Download Brain damage-related Vision Loss - Functional Classification (Word)

(Slide 1 – Title Slide)
Functional Classification
of
Brain Damage-related
Vision Loss
CVI – CVD – TBI – CVA
CVI Workshop – AFB-JLTLI April, 2008
August Colenbrander, MD - San Francisco
Presenter’s Notes
We have heard about the many ways in which cerebral disorders can affect visual behavior. I
have been asked to speak about their functional classification.
(Slide 2)
ASPECTS Of VISION LOSS
Three Objects ?
Slide Graphics
Drawing of three shapes; triangle, square, and circle
Presenter’s Notes
To do so, we must look at different aspects of vision and vision loss. What do we mean when we
speak of aspects? Let me give an analogy. Do you see three objects here?
(Slide 3)
Three Objects?
Slide Graphic
Similar drawing to graphic in Slide 2, but now there are objects placed over the drawings. They
represent a cone for the triangle, a cube for the square, and a ball for the circle.
Presenter’s Notes
Or could it be that you are just looking at three aspects of an unfamiliar object?
(Slide 4)
Different Aspect – Same Object
Slide Graphic
Drawing of an object that first appears within the outline of the triangle. The second drawing is of
the same object being rotated on its vertical axis. The third drawing is of the object rotated and
appearing inside the square outline drawing.
Presenter’s Notes
Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Turning the object around to look at it from different view points, we see that what seemed
different objects may just be different aspects of the same object.
(Slide 5)
Aspects
Reveal properties of the object
they also
Reveal the point of view of the beholder
Presenter’s Notes
I like the concept of ASPECTS, because it informs us not only about properties of the object, we
also gain insight in the point of view of the beholder.
(Slide 6)
ASPECTS of an Office Visit
Patient with AMD . . .
Front desk: When can I schedule?
Doctor:
PDT or Avastin?
Manager: Will insurance pay?
Daughter: Can mother still drive?
Presenter’s Notes
Consider a patient with AMD, who comes to make an appointment. The front desk will think
about when to schedule her. The doctor will think about which treatment to select. The office manager
may worry whether the insurance may pay. The daughter worries whether mother can still drive. Those
are all very different aspects of the same clinical case.
(Slide 7)
Aspects of Visual Functioning
Slide Graphic
Diagram containing two major headings: The Organ (on the left side) and The Person (on the right
side). Each of these headings has subheadings underneath that are displayed in rectangular boxes. A
right point arrow appears between each of these boxes indicating a direction of flow. Four of these
subheadings also have subheadings and several points listed under each. They will be listed below in an
outline format. The final subheading and the list appear as the presenter talks about each point.
The Organ
Cause
Structure
Tissue
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Scar
Atrophy
Loss
Photograph of a man preparing to look through a microscope
Function
Organ
Acuity
Field
Contrast
Photograph of an eye care specialist testing a patient’s visual acuity with an eye chart.
The Person
Ability
Person
Reading
Mobility
ADLs
Photograph of a woman using a hand-held magnifier to read.
Consequences
Society
Participation
Quality of Life
Photograph of a woman knitting.
Presenter’s Notes
Similarly, depending on our point of view, we can consider many different aspects of vision loss
when we discuss visual functioning. First we may consider how various causes may result in structural
changes at the organ level, such as scarring, atrophy or loss. Here we need the pathologist to look at the
structure of the organ.
However, the structural changes do not tell us how well the eye can function. We need to widen
our view to include functional changes, and measure aspects such as visual acuity, visual field and
contrast sensitivity.
Knowing how the eye functions, does not tell us yet how the person functions. So we need to
widen our perspective again to consider tasks, such as reading, mobility, face recognition. Here we need
various low vision professionals to work with the patient, in this picture an elderly patient with macular
degeneration.
Beyond that, we need to look at the consequences in a societal context. Do these changes impact
on the person’s participation in society, causing job loss or reduced quality of life? How can we be sure
of a happy patient, which is the end goal of all our interventions?
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(Slide 8)
Aspects of Visual Functioning
Slide Graphic
This slide uses the same diagram as in Slide 7. The photographs have been removed and two other
points have been added at the bottom. A vertical line has been inserted to separate the Organ side from
the Person side.
The Organ
Cause
Structure
Tissue
Scar
Atrophy
Loss
Function
Organ
Acuity
Field
Contrast
VISUAL FUNCTIONS – How the EYE functions
The Person
Ability
Person
Reading
Mobility
Face recognition
Consequences
Society
Participation
Quality of Life
FUNCTIONAL VISION – How the PERSON functions
Presenter’s Notes
For today's discussion it is useful to draw a line in the middle; on the organ side we speak of
visual functions, on the person side of functional vision.
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
(Slide 9)
Aspects of Reading
Slide Graphic
This slide uses the same basic diagram used in Slide 7. The item Reading under The Person,
Abilities, has been moved down to use as an example. There are three additional points pulled out from
this item: Print size, speed; Reading endurance; and Reading enjoyment.
Presenter’s Notes
Various activities may cover more than one aspect. When we consider READING, the
measurement of print size and reading speed belong in the organ function column. Yet, it is not only
important how many words per minute we can read, but also how many hours per day. Reading
endurance belongs in the ability column. Reading enjoyment, finally, belongs with the aspect of Quality
of Life.
(Slide 10)
Traditional Medical Focus
Slide Graphic
This slide uses a similar diagram to the one used in Slide 7. It contains the two large headings; The
Organ, and The Person. It also contains the subheadings with the arrows connecting them.
The Organ
Cause – Structure – Function
The Person
Abilities – Consequences
Under The Organ side of the diagram an additional point has been added.
MEDICAL FOCUS
How do anatomical changes affect visual functions?
Presenter’s Notes
The traditional medical focus is on the organ of vision, its structure and its functioning.
(Slide 11)
Rehabilitation Focus
Slide Graphic
Similar diagram to Slide 10. Medical Focus is replaced with
FOCUS ON REHABILITATION
How do changes in the EYE and in the BRAIN affect functional vision?
Presenter’s Notes
The rehab focus extends this to the functioning of the person.
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
(Slide 12)
Traditional Medical Focus
Slide Graphic
Continued use of same diagram as before with the two major headings and the five subheadings.
The subheading Structure under The Organ has an additional point underneath it with several sub-points
which will be listed in outline format.
CAUSES of Vision Loss
Anatomical classification
Ocular
Optical
refractive error
opacities
Retinal
scars
dystrophies
Cerebral
Pathways
Lesions
PVLM
Cortex
Lesions
amblyopia
Presenter’s Notes
For the traditional focus on the causes of CVI, we need an anatomical classification. We consider
eye conditions, which can involve either the optics or the retina. We also consider cerebral conditions,
which can involve either the pathways or the cortical structures. That cerebral causes can involve more
than just the cortex is a clear reason why we should speak of CEREBRAL, rather than CORTICAL
visual impairment.
(Slide 13)
Consequences of Vision Loss
Slide Graphic
Continuing with same basic diagram. The subheading Function under The Organ has a new subpoint.
VISUAL FUNCTIONS
Standardized Measurement of
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Visual Acuity
Contrast Sensitivity
Visual Field
Cognitive problems
how to define
how to measure
Presenter’s Notes
To discuss the consequences of CVI we need a functional classification. That will be my topic.
In the area of VISUAL FUNCTIONS, we have good standardized methods to measure things such as
Acuity, Field and Contrast Sensitivity. We need to extend that to the area of cognitive dysfunctions. We
need to define the problems and standardize the assessment.
(Slide 14)
Consequences of Vision Loss
Slide Graphic
Same basic diagram. The Abilities subheading under The Person has a new sub-point.
FUNCTIONAL VISION
Visual Communication
Activities of Daily Living
Orientation and Mobility
Sustained Near Vision
Cognitive problems
Presenter’s Notes
In the area of the ABILITIES of the person, we can look at the four categories promoted by Lea
Hyvärinen. We again need to look in more detail at cognitive problems for each activity.
(Slide 15)
The Visual Process
Slide Graphic
The same basic diagram, similar to the one in Slide 8 in that it has the two major heading, The
Organ and The Person with the first level of subheadings; Cause, Structure, Function under The Organ,
and Abilities, Consequences under The Person. The vertical line is present again separating the two
major headings. The following items are listed under The Organ side.
VISUAL FUNCTIONING – how the VISUAL SYSTEM functions
Defects: VISUAL IMPAIRMENT
Refers to lower visual functions with retinotopic organization
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August Colenbrander, MD, April 2008
Items listed under The Person side
FUNCTIONAL VISION – how the PERSON functions
Defects: VISUAL DYSFUNCTION
Refers to higher visual functions with conceptual, cognitive organization
Presenter’s Notes
Going back to the earlier distinction between visual function and functional vision, we use the
tem VISUAL IMPAIRMENT to indicate deficits in how the eye and the visual system function. I prefer
to use the term VISUAL DYSFUNCTION for deficits in functional vision. I prefer these separate terms
to emphasize the differences in approach.
At the cerebral level, visual impairments deal with lower visual functions, mainly in
retinotopically organized cortical areas. Visual dysfunction refers to higher visual functions in areas with
conceptual and cognitive organization.
(Slide 16)
The Visual Process
Slide Graphic
Same basic diagram as in previous slide with new information under the Deficits points.
Deficits: VISUAL IMPAIRMENT
Lower visual functions
Tests use a variable stimulus to obtain a constant response
(threshold, 50% correct)
Deficits: FUNCTIONAL VISION
Higher visual function
Tests use a fixed task and record a variable response
(sustainable performance, must be > 50%,)
Presenter’s Notes
The assessment of the two areas is very different. On the impairment side, we typically test one
parameter at a time, in an artificial environment.
We record the stimulus level that results in a fixed endpoint: the threshold level, where the responses are
50% correct.
On the dysfunction side, we present a fixed task and record the variable performance of the
subject. That performance must be at a sustainable level, which always is well above 50% correct.
(Slide 17)
Tests - One Parameter at a Time
Slide Graphic
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Three photographs of familiar threshold tests: Visual Acuity Threshold, Contrast Sensitivity
Threshold, and Dark adaptation Threshold.
Presenter’s Notes
Here I show three familiar threshold tests, each measuring a different parameter. Visual acuity,
contrast sensitivity and dark adaptation. Each test varies only one parameter at a time.
(Slide 18)
Real Life – Multiple Parameters
Need for SUSTAINABLE performance
Slide Graphic
Photograph taken from inside a boat looking over a woman’s shoulder as she looks out of a
window at the approaching scenery. The photo illustrates the variation in details, contrasts, and
illumination found in most real world scenes.
Presenter’s Notes
In real life, however, we always have to deal with multiple parameters. Detail varies, as does
contrast, as does illumination. Furthermore, we ask for sustainable performance.
(Slide 19)
Stages of Visual Functioning
Slide Graphic
Diagram divided into two vertical sections: VISUAL FUNCTIONS; how the EYE functions, and
FUNCTIONAL VISION; how the PERSON functions. There are three stages that will be discussed.
OPTICAL STAGE
Provides clear optical image on the retina
Problems:
refractive error
opacities
Ages old
RETINAL STAGE
Translates optical image to neural impulses
Problems:
retinal disease
Since ophthalmoscope
NEURAL STAGE
Processes neural signals from inner retina to visual cortex to higher centers to allow visual
functioning
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Often overlooked
Presenter’s Notes
In visual functioning, we can very broadly define three stages, with very different properties: the
optical, the retinal and the neural stage. In the optical stage, an image of the outside world is projected
onto the retina. In the retina this optical image is translated into neural impulses. The neural stage
processes these signals, beginning in the inner retina and proceeding to the visual cortex and higher
centers to finally allow visual functioning.
The optical stage has been known for many centuries. Retinal diseases have been known since
the invention of the ophthalmoscope, a century and a half ago.
Neural processing has often been overlooked and is gaining more attention only in the last
decades.
(Slide 20)
Neural processing
Transcriber’s Note – Most of the text below in the Presenter’s Notes is displayed on the screen in chunks
as the presenter speaks about each point. The text appears at various locations on the screen illustrating
the presenter’s point.
Presenter’s Notes
How do we get from the retinal image to visually guided action? A significant intermediate step
that is often insufficiently studied is that of the MENTAL MODEL of the environment. The initial
transition from retinal image to mental model is largely subconscious and involuntary. The transition
from mental model to visually guided action involves perception and cognition and conscious decision
making.
We know that this intermediary step exists,
because we cannot interact directly with a retinal image that changes with every eye movement,
we need a stable model of the environment to plan our actions and to execute our locomotion through
and our manipulation of that environment.
(Slide 21)
Slide Graphic
Diagram of the left side of the brain showing different colored boxes representing various areas
of the brain. There are numerous arrows drawn to demonstrate the inter-relationship between all the
different areas of the brain in visually-related activities.
Presenter’s Notes
Modern imaging techniques have given us a better idea of where various brain areas involved
with these processes are located. I will not discuss those details.
I just want to point out that it speaks to the incredible plasticity of the brain that, while the neural
processing undoubtedly is the most complex part of vision, it also is the part that most rarely presents
problems, except in the cases that we are discussing today.
(Slide 22)
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Seamless Involuntary Integration
Slide Description
A table containing two columns labeled, SENSORY INPUTS and CONFLICTS with four items in
each column. The information from each column is listed below and separated by a comma.
SENSORY INPUTS, CONFLICTS
Visual Vestibular, Motion sickness
Left eye Right eye, Diplopia
Left hemisphere - Right hemisphere, Edge not detectable except in hemianopia
Ventral stream (what?) - Dorsal stream (where?), Deficits only in brain damage (CVI, TBI, CVA)
Presenter’s Notes
The previous slide depicted the many brain areas that are involved in different components of
functional vision. Yet, the processing from all those areas is seamlessly integrated. We would never
know that all this integration occurs, if it were not for cases where it fails.
Vestibular and visual cues are normally integrated. But if they contradict each other, we
experience motion sickness.
The images from the right and the left eye are integrated into a single perception. If that fails, we
experience diplopia.
Information from the left and the right hemisphere is integrated. However, we cannot detect any
boundary, except in cases of hemianopia.
Information from the ventral stream (the “what” stream) and the dorsal stream (the “where”
stream) is similarly integrated. But we notice problems only in cases of brain damage.
(Slide 23)
Retinal Image vs. Mental Model
Slide Description
A table with two columns and three items in each column.
RETINAL IMAGE, MENTAL MODEL
Changes constantly, Stable
Eye-centered, Environment-centerd
Presenter’s Notes
Let us look a little closer at the differences between the retinal image and the mental model.
We already mentioned that the retinal image is constantly changing, but that the mental model is stable.
Also, the retinal image is eye-centered, whereas the mental model is environment-centered.
(Slide 24 & 25)
Slide Graphic
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Photograph of an eye care specialist examining a woman in his office. Only a small portion of the
scene is visible at any one time as if looking through the cardboard tube of a paper towel roll. The image
is placed in motion by the presenter and moves around the photograph revealing different aspects of the
photograph. The presenter’s notes below explain the purpose of this image.
Presenter’s Notes
We can simulate what a video camera sees when it scans the room. That shifting image looks
unnatural and may make you feel sea sick. When we simulate the same with roving eye movements
across a stable environment, the image looks far more natural.
(Slide 26)
Retinal Image vs. Mental Model
Slide Description
This slide shows the same table as in Slide 23 with the addition of one more item in each column.
RETINAL IMAGE, MENTAL MODEL
Changes constantly, Stable
Eye-centered, Environment-centerd
2-dimensional images, 3-dimensional objects
Presenter’s Notes
Another important difference is that the retinal image is made up of 2-dimensional figures,
whereas our mental model is filled with 3-dimensional objects.
(Slide 27)
One 2-dimensional retinal image
Three distinct domains in the 3-dimensional Mental Model
Slide Graphic described in Presenter’s Notes
In this image from Escher, we see a pond with the reflection of some trees above, we see leaves
floating on the surface and we see a fish swimming under the surface. On the retina, these three
components are intermixed, but in our mental model they represent three distinct domains.
(Slide 28)
Retinal Image vs. Mental Model
Slide Description
Same table as in Slide 26.
Presenter’s Notes
Different activities have different visual demands.
In reading the emphasis is on recognition of finely detailed, 2-dimensional letter and word shapes. The
question of WHAT we see is relatively more important than WHERE we see it. In mobility, on the other
hand, we want to avoid obstacles. To determine WHERE a 3-dimensional obstacle is, is relatively more
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important than determining WHAT it is. In the manipulation of objects, the 2-dimensional detail and the
3-dimensional shape and location are both important.
(Slide 29)
Retinal Image vs. Mental Model
Slide Description
Same table as in Slide 28 with a new item in each column.
RETINAL IMAGE, MENTAL MODEL
Changes constantly, Stable
Eye-centered, Environment-centered
2-dimensional images, 3-dimensional objects
Strictly visual, Multi sensory - the blind have a mental model of their environment
Presenter’s Notes
The retinal image is strictly visual. However, the mental model is multi-sensory. Even the blind
have a mental model of their environment, built entirely from non-visual information.
(Slide 30)
Retinal Image vs. Mental Model
Slide Description
Same table as in Slide 29 with a new item in each column.
RETINAL IMAGE, MENTAL MODEL
Changes constantly, Stable
Eye-centered, Environment-centered
2-dimensional images, 3-dimensional objects
Strictly visual, Multi sensory
Attention shifts drive visual search, Attention shifts occur in the mental model
Presenter’s Notes
When we shift our attention, we do that in the mental model. Those attention shifts then drive
our eye movements and visual search.
(Slide 31)
One 2-dimensional retinal image
Three distinct domains in the 3-dimensional Mental Model
Attention shifts can occur between the domains of the Mental Model
Slide Graphic described in Presenter’s Notes
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Looking at Escher’s picture again, we can shift our attention from the trees to the leaves, or to
the fish, because they represent different domains in the mental model. We could never do that in the
retinal image, where the three are completely interwoven.
(Slide 32)
Retinal Image vs. Mental Model
Slide Description
Same table as in Slide 30 with a new item in each column.
RETINAL IMAGE, MENTAL MODEL
Changes constantly, Stable
Eye-centered, Environment-centered
2-dimensional images, 3-dimensional objects
Strictly visual, Multi sensory
Attention shifts drive visual search, Attention shifts occur in the mental model
Ends at field limits - scotomata cause gaps, Extends around us - no gaps - accumulates in memory
Presenter’s Notes
Finally, the retinal image ends at the limits of our visual field and has gaps where the retina has
blind spots. The mental model extends around us, although the area behind our backs has vague details,
because we have gathered less information about that area. The retinal image changes from moment to
moment. The mental model is persistent and filled with the best available information, accumulated in
memory.
(Slide 33)
Central Scotoma
Slide Graphic
Same photograph of woman being examined by eye care specialist in office. This photo has a
grayed out oval in the middle of the image representing what someone with a central scotoma would see.
Presenter’s Notes
The vision of people with a central scotoma is often simulated with a picture as shown here. In
reality, people never see their central scotoma as a hole in their vision. The stationary picture is
unnatural because it eliminates eye movements. When we introduce eye movements, we see that the
scotoma disappears from our awareness, as long as it is moving. As soon as it stops, we see it again as
one big gaping hole.
(Slide 34)
Steps in the Visual Process
Image formation
optical process, refractive error, opacities
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Image detection
retinal process, topographic variations, visual field
Image processing
pre-processing in retina, analysis in visual cortex, synthesis (right arrow) visual perception
(mental model)
Interpretation (in higher brain centers)
visual perception (right arrow) cognitive understanding, involves memory, recognition, other
senses
Interaction with the multi-sensory mental model,
involves motor response
Presenter’s Notes
Having discussed the various stages, we can now summarize the steps in the visual process. The
first step is image formation. It is an optical process. Its clarity is judged mainly by the fovea.
The next step is image detection in the outer retina. It introduces possible topographic variations
due to the distribution of retinal disease. This introduces the importance of the visual field.
The next steps, starting in the inner retina, involve image processing. After analysis of the
components in various brain centers and the synthesis of the result, it provides us with a visual
perception, the mental model of our environment.
Next is interpretation of that mental modal and cognitive understanding. It involves memory,
recognition and integration with other senses.
Finally, we are ready for a motor response to interact with the mental model of our environment.
(Slide 35)
The Visual Process
Slide Description
This slide contains a table with four boxes on the left side of the screen with the following text.
Box 1
Image formation
Image detection
Box 2
Image processing
analysis (right arrow) basic elements
Box 3
synthesis (right arrow) visual perception (right arrow) cognitive interpretation
Box 4
Interaction,
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
motor response
Presenter’s Notes
We can now summarize the steps in the visual process in these four boxes.
Image formation and image detection.
Basic image processing.
Synthesis to a visual perception and its cognitive interpretation, and finally,
Interaction and motor response.
(Slide 36)
The Visual Process
Slide Description
This slide, and the next 4 slides (36-40) use the same basic table as in Slide 35, with an additional
table on the right side. In this slide the table on the right contains two columns titled Anatomy and
Function. Each column has two boxes underneath.
Anatomy
Ocular
Cerebral
Function
Lower neural processes
Higher functions
These four boxes do not line up exactly. The boxes in the Function column are to the right of the boxes
in the Anatomy column but the box for Lower neural processes aligns partly with the bottom half of the
Ocular box and the top half of the Cerebral box. The Higher function aligns with the lower half of the
Function box.
Presenter’s Notes
At this point it is important to note that our functional and anatomical divisions do not coincide.
This is because the eye is not just a peripheral organ, in its development the retina is part of the brain.
(Slide 37)
The Visual Process
Slide Description
Same table as Slide 36 with additional box on right side labeled Visual Impairment. This box is
aligned to the right of Box 1&2 from the other table that contain the text
Image formation, Image detection
Image processing, analysis (right arrow) basic elements
Presenter’s Notes
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
We are now ready to talk about terminology.
We can apply the term visual impairment to the top two boxes.
(Slide 38)
The Visual Process
Slide Description
Same table as in Slide 37 with an additional box on in the right side column labeled Visual
Dysfunction. This box is aligned to the right of Box 3 from the other table that contains the text
synthesis (right arrow) visual perception (right arrow) cognitive interpretation
Presenter’s Notes
And the term visual dysfunction to the next, rather complex, group of steps that lead to cognitive
interpretation.
(Slide 39)
The Visual Process
Slide Description
Same table as Slide 35 containing the 4 boxes. This slide has an additional table on the right
side containing two columns that are not labeled. The first column has two boxes labeled Ocular,
Cerebral. The second column has a box labeled Visual Impairment. The box labeled Visual Impairment
aligns with the Ocular and Cerebral boxes and these align with Boxes 1&2 in the table on the left side. A
third box is present in the table on the right and is labeled Cognitive – Visual Dysfunction. This box is
aligned with Box 3 of the table on the left side that contains synthesis (right arrow) visual perception
(right arrow) cognitive interpretation
Presenter’s Notes
Adding adjectives, we can divide the impairment box into Ocular Visual Impairment (OVI) and
Cerebral Visual Impairment (CVI), to make an anatomical division.
At the visual dysfunction level we could speak of cerebral visual dysfunction. However, this
would be a pleonasm, since all higher functions are cerebral. I prefer to use the term Cognitive Visual
Dysfunction (CVD) to emphasize that dysfunctions are qualitatively different from impairments.
Using a separate term also solves the dilemma with some professionals who do not want to use
the term CVI unless there is visual acuity or visual field loss. We can now say that disorders such as
prosopagnosia or simultanagnosia are visual dysfunctions, rather than simple visual impairments.
(Slide 40)
The Visual Process
Slide Description
Same table as Slide 39 with one additional box at the bottom of the table on the right side labeled
Motor Dysfunction. This box is aligned with Box 4 from the table on the left side that is labeled
Interaction, motor response.
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Brain damage-related Vision Loss – Functional Classification
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Presenter’s Notes
Adding the interaction with the environment, we add the possibility of motor dysfunctions.
(Slide 41)
Examples
Slide Description
This slide shows some examples for each of the categories.
Presenter’s Notes
Ocular Visual Impairments (OVI) include cases of optical scatter (cataracts) or defocus
(refractive error) and of retinal scars and dystrophies.
Cerebral Visual Impairments (CVI) include sensory functions, such as visual acuity (amblyopia),
field (hemianopia) and motion perception and oculo-motor functions such as fix and follow. So far,
these functions are entirely visual.
Moving to visual dysfunction, other senses come into play as well. Examples include: visual
neglect, hand-eye coordination (foot-eye coordination in mobility), figure-ground separation, color
naming, etc.
In the motor dysfunction box we can mention that children in these groups often exhibit
inconsistent behavior and are easily tired.
(Slide 42)
Role of Visual Acuity (and optical aids)
Presenter’s Notes
Looking again at visual acuity, we see that it can play a role at all levels.
At the optical level it plays a major role, but as we proceed the role of visual acuity lessens.
Field defects outside the fovea, even a hemianopia, do not affect acuity.
Acuity describes the magnification requirement, which is irrelevant for cognitive problems.
Normal cognition can coexist with total blindness; abnormal cognition can also coexist with normal
visual acuity.
At the motor level, eccentric viewing may disrupt hand-eye coordination and acuity, but the
acuity loss does not cause the eccentric viewing.
(Slide 43)
Interactions
Slide Description
This slide contains the diagram shown earlier with the two headings THE ORGAN & THE
PERSON. The Organ has the subheadings Cause, Structure, Function. Sub-topics under these include
Visual Functioning (how the EYE functions) and the Deficits under this, Visual Impairment.
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
The other side of the diagram, THE PERSON, has two subheadings; Abilities, Consequences.
The sub-topics under these are Functional Vision (how the PERSON functions) and the Deficits under
this, Visual Dysfunction.
Under this the presenter speaks about 4 points individually.
Defects at several levels (OVI, CVI, CVD) may coexist
Interactions may go both ways
Occlusion
Deprivation amblyopia
Suppression amblyopia
avoid diplopia
These are additional reasons to reject the automatic association of the word impairment with
visual acuity deficits.
Some quick notes about interactions.
OVI, CVI and CVD may well coexist. They may also interact.
That interaction can go both ways. For example: Deprivation amblyopia is caused by lack of
input. Suppression amblyopia is caused by negative feedback from a higher level.
Early visual impairments may limit a child’s general development if not properly addressed by
the Blind Babies Foundation or other groups.
In cases where visual dysfunction and general dysfunction coexist, we may say that Cognitive
Visual Dysfunction exists if the visual developmental age is less than the general developmental age.
That statement, of course, assumes that we have adequate scales for both.
(Slide 44)
In Summary
Slide Description
This slide displays two tables. The first table to appear on the left is labeled Functional Categories
and contains the boxes presented earlier that have Ocular & Cerebral aligned with Visual Impairment;
Cognitive aligned with Visual Dysfunction; and Motor Dysfunction underneath.
The second table appears on the right suggests that you also consider, and is labeled Ability
Ranges. The left column of this table contains two items. The first item, Normal (or adequate)
performance is aligned with three boxes in the right column labeled; with reserve, lost reserve, with
effort/aids. The second item in the left column, Restricted performance is aligned with three boxes in the
right column labeled; restricted, marginal, impossible.
Underneath all of this are two points that will be displayed independently.
To be coordinated with anatomical insights
To be referenced to rehabilitative needs
Presenter’s Notes
In summary, we have provided you with functional categories to describe visual functioning.
Those categories must be combined with ability ranges to describe whether the deficit is mild, moderate,
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
severe or profound. Our time does not allow us to go into detail in this area. Additionally, these
categories need to be coordinated with our developing anatomical insights, and also with the
rehabilitative needs of the children or adults involved.
(Slide 45)
Proposed terms
Slide Description
This slide contains the same basic diagram in Slide 43 with the two major headings; THE
ORGAN & THE PERSON. Under The Organ there are 3 subheadings; Cause, Structure, Function.
Underneath this is the topic Visual Functions (how the VISUAL SYSTEM functions). Underneath this
is Deficits: Visual Impairments. There are two items under Visual Impairments.
Ocular Visual Impairment
Cerebral Visual Impairment
(may or may not include VA loss)
The other side of the diagram, THE PERSON, contains two subheadings; Abilities, Consequences. The
topic under these is Functional Vision (how the PERSON functions). Underneath this is the Deficit:
Visual Dysfunction. There is one item under Visual Dysfunction; Cortical Visual Dysfunction
Presenter’s Notes
This slide summarizes the terms I propose to use.
We distinguish between visual functions, which describe how the eye and the visual system function and
functional vision, which describes how the person functions.
When visual functions are disturbed, we speak of visual impairment. When functional vision is
disturbed, we speak of visual dysfunction.
On the impairment side we distinguish between ocular and cerebral impairments.
On the dysfunction side, we speak of cognitive visual dysfunctions to emphasize the differences.
(Slide 46)
What next?
Researchers need to know
Which impairments and dysfunctions can be lumped, which to separate.
Educators need to know
How to distinguish visual dysfunctions from visual impairments and how to address both.
Third Parties (insurance) need
Simple guidelines for coverage, services
Presenter’s Notes
What should be next on our agenda? Creating better definitions will be helpful for many groups.
Researchers need to know not to lump dissimilar impairments and dysfunctions into one group.
Educators, who have predominantly learned how to deal wit visual impairments, need guidance
to distinguish visual dysfunctions as a separate group that needs a very different approach.
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Brain damage-related Vision Loss – Functional Classification
August Colenbrander, MD, April 2008
Finally, the guidelines need to be simple enough to be understood by administrators, insurance
and other third parties to prevent inappropriate denial of services.
(Slide 47 – final slide)
Thank you for your attention.
[email protected]
www.ski.org/Colenbrander
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