Hemispatial visual defect in Alzheimer's disease

We describe a 56-year-old woman with Alzheimer's disease with left hemispatial neglect and left homonymous hemianopsia with macular sparing considered a manifestation of Alzheimer's disease resulting from severe degenerative change in the right primary visual cortex. Hemispatial neglect normally results from brain damage to the right cerebral hemisphere. Homonymous hemianopsia is commonly the result of localized brain disease, especially cerebral infarction or hemorrhage. To our knowledge, a patient with Alzheimer's disease showing hemispatial neglect and homonymous hemianopsia with macular sparing has not previously been reported.     

Just Thinking about Targets Can Aggravate Neglect on Cancellation Tests

While many studies investigate how the visual features of targets influence cancellation performance in neglect, few, if any, even consider that thought processes, such as the use of an algorithm to identify targets, might similarly aggravate neglect. This single-case study of a patient with chronic neglect compared cancellation performance after manipulating (1) ease of visual target identification, (2) the use of an algorithm to identify targets, and (3) the material-specific nature of target cancellation. Neglect severity was defined by the number and location of target omissions. While each manipulation had a differential impact on neglect severity, the novel and interesting finding occurred during the second condition, when a math algorithm was used to identify targets. In this condition, target omissions increased relative to other tests and target cancellations were confined to the right half of the page. This is the first report, to our knowledge, that neglect on cancellation tests can be aggravated by an internal thought process, a math algorithm, as opposed to external manipulations of visual stimuli and procedural characteristics of cancellation tests. An important characteristic of the algorithm used in this study is that it appeared to activate the intact left cerebral hemisphere.     

Just thinking about targets can aggravate neglect on cancellation tests

While many studies investigate how the visual features of targets influence cancellation performance in neglect, few, if any, even consider that thought processes, such as the use of an algorithm to identify targets, might similarly aggravate neglect. This single-case study of a patient with chronic neglect compared cancellation performance after manipulating (1) ease of visual target identification, (2) the use of an algorithm to identify targets, and (3) the material-specific nature of target cancellation. Neglect severity was defined by the number and location of target omissions. While each manipulation had a differential impact on neglect severity, the novel and interesting finding occurred during the second condition, when a math algorithm was used to identify targets. In this condition, target omissions increased relative to other tests and target cancellations were confined to the right half of the page. This is the first report, to our knowledge, that neglect on cancellation tests can be aggravated by an internal thought process, a math algorithm, as opposed to external manipulations of visual stimuli and procedural characteristics of cancellation tests. An important characteristic of the algorithm used in this study is that it appeared to activate the intact left cerebral hemisphere.     

Right sided hemispatial neglect and bilateral cerebral lesions.

This study compared the frequency with which unilateral and bilateral cerebral disease gives rise to right sided visual hemispatial inattention. A retrospective survey identified brain injured patients for whom target omissions on visual target cancellation tasks significantly exceeded control values. Subjects consisted of 40 right handed patients referred for clinical evaluation or research study of hemispatial inattention. Right sided visual hemispatial inattention occurred with greater frequency and severity in patients with bilateral lesions than in patients with unilateral left sided or right sided lesions. All eight patients with bilateral lesions manifested right sided hemispatial inattention and failed to detect more targets overall than patients in the other two groups. Of the 13 patients with left sided lesion, seven ignored more targets on the right and six ignored more targets on the left. All but one of the 19 patients with right sided lesions ignored more targets on the left. The association of severe right sided visual hemispatial inattention with bilateral cerebral disease extends previous findings and showed that, in this sample, the most common setting for right sided hemispatial neglect occurred in patients with bilateral cerebral lesions.     

Developmental neglect dyslexia in a Hebrew-reading child

This paper describes for the first time a detailed study of a child with neglect dyslexia. NT is 10-year-old child, with left word-based neglect dyslexia, without clinical signs of visuo-spatial neglect. Since he is a native speaker of Hebrew, which is read from right to left, his neglect dyslexia manifests in omissions and substitutions of final letters. He is severely impaired in single words, with 96% of his errors being omissions and substitutions of final letters. When presented with more than one word, in word pairs, sentences or text, he neglects the left part of each word, but never omit whole words on the left side of the page. His reading improves considerably when the same word is presented vertically or when manipulations are done to shift his attention to the left--with coloured final letters, flashing light, or tapping his finger to the left of each word. NT's neglect dyslexia is very selective, with good reading of numbers and symbols, and even good performance on letter sequences when no reading is required. A dissociation is also detected between his impaired reading due to neglect dyslexia and his normal performance on conventional clinical tests of general visual neglect visual of line, object and letter cancellation, line bisection, object drawing and copying. His neglect dyslexia seems to be developmental as no abrupt onset is reported.     

Restorative and compensatory therapy approaches in cerebral blindness - a review

In the first part of this review, different types of homonymous Visual Field Disorders (VFDs) and their resulting visual disabilities are analyzed in 313 patients with VFDs and 141 patients without VFDs from a neurorehabilitation centre for adults. Homonymous hemianopia was the most frequent visual field loss (54.7 %), followed by hemiamblyopia (23.3 %), quadrantanopia (15.3 %) and paracentral scotomata (6.7 %). About 70 % of all VFD patients had a visual field sparing of 5 degrees or less (macula or foveal sparing). Patients with VFDs frequently showed two types of disabilities: hemianopic alexia was subjectively reported and objectively found in 50-90 % of all patients, and visual exploration deficits in the scotoma were complained and found in 17-70 % of the VFD patients. While hemianopic alexia was related to parafoveal visual field sparing, and additionally to visual acuity in patients with bilateral VFDs, visual exploration deficits were correlated to the size of the area in the scotoma in which the patient searched for a stimulus with saccadic eye movements (search field). The size of the search field in the intact hemifield was not related to visual exploration deficits in unilateral VFDs. As a third disability, visual-spatial deficits in VFD patients are summarized. In the second part, restorative and compensatory treatment approaches for postchiasmatic VFDs are reviewed. Partial restitution of blind regions in the visual field is achieved in the majority of patients treated with purely restorative methods including saccadic localization or light detection in the scotoma. However, the amount of the visual field recovered is limited to 5-12 degrees (mean) in 90 % of these patients. Compensatory treatments seek to improve the substitution of the lost field region by large-scale saccadic eye movements to the scotoma, spatially organized search strategies in both visual hemifields, and by training small-scale eye movements required for reading. Significant improvements in these areas are achieved in 95 % of all VFD patients with these treatment techniques, with documented transfer to visually related activities of daily living. Furthermore, a significant though limited visual field increase of 5-7 degrees is achieved in 30-50 % of patients treated in this way. In the final section, promising approaches that might lead to new treatment techniques for VFDs are reviewed. Among these are the gaze-dependant modulation of scotomata, training-dependant enlargement of the useful field of view, a nd t he uncovering of residual visuomotor capacities to visual stimuli in a scotoma.     

Evidence of foveal splitting in a commissurotomy patient

A bilateral projection of the central fovea, produced by naso-temporal overlap at the retinal vertical meridian, has been proposed as the anatomical basis of macular sparing. To evaluate this claim, a commissurotomy patient was required to compare target figures presented 1 degrees or less from the retinal midline with reference figures presented 2.5 degrees from the midline in the same or opposite visual field. The subject judged whether the target and reference were the same or different. It was found that the subject's fovea was effectively split with respect to the cerebral hemispheres; targets in the same visual field as the reference were readily matched with the reference, but accuracy dropped to chance for targets in the opposite field. Ways of reconciling this data with anatomical evidence of nasotemporal overlap and reports of macular sparing are discussed.     

Ambulatory autonomy and visual motion perception in a case of almost total cortical blindness]

A 37-year-old man experienced cortical blindness following a bilateral stroke in the territory of the posterior cerebral arteries. Four years later, the measurement of visual field defects (Goldmann perimeter) showed persistence of bilateral blindness with a 2-degree preservation of macular vision and a perifoveal sparing between 10 to 30 degrees of eccentricity in the left inferior quadrant. Despite this visual impairment, the subject was able to perform visually-guided locomotion. Moreover he consciously perceived visual motion in the blind parts of his visual field. CT and MRI showed a lesion involving most of the striated cortex. The visual cortex located in the internal occipito-parital regions was relatively spared. The contribution of this structure to extra-striated vision of motion is discussed.     

Isolated homonymous hemianopsia due to lateral posterior choroidal artery region infarction: A case report

An 86-year-old, right-handed, hypertensive man suddenly experienced blurring of vision predominating in the left visual field. Neurological examinations were normal, except for left homonymous hemianopsia. Goldmann visual field testing revealed a left congruent incomplete homonymous hemianopsia with macular splitting. Brain MRI, with a T2-weighted image, demonstrated a lesion of high intensity in the right lateral geniculate body (LGB), as well as the posterior part of the caudate nucleus, posterolateral thalamus, and dorsolateral thalamus. MRA revealed severe stenosis at the second segment of right posterior cerebral artery (PCA). SPECT revealed significantly decreased blood perfusion in the striate cortex. To the best of our knowledge, this is the first case of an isolated, congruent, incomplete, homonymous hemianopsia due to lateral posterior choroidal artery (LPChA) region infarction. The LPChA possibly supplied the LGB through the PCA system. A horizontal, homonymous sectoranopia is typically the hallmark of an LPChA region infarction. However, a homonymous hemianopsia may also occur when the entire LGB has been affected. In the case of homonymous hemianopsia, LGB damage due to LPChA region infarction should be considered, in addition to lesions of the visual pathway, such as the optic tract, optic radiations, and occipital cortex.     

Measuring unconscious actions in action-blindsight: exploring the kinematics of pointing movements to targets in the blind field of two patients with cortical hemianopia

We tested two patients with posterior cerebral lesions on two pointing tasks. In the first task, the patients pointed to targets presented on a touch screen monitor and pointing accuracy was recorded. One patient (JR) demonstrated good localisation of targets presented to her blind field while the other patient (YP) did not. Movement kinematics were measured in the second task to compare the kinematics of movements made to sighted field targets with those made to blind field targets. For this version of the task both patients demonstrated above chance localisation of blind field targets although the slope of the relationship between the end of pointing movements and the target locations was significantly steeper for JR than for YP. Furthermore, JR showed a kinematic profile for movements made to blind field targets that mirrored the profile of kinematics to sighted field targets. That is, both peak velocity and time to peak velocity increased with increasing target eccentricity for movements made to blind and sighted field targets alike. Although patient YP now showed more reliable spatial localisation on this pointing task when compared with the touch screen task, his kinematics for movements made to targets in his blind field were quite different from those made to targets in his sighted field. Based on the patients' CT scans, we suggest that the superior performance of patient JR is a consequence of greater sparing of her parietal cortex in the damaged hemisphere.     

Saccadic visual search training: a treatment for patients with homonymous hemianopia

OBJECTIVES: We describe a novel rehabilitation tool for patients with homonymous hemianopia based on a visual search (VS) paradigm that is portable, inexpensive, and easy to deploy. We hypothesised that by training patients to improve the efficiency of eye movements made in their blind field their disability would be alleviated. METHODS: Twenty nine patients with homonymous visual field defects (HVFD) without neglect practised VS paradigms in 20 daily sessions over one month. Search fields comprising randomly positioned target and distracter elements, differing by a single feature, were displayed for three seconds on a dedicated television monitor in the patients' homes.Improvements were assessed by examining response time (RT), error rates in VS, perimetric visual fields (VFs) and visual search fields (VSFs), before and after treatment. Functional improvements were measured using objective visual tasks which represented activities of daily living (ADL) and a subjective questionnaire. RESULTS: As a group the patients had significantly shorter mean RT in VS after training (p<0.001) and demonstrated a variety of mechanisms to account for this. Improvements were confined to the training period and maintained at follow up. Three patients had significantly longer RT after training. They had high initial error rates which improved with training. Patients performed ADL tasks significantly faster after training and reported significant subjective improvements. There was no concomitant enlargement of the VF, but there was a small but significant enlargement of the VSF. CONCLUSION: Patients can improve VS with practice. This usually involves shorter RTs, but occasionally a longer RT in a complex speed-accuracy trade-off. These changes translate to improved overall visual function, assessed objectively and subjectively, suggesting that they represent robust training effects. The underlying mechanism may involve the adoption of compensatory eye movement strategies.     

Compensatory strategies following visual search training in patients with homonymous hemianopia: an eye movement study

A total of 29 patients with homonymous visual field defects without neglect practised visual search in 20 daily sessions, over a period of 4 weeks. Patients searched for a single randomly positioned target amongst distractors displayed for 3 s. After training patients demonstrated significantly shorter reaction times for search stimuli (Pambakian et al. in J Neurol Neurosurg Psychiatry 75:1443–1448, 2004). In this study, patients achieved improved search efficiency after training by altering their oculomotor behaviour in the following ways: (1) patients directed a higher proportion of fixations into the hemispace containing the target, (2) patients were quicker to saccade into the hemifield containing the target if the initial saccade had been made into the opposite hemifield, (3) patients made fewer transitions from one hemifield to another before locating the target, (4) patients made a larger initial saccade, although the direction of the initial saccade did not change as a result of training, (5) patients acquired a larger visual lobe in their blind hemifield after training. Patients also required fewer saccades to locate the target after training reflecting improved search efficiency. All these changes were confined to the training period and maintained at follow-up. Taken together these results suggest that visual training facilitates the development of specific compensatory eye movement strategies in patients with homonymous visual field defects.     

Troubled reaching after right occipito-temporal damage.

We encountered a man with an unusual reaching disturbance due to a stroke in the right occipito-temporal cortex and subjacent white matter. We studied his behavior in detail including vision and hand control. He had a left homonymous hemianopia. In his remaining fields static visual acuity and stereoacuity were normal, but he could not detect a coherent motion signal or follow moving targets with smooth pursuit. Transduction of limb movements using an optoelectronic technique showed abnormal morphology, increased variability and markedly prolonged latencies for transport to external visual targets, yet he achieved these targets with precision. Reaching to self-bound targets, and to the remembered locations of external targets with vision blocked was 5 x faster. The findings may be explained by: (1) damage in regions homologous to areas TF and TH in the monkey, which provide visual inputs to hand and forelimb representations in the cortex; (2) injury in human regions homologous to the monkey's MT complex, with inability to use visual information on the movement of the limb due to a visual motion processing defect; and (3) disruption of visual cortical-subcortical connections mediating crucial transformations among limb and target representations.     

A case of agnosia for streets without visual memory disturbance]

A 70-year-old, right-handed man was admitted to our hospital for his sudden-onset topographical disorientation. He failed to find his way to familiar places, but he knew distance and direction to the places. Neurological examination revealed homonymous left-upper quadrantanopsia on Goldmann perimeter and hypoesthesia over the left side of his body. Magnetic resonance imaging showed an abnormal intensity area at the right medial temporo-occipital region, due to the infarct of the right posterior cerebral arterial territory. The neuropsychological examination revealed agnosia for streets, and prosopagnosia without any other disturbance of visual perception. Both visual and topographical memories were intact. It is suggested that, in this case, the agnosia for streets was caused by impairment of recognizing familiar streets and houses or disconnection between their recognition and memory.     

DOES ALEXIA WITHOUT AGRAPHIA ALWAYS INCLUDE HEMIANOPSIA?

A patient with alexia without agraphia (pure alexia) is reported. Bedside examination of the visual fields disclosed no abnormalities, but perimetric examination demonstrated an incomplete right homonymous hemianopsia with some sparing of the peripheral part of the visual field. The literature on pure alexia without hemianopsia is reviewed and it is concluded that this syndrome has hardly been described with certainty.     

Palinopsia and visual allesthesia

Two cases of palinopsia are reported. The first patient had palinopsia and visual allesthesia secondary to an occipital calcified cysticercus. Symptoms were more prominent during treatment for his parasitic infection. The second case was a patient with long standing vascular headaches associated for many years with episodes of visual persistence; he had a right occipital lobe infarct; he reported deformation of images, illusion of movement and macropsia in his left homonymous hemianoptic visual field. Different hypotheses for explaining palinopsia have been proposed. An analysis of our cases does not prove or disprove any of the current hypotheses. However, the current hypotheses do not necessarily contradict each other. Implications of the two cases reported are analyzed.     

Unusual spontaneous and training induced visual field recovery in a patient with a gunshot lesion

Over a period of more than 3 years, changes in visual and neuropsychological functions were examined in a patient with a visual field defect caused by a cerebral gunshot lesion. Initially, the patient had been completely blind, but after 6 months of spontaneous recovery, he showed a homonymous bilateral lower quadrantanopia and impairment of higher visual functions. Unexpectedly, recovery still continued after the first 6 months. This process was documented in detail by visual field examinations using high resolution perimetry. When visual field size had stabilised almost 16 months after the lesion, further improvement could be achieved by visual restitution training. The duration and extent of spontaneous recovery were unusual. In spontaneous as well as in training induced recovery, progress was mainly seen in partially defective areas (areas of residual vision) along the visual field border. Thus, it is speculated that modulation of perceptual thresholds in transition zones of visual field defects contributes to spontaneous and training induced recovery.     

A case of topographic disorientation without right occipital lesion]

A 73-year-old right-handed man developed topographical disorientation, left homonymous hemiianopsia, left visuospatial neglect and mild visual memory disturbance following the right hemispheric infarction. The visual agnosia is very similar to agnosia for streets because he could not identify familiar buildings and streets even though he could remember their way. He did not have prosopagnosia. His brain MRI demonstrated infarction at the right anterior choroidal artery area, including right thalamus, caudate tail and optic radiation. SPECT showed the mild decrease of rCBF at the right temporoparietal cortex. His topographic disorientation faded and finally disappeared about 3 weeks after its onset. Our case is atypical because of sparing the posterior part of the right parahippocampal gyrus where plays an important role in the development of agnosia for streets.     

"Bottom-up" and "top-down" effects on reading saccades: a case study

OBJECTIVE: To investigate the role right foveal/parafoveal sparing plays in reading single words, word arrays, and eye movement patterns in a single case with an incongruous hemianopia. METHODS: The patient, a 48-year-old right handed male with a macular sparing hemianopia in his left eye and a macular splitting hemianopia in his right eye, performed various reading tasks. Single word reading speeds were monitored using a "voice-trigger" system. Eye movements were recorded while reading three passages of text, and PET data were gathered while the subject performed a variety of reading tasks in the camera. RESULTS: The patient was faster at reading single words and text with his left eye compared with his right. A small word length effect was present in his right eye but not his left. His eye movement patterns were more orderly when reading text with his left eye, making fewer saccades. The PET data provided evidence of "top-down" processes involved in reading. Binocular single word reading produced activity in the representation of foveal V1 bilaterally; however, text reading with the left eye only was associated with activation in left but not right parafoveal V1, despite there being visual stimuli in both visual fields. CONCLUSIONS: The presence of a word length effect (typically associated with pure alexia) can be caused by a macular splitting hemianopia. Right parafoveal vision is not critically involved in single word identification, but is when planning left to right reading saccades. The influence of top-down attentional processes during text reading can be visualised in parafoveal V1 using PET.