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Home » Neuro-Optometric Rehabilitation » Unilateral Spatial Neglect (USN)

Unilateral Spatial Neglect (USN)

About Unilateral Spatial Neglect

Unilateral spatial neglect (USN) is defined as a failure to detect, act or form a mental picture on one half of space opposite to the side of the brain lesion. Visual neglect (VN) or unilateral spatial inattention (USI) is often used interchangeably with USN and is the decreased, or lack of, awareness of the sensory input to the contralesional side of the brain even though the sensory pathways and the primary sensory cortical areas are intact because curiosity and exploration on the affected side are not there. A phenomenon called extinction can also occur whereby an individual can see and describe things on the affected side but cannot do so when, and if, competing stimuli are present on the unaffected, ipsilateral side.

The main etiology of USI or VN is a cerebrovascular disease; hence, any “physical” trauma or injury to the same network of anatomic areas mediating attention such as posterior parietal cortex, frontal lobe, cingulate gyrus, striatum, thalamus, or specific brain-stem nuclei will produce the same sequelae and limitations in functional activities as in a cerebrovascular accident (CVA). When there are no neurological events, the right hemisphere is said to attend globally to both the right and left sides while the left hemisphere attends for the most part to the right side. An event affecting the left hemisphere does not give USN because the right hemisphere is still there to attend globally; whereas, damage to the right hemisphere will result in left side neglect because the left hemisphere can only attend to the right side.

Different facets of neglect were seen in up to 82 percent of patients following a right CVA and up to 65 percent of patients following a left CVA. Left neglect is most common and is associated with a right CVA. Recovery is most effective within the first month of the CVA and can vary from interminable neglect to full amelioration.

Identifying Unilateral Spatial Neglect

Clinically, the visual field in patients with USI may or may not show homonymous hemianopia. The signs of USI are usually observed by a family member, therapist, or another health care practitioner in a change in the behavior where the individual does not seek out information on one side of space. Persons with neglect do not attend to either one side of the body (personal neglect) or the area within reaching distance (peri-personal neglect) or the area beyond the vicinity of the body (extra-personal neglect) or a combination thereof. They may include activities of daily living (ADL) such as not doing self-care activities on one side of the body: bathing, dressing (personal neglect), ignoring food on one side of the plate (peri-personal neglect), and bumping into his/her environment while walking (extra-personal neglect). Moreover, there is often a postural imbalance from a shift in the person’s midline similar to hemianopia which increases the risk for falls and injuries and requires lengthier rehabilitation.

Persons with USI often do not have symptoms because there is an absence of awareness of their disconnections and in some cases, even an inability to cognitively accept its presence (anosognosia) which can make rehabilitation challenging.

The clinical value of most USI assessment is restricted to peripersonal space where tests such as the letter/star cancellation tasks (omit elements on one side), line bisection (marks err to one side), clock/house drawing (omit content on, or squish content to, one side), coin-sorting (omit coins on one side), book reading, (omit beginning words in left neglect) or copying tasks (squish words to one side) are placed on tabletops to evaluate a person’s ability to perform active spatial searches of the visual space. In deciphering the results, it is incumbent on the assessor to rule out spatial attention favoritisms from first, the concurrent primary visual field deficit (hemianopia) with the Extinction Visual Field Test, then second, the perceptual neglect (difficulty seeing) with the Montreal Cognitive Assessment and third, the motor neglect (difficulty executing) because USN can encompass many other functional disorders such as the aforementioned. Likewise, fatigue, the setting and practice can affect the severity and presentation of the USI.

Neuro Optometric Rehabilitation & Unilateral Spatial Neglect

There is a range of rehabilitation strategies for the varied presentations of USI and many focus on training attention and increasing/sustaining arousal in the neglected space. They include powerful auditory cues or commands to alert the person to look in, and pay attention, to the neglected space, eye tracking/scanning training with emphasis during ADL on the conscious leftward scanning as in right hemispheric lesions, a colorful symbol/mark or physical tactile line guide at the beginning or end of a sentence while reading, changing the visual input with prism lens adaptation, touching objects at different distances, visualization and visual memory of the scenery seen, hemifield sector occlusions over the non-neglected half of each lens to reinforce scanning to the neglected space while performing ADL, limb activation training using a full-length mirror or with visually guided bimanual circles and active awareness of making the movements. Lastly, using yoked prisms with the bases toward the affected side have been shown to rebalance the visual space for better ambulation.