Download Fusion and Binocularity

Accomodation, Fusion and
Binocularity
Amy C. Nau, OD
Outline
Accommodation
 Binocular sensory function
 Vergence
 Pathophysiology of common
accommodative and binocular anomolies

Ken Cuifredda, OD PhD, Glen McCormack, OD PhD in
Borish, Clinical Refraction
History of Accomodation
Descartes (1677)- proposes lenticular
based focusing
 Thomas Young- (1801)- demonstrates that
the lens changes shape
 Hermann von Helmholtz (1866)- first
accurate description of accommodative
processes

Physiology of Accommodation
The Eye
Ciliary m. relaxed
Ciliary m. contracts
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/imgvis/accom2.gif
Neural basis for accommodation
Magnocellular
LGN
http://bicmra.usuhs.mil/MRA/Histology/Eye/Images/eye01.jpg
http://static.howstuffworks.com/gif/brain-intro.gif
Neural basis for accommodation
EWN- CN3 (PS)-CilGShort Cil N/Long Cil N.
http://info.med.yale.edu/caim/cnerves/cn3/cn3_graphics/cn3_9.jpg
Types of Accommodation
Reflex, +/ Vergence, +/ Proximal, +/ Tonic, +/
Systems Analysis of
Accommodation
Adapt.
tonic
-
Stimulus
(D)
S
retina
Depth of
focus
gain
S
Cm/lens
Reflex
Accom
+
Influences on Blur Accommodation
Responses

Optical Cues



Nonretinal Image

H.O. Aberrations
Microfluctuations in EOM
and AR





Non Optical Cues





Size
Proximity
Apparent Distance
Disparate retinal images
Monocular depth cues

Vestibular stimulation
Mood
Effort
Cognitive Demand
Instruction set
Retinal Image






Frequency
Contrast
Eccentricity
Luminance
Size
Depth of focus
Fusion



How do the two eyes,
separated in space, give us
a single precept?
How are the eye
movements coordinated
with the retinal image to
maintain singularity?
How does stereo vision
enhance our perceptions of
our surroundings?
Stereograms
http://www.lri.fr/~marche/images/cameleon-3d.gif
Space Perception
Object Space “the real world”
 Visual Space - the world as it is captured
by our retina and processed by the visual
cortex.
 Visual space must reproduce object space

The Cyclopean Eye
We percieve the world as though we have
one eye which exists between our two
eyes.
 “egocenter”

http://bearah718.tripod.com/sitebuildercontent/sitebuilderpictures/cyclops.jpg
Visual Localization and Visual
Direction

Egocentric localization of an object
Where is the object in 3D space in relation to
my own position?
 Can judge distance in a unit of measurement
(i.e., feet or meters)


Imaginary arrow from the cyclopean eye to
the object (i.e. straight ahead, etc.)
Egocentric localization

The sense of direction from retinal locus is
a property of oculo-cortical mapping
Each retinal point has a location relative to
other retinal points in this map
 Local sign is the term that refers to the unique
direction for each retinal point.

 Related
to va and retinal location (fovea vs periph),
amblyopia
Principal visual direction
Elicits the sensation of “looking” at
something
 Associated with the fixation point /origin
 Center of anatomic fovea
 Center of oculocentric direction
 Guides foveation


Registration…
Example: Paretic strabismus


Past pointing test
Used to detect
labyrinth disease but
also can be used for
paretic eom.

Egocentric direction
judgement errors
when monocularly
fixating with the paretic
eye
Depth and Distance Perception

Distance perception = absolute depth
How far any object is from the observer, from
another object, able to judge in meters, etc.
Depth perception (relative), perception of
relative proximity of one object to another or
the relative depth between two or more points
in space.
Depth: coffee cup is 50% farther than pencil
Distance: 10 cm
Monocular Cues to Depth









Object distance form observer is inversely proportional to
retinal image size.
Linear/perspective
Texture density
Luminance variations, shadows, color
Atmospheric perspective
Overlay cue
Parallax
Head motion
Kinetic depth effect
http://www1.cs.columbia.edu/~paley/spring03/assignments/HW5/bg2020/size.jpg
Visual cliff experiment. Are cues learned or innate?
Binocular cues to stereopsis
Separation of the eyes
 Accommodation
 Convergence

Stimulus to Stereopsis
Lateral separation of eyes= different views
of the world (binocular parallax)
 Elicits convergence/divergence
 The magnitude of horizontal disparity for
any given point is a function of the lateral
separation of the eyes divided by object
distance

Binocular Contribution to Depth
and Distance Perception
Horizontal geometric disparity is
insufficient to calculate percieved distance.
 Registered convergence

Spatial Stereopsis Limits
Retinal disparity is not compared with all
retinal points
 Actually any given retinal locus only
interacts with a limited area of retinal
points in the fellow eye

Horopter




Center of the region of stereopsis
Defined by all those points in object space that
stimulate corresponding retinal points (points in
each eye that retain the same sense of visual
direction).
Any object not on the horopter may appear to be
in different directions ot the two eyes.
It is the center of range of binocularity and
region of highest stereoscopic acuity
Horoptor

Crossed disparity- closer to observer than
the horopter,image is observed on
opposite side , (images fall temporal)

Uncrossed disparity - object is farther
from observer than the horopter (images
are nasal from corresponding points )
observed on same side
Measuring retinal disparity

Maddox rod test
Exophoria- streak falls on temporal retina,
stimulates crossed disparity
 Esophoria-streak falls nasally, simulates
uncrossed disparity.


Anomalous retinal correspondence_
identical sense of visual direction with very
dissimilar retinal points
Spatial Limits of Fusion





Occurs only when corresponding points are
stimulated
Small to moderate retinal disparities are
stimulated.
Pannum’s space the space around the current
fixation point which can be fused, extents around
15 minarc.
Outside this region, some qualitative depth can
still be perceived, but stimuli can not be fused.
Humans and many other animals sample the
surrounding space by constantly changing the
fixation point of their eyes.
Nonspatial Limits of Fusion

As images become more dissimilar fusion is
interrupted (color/shape etc).
Diplopia
Binocular rivalry
Sustained suppression
Luminance Luster

You can get partial fusion





Red green glasses…..
Anomalous retinal correspondence
Fine and Coarse Stereopsis

Fine: parvocellular, higher spatial frequency,
smaller retinal disparities, stationary targets.
Foveal vision, similar size and shape images
necessary.

Coarse: magnocellular, lower spatial frequency,
larger retinal disparities, moving targets,
periphery, similarity of images not such an issue.
(motion in depth mechanism)
Local and Global Stereopsis


Stereo contributes to pattern recognition
Randot: visual system performs interocular image
disparity computations across binocular visual field in a
process known as global stereopsis

Stereograms: When color and contrast reveal the form,
dispartiy processing limited to the immediate vicinty of
the form is sufficient to reveal the depth = local
stereopsis.

Fine and coarse = local
Fine= global

LOCAL STEREOPSIS
http://archive.museophile.org/3d/pub/tunnel.gif
Stereo Acuity
Ability to discriminate very fine differences
in depth from geometric disparity
 Minimum geometric disparity that elicits a
sensation of depth.
 Fine- 2 sec arc
 hyperacuity

Binocular Sensory Fusion
Summary
Single precept from two ocular images
 Ensures visual space represents object
space. (no diplopia)

Binocular Motor Function
Eye Movements

support foveal vision


support stable retinal imagery


Supranuclear level- different from horizontal
Torsional eye movements


Vestibular/optokinetic
Vertical eye movements


Saccades/smooth pursuits/vergence
Compensate for head tilts
Hering’s law- motor embodiment of cyclopean
vision
Horizontal Vergence Movements
Tonic, +/ Accommodative, +/ Proximal, +/ Fusional, +/
Maddox, 1893
Disparity Vergence (allows stereo)
Vergence innervation is stimulated by
retinal disparity
 Corresponding retinal points are not
stimulated
 Purpose is to place targets of interest on
the horopter to maximize steropsis
 Coarse –v- Fine innervation

Feedback Control of Disparity
Vergence and Fixation Disparity
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Convergence Accommodation
Adapt.
tonic
-
Stimulus
(D)
Depth of
focus
S
S
gain
Cm/lens
retina
Reflex
Accom
+
CA/C
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Accommodative Convergence
Adapt.
tonic
Stimulus
(D)
Depth of
focus
S
gain
S
Cm/lens
retina
Reflex
Accom
+
AC/A
CA/C
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Proximal Vergence
Adapt.
tonic
Stimulus
(D)
Depth of
focus
S
S
Cm/lens
retina
Prox Accom gain
Percieved
Nearness
gain
Reflex
Accom
+
AC/A
Prox Vergence gain
CA/C
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Pathophysiology of common
binocular anomolies



Accommodative
insufficiency
Accommodative
excess
Accommodative
infacility


Convergence
Insufficiency
Convergence Excess
Accommodative Insufficiency

Accomodation is about 2D lower than age
expected norms
Ill sustained/fatigue
 Paralysis or paresis
 Unequal

Accommodative Excess

Accommodative response is greater than
expected
Accommodative spasm
 Usually presents with convergence
insufficiency

Accommodative Infacility
Dynamics of latency/ velocity/ time
constant are slower than normal
 Accommodative amplitudes are normal
 Difficulty changing focus from far to near
and back.


flippers
Convergence Insufficiency
High near exophoria, low AC/A ratio, low
positive relative convergence, excess
accommodation at near
 Poor or nonexistant convergent adaptation
 Reduced accommodative vergence=low
ac/a
 Abnormallly high convergence
accommodation

Convergence Insufficiency
Adapt.
tonic
Stimulus
(D)
Depth of
focus
S
S
Cm/lens
retina
Prox Accom gain
Percieved
Nearness
gain
Reflex
Accom
+
AC/A
Prox Vergence gain
CA/C
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Convergence Excess

High esophoria at near, high AC/A ratio,
lag of accommodation
Convergence Excess
Adapt.
tonic
Stimulus
(D)
Depth of
focus
S
S
Cm/lens
retina
Prox Accom gain
Percieved
Nearness
gain
Reflex
Accom
+
AC/A
Prox Vergence gain
CA/C
Disparity
(MA)
Pannum’s
Area
S
gain
S
Adapt.
tonic
retina
-
EOMs
+
Verg.
Resp.
Effect of blur on binocular vision
BI prism and minus lenses: demand
increases of negative disparity vergence
innervation and positive reflex
accomodation innervation
 BO prism and plus lenses: demand
increases of positive dispartiy vergence
innervaiton and negative reflex
accommodation innervaiton.

Summary- it is all connected..
http://www.mabot.com/images/2001/w2/brain-render.jpg