DVT.08.09.16
Suppression
 Development of Sensory Fusion
o At birth, you start with a very low VA and very high refractive state
o With development, there is improvement of retinal and cortical systems, and an increase in VA with decrease of
the refractive state/ammetropia
st
o 1 relay station of visual pathway is the LGN
 2 types of cells in the LGN
 P-cells (Parvocellular)
o Sensitive to high spatial and low temporal resolutions
o Sensitive to color
o Associated with central retinal processing and macular area
 M-cells (Magnocellular)
o Sensitive to high temporal and low spatial resolutions
o NO color sensitivity
o Sensitive to illumination/luminance
o At the cortical level, after the LGN, you have the occipital cortex
 Initially, processes OD and OS separately (monocularly)
 At close to 3-4 months, you have development of binocularity
o If the ammetropia/refractive state of the two eyes is similar, and the eyes are aligned most of the time, then there
should be adequate development of binocularity
 Levels of Sensory Fusion
o Diplopia – No real sensory fusion
 Is NOT real sensory fusion, but it usually accompanies superimposition in patients with strabismus
 Definition: The same object falling on non-corresponding retinal points
st
o Superimposition – 1 degree fusion
 Definition: 2 different objects falling on corresponding retinal points
nd
o Flat fusion – 2 degree fusion
 Definition: Cortical summation of the same 2D objects falling on corresponding retinal points
 Reading uses flat fusion
rd
o Stereopsis – 3 degree fusion
 Definition: Different monocular perspective of the same object causes retinal disparity leading to depth
perception
 Normally develops around 6 months of age
 Writing uses stereopsis
Stereopsis
 Normal Sensory Fusion
o Stimulation of corresponding retinal points will lead to sensory fusion
 Corresponding retinal points are those that when stimulated in each eye at the same time give rise to
sensory fusion
o Of all levels of sensory fusion, stereopsis is the highest
 Disruption of Sensory Fusion
o In any previously normal binocular vision system, any oculomotor imbalance that causes strabismus or different
cortical image sizes will cause disruption of the normal sensory state
o Disruption manifests as:
 Diplopia (same object on non-corresponding points)
 Superimposition (different objects on corresponding points)  Is the one that causes the most disruption
OS fixating
OD turned in
 What is Suppression?
o Suppression is a defense mechanism to disturbances of binocular vision
o Defined as: lack of perception of objects in all or part of the field of vision of one eye, due to cortical inhibition
under binocular vision
o Can occur with…
 Non-strab binocular anomalies
 Strabismus
 Functional amblyopia
 Aniseikonia (different image sizes at the cortical level)
 Any other binocular vision disturbance
o WILL NOT occur with accommodative anomalies!!
o Types of Suppression
 Physiologic suppression (Is normal)
 Occurs when an object falls outside the singleness horopter
 Pathologic suppression (Is abnormal)
 Active cortical inhibition of all or part of the visual field in the presence of a binocular vision
disturbance
 Origin of Suppression
o The driving mechanism behind suppression is retinal rivalry!
 Retinal rivalry is basically the brain’s choice on which image it prefers more, in order to use less energy
o Occurs under anomalous binocular vision in the V1 (primary visual cortex)
o Inhibition of cortical binocular cells
o Effect on ocular dominance histogram
 Development of binocular cells affected
 Effect on development of monocular cells depends on the onset of the disturbance
 Ocular Dominance Histograms
o Normal ODH

1 2 3
Contralateral
4
5 6 7
Ipsilateral
Laterality
 Columns 1-3 represent the contralateral eye.
Columns 5-7 represent the ipsilateral eye.
 Column 4 represents purely binocular cells with
equal input from contralateral and ipsilateral

o
Monocular vs. Binocular
 Columns 1 and 7 = Purely monocular only
 Columns 2 and 6 = More monocular than binocular
 Columns 3 and 5 = More binocular than monocular
 Column 4 = Purely binocular only
Abnormal ODH
Interpretation  NO development of binocular vision at all
Possible causes  Constant alternating strabismus
1
2
3
4
5
6
7
Interpretation  NO development of BV at all, and only 1 eye had cortical
development (If this was ODH of right cortex, then only OS developed)
Possible causes  Constant unilateral strabismus , Congenital cataract
1
2
3
4
5
6
7
Same as above, just opposite eye
1
2
3
4
5
6
7
Interpretation  Very low development of BV
Possible causes  Strabismus with anomalous correspondence
1
2
3
4
5
6
7
 Developing Suppression
o BV anomaly should be present before the age of 6 in order to develop suppression
 Suppression = involuntary
 Ignoring = voluntary
 Ignoring requires the patient to concentrate on only one image, while still being aware of the
different images. When patient is older than 6 years old, tends to ignore rather than suppress
o Both suppression and ignoring require energy
o Suppression depends on the nature of the ABV
o Trigger in:
 Strabismus: diplopia and superimposition
 Anisometropia: superimposition
 Non-strab binocular anomalies: constant motor fusion stress
o It is very unusual for patients to suppress the full VF of an eye
 Constant strab  constant suppression
 Intermittent strab  intermittent suppression
 Alternating strab  alternating suppression
 Effects of Suppression
o Normal visual field = 180°
o Normal binocular overlap = 120°
o Effect on cyclopean field
 ESO: reduces
 EXO: increases
o Effect on binocular overlap
 ESO: potentially increases
 EXO: potentially decreases
EXO
ESO
o
Smaller VF
Larger overlap
-
Larger VF
Smaller overlap
Area and depth of suppression
 ESO: D-shaped scotoma deeper at the fovea and shallow peripherally
 EXO: most of the temporal retina and equal depth throughout
ESO
EXO
Deep
Shallow
o
o
o
ESO patients are more likely to have anomalous correspondence
EXO patients are more likely to have panoramic anomalous correspondence. They also do not tend to suppress
the fovea as much because they have very little binocular overlap so little superimposition
Suppression eliminates central sensory fusion
 Alternative is anomalous correspondence
 Results in very small scotomas and still allows some sensory fusion and gross stereopsis
o Suppression will NEVER have stereopsis. With anomalous correspondence, you may
have some gross stereopsis