Journal of Neuro-Ophthalmology, March 1990, Volume 10, Issue 1

Disorders of the visual system in Alzheimer's disease.

Alzheimer's disease (AD) is associated with disturbances in basic visual, complex visual, and oculomotor functions. The broad range of visual system disorders in AD may result from the concentration of neuropathology in visual association cortex and optic nerves in this disease. AD patients and their caregivers frequently report visuospatial difficulties in these patients. Examination of the visual system in AD may reveal visual field deficits, prolonged visual evoked potentials, depressed contrast sensitivities, and abnormal eye movement recordings. Complex visual disturbances include constructional and visuoperceptual abnormalities, spatial agnosia and Balint's syndrome, environmental disorientation, visual agnosia, facial identification problems, and visual hallucinations. The purpose of this article is to review the spectrum of visual system disturbances found in AD and, in particular, to describe the methods used to screen for complex visual abnormalities in these patients.

© 1990 Raven Press, Ltd .. New York Disorders of the Visual System in Alzheimer's Disease Mario F. Mendez, M. D., Robert L. Tomsak, M. D., Ph. D., and Bernd Remler, M. D. Alzheimer's disease ( AD) is associated with distur­bances in basic visual, complex visual, and oculomotor functions. The broad range of visual system disorders in AD may result from the concentration of neuropathol­ogy in visual association cortex and optic nerves in this disease. AD patients and their caregivers frequently re­port visuospatial difficulties in these patients. Examina­tion of the visual system in AD may reveal visual field deficits, prolonged visual evoked potentials, depressed contrast sensitivities, and abnormal eye movement re­cordings. Complex visual disturbances include construc­tional and visuoperceptual abnormalities, spatial agno­sia and Balint's syndrome, environmental disorienta­tion, visual agnosia, facial identification problems, and visual hallucinations. The purpose of this article is to review the spectrum of visual system disturbances found in AD and, in particular, to describe the methods used to screen for complex visual abnormalities in these patients. Key Words: Alzheimer's disease- Dementia­Visual- Visual perception- Visuospatial- Balint's syn­drome--- Oculomotor. From the Alzheimer Center and the Department of Neurol­ogy ( M. F. M.) and the Division of Neuro- Ophthalmology, De­partment of Neurology, and Department of Ophthalmology ( R. L. T., B. R.), University Hospitals of Cleveland and Case Western Reserve University, Cleveland, Ohio. Address correspondence and reprint requests to Dr. M. F. H., · !. f'... I I' Medic, 1 C" nter, Jackson University, 62 Alzheimer's disease ( AD) is the most prevalent form of dementia affecting greater than 2.5 million people in the U. S., with the numbers expected to double by the year 2040 ( 1). Despite the absence of a clinical test for AD, the recent establishment of highly accurate clinical criteria permit a more pre­cise evaluation of the deficits associated with this disorder ( 2- 4) ( see Table 1). In addition to the usual memory and other cognitive deficits, AD pa­tients have disturbances in basic visual, complex visual, and oculomotor functions, and AD patients in greater numbers are undergoing more thorough evaluations of their visual systems ( 4- 8). Physicians are just beginning to understand the significance of visual system involvement in AD ( 9,10). Consistent with the clinical heterogeneity of this disorder, individuals with AD vary in the ex­tent of their visual system pathology and in their visual problems ( 7,11). The visual system prob­lems are not simply due to global cognitive impair­ment and can occur in the absence of other cogni­tive deficits, increased dementia severity, or pro­longed duration of dementia ( 4). However, the visual system abnormalities may contribute greatly to the disability caused by AD and may magnify the effects of other cognitive deficits. For these rea­sons, any management strategies that improve vi­sual functions can help alleviate the huge burden of taking care of these patients. Furthermore, there is a need to both identify higher visual tests that could be used for the early diagnosis of AD and to determine the visual physiological mechanisms that are disturbed in dementia. NEUROPHYSIOLOGY AND NEUROPATHOLOGY AD affects the visual association cortex with rel­ative sparing of primary visual areas ( 12- 14). Se­nile plaques are located throughout the visual cor- VISUAL SYSTEM AND AD 63 TABLE 1. NINCDS- ADRDA criteria for clinically probable Alzheimer's disease ( 2) '( 1) Dementia established by clinical exam and documented by mental status questionnaire or neuropsychological testing ( 2) Deficits in two or more areas of cognition ( 3) Progressive worsening ( 4) No disturbance of consciousness ( 5) Onset between the ages of 40 and 90 ( 6) Absence of other potentially causative disorder( s), such as systemic disorders or brain disease, that could account for dementia tex; however, in early and middle stages of AD, neurofibrillary tangles, which are associated with the severity of dementia ( 15), are located in greater amounts in higher visual areas ( 12,13), Neurofibril­lary tangles are rare in area 17, increase 20- fold in area 18, and nearly double again in area 20 ( 13), Positron emission tomography scanning studies also show cerebral hemispheric hypometabolism concentrated in the posterior parietal lobes and ad­joining areas, with sparing of the primary visual occipital cortex ( 16- 18), This distribution of neuro­pathological and metabolic changes predicts pre­dominant deficits in complex visual functions ( 19), Furthermore, the pattern of complex visual distur­bances in AD, with prominent visuospatial prob­lems, suggests differential disease of the magno­cellular- occipitoparietal visual system, dealing with spatial concepts, rather than the parvocellu­lar- occipitotemporal visual system, dealing with form and color ( 20- 22), In addition to the greater disease in visual asso­ciation areas, there is prominent optic nerve de­generation in AD, with dropout of retinal ganglion cells and their axons ranging from 15 to 80% ( 6), One study found decreased retinal M cell degen­eration in 8 of 10 patients ( 23). This optic neurop­athy results in minimal clinical evidence of visual impairment ( 6), and most of the observed visual system abnormalities in AD probably result from disease in visual association cortex. However, a late decrease in visual acuity and color vision may be consequences of the optic neuropathy in AD ( 4,6,7,24,25). CLINICAL EVALVAnON The most common visual complaints in AD are problems in visuospatial functioning ( 4- 8). In a study of 30 community- based patients with clini­cally probable AD, almost half ( 43%) had visual symptoms, and these were predominantly visuo­spatial ( 4) ( see Table 2). Visuospatial difficulties oc­cur in general spatial orientation ( e. g., walking TABLE 2. Visual symptoms in 30 patients with Alzheimer's disease ( 4) Spatial agnosia: Five patients had prominent difficulties finding objects, looking at them, and reaching for them. These patients were unable to walk without bumping into things and could not judge distances. Visual localization problems: Seven additional patients had less severe difficulties visually finding objects. Environmental disorientation: Five patients had an isolated problem finding their way in familiar surroundings that was not due to a general spatial agnosia. Spatial alexia: Three patients had reading difficulties not due to language disturbances or a general spatial agnosia. On reading, these patients easily lost their place, Possible mild optic ataxia: Two patients had difficulties with fine hand- eye coordination tasks that was not due to general spatial agnosia. Visual agnosia: Three patients had difficulty recognizing common objects when visually presented. Facial identification problems: One patient had prosopagnosia. Visual hallucinations: Three patients had formed hallucinations that were not otherwise explainable by medications or confusional states. without bumping into things), in visual localiza­tion ( e. g., finding door handles or other common objects), in environmental orientation ( e. g., find­ing their way in their surroundings), in reading ( e. g., locating the next word or line of print), and in performing fine hand- eye coordination activi­ties ( e. g., sewing) ( 4- 9) ( see Table 2). AD patients and their caregivers complain less frequently of difficulties in visually identifying objects, scenes, or faces ( 5) and of visual hallucinations ( 26). Examination of the visual system in AD patients reveals a broad range of disturbances. All visual functions are not uniformly affected in AD; there are specific patterns of involvement. Frequently impaired basic visual functions include peripheral vision, visual evoked potentials ( VEPs), and con­trast sensitivities ( 4,6,24,25,27,28). Difficulties with constructions, figure- ground discrimination, and visual synthesis are present in the majority of pa­tients with AD and are the most common findings potentially attributable to complex visual dysfunc­tion in this disorder ( 4,29). Other common com­plex visual abnormalities involve visuospatial abil­ities ( 4- 9) and visual object and face recognition ( 4- 9). Finally, patients with AD have abnormal oc­ulomotor functions, such as increased saccadic la­tency and an inability to inhibit anticipatory sac­cades ( 30- 35). The rest of this article discusses spe­cific visual system abnormalities in AD and visual system testing in demented patients, particularly the screening tests used for complex visual distur­bances ( see Table 3). 1Clin Neuro-{) phthalmol, Vol. 10, No. 1, 1990 64 M. F. MENDEZ ET AL. TABLE 3. Screening test for complex visual functions Constructions: Two- dimensional design or cube, three- dimensional cube or open box, complex design, e. g., clock face Perception: Tests of figure- ground discrimination ( overlapping, cross- hatched, or hidden figures) and visual synthesis tasks ( completion or visual closure tasks) Visuospatial: Tests of inattention or neglect ( line bisections), localization ( dot circling or picture searching), simultanagnosia (" linked" versus " unlinked" figures or embedded figures), oculomotor apraxia ( eye movements to visual stimuli), and optic ataxia ( hand movements to visual stimuli) Environmental orientation: Tests of topographic amnesia and topographagnosia ( follow, describe, draw, and learn route) and geographical orientation ( map reading or placing landmarks on map) Object recognition: Visual naming, describe or demonstrate use, tactile naming, and matching ( actual objects, pictures of common objects, and drawings of common objects) Face identification: Tests of prosopagnosia ( identification of pictures of famous faces) and facial discrimination ( matching unfamiliar faces) There are two special problems involved in the visual evaluation of AD patients. First of all, basic visual deficits may affect tests of complex visual functions. The evaluation of basic visual functions must precede the administration of complex visual tests. Secondly, other cognitive impairments, such as deficits in general comprehension, language, or memory, can interfere with performance on visual tasks. The testing methods can partially compen­sate for deficits in other areas of cognition by keep­ing the task and instructions as simple as possible, by allowing as much time as needed for a re­sponse, and by allowing the patients to respond by description or demonstration as well as by a spe- 200 ,,+- --------------+-. 100 40 cific verbal answer. Ultimately, clinicians must in­terpret critically the results of visual system testing in demented patients, as abnormal performance may be due to a combination of several visual and cognitive disturbances. BASIC VISUAL FUNCTIONS Investigations of basic visual functions in AD have found abnormalities particularly in periph­eral vision and in VEPs ( 6,24,27,28,36). Sadun et a1. ( 6) reported binasal field loss, inferior field loss, or constriction of the visual fields in 3 of 12 AD patients. Others have also found constriction of the visual fields ( 27) or left homonymous deficits ( 36). On VEPs, some investigators have found that flash stimuli, but not pattern reversal stimuli, may result in an increased latency and a loss of ampli­tude ( 19,24). This pattern of YEP findings suggests that the main problems in the visual system in AD are not in the visual pathways up to the primary visual cortex, but in the visual association areas ( 28). However, late in the course of AD, some pa­tients have optic nerve pallor, afferent pupillary reflexes, mild diminutions in visual acuity, and dy­schromatopsia, particularly for blue- yellow ( 6,23,25). The most common basic visual dysfunction in AD may be abnormal contrast sensitivity func­tions. Several studies show a general depression across all spatial frequencies in AD ( 37,38) ( see Fig. I), and a subgroup of AD patients with more prominent visuospatial problems have a greater depression at the lower spatial frequencies ( 36,38). Others may have failed to find contrast sensitivity difference between dementia and normal aging, FIG. 1. Contrast sensitivity function curves for 19 patients with moderately advanced clinically probable Alzhei­mer's disease and 19 normal age­matched controls. + NORMAL CONTROLS ( n- 19) -& AD PATIENTS ( n- 19) 20 ! I: l- ----'- L-_.... L..._. i-- L----'-----'----'----'- -' 0.6 1.0 2.0 4.0 8.0 SPATIAL FREQUENCY J elm Nt'urv- ophtfwlnwl. Vol. 11), '\ ilI i, 1: 14{} VISUAL SYSTEM AND AD 65 possibly because of methodological differences ( 10). Furthermore, in a recent study of 19 AD pa­tients compared to 19 normal elderly controls, lower contrast sensitivities at a low spatial fre­quency ( 2 cycles per degree [ cpd] alternating at 7.5 Hz) correctly predicted the presence of AD in 89.5% of the patients ( 37). The decrease in contrast sensitivities may be the source of much of the vi­sual impairment found in AD patients and may be a consequence of the pathology in both the optic nerves and the visual association cortex. COMPLEX VISUAL FUNCTIONS Constructional Disturbances Visual system dysfunction contributes to the constructional disturbances in drawing, copying, and block assembly that are common in dementia and widely used to screen for AD ( 29). However, constructional disturbances are nonspecific and may reflect not only visual disturbances, but also problems with motor praxis, conceptual abilities, executive functions, or some combination of these ( 39). Constructional disturbances occur in AD, par­ticularly with decreased metabolism in the poste­rior right hemisphere ( 18); however, these distur­bances may also result from lesions in different parts of the brain ( 39). Screening tests for constructional difficulties most frequently involve drawing or copying sim­ple two- dimensional objects, such as a simple de­sign or a cross, and simple three- dimensional ob­jects, such as a cube or an open box ( see Fig. 2). Drawings of more complex spatial figures, such as the face of a clock, are frequently abnormal in AD, but can result from disturbances in several areas of cognition. Copying or assembling blocks are also good tests for constructional difficulties ( 40). Con­structional errors on these tests include impover­ishment ( omission of essential features), fragmen­tation ( loss of spatial relationships and faulty ori­entation), cramping ( smaller with perseveration across items), and, on copying, a " closing- in phenomenon" ( the copy overlaps the model) ( 29). These elements may reflect a disturbance in both hemispheres, with impoverishment related more to the left hemisphere and fragmentation more to the right posterior hemisphere ( 29). Perceptual Disturbances Several visuoperceptual processes are com­monly disturbed in AD ( 4). Abnormal figure­ground discrimination occurs in most AD patients, and abnormal visual synthesis, the ability to con-d~~ l- Irt- llJ --~ FIG. 2. Example of typical constructional tasks in a patient with Alzheimer's disease. The patient at · tempted to copy the drawings on the left. join different parts of a stimulus, is frequently present ( 4). AD patients also have difficulties on complex visual form discrimination tasks, al­though, when administered untimed, they may be able to successfully perform these tasks in a slow, serial feature- by- feature fashion ( 4,7,41). Other ar­eas of visual perception in AD need further explo­ration; however, there is some evidence for de­clines in depth perception ( 6,19,42), the discrimi­nation of line orientation ( 43), backward pattern masking ( 10), and possibly, visual memory, visual imagery, and the detection of movement. Screening tests for visual perceptual difficulties in AD most commonly include tests of figure­ground discrimination ( overlapping, cross­hatched, or hidden figures) and visual synthesis ( visual completion or closure tasks) ( 39,44,45) ( see Fig. 3). More detailed assessment of visual percep­tion involves the administration of neuropsycho­logical tests ( 44). Spatial Agnosia and Balint's Syndrome Patients with AD frequently have difficulties lo­cating objects in space ( 4- 9). They have lost the I Gin Neuro- ophthalmol, Vol. 10. No. 1. 1990 66 M. F. MENDEZ ET AL. FIG. 3. Examples of tests of visual perception. Figure­ground discrimination tasks: ( A) overlapping figures ( reproduced from the Southern California Figure Ground Test with permission from Western Psycho­logical Services); ( B) cross- hatched figures ( Luria fig­ures). Visual synthesis tasks: ( C) completion ( repro­duced from the Hooper Test of Visual Organization with permission from Western Psychological Ser­vices); ( 0) visual closure ( from the Street figures). sense of " whereness" ( 9) and are clumsy in their attempts to reach for objects or avoid bumping into them. This " spatial agnosia" is responsible for the most common visual complaints in AD, such as visual localization difficulties and spatial reading problems (" spatial alexia") ( 5,6) ( see Table 2). Spa­tial agnosia is associated with abnormal spatial at­tention or the ability to focus on some spatial lo­cation to the exclusion of others. What little work has been done suggests that AD patients have a decreased capacity of spatial attention, difficulties in moving their focus of attention to a new focus in the periphery, and, even when their visual fields are normal, have a smaller, constricted field of view ( 8,45,46). The spatial agnosia may result in abnormalities in scanning, searching, and hand- eye coordina­tion severe enough to constitute Balint's syndrome in up to 20% of AD patients ( 4). These patients " see," but may have to be led as if blind because of the degree of visuospatial impairment ( 8,47). Pa­tients with Balint's syndrome can only attend to a single visual object at a time (" simultanagnosia"), have inaccurate eye movements to visuospatiallo­cations ( oculomotor apraxia), and cannot accu­rately direct hand or other movements by visuo­c; rnr;, J! . ill · 11) ( 4R) Simultanagno-sia may result in part from a relative weakness of the peripheral fields ( 49,50) with suppression of extrafoveal images ( 51,52), or from the interfer­ences of low spatial frequencies necessary for the spatial integration of images ( 36). The visuomotor disturbances of oculomotor apraxia and optic ataxia may result in an inability to explore the pe­ripheral fields due to disruption of saccadic and fixation neurons in the posterior parietal lobe ( 53­55). Finally, investigators have questioned whether or not demented patients with full- blown Balint's syndrome constitute a separate degenera­tive disorder; however, it is likely that these pa­tients are a subpopulation of AD, consistent with the broad spectrum of visual disturbances that oc­cur in this disorder ( 4,8,47). Screening tests for spatial agnosia and Balint's syndrome include tests for spatial inattention, spa­tial localization, simultanagnosia, oculomotor praxis, and optic ataxia. Line- crossing tasks, where various lines on a paper are presented for bisec­tion, are tests for visual heIDi- inattention or neglect of a part of the visual field. Spatial localization tests include finding random dots in a visual field or searching for specific items in a picture. Simulta­nagnosia tests include distinguishing the larger pic­ture when there are " unlinked" items ( e. g., two unconnected circles versus two circles " linked" to make a pair of glasses) or when there are smaller embedded figures ( e. g., smaller letters combined to form a larger letter). Oculomotor praxis tests involve moving the eyes to visual stimuli, particu­larly into the peripheral fields, and optic ataxia tests involve moving the hands under visual guid­ance in reaching for objects or through openings in a box ( 55). Environmental Disorientation Disorders of environmental orientation are com­mon in AD and are operationally defined as diffi­culty with following a route ( 5,56,57). Patients with environmental disorientation are unable to find their way around unfamiliar surroundings, a hospital ward, or even their homes, and may have a tendency to wander ( 56- 58). The inability to fol­Iowa route may be due to a primary memory dis­order for spatial concepts (" topographic amnesia") or to a primary disorder in the visual recognition of landmarks and spatial relationships (" topo­graphagnosia"). Both of these forms of environ­mental disorientation occur in AD. In addition, a related disturbance that is common in AD is geo­graphical disorientation- the inability to read a map. Looo I. t-' ~ " - jill ~ ......, ~ V' ./ B I' I , J Clm Neuru- ophtiullmul, Vol. W, No. J, l~~ O VISUAL SYSTEM AND AD 67 Environmental orientation is tested by follow­ing, describing, drawing, or learning a route. With topographic amnesia, the patients are unable to describe or draw a previously familiar route and are unable to learn a new route. When topograph­agnosia, patients may be able to describe or draw a previously familiar route or even learn the map of a new route, but they cannot recognize the route itself or its landmarks. Geographical disorientation tests involve placing well- known cities or land­marks on a map. Visual Agnosia Visual object recognition problems or " agnosia" are present in almost half of AD patients and can be a major source of disability from the dementia ( 4,6). Visual agnosias are deficits in the recognition of visually presented material in the absence of basic visual or general cognitive deficits suffi­ciently severe to otherwise account for the recog­nition problems ( 41,45,59). There are traditionally two forms of visual agnosia: an " apperceptive" form, where the inability to recognize an object is associated with significant impairments in visual perception, and an " associative" form, where per­ception is sufficiently intact, as indicated by the ability to visually match objects, but the object's visual representation is isolated from its other cog­nitive associations. The existence of a true visual agnosia in AD has been controversial, as de­mented patients may fail to recognize an object from failure to understand or cognitively interpret the visual representation, especially if it was al­tered by an abnormality in basic visual functions ( 52,60). However, some AD patients have had vi­sual recognition difficulties in the presence of nor­mal basic visual functions and only mildly im­paired general cognition ( 4,6,61). In sum, the vi­sual recognition problems in AD represent a true visual agnosia and may be either of the " ap­perceptive" or of the " associative" form. Screening tests for visual agnosia in AD involve the identification of actual common objects, simple photographs of common objects, and simple draw­ings of common objects. Actual objects are less dif­ficult to recognize than photographs or line draw­ings. Testing for agnosia involves excluding lan­guage difficulty, causing inability to name the objects, excluding global recognition difficulties not restricted to the visual sphere, and assessing the apperceptive- associative dichotomy. In order to exclude the effects of language difficulties, pa­tients must identify incorrectly named objects by description or demonstration of use. In order to exclude global recognition difficulties, patients must identify visually missed objects, unseen, by touch or sound. Finally, in order to assess the ap­perceptive- associative dichotomy, patients must identify missed objects by visual matching with a second series of identical objects ( or, alternatively, correctly copy unrecognized drawings). Facial Identification Problems There are several forms of facial identification problems in AD. Prosopagnosia, the inability to recognize famous faces, is a perceptual distur­bance usually associated with other perceptual dis­crimination difficulties ( 62) and occurs to some de­gree in most moderately advanced AD patients ( 5). True prosopagnosia is distinct from an inability to remember the specific faces tested and, when ex­treme, demented patients may not recognize themselves in the mirror ( the " mirror sign"). Test­ing involves the presentation of photographs of famous individuals that cannot otherwise be dis­tinguished on the basis of salient features, such as beards or glasses. Patients with AD also have dif­ficulty discriminating unfamiliar faces, as tested by the Benton Facial Recognition Test ( 40). Finally, many AD patients suffer from Capgras syndrome, a related form of misidentification of others ( 26). In Capgras syndrome, the AD patient denies the identity of a person and claims that the person has been replaced by a look- alike, often with a malev­olent intent. The Capgras syndrome appears to be tied to paranoid thinking, but complex visual pro­cessing may contribute to this phenomena. Hallucinations Hallucinations may occur in up to 20% of pa­tients with AD, and 80- 90% are in the visual sphere ( 26). Visual hallucinations in AD are usu­ally formed, animate, changing, and often in color, lilliputian, and frightening ( 26). The hallucinations are not associated with clear evidence of eye pa­thology or basic visual impairment; however, the combination of visual perceptual disturbances and paranoid thinking in AD may predispose to para­noid hallucinatory experiences. Other positive phenomena, such as illusions or palinopsia, are much rarer in AD. OCULOMOTOR FUNCTIONS Eye movement recordings in AD patients show saccadic pursuit ( 33), increased latency and hypo­metric saccades ( 30,32), fixation instability ( 30,35), JClin Neuro- ophlhalmol, Vol. 10, No. I, 1990 68 M. F. MENDEZ ET AL. inability to inhibit anticipatory saccades ( 30,31), disorganized scanpaths ( 34), and, as previously discussed, oculomotor apraxia ( 8) ( see Table 4). In addition to nonspecific disturbances in pursuit eye- tracking, patients with AD show a prolonga­tion of saccadic latency, are likely to undershoot a small target displacement by 10- 30%, and may have a decreased peak velocity for large amplitude saccades ( 40°) but not for small ones ( 30,31). The cortical neuronal loss in AD may also impair the ability to maintain or release fixation, and saccadic intrusions, such as large square- wave jerks, may intrude into fixation ( 30- 35). There are difficulties in suppressing anticipatory saccades, which, in the extreme, may constitute a " visual grasp reflex" with inability to inhibit a saccade to an extraneous visual stimuli ( 30,31). Patients with AD also have abnormal scanpaths with inability to concentrate on high information areas of a picture or scene ( 34). In sum, the prolonged saccadic latency and the inability to suppress anticipatory saccades may be the most characteristic oculomotor findings in AD ( 31). CONCLUSIONS A range of disturbances of the visual system is common in AD. The most common complaints in­volve difficulties in visuospatial orientation, but these patients also have visual recognition difficul­ties, such as visual agnosia and abnormal facial identification. On examination, AD patients may have abnormal visual fields, VEPs, contrast sensi­tivity functions, and eye movement recordings, as well as tests of complex visual processing. The evaluation of complex visual functions requires special attention to the effects of basic visual prob­lems and other cognitive deficits on complex visual tasks. Difficulties with constructions, figure­ground discrimination, and visual synthesis are al­most universally present in moderately advanced AD. Visual agnosia, although less common, may TABLE 4. Oculomotor disturbances in Alzheimer's disease Abnormal pursuit: Saccadic pursuit, catch- up saccades Abnormal saccades: Prolonged latency, hypometric/ dysmetric. decreased velocity for long jumps Abnormal fixation: " Sticky" or " wandering"; saccadic intrusions Inability to inhibit anticipatory saccades; " visual grasp reflex" Abnormal visual search and scan paths Abnormal visually guided eye movements ( oculomotor praxi<;) J C/ m Neuro- ophtlUJI11Io/. Vol. JiJ. Nv. 1. I~ YIJ contribute disproportionately to the disability from AD. Finally, some demented patients develop spa­tial agnosia sufficiently to constitute Balint's syn­drome. 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