Disorders of higher visual processing in patients with acquired brain injury

Abstract

BACKGROUND:

Disorders of higher visual processing often impact patients with acquired brain injury. Even with treatment, these vision conditions can cause chronic challenges for patients. Understanding these conditions and their management can help improve functional independence and quality of life.

OBJECTIVES:

To discuss the various disorders of higher visual processing that result from acquired brain injury. Discussion to include classification, evaluation, and treatment techniques available to clinicians.

METHODS:

Peer reviewed journal articles were searched, primarily through PubMed. Articles spanning several decades were included in the review for historical context of these conditions, however an emphasis was placed on more recent publications for purposes of a discussion regarding clinical management of these conditions.

RESULTS:

Peer-reviewed articles and clinical trials from across several disciplines were included to frame a discussion of this varied group of conditions.

CONCLUSION:

Visual processing disorders have debilitating impacts on both the rehabilitation process as well as functional independence. Varied approaches are utilized in the treatment of these conditions with limited success. Understanding the benefits and limitations of both restorative and compensatory treatments will better help clinicians manage patients with these conditions.

Keywords

Visual processing disorder visual neglect hemi-neglect unilateral visual inattention visual agnosia object agnosia prosopagnosia akinetopsia topographagnosia alexia achromotopsia

1 Introduction

Visual information processing is a complex aspect of visual functioning. Extracting meaning from visually-presented information in the world involves two important pathways; the dorsal pathway and the ventral pathway. The dorsal pathway is responsible for processing spatial information while the ventral pathway is responsible for fixed properties of objects (Haque et al., 2018). This has led to the dorsal pathway being referred to as the ‘where’ pathway and the ventral pathway as the ‘what’ pathway.

Acquired brain injury can cause damage to these pathways, which in turn results in disorders of higher-level visual processing. For the purposes of this article, these disorders will be discussed in the context of the dorsal and ventral pathways. Visual neglect is a condition associated with damage to the dorsal pathway while visual agnosias are caused by damage to the ventral pathway (Burns, 2004; Haque et al., 2018; Parr & Friston, 2018).

2 Visual neglect

Understanding visual neglect, as a condition, is somewhat complicated by the multitude of descriptions and terminologies used throughout its history. Visual neglect has been identified and described clinically for a century but was only widely recognized as a syndrome in the 1970s (Langer et al., 2019). For the purposes of this article, the term ‘visual neglect’ will be used to reference a condition that can be found in literature as: hemi-neglect, hemi-inattention, imperception, inattention, unilateral visual inattention, and unilateral spatial agnosia. Determining the incidence of visual neglect in the acquired brain injury population is likely complicated by a lack of awareness; either due to personal knowledge or insufficient testing at the point of care. Incidence of visual neglect in stroke patients varies from 8% to 90% in the literature (Massironi et al., 1988; Sunderland et al., 1987).

Visual neglect describes a condition wherein the person is unable to attend or respond to stimuli on the left side of either self, space, or the object of interest (Brain, 1941; Langer et al., 2019; McFie et al., 1950). The specific characteristics of the omitted information allows visual neglect to be divided into sub-types. Visual neglect can be classified by domain to include: personal, peripersonal, and extrapersonal (Langer et al., 2019; Spaccavento et al., 2017). Classification of visual neglect by domain is summarized in Table 1.

Table 1
Visual neglect –Affected areas and testing methods

Type of visual neglect Affected area Testing methods

Personal Left side of body Observe or test self-care

(shaving, make-up, dressing, personal hygiene)

Peripersonal Left side of space within arm’s reach Cancellation

Bisection

Copying

Visual scanning

Extrapersonal Left side of space in the distance Picture of scene description

Type of visual neglect	Affected area	Testing methods
Personal	Left side of body	Observe or test self-care
		(shaving, make-up, dressing, personal hygiene)
Peripersonal	Left side of space within arm’s reach	Cancellation
		Bisection
		Copying
		Visual scanning
Extrapersonal	Left side of space in the distance	Picture of scene description

Personal visual neglect impacts a person’s ability to attend to the left side of the body. This form of visual neglect can be particularly alarming as an individual may fail to shave the left half of the face or may apply make-up to the right side of the face only. He or she will then report completeness of the task. Peripersonal visual neglect impacts the immediate space within reaching distance. This form of visual neglect can be especially disruptive during the rehabilitation process as the patient may fail to respond to stimuli the therapist presents to the patient’s left visual space. Extrapersonal visual neglect impacts a person’s ability to attend to the left visual scene viewed at a distance. This form of visual neglect can have a great impact on mobility and navigating daily life. Visual neglect can also be classified as either egocentric or allocentric depending on the reference point of the visual neglect (Spaccavento et al., 2017). A person with egocentric visual neglect will omit information to their left, as neglect is experienced from a viewer-centered perspective. A person with allocentric visual neglect will omit the left portion on an object, as neglect is experienced from an object-centered perspective. An example of this distinction would be a person with egocentric visual neglect would not attend to a plate of food placed to their personal left while a person with allocentric visual neglect would not attend to the food on the left side of the plate.

A distinguishing feature of visual neglect is the patient’s lack of awareness of the omissions or deficit. The patient perceives the visual scene as whole despite the inability to attend to pertinent information within the left field (Heilman et al., 2000; Langer et al., 2019; Spaccavento et al., 2017). This feature helps distinguish visual neglect from homonymous hemianopsia; a visual field defect impacting one half of a person’s visual field. A homonymous hemianopsia results from damage to the optic tract posterior to the chiasm. This damage creates a pattern of visual field loss where the temporal (outside) visual field in one eye is affected while the nasal (inside) visual field is impacted in the other (Parr & Friston, 2018). This creates vision loss to one side; either the patient’s right or left visual field. In the case of a homonymous hemianopsia the patient is aware, or can be made aware, of the visual deficit. Conversely, patients with visual neglect are unaware of/unable to perceive their deficit (Langer et al., 2019; Spaccavento et al., 2017),

3 Causes of visual neglect

In general terms, visual neglect is caused by cerebral dysfunction within the right hemisphere (Burns, 2004; Langer et al., 2019; Parr & Friston, 2018; Spaccavento et al., 2017). Commonly, visual neglect is caused by a right middle cerebral artery stroke (Parr & Friston, 2018). Visual neglect has also been reported in cases of inflammatory disease, metabolic disease, and degenerative conditions (Andrade et al., 2010; Auclair et al., 2008; Gilad et al., 2006; Ho et al., 2003). The common feature of these reports is the damage to the right cerebral hemisphere.

The specific cause of visual neglect is often discussed in the context of the dorsal and ventral pathways of information processing (Burns, 2004; Haque et al., 2018; Parr & Friston, 2018). The ventral pathway is often referred to as the ‘what’ pathway. This pathway runs inferior along the occipital and temporal lobes and is responsible for the fixed properties of objects (Haque et al., 2018). Examples of fixed object properties would include size and color. Agnosias are the group of higher visual processing disorders associated with damage to the ventral pathway. The dorsal pathway is often referred to as the ‘where’ pathway. This pathway runs superior to the parietal lobes and is responsible for spatial information (Haque et al., 2018). Examples of spatial information would include position, distance, and movement. Visual neglect is often associated with damage to the dorsal pathway (Burns, 2004; Haque et al., 2018; Parr & Friston, 2018).

One issue with defining visual neglect as a dorsal pathway disorder is that a patient cannot appreciate what is present on their left side or in their left visual space. This would seem that visual neglect could be classified as a ventral pathway disorder. This concept was further supported by Parr when it was noted that the ventral attentional network is located in the right cerebral cortex while the dorsal attentional network is more symmetric between the two hemispheres (Parr & Friston, 2018). From an anatomical perspective, this would support why visual neglect is experienced on the contralateral left side.

Ultimately, it appears that visual processing is not as simplistic as two independent pathways working simultaneously to form a perception of the visual world (Bell et al., 2014; Freud et al., 2016; Haque et al., 2018). More likely, visual neglect results from disrupted interaction between the dorsal and ventral pathways. As Parr & Friston (2018) stated ‘visual neglect involves dysfunction of the dorsal network as a consequence of the failure of the ventral network’.

4 Evaluation of visual neglect

Visual neglect is a deficit of higher level visual processing, rather than a sensory or motor deficit. An ophthalmic examination remains important to rule out a visual input deficit that may interfere with higher level visual processing abilities. A patient may perform well on tests of visual sensory input, but will display significant functional challenges. For this reason, testing specific to visual neglect should also be used in the assessment of patients at risk for visual neglect. Additionally, testing for neglect should be mindful of the multiple sub-types of visual neglect.

Evaluation of personal visual neglect, outlined in Table 1, can primarily be achieved through clinician observation and functional evaluation (Langer et al., 2019; Spaccavento et al., 2017). A person with personal visual neglect may fail to dress the left side of the body or may neglect personal hygiene on the left side. This may be innately observed upon meeting the individual. If not immediately obvious, the clinician can instruct the patient to demonstrate the use of an everyday grooming item. The person can be asked to use a comb, razor, or make-up brush. One would expect an asymmetric demonstration of the task for an individual with personal visual neglect, with performance highly biased or restricted to the right side of the body (Spaccavento, 2017).

Evaluation of peripersonal visual neglect can feel more familiar to clinicians as the tests are often paper-and-pencil tasks that produce a physical representation of the visual neglect experienced by the patient. Testing for peripersonal visual neglect includes: cancellation tasks, bisection tasks, copy tasks, and visual scanning tasks (Langer et al., 2019; Spaccavento, 2017). Cancellation tasks require the person to mark a specific symbol (picture, number, or letter) among a group of symbols spread across the testing area. An individual with peripersonal visual neglect would be expected to predominantly mark the symbols on the right side of the testing sheet. Bisection tasks require the individual to divide a line segment in half. One would expect an asymmetric marking of the line to the right in cases of peripersonal visual neglect, with a much longer segment to the left of the mark and a shorter segment to the right. Copy, or drawing, tasks can either request spontaneous drawing or drawing to command. When asked to draw a clock, for example, a patient with peripersonal visual neglect may place the clock hours one through twelve on the right side of the clock rather than evenly disbursing them. If asked to copy a picture presented to them, a patient with peripersonal visual neglect may copy only the right side of the picture. Visual scanning tasks include counting objects scattered throughout the visual field or asking a patient to describe a picture presented to them. Similar to the other forms of testing, one would expect a patient with peripersonal neglect to attend to only the items on the right side. Observation of daily tasks can also be helpful in identifying peripersonal visual neglect. A reading or writing sample can be helpful in identifying peripersonal visual neglect as the person may omit the left side of the task (Langer et al., 2019; Spaccavento, 2017).

Evaluation of extrapersonal visual neglect can apply some of the same testing mechanisms as peripersonal visual neglect performed at a greater distance. Picture description and scene description are especially useful (Langer et al., 2019). Requesting a patient describe the room they are in provides insight into extrapersonal visual neglect. For a patient with language restrictions, a non-verbal task with aspects beyond arm’s reach can also test for extrapersonal visual neglect. Dealing cards, for example, requires them to attend to a group of people situated in a semi-circle beyond arm’s reach. One would expect a person with extrapersonal visual neglect to only deal to the players in front of themselves and to their right.

Through testing in the different domains (personal, peripersonal, and extrapersonal), the clinician would gain insight as to whether the visual neglect was egocentric (viewer centered) or allocentric (object centered). This distinction would be made by the patient’s performance. Egocentric visual neglect would present as omission of visual information in the left visual space while allocentric would present as omission of the left half of the object.

5 Impacts of visual neglect

Visual neglect is highly disruptive to all phases of recovery. Visual neglect negatively impacts participation in rehabilitation, length of hospitalization, discharge destination, and independence with activities of daily living (Barer, 1990; Bernspang et al., 1987; Jehkonen et al., 2006; Neistadt, 1993). Visual neglect is one of the main causes of long-term disability following a stroke (Spaccavento, 2017).

Visual neglect negatively impacts the overall rehabilitation process as it interferes with treatment of comorbid conditions (Spaccavento, 2017). Personal visual neglect, for example, can impact treatment of hemiparesis if the patient does not attend to the left side of the body. Peripersonal visual neglect interferes with a multitude of rehabilitation efforts performed within a few feet of the patient. Visual neglect of items in the left field, or neglect of the left side of objects, can complicate participation and feedback during visual-motor, physical, and language tasks. It can create confusion as to the patient’s primary barrier to the task. Failure to reach for an object to the left or failure to match an auditory cue to a visual reference to the left of the patient may be interpreted as a failure of a visual-motor or auditory/language skill when in fact the patient’s poor response is a reflection of visual neglect. Similarly, a patient with peripersonal or extrapersonal visual neglect may struggle to achieve mobility goals and motor recovery (Barer, 1990; Bernspang et al., 1987; Neistadt, 1993; Spaccavento, 2017).

Visual neglect also has long-term impacts on independence with activities of daily living and quality of life (Barer, 1990; Bernspang, 1987; Jehkonen et al., 2006; Neistadt, 1993; Spaccavento, 2017). Persistent visual neglect can impact a person’s basic needs, for example preventing them from eating food on the left side of the plate, finding food on the left side of the refrigerator or pantry shelf, or dressing themselves. Visual neglect can also prevent a patient from participating in leisure activities, such as reading, writing, or socializing with friends. Mobility can also be affected, which can inhibit independence and lead to isolation. Additionally, individuals with neglect often collide with obstacles even in their own home, which puts them at greater risk for falls and repeat acquired brain injury (Barer, 1990; Bernspang, 1987; Jehkonen et al., 2006; Neistadt, 1993; Spaccavento, 2017).

6 Treatment of visual neglect

Several therapeutic interventions have been at-tempted, and are currently used, for the treatment of visual neglect. Both top-down and bottom-up treatments are utilized in the rehabilitation of visual neglect (Bowen et al., 2013). Top-down treatment focuses on the level of disability, rather than impairment, and is designed to train the individual to compensate for the visual neglect. Perhaps the greatest challenge with a top-down treatment approach for visual neglect is the need for awareness of the deficit. One distinct feature of visual neglect is the person’s lack of awareness for the omitted information as they perceive their visual space as whole (Haque et al., 2018; Langer et al., 2019; Spaccavento, 2017). A bottom-up treatment approach does not require awareness by the individual. Instead, this treatment approach aims to modify the impaired representation of visual space (Bowen et al., 2013). Treatment approaches for visual neglect can largely be divided into five broad groups that consist of both restorative and compensatory strategies.

The primary top-down approach utilized for the treatment of visual neglect is a modified scanning strategy (Cherney et al., 2003; Fanthome et al., 1995; Ferreira et al., 2011; Kerkhoff et al., 2012; Luukkainen-Markkula et al., 2009; Van Kessel et al., 2013). Functionally, a modified scanning technique would be beneficial for a patient with visual neglect. Evaluation of eye movement patterns in patients with visual neglect has shown a significant asymmetry in saccadic eye movements with a bias toward the right visual field (Fruhmann et al., 2008). Approaches to train a modified scanning pattern have consisted of patient instruction prior to the therapeutic activity as well as biofeedback throughout the activity (Cherney et al., 2003; Fanthome et al., 1995; Ferreira et al., 2011; Kerkhoff et al., 2012; Luukkainen-Markkula et al., 2009; Van Kessel et al., 2013). One example of biofeedback in the treatment of visual neglect is the use of goggles that have an indication tone if the patient fails to scan to the left at a pre-determined frequency (Fanthome et al., 1995).

A second group of treatment approaches utilize motor input or motor stimulation on the affected left side (Fong et al., 2007; Luukkainen-Markkula, 2009; Polanowska et al., 2009). This group of interventions uses sensory stimulation in the motor domain with the hope of a sensory change in the visual domain. It is possible that these interventions create a form of biofeedback during the activity that may not generalize to activities of daily living when the same stimulation is no longer present (Bowen et al., 2013).

A perceptual or visualization approach to treatment has also been utilized in the treatment of visual neglect (Edmans et al., 2000; Ferreira et al., 2011; Thieme et al., 2013). The perceptual skills that would, in theory, be most beneficial for patients with visual neglect would be visual figure-ground and visual closure. Development of these skills would hope to improve an individual’s ability to extract pertinent information from the visual scene and to recognize a complete object of interest even if perceiving only a portion. In a more concrete representation of a visual scene has also been attempted with mirror therapy (Thieme et al., 2013). One limitation of mirror therapy for visual neglect is the inherent asymmetry of visual scenes encountered in daily life.

The final two groups of treatment aim to modify the patient’s visual input. First, sector or selective occlusion has been utilized in the treatment of visual neglect (Fong et al., 2007; Tsang et al., 2009). This treatment approach involves occlusion, or patching, of the right half of the visual field in each eye. In theory, this would force the patient to attend to the affected left field. The limitation of this strategy is once the occlusion is discontinued, the dominant right visual field would again be visible. The second visual approach is the use of prism to shift the visual field toward the right side (Mizuno et al., 2011; Nys et al., 2008; Rossi et al., 1990; Turton et al., 2010). Prism is oriented in a manner that shifts visual information toward the right side of the field. In most cases, prism was worn during training session and then later removed. The limitation with this approach is shifting the entire visual space to the right does not change the relative leftward position of items in the left visual scene.

While many approaches are used in the rehabilitation process, the benefits are fairly limited and not well supported in randomized clinical trials. A review in the Cochrane library found that some of the interventions discussed above provided immediate improvements in standardized neglect assessments, but failed to produce long-term benefits. Ultimately, it was determined that clinical trials did not support treatment having a positive impact on activities of daily living or quality of life (Bowen et al., 2013). While testing in the acute care setting may show improvement, the patient’s functional independence may be better supported by compensatory strategies. Vertical presentation of visual material, tactile and auditory support for visual information, and visual anchoring of material in the left field may serve as more practical approaches to visual neglect management (Langer et al., 2019).

7 Visual agnosias

Visual agnosia is used as a general term to describe a group of visual processing disorders impacting the ability to identify objects or certain aspects of visual information (Haque et al., 2018; Riddoch et al., 2008). In the case of visual agnosia, the impaired recognition is confined to visually-presented information and occurs in the absence of sensory deficits (Riddoch et al., 2008). Visual acuity, visual field, and other aspects of visual input remain intact. Additionally, attention, memory, intellect, and language abilities are unaffected. This creates a situation where the individual can ‘see’ objects but is unable to derive meaning of some or all aspects of that object. In the case of isolated visual agnosia, the person would be able to acquire meaning from that same object utilizing alternate sensory input; through tactile, olfactory, or auditory means (Burns, 2004).

Visual agnosias can impact specific, fixed, properties of a visual object (Haque et al., 2018). The specific impairment is used to classify and categorize visual agnosias; outlined in Table 2. Visual agnosias can be classified as either apperceptive or associative (Burns, 2004; Haque et al., 2018; Riddoch et al., 2008). Apperceptive visual agnosia describes an impairment in basic visual processing of an object. This causes a situation where an individual is unable to match objects when they are identical, match an object to its drawing, or create a copy of an object (Burns, 2004). Associative visual agnosia describes an impairment in accessing stored memories, visual concepts, or meaning associated with particular objects. In the case of associative visual agnosia, the individual would be able to match or copy an object but would be unable to identify the object on command or match different examples of the same object (Burns, 2004; Haque et al., 2018; Riddoch et al., 2008). Individuals with either apperceptive or associative visual agnosia would be expected to identify objects using non-visual cues.

Table 2
Visual agnosias –Affected areas and testing methods

Type of agnosia Affected area Testing methods

Pure object agnosia Object recognition Efron Shape Test, Birmingham Object Recognition Battery, Object &Space Perception Battery, Overlapping Figures Test, Pyramid &Palm Trees Test

Prosopagnosia Face recognition Famous Faces Test, Benton Facial Recognition Test, Warrington Recognition Memory Test, Cambridge Face Memory Test

Akinetopsia Perception of visual motion Patient descriptions

Topographagnosia Placing objects in environment Scene description, limitation of daily activities

Navigating to a location

Pure alexia Visual word recognition Word recognition tests, Reading and writing samples

Color anomia Color naming Naming of colors

Color agnosia Color recognition Color matching

Type of agnosia	Affected area	Testing methods
Pure object agnosia	Object recognition	Efron Shape Test, Birmingham Object Recognition Battery, Object &Space Perception Battery, Overlapping Figures Test, Pyramid &Palm Trees Test
Prosopagnosia	Face recognition	Famous Faces Test, Benton Facial Recognition Test, Warrington Recognition Memory Test, Cambridge Face Memory Test
Akinetopsia	Perception of visual motion	Patient descriptions
Topographagnosia	Placing objects in environment	Scene description, limitation of daily activities
	Navigating to a location
Pure alexia	Visual word recognition	Word recognition tests, Reading and writing samples
Color anomia	Color naming	Naming of colors
Color agnosia	Color recognition	Color matching

Pure object agnosia describes global impairment of object recognition (Musalam, 2000). Several specific visual agnosias have been classified by the particular aspect of stimulus recognition that has been impaired.

Prosopagnosia impairs an individual’s ability to identify faces for both familiar and unfamiliar people (Barton et al., 2002; Davies-Thompson et al., 2014; Malone et al., 1982). Prosopagnosia has been further sub-classified to include apperceptive and associative forms. Apperceptive prosopagnosia prevents identification of specific facial features; eyes, nose, mouth (Haque et al., 2018). Associative prosopagnosia prevents identification of a person based on their face (Haque et al., 2018).

Akinetopsia, sometimes referred to as ‘motion blindness’ causes an inability to perceive visual motion (Burns, 2004; Haque et al., 2018). This condition causes an individual to perceive objects in motion as a series of still shots (Rapp, 2001). A patient with akinetopsia may be able to recognize that an object has changed location, but would be unable to perceive the fluid motion of said object.

Topographagnosia, or environmental agnosia, creates an inability to place objects in familiar sur-roundings (Haque et al., 2018). An individual with topographagnosia may be unable to navigate to a specific location. This could prevent them from orienting to a specific room in their own home or to a previously known building in their city (Burns, 2004; Damasio et al., 2000).

Pure alexia, or alexia without agraphia, disrupts visual word recognition. It has been proposed that words are treated as ‘objects’ when processed and this form of visual agnosia prevents a person from identifying written text (Burns, 2004; Haque et al., 2018). In the case of pure alexia, the person would retain their ability to write words, but would lose the ability to read those same words.

Color perception can also be impacted in cases of visual agnosia. Color anomia describes an inability to name colors, even though color perception is intact, while color agnosia is an inability to recognize colors (Haque et al., 2018). These conditions have been differentiated from central or cerebral achromotopsia, where a person’s color perception is impaired (Burns, 2004; Damasio et al., 2000; Musulam, 2000). Cerebral achromatopsia can be either complete or partial. This causes the world to appear in shades of black and white or depleted of color. Achromatopsia has been described to affect the entire visual field or one half of the visual field. A lesion in a very particular location within the visual cortex can cause contralateral loss of color perception, referred to as hemiachromatopsia (Burns, 2004).

Simultagnosia describes an inability to perceive a visual scene as a whole. Instead, the individual perceives and identifies the individual aspects of the scene but fails to perceive the greater meaning of the whole (Burns, 2004). Simultagnosia is often observed in cases of damage to the parietal lobe and is thought to reflect a restriction of visual attentional field (Haque, 2018). This local, versus global, interpretation of visual scenes is extremely debilitating and results in objects appearing fragmented or incomplete.

8 Causes of visual agnosia

Visual agnosias, as a group of disorders, are caused by occipital or occipital-temporal lobe damage (Burns, 2004; Haque et al., 2018; Parr & Friston, 2018). Within the context of the dorsal and ventral pathways, visual agnosias are the group of higher visual processing disorders associated with damage to the ventral pathway (Burns, 2004; Haque et al., 2018; Riddoch et al., 2008).

The specific visual agnosia experienced by a patient is a manifestation of a lesion with a very specific cerebellar location (Burns, 2004; Davies-Thompson et al., 2014). Prosopagnosia, impacting the ability to recognize faces, has been localized to damage at the fusiform gyrus (Barton et al., 2002; Davies-Thompson et al., 2014). The visual cortex is expectedly impacted in multiple forms of visual agnosia. Akinetopsia is caused by a lesion in V5 that creates an inability to perceive motion. A unilateral lesion in V4 causes a contralateral loss of color perception; hemiachromatopsia. Color anomia, or the inability to name colors despite intact color perception, is caused by a lesion that disrupts communication between V4 and the area of the cortex responsible for processing language (Haque et al., 2018). Given the highly specific relationship between cortical damage and visual agnosias, a more pervasive disruption of visual processing, like pure object agnosia, has been suggested to result from diffuse lesions within the visual cortex (Haque et al., 2018).

A clear understanding of the neurological underpinnings for visual agnosias has been important in furthering our understanding of these complex conditions. Knowledge of the specific location impacted by a patient’s acquired brain injury may help a clinician confirm suspected visual agnosia. In many cases, however, a clinician may instead be dependent on clinical observation and clinical testing to confirm the presence of a visual agnosia without confirmatory diagnostic imaging. For this reason, thorough evaluation to rule out a visual agnosia should be completed for patients with a clinical history suggestive of damage to the ventral pathway.

9 Evaluation of visual agnosia

Similar to other deficits of higher visual processing, patients suspected of visual agnosia should undergo a thorough ophthalmic examination to rule out visual input deficits. Blurred vision, diplopia, or other symptoms caused by disrupted visual input can create confusion for both the patient and the clinician performing the evaluation for visual neglect. It is also important to determine that the patient is alert, possesses intact intelligence and has adequate language abilities (Burns, 2004; Musulam, 2000; Rapp, 2001). At this point in the evaluation process, testing can be performed to identify the specific visual agnosia. Testing approaches for visual agnosias are outlined in Table 2.

A critical consideration when testing for visual agnosia is the need to restrict testing to the visual domain (Musulam, 2000; Rapp, 2001). This allows for the isolated evaluation of visual processing and the comparison of the visual modality to other forms of sensory input, such as auditory or tactile. A patient with visual agnosia would be unable to identify visually-presented objects, or specific characteristics of visual objects. The patient may be able to identify those same objects if provided alternative sensory input, such as feeling or hearing a sound made by that object (Burns, 2004).

Patient responses during the testing process for visual agnosias will allow the clinician to distinguish apperceptive from associative agnosia. In cases of apperceptive visual agnosia, the patient will be unable to match identical objects, unable to match an object to its drawing, and unable to copy a visually-presented object (Burns, 2004; Riddoch et al., 2008). In cases of associative visual agnosia, the patient is able to match and copy visual objects, but is unable to match differing examples of the same object (Riddoch et al., 2008). For example, a patient would not be able to identify a wooden pencil and mechanical pencil as the same type of writing utensil. Patients with associative visual agnosia would also be unable to identify, or name, a visual object to command (Burns, 2004; Riddoch et al., 2008).

The general format of matching and naming of visually-presented stimuli can be applied to the testing for a specific visual agnosia. Prosopagnosia, for example, can be evaluated by showing a patient photographs of famous individuals and individuals known to the patient (Burns, 2004). This type of evaluation has been formalized in several tests, including: Famous-Faces Test, Benton Facial Recognition Test, Warrington Recognition Memory Test, and Cambridge Face Memory Test (Haque et al., 2018). Pure alexia can be assessed utilizing reading and writing tasks (Haque et al., 2018). One would expect a patient with pure alexia to fail in recognition of written words, but retain the ability to recognize those same words while copying or tracing the letters of the word. Object agnosia assessment requiring naming, drawing, copying, and matching of visually-presented objects has been formalized in tests such as: Efron Shape Test, Birmingham Object Recognition Battery, Visual Object and Space Perception Battery, Overlapping Figures Tests, and Pyramid and Palm Trees Test (Haque et al., 2018).

10 Impacts of visual agnosia

Visual agnosias can impact both the rehabilitation process and a person’s future functional independence. Various members of the rehabilitation team use visual cues or present visual information to patients to rehabilitate both visual and non-visual skills. The presence of a visual agnosia can either prevent patient success with an activity or be interpreted as a deficit in another sensory domain. Language rehabilitation, for example, may be impacted by pure object agnosia or pure alexia. This inability to name objects or visually-process words would require the therapist to modify presentation and rehabilitative techniques. Akinetopsia and topographagnosia may impact efforts to restore patient mobility (Burns, 2004; Haque et al., 2018).

Functional independence can also be impaired when visual agnosias are present. Disruptions in the ability to perceive or process one’s visual environment can have significant impacts on quality of life. Understanding the nuances of the various visual agnosias helps members of the care team to predict future struggles. Inability to recognize faces can limit social engagement and lead to a sense of isolation. Challenges navigating to a specific location can similarly lead to isolation as a person may limit trips away from their home. The inability to match and compare visual objects, or recognize written words, can prevent independent living. Grocery shopping, maintaining a budget, and many household tasks may become challenging for these individuals. Fortunately, patients with visual agnosia are aware, or can be made aware, of their limited visual processing (Burns, 2004). This allows compensatory strategies to be implemented to increase functional abilities.

11 Treatment of visual agnosia

Individuals with visual agnosia are often acutely unaware of their visual processing deficit (Burns, 2004). Building awareness of the visual agnosia is an important early goal in the rehabilitation process. Increased awareness of the deficit sets the foundation for compensatory strategies. Visual agnosias are primarily treated using compensatory efforts as direct remediation of the visual processing deficits has not shown to be a viable treatment approach (Burns, 2004; Haque et al., 2018; Riddoch et al., 2008)

Two main categories of compensatory strategies are utilized with visual agnosias. First, alternate visual cues can be utilized to identify visual information (Barton et al., 2002; Davies-Thompson et al., 2014; Malone et al., 1982). This approach can be more beneficial when a patient has an isolated visual agnosia rather than the more pervasive form of pure object agnosia. The concept behind this strategy is to cue patients to aspects of visual information processing that remain intact to supplement those that have been lost due to visual agnosia/neurological damage. A patient with prosopagnosia will be unable to identify the faces of familiar individuals, but could use distinctive facial features or clothing accessories to identify those individuals. A mustache, glasses, or a hat that is worn on a consistent basis can be used to cue recognition (Barton et al., 2002; Davies-Thompson et al., 2014; Malone et al., 1982). A consistent system of object placement, color coding, or labeling with symbols or words can be implemented where appropriate for other forms of visual agnosia.

The second strategy involves using intact sensory processing domains to compensate for the visual agnosia (Burns, 2004; Haque et al., 2018). Patients with isolated visual agnosia can utilize tactile and auditory cues to identify visual information. Providing auditory support or tactile exploration of visual items will better allow an individual with visual agnosia to function at a higher level. Many treatment devices and strategies from low vision rehabilitation can be successfully applied to visual agnosia. Important visual information around the house can be marked with elevated or textured ‘buttons’ for the patient to locate. Foam number stickers, for example, can be placed on the microwave to allow the individual to feel the buttons when preparing food. Rugs or alternate flooring can be used to guide a person with topographagnosia to the bathroom and bedroom in their home. Ultimately, the collaboration between multiple members of the rehabilitation team will provide the greatest level of success for patients with visual agnosia. Communication regarding limitations across all sensory domains will allow for an individualized plan of care to maximize functional independence.

12 Conclusion

Patients with acquired brain injury face a number of potential sequelae that can impact their recovery and quality of life. These patients require collaborative care from a multidisciplinary care team. Given the multitude of potential visual sequelae, it is important that patients with acquired brain injury undergo a thorough ocular examination and visual sensorimotor evaluation with an eye care provider shortly after their injury. These evaluations will allow for identification of visual input deficits as well as conditions of higher visual processing. These conditions can result in a number of visual symptoms and limit progress during visual-auditory, visual-motor, and visual-vestibular tasks. It is important to ensure that the patient has intact visual input skills, is alert, possesses intact intelligence, and has adequate language abilities prior to an evaluation of higher visual processing deficits (Burns, 2004; Musulam, 2000; Rapp, 2001).

Disorders of higher visual processing should be ruled out by an appropriate member of the care team in those patients with confirmed or suspected damage to the dorsal or ventral pathways. The dorsal pathway runs superior to the parietal lobes and is responsible for spatial information (Haque et al., 2018). Visual neglect is often associated with damage to the dorsal pathway in the right hemisphere (Burns, 2004; Haque et al., 2018; Langer et al., 2019; Parr & Friston, 2018; Spaccavento et al., 2017). The ventral pathway runs inferior along the occipital and temporal lobes and is responsible for the fixed properties of objects (Haque et al., 2018). Agnosias are the group of higher visual processing disorders associated with damage to the ventral pathway (Burns, 2004; Haque et al., 2018; Parr & Friston, 2018). While damage following an acute event may be top of mind, it is important to also consider disorders of higher visual processing in patients with inflammatory disease, metabolic disease, and degenerative conditions (Andrade et al., 2010; Auclair et al., 2008; Gilad et al., 2006; Ho et al., 2003).

Management of these conditions often involves multiple members of the care team working in conjunction to develop and implement compensatory strategies. Developing strategies to maximize functional independence is especially important given how debilitating disorders of the dorsal and ventral pathways can be (Burns, 2004; Haque et al., 2018). Additionally, these strategies often utilize non-visual input that will be impacted by deficits in those domains. Evaluation of auditory, language, physical, and executive functioning abilities should be performed prior to offloading visual tasks to those areas.

Given the complexity and chronicity of these vision conditions, extensive patient and family education are necessary. Consistent evaluation with various members of the care team should be encouraged in the future to ensure the patient remains successful with compensatory strategies and maximizes functional independence.

Conflict of interest

The author has no conflicts of interest related to the contents of this review.

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