Clinical Assessment of Complex Visual Dysfunction

Department of Neurology, Division of Behavioral Neurology and Cognitive Neuroscience, University of Iowa, Iowa City, Iowa.

Semin Neurol. 2000;20(1) 

In This Article

Bálint Syndrome and Related Visuo-Spatial and Visuo-Motor Disturbances

Bálint[110] reported chronic visuoperceptual and eye-hand coordination deficits in a man who had bihemispheric strokes in 1894. Hécaen and de Ajuriaguerra[123] used the term Bálint's syndrome to describe a triad of similar deficits.[124] First, Balint's patient had a "spatial disorder of attention." This included trouble perceiving more than one object at a time ("no matter what size") and constriction of the attentive field in the context of probable left hemispatial neglect. This spatial disorder came to be equated with "simultanagnosia" (the term that remains), an inability to interpret a whole scene despite preserved ability to apprehend individual parts.[125] It has also been compared with "visual disorientation," a condition identified in soldiers with occipital wounds.[126] causing inability to localize the spatial position and distance of objects (despite adequate acuity and stereoacuity), to scan the environment, to walk around obstacles, and to count or touch objects presented in central or peripheral vision.[126,127] Second, Bálint's patient had "psychic paralysis of gaze" difficulty initiating voluntary saccades to visual targets despite unrestricted range of eye movements, which is now commonly referred to as ocular apraxia.[6] One proposed mechanism for the gaze defect was the spatial disorder of attention.[110,128] Another was "spasm of fixation" ("sticky fixation"),[123,129] the inability to disengage fixation from one object to look at another.[126,130] Third, Bálint's patient had defective hand movements under visual guidance (especially with the right hand) despite normal limb strength.[128] known as "optic ataxia." Bálint argued that if this defect were purely visual, it should have affected both hands equally. He discounted defective position sense (as with dorsal column lesions in tabetic ataxia) because when he positioned the patient's left hand the man could imitate it with the right.

Bálint inferred that the basic problem in his patient was that the man could see only one object at a single time, no matter what size. He attached special significance to bilateral lesions of the angular gyri identified at autopsy, although there was also damage to other vision-related structures including the corpus callosum, posterior white matter, and pulvinar. Holmes131 reported similar bilateral lesions in his soldiers from estimates of missile trajectories and from autopsy. However, the validity of Bálint's syndrome has been questioned due to lack of autonomy of the syndrome from other impairments. Also the triad of defects (simultanagnosia, ocular apraxia, optic ataxia) syndrome is not as closely bound as once supposed, and individual components of the triad may each represent a variety of combined defects.[124]

Angular gyrus lesions often cause additional deficits outside Bálint's triad. This includes hemineglect with right-sided lesions, aphasia and Gerstmann's syndrome with left-sided lesions.[132] and profound defects of visual motion perception with bilateral lesions.[83,133,134] Features of Bálint's syndrome have been reported with bifrontal[135] and pulvinar lesions.[136] Simultanagnosia has been reported with lesions of the dorsal occipital lobes in Brodmann's areas 18 and 19.[25,137] Lesions of the frontal eye fields (Brodmann's areas 6 and 8) may impair voluntary saccades and ocular search, as in acquired ocular apraxia. Impaired saccades under visual guidance have been described with bilateral damage to the inferior parietal lobules.[112] Impaired reaching under visual guidance is associated with lesions of a wide range of areas, including Brodmann's areas 5, 7, 19, 37, 39 and even with cortex inferomesial to the angular gyri.[138]

Patients with elements of Bálint's syndrome should be assessed with valid and reliable tests of basic visual and cognitive function. Reports on Bálint's syndrome (and other central visual disorders) can be criticized based on failure to exclude disorders of anterior visual pathways, assess basic visual functions besides acuity, and adequately test the visual fields. Even patients with normal visual fields (measured by standard perimetry) can be shown to have shrinkage in the useful field of view due to reduced processing speed and attention.[139,140] This reduction can occur with cognitive aging, neurodegenerative impairments including Alzheimer's disease, and cerebrovascular lesions in visual association cortex[141] as in Bálint's patient. Bálint's patients' visual fields were easily fatigable, resembling a pathological enhancement of the effects of fatigue noted with prolonged monitoring of visual displays by normal observers performing in experiments of vigilance or sustained attention.[142,143,144] The patient failed to detect objects in the periphery, more so on the left, due to constriction of the attention field, as in the hemineglect syndrome.

Simultanagnosia can be operationally defined as an inability to report all of the major items and relationships among items in a complex visual display, despite unrestricted head and eye movements. An appropriate screening tool is a complex picture such as the Cookie Theft Picture from the Boston Diagnostic Aphasia Examination.[145] which contains a balanced distribution of information in all quadrants. The patient's report can be correlated with a checklist of items in the picture. It is important to consider that a defective report could be due to co-existent aphasia or visual field defects. Extensive peripheral scotomata (double homonymous hemianopia) can cause "keyhole" or "tunnel" vision that hinders visual search and simultaneous perception. Objects falling into the fields of a central or paracentral scotoma may seem to vanish, resembling simultanagnosia. Note that simultanagnosics may fail to recognize familiar objects and faces due to perceptual impairment, that is, apperceptive agnosia[6,7,82] rather than to associative agnosia, a condition in which percepts are effectively stripped of their meanings.[8]

Acquired ocular motor apraxia is difficult to separate from, and may not occur independently of, simultanagnosia. Patients are unable to make saccades to visual targets on command, yet may still generate reflexive saccades to visual targets, as at passers-by. Failure to disengage the eyes from one target and move them to another is compatible with spasm of fixation. This type of problem can be observed in the clinic and quantified in a laboratory with eye movement recording equipment. Clinical observations of impaired visual search should consider the patient's visual field defects, and so should judgments of optic ataxia.

The examiner should not restrict the patient's head or eye movements and should ensure that the patient has seen a visual target before reaching and grasping commence because inaccurate reaches to targets within a blind field are expected and do not prove optic ataxia.[146] Optic ataxia can occur with unilateral cerebral lesions and is generally worse for reaches with the hand opposite to the side of the lesion and in the field opposite the lesion. Compared to cerebellar dysmetria there is greater selectivity for vision and lack of intention tremor or dysdiadochokinesia. Optic ataxics can reach accurately for targets located on their own bodies, because body parts are defined by kinesthetic rather than visual coordinates.

Reaching, grasping, lifting, and manipulation of objects under visual guidance demand the coordination of multiple neural functions.[147,148] The brain must transform a target's visual coordinates to body-centered space, plan a hand path and trajectory (sequence of hand position and velocity to target), compute multiple joint torques (especially about the shoulder and elbow), specify the necessary limb segment orientations from among many possibilities, and activate appropriate muscle groups and inhibit others to meet those specifications. When lifting these objects we rely on vision to apply forces scaled for object properties like weight, shape, and visual memory (for commonly encountered objects). The sensory feedback, frames of reference, neural mechanisms, and visual pathways (e.g., dorsal vs. ventral) involved in these complex visuomotor control problems are active research topics.[149,150,151,152,153] Quantitative measurements of reaching in patients suspected of having optic ataxia require special techniques and, not surprisingly, show a rich spectrum of defects. These include increased latency of initiation, abnormal hand trajectories, increased endpoint variability, tendency to reach to one side, dissociations of distance and direction control, and abnormal grip force application.