis
 Enlargement of visual field
 Compensation for blind spot and other
differences in the field of vision

Normal Binocular Single Vision
Requirements
 Clear visual axis
 Sensory fusion
 Motor fusion

Sensory Obstacles
 Dioptric obstacles – refractive errors,
anisometropia
 Prolonged monocular activity – severe
ptosis, media opacities
 Retinoneural – lesions of retina, optic nerve
 Proprioceptive

Motor Obstacles
 Congenital craniofacial malformations
 Conditions affecting extraocular muscles
 CNS lesions – involving upper motor
neurons

The Perception of Depth
 Stereopsis
 Monocular clues to depth

Monocular Clues to Depth
 Relative size
 Interposition
 Linear perspective
 Aerial perspective
 Light and shade
 Motion parallax

Visual Direction
 Local sign – positional information
transferred from the retina to the motor
system – the fovea has a retinomotor value
of zero
 Retinal correspondence = single vision
 Retinal disparity = diplopia

The Perception of Space
 Retinal corresponding points
 Horopter
 Retinal disparity
 Panum’s fusional area
 Physiological diplopia

The Horopter
 Vieth-Muller Circle
 Empirical Horopter

 Normal binocular single vision – the images
of the fixated object are bifoveal with no
manifest deviation of the eyes
 Anomalous binocular single vision – the
images of the fixated object are projected
from the fovea of one eye and an
extrafoveal position in the other eye – there
is a small manifest deviation of the eyes

 Misalignment of the two eyes can lead to
diplopia and confusion
 Diplopia – occurs when one object is seen in
two places
 Confusion – occurs when two dissimilar
objects are seen in the same place

Suppression and Retinal Rivalry
 Suppression
 Normal – physiological diplopia – also
known as suspension
 Anomalous – pathological diplopia and
confusion – cortical inhibition of suppressed
eye
 Retinal or binocular rivalry – rapid
alternation of dissimilar images

Testing Retinal Correspondence
 Bagolini lenses
 Red filter test
 Worth four dot test
 Hering-Bielschowsky afterimage test
 Foveo-foveal test of Cuppers

Testing Suppression
 Worth four dot test
 Polaroid vis-à-vis test
 Amsler grid
 4 prism diopter base out test
 Red filter test
 Bagolini lenses

 Versions – conjunctive eye movements –
the two eyes move in the same direction
 Pursuits
 Saccades

 Vergences – disconjunctive eye movements
– the eyes move in opposite directions
 Convergence
 Divergence
 Vertical vergence

Vergence
 Tonic
 Proximal
 Fusional
 Accommodative

Accommodation
 Tonic – in the absence of a visual stimulus, the
accommodation adopts an intermediate position of
0.5-1.0 D
 Proximal – resulting from apparent nearness of an
object
 Convergence – accommodation linked to
convergence
 Reflex – involuntary response to blur to maintain a
clear image
 Voluntary – not dependent on a stimulus

binocular-vision-fusion-and-accommodationluchansky-1937-1937.ppt

binocular-vision-fusion-and-accommodationluchansky-1937-1937.ppt

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