Pedretti Ch. 24 - Assessment of Visual Deficits Flashcards
(154 cards)
1
Q
Role of Vision in the Adaptation Process
A
According to Ayres, the brain is responsible for filtering, organizing and integrating sensory information in order to generate an adaptive response to a particular context.
Vision dominates other senses because it “takes us farther into the environment” and is faster
Vision helps us to anticipate developing situations and create a plan to handle them
2
Q
Successful adaptation depends on
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Successful adaptation depends on the ability to anticipate situations and context by utilizing sensory context.
eg. “It looks like rain, I’d better take an umbrella.”
3
Q
We use vision in the decision-making process to:
A
- avoid objects
- “size up” situations (e.g. “that looks delicious”)
- Social communication (“reading” body language)
4
Q
The speed of information processing through vision allows us to:
A
The speed of information processing through vision allows us to successfully adapt to dynamic environments. Monitoring our own movement against movement of other objects around us.
-This is why reintegrating someone with a visual impairment into the community can be so difficult.
5
Q
Visual impairment can occur secondary to:
A
Visual impairment can occur secondary to: disease, trauma and aging. Often a combination of two of these.
6
Q
Impairment can:
A
Impairment can alter the quality, quantity and speed of visual info sent to CNS OR how the CNS processes and responds to this info.
Impairment has the potential to change a client’s interaction with all aspects of the environment and people in it
7
Q
Why are effects of visual impairment are often attributed to other causes
A
Effects of visual impairment are often attributed to other causes because visual impairment is “a hidden disability”
8
Q
Visual Perception
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Raw visual information (light) must be transformed into images and compared with stored memories, other sensory input and knowledge in order to be used for decision making. This is known as Visual Perception
9
Q
Route of visual information
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Information follows a circular route from the retina in anterior of the brain to the occipital lobe in posterior brain and back again
Along the way, visual info is sorted, fine-tuned, combined and repackaged to create a product for adaptation.=
10
Q
Visual perception process
A
- Light enters eye and passes through cornea & lens to focus on the retina
- Information conveyed over optic nerve and tract to the lateral geniculate nucleus (LGN) of the thalamus
because of the optic chiasm, the LGN receives info from both eyes - Information then travels over the geniculocalcarine tracts (GCT) to V1 of the visual cortex
- Visual cortex sorts info, sharpens and fine-tunes features and then disperses info for cortical processing
- Info processed by temporal and parietal circuitry
- Info combined/integrated with other incoming sensory info to establish relationships between the body and the environment
- Info sent to prefrontal circuitry for cognitive processing to make decisions and plans
- This area, in conjunction with premotor circuitry, is responsible for planning skilled body movements (including eye movements)
- Important structures in this region are the frontal eye fields: responsible for voluntary visual search of space on the contralateral side of body based on expectation where visual info will be found in environment (e.g. light switches on walls, not ceilings)
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Q
Parallel-distributed sensory processing
A
To integrate, info sent to prefrontal area over two routes, a process known as “Parallel-distributed sensory processing”
12
Q
Northern route
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“Northern route” through posterior parietal circuitry:
- Parietal lobe is a synthesizer of sensory info, creating internal sensory maps to orient the body in space
- Info used to tune the CNS to presence of objects surrounding the body and spatial relationships of the objects to the body and to each other
- In order to do this, the visual info is integrated with other sensory info
- The “map” created is body centered and dynamic, changing in shape and content as the body moves through space
- Each hemisphere contains a map of the contralateral side of the body
- Map is not detailed, a general impression of objects in space on that side of body
- CNS relies on visual info from peripheral areas of retinal fields to create & maintain maps
13
Q
Southern route
A
“Southern route” through posterior temporal circuitry:
- info combined with language and auditory input
- processed for visual object info and recognition
- Purpose is to identify objects and classify them.
- Uses precise input from the macular-foveal area to tune into visual details of objects
- Critical to distinguish discrete features of objects (e.g. facial features)
14
Q
Does all info travel over GCTs?
A
Not all info travels over GCTs. Many pathways leave optic nerve & tract to subcortical areas including hypothalamus & brainstem
15
Q
Brainstem contains
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Superior colliculi (located in midbrain), the primary brainstem processing centers for visual input. Responsible for detecting moving visual stimuli in peripheral visual fields. When motion is detected, automatically initiates eye movement toward that direction. Thus, serves as an early warning system.
Nuclei of cranial nerves III, IV and VI which control the extraocular muscles of the eyes.
Basic visual functions such as light (pupillary) reflex and the accommodation reflex
16
Q
Hierarchic Model of Visual Perceptual Processing
A
- Visual perceptual function can be conceptualized as a hierarchy of processes that interact with each other in a unified system, where each process is supported by the one that precedes (bottom-up) it and can’t properly function without integration of the lower-level process.
- Ability to adapt to vision is a result of each processes working in synergy. Although discrete processes can be identified, they do not work independently of each other.
17
Q
Hierarchic Model of Visual Perceptual Processing: 3. Explanation of hierarchy: Visual Cognition
A
- Explanation of hierarchy:
Visual Cognition: ability to use vision to complete cognitive processing (manipulate and integrate visual input with other sensory info to gain knowledge, solve problems, make plans and decisions). - begins in childhood
- e.g. if we see a 12 inch adult, by applying size constancy, we assume the adult must be a good distance away
- Serves as a foundation for all academic endeavors
- Can’t occur without visual memory
18
Q
Explanation of hierarchy: Visual Memory
A
Visual Memory: mental manipulation of visual stimuli requires ability to create and retain a picture of the object in the mind’s eye while visual analysis is completed. Must also be able to store and retrieve images from long-term memory.
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Q
Explanation of hierarchy: Pattern Recognition
A
Pattern recognition:
Identifying the salient features of an object and using them to distinguish the object from its surroundings.
1. Salient features: one that distinguishes a particular object from another. E.g. the salient feature that distinguishes an “E” from an “F”
2. Involves two abilities:
- identify the configural and holistic aspects of an object (general shape, construe and features)
- ability to identify specific features of an object (color, shading, texture)
20
Q
Explanation of hierarchy: Visual Scanning
A
Visual Scanning: organized and thorough scanning of the visual array through use of saccadic eye movements (eye moves toward an object of interest)
1. Most important details re-examined multiple times through a cyclic saccades to ensure correct identification
21
Q
Explanation of hierarchy: Visual Attention
A
Visual Attention: saccadic movements reflect engagement of visual attention shifting from object to object.
- Occurs on two levels:
- Automatic/reflexive level controlled mainly by brainstem. Engaged by novel stimulus occurring in the peripheral visual field (e.g. flash of light). Serves as protection from intrusions.
- Voluntary level driven by cortical processes of cognition. Completed for purpose of gathering info, driven by desire to locate an object in the environment or obtain particular info (e.g. looking for keys OR locating exit). - How a person attends to an object determines if that visual input is analyzed by the CNS
- A critical prerequisite for visual cognitive processing
- Type of visual attention engaged by CNS depends on type of visual analysis needed → Global awareness (e.g. awareness chair is in a room) vs. selective visual attention (e.g. identify style of chair). It is necessary to use more than one type of visual attention simultaneously.
- Visual attention requires large amount of neural processing and therefore can easily be disrupted by brain injury, BUT is highly resilient.
22
Q
All levels of hierarchy can’t occur without visual input from visual functions of:
A
- oculomotor control: enables eye movements to be completed quickly and accurately and ensures perceptual stability
- visual fields: register the visual scene and ensure CNS receives complete information
- visual acuity: ensures visual information sent to CNS is accurate.
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Q
Deficits in the hierarchy
A
Brain injury or disease can disrupt visual processing at any level in the hierarchy.
Because of the way the hierarchy is structured, a client can appear to have a deficit in higher level process, even though the deficit is actually at a lower level.
24
Q
Intervention: ophthalmologist
A
Opthamologist - medical doctor who completed residency in ophthalmology. Primarily responsible for diagnosing and treating medical condition that cause visual impairment. Neuro-ophthalmologists are board certified and treat the largest number of persons with visual impairments from brain injury.
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Intervention: optometrist
Optometrist - independent healthcare provider with a doctorate in optometry from a postgraduate university program. Specialize in variety of areas: neurorehabilitative, developmental and behavioral optometry. NOT medical doctors. Also treat and diagnose medical conditions resulting in vision loss. Provide nearly ⅔ of primary eye care in US.
*Which specialty the team uses depends primarily on availability and reimbursement
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OT Eval
To develop an intervention plan, OT must link limitations in occupation and performance to the presence of a visual impairment
Assessments are utilized by the OT to establish this link. Also known as establishing “medical necessity” → prerequisite for reimbursement for OT services.
Ophthalmologist or optometrist are rarely part of the rehab team. Process is time-consuming and difficult.
OT practitioner must convince physician/case manager that a deficit exists and is limiting occupational performance and that a referral to specialists is needed. Requires OT to be well versed in basic visual assessments such as: acuity, contrast sensitivity function and visual field.
One example of assessment by textbook author: Brain Injury Visual Assessment Battery for Adults (biVABA). Designed specifically for OTs in developing intervention plans. Consists of 17 subtests including tools used by ophthalmologists and optometrists.
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Occupational Therapy Intervention: Main focus
Main focus is to change outcome in categories of visual disability and visual handicap
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Occupational Therapy Intervention: two approaches
Remediation: attempts to establish or restore client’s ability to complete visual processing
Compensatory: emphasis is on changing the context of the environment or task to enable client to successfully use current level of visual processing
- Approaches may be used alone or together depending on client needs
- Education of client and family is always used in conjunction with the two approaches
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Visual acuity
Visual acuity: the ability to see small visual details, contributes to CNS recognizing objects by providing clear and precise visual information.
Greater quality visual input → More precise image created by CNS processing → faster and more accurate CNS in recognizing and discriminating objects → faster and more accurate information processing to facilitate decision making
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Acuity process
1. Light rays enter eye through pupil and are focused precisely on the retina by the cornea, lens and optic media.
2. Retina processes the light and records a “picture” that’s relayed to the CNS via the optic nerve and pathway
- Process requires: precise focus of light on retina, maintaining sharp focus over various focal distances, sufficient illumination of retina to capture a quality image, optic nerve transmitting image through CNS for processing.
- Any compromise of these structures results in degradation of the image and reduced acuity
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Measuring visual acuity
Most commonly measured by reading progressively smaller optotypes on a chart. Common measurement: Snellen fraction (e.g. 20/20 vision) which is a ratio of distance to the size of the optotype.
- 20/50 = Standing at a distance of 20 feet, person can see a letter that a person with normal vision would see at 50 feet.
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Visual acuity is a continuum
Visual acuity is a continuum of visual function ranging from detection of high-contrast features to detection of low-contrast features
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Low-contrast acuity AKA contrast sensitivity function (CSF):
Low-contrast acuity AKA contrast sensitivity function (CSF): ability to detect borders of object as they decrease in contrast from background
Because environment is made of low-contrast features (curbs and steps, faces), CSF is critical to negotiating an environment safely.
CSF can be impaired even when high-contrast acuity is intact.
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Two forms of high-contrast acuity:
Distance acuity and reading acuity
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Distance acuity:
Distance acuity: ability to see objects at a distance
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Reading acuity:
Reading acuity: ability to see objects clearly as they come closer to the eye. Near vision range → 3-16 inches from eye. Measured by reading progressively smaller print. Dependent on brainstem neural processing of accommodation.
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Accommodation
Accommodation: enables eye to maintain clear focus on object as it comes closer. As object approaches eye, point of focus on retina is pushed farther back, causing it to go out of focus. CNS adjusts through three step process of accommodation:
1. Eyes converge to ensure light rays stay parallel and in focus
2. Crystalline lens thickens to refract light rays more strongly and shorten focal distance
3. Pupil restricts to reduce light ray scattering
Controlled by cranial nerve III (oculomotor). Injuries that affect brainstem (where nuclei of CN III is located) or this nerve, can disrupt accommodation.
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Presbyopia
Accommodation works effectively until 4th decade of life. At age 50 lens becomes less flexible, creating presbyopia
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Why do both forms of acuity need to be measured
Because of the influence of accommodation, both forms of acuity need to be measured to gain accurate assessment of acuity function
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Deficits in Visual Acuity
Most deficiencies are due to defects in optical system which cause image to be poorly focused on retina
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Myopia
Myopia (nearsightedness): image of object is focused on a point in front of the retina and is blurred once it reaches retina. Corrected via a concave lens in front of retina.
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Hyperopia
Hyperopia (farsightedness): image comes into focus behind the retina causing image to remain out of focus on retina. Corrected via a convex lens in front of retina.
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Astigmatism
Astigmatism: light is focused differently by two meridians 90 degrees apart. Caused by cornea that are not perfectly smooth and spherical (spoon shaped or dimpled) which blurs image because both meridians can’t be focused on the retina. Corrected via cylindrical lens in front of eye.
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Optical defects primarily occur because of impairments in 3 areas of processing
1. Disruption of the ability to focus light onto retina
2. Inability of retina to accurately process the image
3. Inability of optic nerve to transmit info to the rest of CNS
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Impairments may occur from:
brain injury or disease
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Disruption of the Ability to Focus an Image on the Retina
Focusing an image depends on the transparency of structures between outside of the eye and the retina and their ability to focus light rays
```
Light passes through four transparent media:
Cornea
Aqueous humor
Crystalline lens
Vitreous Humor
```
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Disruption of the Ability to Focus an Image on the Retina
Conditions that can occur with head trauma: Corneal scarring
Corneal scarring - may result from direct trauma to eye. Inner layers of cornea are damaged and scar as they heal, creating an irregular surface that refracts light unevenly. Experiences blurred vision similar to astigmatism.
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Disruption of the Ability to Focus an Image on the Retina
Conditions that can occur with head trauma: trauma-induced cataract
Trauma-induced cataract - caused by trauma to crystalline lens which may displace or develop a cataract that clouds the lens and reduces acuity.
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Disruption of the Ability to Focus an Image on the Retina
Conditions that can occur with head trauma: vitreous hemorrhage
Vitreous hemorrhage - trauma to eye can result in bleeding to the vitreous humor. Since blood is opaque, light cannot pass through and client experiences floaters, shadows and episodes of darkness as blood passes in front of retina.
* only vitreous hemorrhage is temporary and resolves w/o treatment
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Disruption of the Ability of the Retina to Process the Image
Health and integrity of retina affects quality of image sent to CNS for processing. Receptor cells of retina can be damaged by injury or disease
Diseases:
Macular degeneration
Diabetic retinopathy
--Both associated with age and increase in incidence in the 7th and 8th decade of life
Retina damage can reduce high- and low-contrast acuity.
Approx. 1 in 4 persons older than 80 has a visual impairment that affects retina
Too often, visual loss resulting from disease is overlooked or misdiagnosed as an impairment in attention or cognition associated with CVA
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Disruption of the Ability of the Optic Nerve to Send the Retinal Image
Can occur from penetrating injury to the nerve
Can also occur from indirect trauma from optic canal fracture from facial or blunt forehead fractures. Most common in children and young adults. Usually results in unilateral injury.
Closed head injuries can cause stretching or tearing of optic nerve. Results in significant and most often bilateral damage.
Compression of nerves from intracranial swelling or hematoma resulting in bilateral damage
Glaucoma damages nerve fibers carrying peripheral visual field input. Can also affect central visual field and reduce visual acuity.
Multiple Sclerosis causes plaques to develop along nerve resulting in optic neuritis causing reduced acuity, sensitivity to light
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Occupational Limitations Caused by Reduced Visual Acuity
Severity of limitation
Severity of limitation depends on extent of loss of acuity and whether there is a loss of central acuity, peripheral acuity or both.
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Occupational Limitations Caused by Reduced Visual Acuity
Central acuity loss
Central acuity loss: inability to discriminate small visual details and to distinguish contrast and color.
- Activities dependent on reading, writing, fine motor coordination are affected (reading recipes, dialing, identifying money, makeup/shaving)
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Occupational Limitations Caused by Reduced Visual Acuity
Peripheral acuity loss
Peripheral acuity loss: mobility is affected. Unable to identify landmarks/obstacles in path, unable to accurately detect motion, may impair ability to safely maintain orientation in environment.
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Assessment of Performance Skills: 1st step
First begin with observation of client performance in daily activities
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Clients with deficits in visual acuity often complain of:
Clients with deficits in visual acuity often complain of: difficulty reading print, print being too small, faint or distorted, parts of words missing or words running together and swirling
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Clients with CSF deficits often complain of:
clients complain of inability to see faces clearly or distinguishing between similar colors or low contrast substances like spilled water on floor
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Both high-contrast and low-contrast acuity measured. High contrast acuity measured for:
High-contrast acuity measured for distance and for reading via a Snellen chart.
- Needs to be illuminated and at an exact viewing distance (remember snellen measurement is a ratio with distance) to get an accurate measurement.
- Acuity level is determined by the smallest line that can be read with majority accuracy
- Standard charts measure primarily in a range of acuity that can be compensated for with glasses, nothing below a 20/200. Below this level, needs to be referred out.
- Test charts for measuring low range visual acuity: LeaNumbers Low Vision Test Chart and the Warren Test Card from the biVABA
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Assessing CSF
CSF also assessed via similar charts, but size of letters remains the same and contrast diminishes down each line
Assessments include: LeaNumbers Low Contrast Screener and Tests & LeaSymbols Low Contrast Screener and Tests
Must also be illuminated properly & at specific distance
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If OT recognizes deficit:
Remember, OT's role is to link the presence of a deficiency to a limitation in occupational performance NOT diagnosing cause. That is the role of the ophthalmologist or optometrist who then determines how to manage condition.
When OT determines an acuity deficiency, that information is used to modify activities and environment
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Visual Field
Visual field: the external world that can be seen when a person looks straight ahead.
Extends 60 degrees superiorly, 75 degrees inferiorly, 60 degrees to the nasal side, 100 degrees to the temporal side
Most of the field is binocular and is seen by both eyes except small portion of peripheral temporal field which is monocular because of occlusion from the nose
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Areas of the field: Fovea
Fovea: located in the center of visual field and is approx. 8-10 degrees in diameter. Records visual details for identification.
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Areas of the field: Central Visual Field
Central visual field: Area includes the macular area with fovea located inside. 20-30 degrees in diameter. Used to identify objects.
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Areas of the field: Peripheral Field
Peripheral field: rest of the visual field. Composed of rod receptor cells which detect general shapes and movement.
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Areas of the field: Blind Spot
Blind spot: locate on the temporal side on the border between central and peripheral visual fields on temporal side. No sensory receptors located here as optic disc pierces retina here.
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Visual Field Deficits (VFD)
Result from damage to receptor cells in retina or on the optic pathway that relays retinal information
Location and extent depends on where damage occurs
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Homonymous hemianopia
Homonymous hemianopia, most common VFD post-brain injury
- Loss of vision in half of the visual field in the eye AND the deficit is the same in both eyes
- Lesion on GCT causes homonymous hemianopia on contralateral side
- Most hemianopias caused by occlusion of posterior cerebral artery, middle cerebral artery can also cause it
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Occupational Limitations Caused by Visual Field Deficits
Changes in visual processing caused by VFD
Changes in visual processing caused by VFD can significantly limit daily performance
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Occupational Limitations Caused by Visual Field Deficits
Most important change
Most important change occurs in the search pattern used by the person with VFD to compensate for blind are of field
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Occupational Limitations Caused by Visual Field Deficits
Scanning
Person tends to narrow the scope of scanning, turning head very little (rather than turning head farther to see around blind field). Limits search to areas immediately adjacent to seeing side body.
- This strategy is caused by perceptual completion
- Perceptual completion: a visual process where the CNS samples a visual array an internally completes a visual scene based on expectations. Provides speed in info processing.
- Viewer thinks he’s seeing complete visual scene
- With visual field loss, perceptual completion makes it difficult for client to determine how field has changed.
- Because of perceptual completion, client not immediately aware of the absence of vision after onset of deficit.
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What about the CNS?
CNS can’t place objects in visual scene that it does not actually see. Client may be unaware of unanticipated objects on blind side. Client may run into objects recently placed on blind side or may not be able to find items placed in blind field.
- Client will have odd perception of a complete visual scene, but with objects seeming to appear and disappear on affected side.
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Narrowed Scanning
Protective strategy may be adapted where client attends to only visual input from intact visual field → narrowed scanning.
- Creates significant limitations in occupations requiring monitoring of full visual field.
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Once person becomes aware of VFD
Once person becomes aware of VFD, search is often slow and delayed again due to perceptual completion. Client slows down scanning toward blind side.
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If hemianopia affects macular portion of visual field
If hemianopia affects macular portion of visual field, especially fovea, client may miss or misidentify visual details. Can create challenges while reading. Reduce width of perceptual scan while reading from 18 characters wide to 3-4 characters.
- May view only part of a word or skip words. “She should not shake the juice” becomes “He should make juice”
- Slows down speed while reading and hinders comprehension
- Reading numbers are more challenging as there is rarely context surrounding it to uncover errors.
- Clients have difficulty paying bills
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VFD on dominant side
If VFD occurs on same side as dominant hand, client may have difficulty guiding the hand in fine motor activities
Handwriting becomes difficult
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Primary activities affected by VFD
Primary activities affected include mobility, reading, writing, and daily occupations reliant on these skills
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More dynamic environments
A more dynamic environment, requiring a larger visual field, the larger the limitation
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Clients with VFD commonly face
Clients with VFD commonly face: anxiety moving in unfamiliar or crowded environments, social withdrawal, loss of self-confidence due to numerous mistakes, depression because of limitations
Sometimes anxiety becomes so severe, they experience an autonomic nervous system reaction and become physically ill
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Visual Field Assessment: perimetry
Perimetry: the process of measuring the visual field (VF)
The perimetry test selected depends on availability, cost of test, and ability of the client to participate
- Can be a simple bedside assessment (like the confrontation test) or a scanning laser ophthalmoscope (SLO)
- Confrontation test is inexpensive and performed anywhere. SLO needs trained technician and the instrument
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All perimetry testing involves 3 parameters:
1) Fixation on a central target by the client
2) Presentation of a target of a specific size and luminosity in a designated area of the visual field
3) Acknowledgement of the second target without breaking fixation on the central target
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Testing is done with either static or kinetic presentation of the target
Static presentation: target appears in a specified area of the visual field w/o being shown moving to that location
Kinetic presentation: target moves in from the periphery until it is ID’ed
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Most accurate perimetry test:
Computerized, automated perimetry, completed by an ophthalmologist/optometrist
- Automated perimetry: client puts chin on a chin rest and fixates on a central target in a display with lights in various locations and intensities. Client responds to each light seen by pushing a button
- Result: accurate measurement of the areas of absolute loss (no response) and relative loss (decreased retinal sensitivity) w/in the field
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Optometrist may also use the tangent screen, a simpler test
Assesses the integrity of the central visual field
Client sits in front a black felt screen with a grid stitched into it. Client fixates on the center as the examiner moves a white target in a certain area of the screen. Client must fixate on the center and indicate if they see the appearance of the target
If the client does not see the target - that point in the visual field is recorded as a loss
Examiner uses the grid to determine the location of the visual field deficit (VFD)
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OTs can screen VFD by using simple perimetry testing with careful observation of client performance of daily occupations
Confrontation testing:
Bedside exam that provides crude indication of VF loss
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Static confrontation test
OT sits in front of Pt at a meter distance, Pt fixates on a centrally placed target (the OT’s eye). OT holds up 2 targets in each of the four quadrants of the VF (R upper, R lower, L upper, L Lower) and Pt indicates if targets are seen
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Kinetic confrontation test
OT stands behind Pt and moves a target (usually a penlight) in from the periphery while the Pt fixates on a central target. Pt indicates when target is noticed
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Confrontation testing has been shown to be unreliable in all areas except for __
Confrontation testing has been shown to be unreliable in all areas except for gross defects
- OTs that use confrontation testing should correlate their findings with observations of client performance
- If clinical observations suggest a deficit, but confrontation test shows no deficit, the clinical observations should carry more weight
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The Damato Campimeter
A portable test card that provides a precise measurement of the central 30 degrees of the VF
The card has a grid with 30 numbered targets. The Pt moves the eye to each of the targets (rather than the OT moving each target) and indicates if they see a centrally fixated dot. If the Pt can’t see the dot, then the VF is recorded as a loss
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Limits to perimetry testing
Clients w/ limited attention, language, cognition may give unreliable perimetry results
Also hard to distinguish between a VFD and a deficit in visual attention
However, client’s performance of daily activities will strongly indicate a VFD
- Examples: client changes head position when asked to view objects in a certain plane, client consistently bumps into objects on on
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What does perimetry test establish
Perimetry tests ONLY establishes if VFD is present, and its size and location of the deficit
If intervention is needed, OT needs to determine if client is able to compensate for the VFD in daily activities, and the quality and consistency of that compensation
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The level of VFD impairment
The level of VFD impairment will depend on whether the VFD occurs alone, or with visual inattention
If client has difficulty completing an activity, the visual requirements of the activity should be analyzed to see if the VFD is interfering with performance
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Reading also often affected by a VFD
The Visual Skills for Reading Test (VSRT)
The Visual Skills for Reading Test (VSRT): measures interference of the VFD in reading performance
Assesses influence of the scotoma (field loss) in the macula on the visual components of reading (includes visual word recognition and control of eye movement)
Client asked to read single letters and words printed on a card - cards come in three different versions in four font sizes
Test measures reading accuracy and corrected reading rate. Provides info on the prevalent types of reading errors made by client
Performance on the letter/reading charts used to measure visual acuity may also indicate the influence of a VFD on reading
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Telephone Number Copy (part of the biVABA)
Telephone Number Copy (part of the biVABA): measures client’s accuracy in reading numbers
Client copies down telephone numbers with #s easily misread by people with VFD (6, 8 ,9 ,3)
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To effectively compensate for the VFD...
To effectively compensate for the VFD, client must execute organized and thorough search of the blind field by using the seeing portion of the VF
Ex.: person with a left VFD must use the right VF to search both left and right field
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Clients with a VFD have difficulties with...
Clients with a VFD have difficulties searching both peripersonal space (space immediately around the body) and extrapersonal space (space extending from the body into the environment)
Difficulties with peripersonal space may affect: ADLs like grooming, dressing, reading, writing. IADLs like meal prep
Difficulties with extrapersonal space may affect: mobility, driving, shopping
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To navigate community environments with a VFD
To navigate community environments with a VFD, client must use a wide scanning strategy that is initiated on the side of the deficit quickly and efficiently
- must shift attention and search rapidly btw the central VF and the peripheral VF
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Observational tests can be used to measure the ability to compensate for VFD during mobility
Dynavision 2000: objective assessment of the client’s ability to execute compensatory search strategies
Use of a laser pointer to observe the client’s search capability
- Client locates and touches the projected dot
- Strategy used by the client to locate the dot and the efficiency of the strategy are recorded
Integration of visual scanning with ambulation is final component of mobility assessment. Completed to see if client can compensate for the deficit during body movement
- Can be assessed by the ScanCourse from the biVABA
- - Client has to walk through the course and ID targets placed in various locations on both left and right sides.
- - Client’s ability to locate the targets during ambulation is noted
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Addressing Limitations in Mobility
Limitations in mobility occur primarily b/c client does not turn their head far enough, or often enough toward the blind field to take in the info needed for safe mobility
- Ex: if the inferior VF has been affected (like with hemianopia), client may also experience difficulty monitoring the support surface on the side with the deficit -> client may hesitate to walk and have tendency to keep head down and eyes on floor
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A combination of remediation and compensation strategies are used to address deficiencies in mobility
Remediation strategies:
Remediation strategies focus on increasing speed, width, organization of the search pattern
- Client has to learn to quickly turn head and completely search the blind VF
Desired outcome behaviors:
- Initiation of a wide head turn toward the blind field
- An increase in the # of head and eye movements toward the blind field
- Faster completion of head and eye movement toward the blind field
- Execution of an organized and efficient search pattern that begins on the blind side
- Attention to and detection of visual detail on the blind side
- Ability to quickly shift attention and search between the central VF and the peripheral VF on the blind side
- *the Dynavision 2000 has been effective in teaching these components of effective search patterns and is strongly recommended as an intervention tool
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A combination of remediation and compensation strategies are used to address deficiencies in mobility
Compensation strategies:
Compensation strategies: client is taught to ID features in the environment that can cause harm, like steps, curbs, changes in the support surface
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As basic components of the search strategy are developed...
As basic components of the search strategy are developed, they should be incorporated into activities that require combining search with ambulation
- Ex: “I Spy” when walking down hallways
- These activities reinforce keeping the head up during ambulation -> improves orientation
- As skills develop, practice in dynamic and unfamiliar environments should be incorporated (malls, stores)
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Addressing Limitations in Reading
Client’s primary challenges in reading occur because their present saccade strategy does not match the new restricted size of the perceptual span
- The client is trying to read with a saccade strategy designed for a wider unrestricted perceptual span
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- To address this a remediation approach is used:
Prereading exercises (pictured below), word and number searches (for precise eye movements required to see words)
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A compensatory intervention approach is used to address reading and writing challenges. Examples:
- Clients with left hemianopia often have difficulty accurately locating the next line of print on the left margin. Drawing a bold red line down the left margin gives a visual cue as an “anchor” to find the left margin
- Using a ruler to underline sentences to help client from straying from reading a line
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Visual attention
Ability to observe objects closely and carefully to discern info about their features and their relationship to oneself and other objects in the environment
Requires ability to ignore irrelevant sensory input and random thought processes, and to sustain focus for seconds/minutes
Also needs to be able to shift visual focus from object to object efficiently
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Visual attention engagement
Visual attention engagement is accomplished through visual scanning of search
Any change in visual attention will be observed in the client as a change in the scanning pattern used for visual search
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Visual attention can be divided into 2 categories
Visual attention can be divided into 2 categories, both work together to have fully operational and efficient visual system:
1) focal or selective visual attention
- Used for recognition and identification of objects
- Allows us to accurately distinguish visual details, like differences btw letters, numbers, faces
- Visual input from the macular area of the retina is used
2) ambient or peripheral visual attention
- Used for detection of events in the environments and their location in space and proximity to the person
- Allows us to move safely through space and maintain orientation in space
- w/o it, we would collide with objects and be disoriented
Relies on input from the peripheral visual field
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Visual search is completed in an organized, systematic pattern
The type of search pattern used depends on the demands of the task
Ex: reading english - use a left to right, top to bottom search strategy. Or scanning a room - often use a left to right, circular (clockwise or counterclockwise) strategy
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Disruption of the normal visual search strategy can occur after brain injury
Visual search deficits associated with R hemisphere injury are characterized by avoidance in searching the left half of the visual space - aka hemi-inattention
- Instead of the normal left to right visual search pattern, clients with R hemisphere injuries begin and confine the search to the right VF
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Hemi-inattention
Hemi-inattention is associated with injuries to the R hemisphere b/c of the difference in the way our hemispheres are programmed to direct visual attention
- The L hemisphere directs attention to the right half of the visual space surrounding the body
- In contrast, the R hemisphere directs visual attention to BOTH the right and left halves of space surrounding the body
- If there is a lesion in the L hemisphere, visual attention and search in the right is diminished, but some attentional capability is still provided by the R hemisphere. On the other hand, a similar lesion in the R hemisphere could completely eliminate attentional capability toward the left because there is no other area directing attention toward the left side
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Hemi-inattention is often confused with the presence of a left VFD in the client
When left VFD occurs, the client tries to compensate for the loss of vision by engaging visual attention.
- Client directs eye movements toward the blind left side to gather visual info
- But b/c of the left field deficit, the client may not move the eyes far enough to acquire the needed visual info from the left side
In contrast, a client with hemi-inattention has lost the attentional mechanisms in the CNS that drives the search for left visual information
- No attempt will be made to search the lefts visual space. No eye movement or head turns to the left side
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Visual neglect
When a client has both left VFD and hemi-inattention, it creates severe inattention, often called visual neglect
Visual neglect clients show exaggerated inattention toward the left half of the visual space surrounding the body and often don’t move the eyes past midline toward the left, or turn the head to the left side
Visual neglect may also increase the neglect of the limbs on the left side of body, or neglect auditory input from the left side
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Another change in visual search associated with R hemispheric lesions
Another change in visual search associated with R hemispheric lesions is a tendency to fixate first on the most peripheral visual stimuli occurring in the R visual field
If 2 visual stimuli appear in the R visual field at the same time, the client will attend first to the most peripheral stimulus
This client will make frequent head turns to attend to events occurring in the R peripheral field -> client gives the impression that they are distractible
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Only one change in visual search has been observed with clients with L hemispheric lesions
Clients with L hemisphere injury may have symmetric decrease in searching for detail when viewing a visual array (They symmetrically scan the visual array for information but do not examine specific aspects of the visual scene)
Tend to miss visual details and cannot accurately interpret or ID objects around them
L hemisphere injury does NOT result in hemi-inattention or neglect
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In general, clients with injuries to either hemisphere are slower in scanning and have more erratic fixation patterns
Have difficulty engaging selective attention and executing efficient visual search strategy
May be unable to superimpose an organized structure for visual scanning when searching an array of randomly displayed objects
- Example: the client would be able to find someone in the crowd when they are sitting on benches (a structured visual array), but unable to find the same person in a jumbled crowd of people ( a random visual array)
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Occupational Limitations Caused by Visual Inattention
Disruption of visual attention creates
Disruption of visual attention creates asymmetry and gaps in the visual information gathered through visual search
- Quality of one’s adaptation to the environment decreases b/c the CNS is not receiving complete visual info -> cannot make appropriate decisions
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Most activities affected by poor visual attention are...
Most activities affected by poor visual attention are those that need inspection and integration of visual detail, and those completed in dynamic environments
i.e. driving and reading
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Whether a change in visual attention affects occupational performance depends on the task completed
Reading requires more selective visual attention if the book is complex, and less selective attention if the reading is simple
Driving requires continuous global attention to monitor speed and other cars, and sporadic selective attention to landmarks
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Visual attention can be affected by
Visual attention can be affected by deficits in lower-level visual functions (visual acuity, oculomotor function, and visual field). So these functions should be assessed before visual attention is measured
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Aphasia
Presence of aphasia (loss of ability to express/understand speech) and motor impairment can also affect visual attention performance
- How efficiently a person attends to and takes in visual info determines the ability to use that info for adaptation
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The emphasis in assessments is on observing how a client initiates and carries out visual scanning to complete a task requiring visual search
During assessment, OT should answer:
Does the client initiate an organized search strategy?
Can the client carry out the search strategy in an organized and efficient manner?
Does the client obtain complete visual info from a visual search?
Is the client able to ID visual detail correctly?
Does the client’s ability to search for info decrease as the visual complexity of the task increases?
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People with good visual attention
People with good visual attention demonstrate characteristics of search patterns that make them effective in obtaining visual info
These characteristics include strategies that are organized, symmetric, resilient, and consistent -> resulting in good accuracy and speed to complete visual search tasks
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In contrast, people with VFD or inattention have ineffective search strategies
Demonstrate incomplete or abbreviated patterns where only a portion of the visual array is searched, in a random, unpredictable way
Pictured below: examples of ineffective search strategies used on visual search subtests of the biVABA by people with brain injury
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When measuring visual attention, the OT must be aware that visual search can be affected by the presence of a VFD and hemi-inattention
Must be able to distinguish the two to establish an effective intervention plan
Differentiation can be accomplished by observing the strategies used by the client to complete visual search tasks, like on the biVABA
While VFD and hemi-inattention can have decreased accuracy in ID’ing targets, they characteristics of the searches are different.
For example:
- Client with L hemianopia may have a left to right linear search pattern. Pattern may be organized but there are errors on the left
- Client with hemi-inattention may have an asymmetric pattern in which visual search starts in, and confined to the right side with a disorganized and random search pattern. The search also has errors on the left
- Although both have errors on the left, the OT can observe the strategy used to complete the test, and distinguish between the two conditions
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ScanBoard Test (part of biVABA)
Determines how the client applies a search strategy to the broader extra personal space
Consists of a large board with a series of 10 numbers in an unstructured pattern
Client asked to scan board and point the numbers that they see. OT records the pattern the client uses to ID the numbers
Normal visual search: uses an organized, sequential search pattern. From left side of board and proceeding in a clockwise or counterclockwise pattern until all numbers are ID’d
Deficits in visual attention: disorganized, random, abbreviated search strategies w/ numbers being missed on one side of the board
Hemi-inattention: show an asymmetric pattern, with visual search initiated and confined to the right side
VFD: may miss numbers on the blind side but demonstrate an organized search strategy
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Purpose of oculomotor function
To achieve and maintain foveation of an object
Ensures that the object the person wishes to view is focused on the fovea of both retinas (for a clear image) and that focus is maintained as long as needed to accomplish the desired goal
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Foveation
Foveation is achieved by eye movements that keep the target stabilized on the retina during fixation, gaze shift, and head movement
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Oculomotor control also provides binocular vision
Binocular vision: ensures perception of a single image even though the CNS receives two separate visual images (one from each eye)
Sensory fusion: the process of combining two visual images into one
- Corresponding points (or receptor cells) on the two retinas must be stimulated, and if the images match in size and clarity, the CNS is able to fuse the two images into one
- If eyes do not align or if there is a significant difference in acuity between the eyes, a double image (diplopia) may occur
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Deficits in oculomotor control
Deficits in oculomotor control (after a brain injury) generally result in either of two types of disruption:
1) specific cranial nerve lesions causing paresis or paralysis of one or more extraocular muscles that control eye movements
- The message to the extraocular muscles through the cranial nerve is blocked
2) disruption of central neural control of the extraocular muscles affecting the coordination of eye movements
- The message to the extraocular muscles comes through but is scrambled
In both cases, the functional results are decreased speed, control, and coordination of eye movements
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Oculomotor nerve (CN III)
Lesion results in:
- Impaired vertical eye movements
- Lateral diplopia for near-vision tasks
- Dilation of pupil and impaired accommodation
- Ptosis (drooping) of eyelid
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Trochlear nerve (CN IV)
Lesion results in:
- Impaired downward and lateral eye movements
- Vertical diplopia for near-vision tasks
- w/ bilateral lesion assumes downward head tilt
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Abducens nerve (VI)
Lesion results in:
- Impaired lateral eye movements
- Lateral diplopia for far-vision tasks
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Paralytic strabismus
When a cranial nerve lesion is sustained, the muscles controlled by that cranial nerve are weakened or paralyzed
- Eye is unable to move in the direction of the paretic muscles, may be unable to maintain a central position in the eye socket (drift in/out)
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Diplopia
Diplopia (double vision) is the primary functional disruption in clients with cranial nerve lesions
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Diplopia creates __
Diplopia creates perceptual distortion -> may affect eye-hand coordination, postural control, and binocular use of eyes
Limitations on performance depends on where the diplopia occurs within the focal range (the range a person can keep objects in focus)
- Diplopia w/n 20 in. of the face will disrupt reading and activities requiring eye-hand coordination (writing, grooming)
- Diplopia w/ a distance greater than 4 ft. will affect walking, driving, playing sports etc.
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To eliminate the double image...
To eliminate the double image, the client will often assume a head position that avoids the field of action of the paretic muscle
- Example: client with left lateral rectus palsy (abducens nerve CN VI) will turn head to the left to avoid the need to abduct the eye
- OTs have to be careful not to assume that this head position is a result of changing muscle tone, instead of what it really is = a functional adaptation assumed to stabilize vision
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Generally it isn’t the cranial nerves that are damaged in brain injury, but the neural centers that coordinate their actions
These centers are throughout the brainstem and communicate w/ cortical, cerebellar, and subcortical areas of CNS and the spinal cord
If the centers are damaged, the person will have difficulty executing eye movements even though the cranial nerves are intact
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Damage to the pretectal nuclei in the brainstem can cause convergence insufficiency
Convergence insufficiency - an inability to obtain/sustain convergence of the eyes
Convergence insufficiency makes obtaining/sustaining adequate focus during near-vision tasks difficult (tasks w/in 20 in. of the face)
- Clients complain of fatigue, eye pain, headache
- B/c this condition is often missed in the eval since the cranial nerve function is usually intact, the client’s complaints are often instead attributed to inattention lack of effort, or dyslexia
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Convergence
Convergence: the muscle action of moving the eyes inward in adduction, a component of accommodation
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Accommodation
Accommodation: a process that keeps objects in focus as they come into close view
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Assessment
The purpose of the assessment is not to determine if the oculomotor dysfunction is from a cranial nerve lesion or brainstem injury (ophthalmologist’s responsibility), but instead to determine if the client is experiencing limitations of daily occupations
- However, OTs often refer patients for eye evals after an initial screening
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During assessments, a “listen and look” approach is used
OT listens to the complaints by the client or staff, and looks for oculomotor issues in the client.
This approach is part of the biVABA and is as follows:
1) obtain a visual history from client
Need to know if client wore glasses to correct previous vision issues
2) ask client if they are experiencing diplopia, If yes, have the client explain the diplopia
- Their answers may suggest which cranial nerve has been injured
3) ask client to ID any activities that are difficult (if any) b/c of the oculomotor dysfunction
4) observe the client’s eyes and eye movements for deficiencies
- Evaluate for asymmetric pupil size, eyelid function, eye position
-- Dilated pupil or ptosis (droopy eyelid) in one eye might indicate a cranial nerve issue
- Eval movement of the eyes during tracking of moving object through the 9 cardinal directions of gaze plus convergence
-- Most adults can maintain focus and track an object to a distance of 3 inches from the nose, then one eyes breaks fixation and moves outward
-- “Near point of convergence”: the point convergence is broken
- This tests any deviations in strengths and function of the extraocular muscles
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During these tests, the OT observes:
1) symmetry of eye movement
2) whether the eyes move the same distance in each direction
3) whether the eyes are able to stay on target with a min of jerking movements
4) whether the client is able to hold the eyes in a deviated position at the end of the range for 2 to 3 sec
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Restriction of eye movement in a specific direction of difficulty moving the eyes in a specific direction may indicate __
Restriction of eye movement in a specific direction of difficulty moving the eyes in a specific direction may indicate impaired oculomotor function
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Final test: diplopia
Used to determine the severity of the diplopia and if caused by a”tropia” or “phoria”
- -tropia: a suffix applied when there is a deviation of the position of one eye in relation to the other when the client is focusing on an object
- -phoria: suffix when there is a deviation of the eye that is held in check by fusion and is therefore not noticeable when the client is focusing on an object
The suffixes are added onto 4 prefixes, describing the direction of the deviation:
- Eso-: turning in of the eye
- Exo-: turning out of the eye
- Hypo-: turning downward of eye
- Hyper-: turning upward of eye
Example: esotropia - the observable, inward deviation of the eye (cross eyed). Esophoria - eye drifts inward when client is not focusing on the object, but is held in check when the client does focus on the object
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Diplopia testing is based on the principle that
Diplopia testing is based on the principle that when an eye is required to fixate on an object, it will do it with the fovea
- If an eye that is not fixating on a target is suddenly required to foveate, it will achieve foveation by making a saccade toward the target
- By having the client fixate with both eyes on a target, then covering one of the eyes during fixation, OT can determine if both eyes are aligned in focusing on the target OR which eye is the deviant (strabismic) one
2 tests are used:
- cover/uncover test: completed when a -tropia is suspected
- Cross or alternate-cover test: completed when a -phoria is suspected
- Clients w/ tropias complain of constant diplopia when viewing objects and must have one eye occluded to eliminate the diplopia
- Clients w/ phorias complain of diplopia only intermittently, usually when stressed or fatigued by sustained viewing of a target
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Presence of diplopia causes
Presence of diplopia causes perceptual distortion -> confusion and limits participation in daily activities
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Diplopia is eliminated by
Diplopia is eliminated by occluding the image presented to one eye
- Can do this by assuming a certain head position or covering one eye
- Covering one eye is preferred b/c head position affects motor and postural control
- Occlusion of the eye can be achieved through either full or partial occlusion
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Full occlusion
Vision is completely occluded in one eye by a “pirate patch”, clip-on occluder, or opaque tape
- Problem: Full occlusion eliminates peripheral visual input, and disrupts normal CNS mechanisms for control of balance and orientation to space. Also, people generally can’t tolerate long periods of occlusion (esp. If it’s the dominant eye), so occlusion should be alternated between the eyes every hour
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Partial occlusion
Partial occlusion: strip of opaque material (surgical tape) applied to a portion of the eyeglass lens to block visual stim in the ventral visual field, with the peripheral visual field being left unoccluded
- Tape is applied from the nasal rim toward the center of the lens until the clients reports that diplopia is gone when viewing a target
- Tape is applied to the nondominant eye for comfort
- Width of the tape is gradually reduced as the muscle paresis resolves
- Advantages: peripheral vision is left intact -> available for orientation to space and balance
- Disadvantage: client must wear glasses (either prescription or nonprescription) to have tape applied to the frame
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Prisms
Ophthalmologist/optometrists may use a prism to re-establish single vision in the primary directions of gaze (looking straight ahead, looking down)
A prism displaces an image and causes the disparate images created by the strabismus to fuse into a single image
Prism can be ground into the eyeglasses
Is only used as long as it is needed to maintain fusion. If paresis is resolving, the the dioptic strength of the prism is reduced gradually
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Eye Exercises
No research that demonstrates eye exercises will restore binocular function following strabismus
But exercises do not appear to be harmful for muscle function
Exercises can empower the client by increasing participation in recovery
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Surgery
Is recommended when strabismus is too large to overcome, or it does not resolve in 12-18 months
General approach: to make the action of one of the extraocular muscles either weaker or stronger by changing its position of attachment on the eye. Position of eye in the socket is changed by the surgery, and the image is realigned
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Complex Visual Processing
Processes of pattern recognition, visual memory, and visual cognition involves complex processing and integration of vision with other sensory info, past experiences, and cognitive function
Complex visual processing is a learned skill est. by one’s experiences in mastering the environment
- It’s always applied w/in the context used to solve a problem, formulate a plan, or make a decision regarding a situation
- Best way to asess this is having client not complete an abstract, 2D task, but to have them actually complete the task
i. e.: driving should be done with a behind-the-wheel assessment
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Poor visual input will affect performance of complex visual processing
So visual acuity, visual field, oculomotor control, and visual attention and search should be assessed first to see if deficits exist that may contribute to complex processing issues
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Summary
Framework for assessment/intervention rests on the concept of a hierarchy of visual perceptual processing levels
- A process cannot be disrupted at one level w/o having an effect on all perceptual processing
Assessment must be directed at measuring function at all process levels, w/ emphasis on the foundation of visual functions and visual attention and scanning
