Scanning the visual world: a study of patients with homonymous hemianopia

OBJECTIVES: This study examined the scanpaths of patients with homonymous hemianopia while viewing naturalistic pictures in their original and also spatially filtered forms. Features of their scanpaths with respect to various saccade and fixation parameters were examined to determine whether they develop compensatory eye movement strategies. The effects of various lesion parameters including location, size, and age on the evolution of such strategies were considered. METHODS: Eye movements of eight patients with homonymous hemianopia (four left, four right), but lacking neglect, were recorded while they viewed 22 images of real scenes, and they were compared with the eye movements of eight age matched controls. Subjects viewed each image for 3 seconds, initially in a spatially filtered form in which much of the semantic content had been removed, and then in their unfiltered, original form. RESULTS: Patients differed significantly from controls in various fixation and saccade parameters. For fixation parameters patients with hemianopia fixated different spatial positions from controls, made more fixations which were more widely distributed and of shorter duration than controls, and spent a greater proportion of their total fixation time in the area corresponding to their blind hemifield. They did not make significantly more refixations than controls. For saccade parameters patients made more saccades into their blind hemifield, these saccades having shorter latencies and shorter amplitudes than those made into their seeing field, and had longer scanpaths than control subjects. The amplitude of their first saccade was longer than that of controls although its direction did not correlate simply with the side of the field defect. Their mean saccade amplitude was similar to that of controls. Filtering out high spatial frequencies within images seemed to accentuate the described differences between eye movement characteristics of hemianopes and controls. Scanpath differences correlated with increasing age but not location or size of lesions causing the hemianopia. CONCLUSION: Various features of scanpaths produced by hemianopes were different from normal subjects. These differences correlated with lesion age and may reflect the evolution of a compensatory eye movement strategy.     

Impaired reading in patients with right hemianopia

A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition ("pure" alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted ("hemianopic" alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex. The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading.     

Saccade induced cortical activation in patients with post-stroke visual field defects

Substantial disability in patients with hemianopia results from reduced visual perception. Several studies have shown that these patients have impaired saccades but may improve search strategies with appropriate training of saccades. We used fMRI to study the representation of saccades in patients with post-stroke hemianopia to the left. Brain activation during visually guided saccades was measured in 10 patients with a pure occipital cortical lesion causing homonymous hemianopia and in 10 healthy control subjects. Differences in activation between rest and saccades and between controls and patients were assessed with statistical parametric mapping (SPM'99). In normal subjects, significant activation was found in the frontal and parietal eye fields bilaterally and in the supplementary eye field. These areas were also activated in patients, however, to a lesser degree. In contrast, an area of increased activation in patients was found in the posterior parietal cortex of the (non-affected) left hemisphere. Visual field defects after striate lesions are associated with changes in the frontoparietal network underlying the cortical control of saccades.     

Hemianopic line bisection error in a patient with Alzheimer’s disease

Visual symptoms are frequently observed in posterior cortical atrophy compared to typical amnestic Alzheimer’s disease (AD). We report the case of a patient with amnestic AD with long-lasting homonymous hemianopia. A 62-year-old woman, who was diagnosed in amnestic AD, complained of visual disturbance. She had left homonymous hemianopia in the perimetry test and left tactile extinction. Regardless of posture, retinotopically leftward error was observed on 21 cm line bisection test. Brain single photon emission computerized tomography (SPECT) showed bilateral temporoparietal hypoperfusion, which was more severe to the right than left side. This case suggested that long-lasting hemianopia could occur in the patient with amnestic AD and that hemianopic line bisection error might be compensatory mechanism.     

Bilateral occipital infarction with central homonymous hemianopia]

A 45-year-old man of bilateral occipital infarction with central homonymous hemianopia is reported. He was admitted to our hospital with complaints of visual loss and large central scotoma on both eyes. Pupillary light reaction and ocular fundi were normal. On admission, bilateral retrobulbar optic neuritis was suspected. However, congruous, irregular central scotomas with vertical step were observed in both eyes with Goldmann perimetry. X-ray computed tomography (CT) and magnetic resonance imaging (MRI) revealed the infarction in bilateral occipital tips. Bilateral central homonymous hemianopia is considered to be rare and a case in which occipital lobe lesions were detected with X-ray CT and MRI has not been reported. We stress that bilateral central scotomas with vertical step indicate bilateral occipital lesions.     

Hypertensive basal ganglionic hemorrhage with hemianopsia as the sole symptom--report of 2 cases

The majority of patients with sudden onset of homonymous hemianopia are caused by occlusion of the posterior cerebral artery. Apart from a subcortical hemorrhage in the occipital lobe, no previous cases of the hypertensive intracerebral hemorrhage presenting isolated homonymous hemianopia have been reported. Since the introduction of computed tomography (CT), the authors have experienced two cases of hypertensive basal ganglionic hemorrhage (including a thalamic hemorrhage) showing homonymous hemianopia alone as the neurological manifestation. Both patients (age 40 and 45) are right-handed male with known hypertension. The CT scans demonstrated a hematoma laterally and posteriorly along the thalamus on the left side. The cerebral angiography were unremarkable. The authors discussed the mechanism presenting homonymous hemianopia without association of pyramidal signs. These two cases described above are unique, hypertensive basal ganglionic hemorrhage, presenting a localized damage in the optic peduncle with sparing the pyramidal tract. In addition, they are worthwhile to be paid attention, because of showing homonymous hemianopia as a single, neurological manifestation, as well as being able to be diagnosed only by CT.     

Predictive saccades are impaired in biological nonpsychotic siblings of schizophrenia patients

OBJECTIVE: Although impairments in predictive saccades have been reported in patients with schizophrenia, this has never been explored in their biological relatives. We examined predictive saccades in age-and sex-matched siblings of patients with schizophrenia. METHOD: Thirty siblings of schizophrenia patients, 30 healthy matched control subjects and 30 patients with schizophrenia performed a predictive saccades paradigm. Nonanticipated and anticipated saccades were analyzed separately. RESULTS: Compared with control subjects, primary saccades and final eye position were hypometric (they undershot the target) in siblings, as in patients. The proportion of anticipated saccades and latencies did not differ between the 3 groups. The maximum velocity was decreased only in patients. CONCLUSION: Alterations in predictive saccades observed in biological siblings are similar to those seen in patients, although they tend to be of a lesser degree. This finding supports predictive saccades as a valid endophenotypic marker. Further research is necessary to understand the physiopathological value of these disturbances and their link to a visuospatial representation deficit.     

"Crossed homonymous hemianopia" and "crossed left hemispatial neglect" in a case of Marchiafava-Bignami disease.

"Crossed homonymous hemianopia" and "crossed left hemispatial neglect" were observed in a woman with Marchiafava-Bignami disease. Two forms of "crossed homonymous hemianopia" were observed. Initially, Goldmann perimeter testing showed a left homonymous hemianopia with the right hand and vice versa. Later, confrontation tests showed a left homonymous hemianopia, whereas visual field testing using the Goldmann perimeter (kinetic quantitative perimeter) and the OCTOPUS (Interzeag AG, static automated perimeter) showed a right homonymous hemianopia with either hand. "Crossed left hemispatial neglect" was not seen with the left hand, but neglect of the left hemifield was seen with the right hand. CT and MRI showed a lesion occupying almost the entire corpus callosum. PET showed no significant differences between comparable areas of the left and right cerebral hemispheres. These findings indicate that both signs of interhemispheric disconnection were due to the callosal lesion. Moreover, the "crossed left hemispatial neglect" can be explained as being a consequence of the dominance of the right cerebral hemisphere for visuospatial recognition.     

Pure homonymous hemianopia due to anterior choroidal artery territory infarction

The most consistently observed neurological deficits in the anterior choroidal artery (AChA) territory infarction are pure motor or sensorimotor syndromes. Visual field defects and higher cortical dysfunction are occasionally accompanied, but pure homonymous hemianopia without motor and sensory symptom has never been reported yet. We present 2 patients with pure homonymous hemianopia, whose MRI disclosed cerebral infarction in the well-known territory of the AChA. In most patients with ischemic stroke, pure homonymous hemianopia indicates infarction in the posterior circulation, particularly in the posterior cerebral artery territory. However, the present cases provide evidence that it can also be caused by infarction in the anterior circulation, i.e. the AChA.     

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.     

Eye-movement training-induced plasticity in patients with post-stroke hemianopia

Substantial disability in patients with hemianopia results from reduced visual perception. Previous studies have shown that these patients have impaired saccades. Improving exploratory eye movements with appropriate training of saccades may help to partially compensate for the visuoperceptive impairment during daily life activities. The changes in cortical control of eye movements that may be induced by these training strategies, however, are not known. We used functional magnetic resonance imaging (fMRI) to study the training effects of eye-movement training on cortical control of saccades. Brain activation during visually guided saccades was measured in eight patients with an occipital cortical lesion causing homonymous hemianopia. Starting 8 weeks after the stroke, patients received 4 weeks of visual field training. The fMRI measurements were performed at baseline and after training. In five patients, follow-up fMRI was performed 4 weeks after the end of training. Differences in activation between rest and saccades as well as before and after training were assessed with statistical parametric mapping software (SPM’99). Twelve healthy subjects were scanned twice at a 4-week interval. In patients, significant activation at baseline was found in the frontal and parietal eye fields (FEF and PEF, respectively) bilaterally and in the supplementary eye field (SEF). Immediately after training, an area of increased activation was found in the left extrastriate cortex of the affected hemisphere. At follow-up, relatively more activation was found in the right peristriate cortex and in the SEF of the unaffected side. A relative decrease of activation was found in the left FEF. In this group of patients, eye-movement training induced altered brain activation in the striate and extrastriate cortex as well as in oculomotor areas.     

Horizontal space misrepresentation in unilateral brain damage. II. Eye-head centered modulation of visual misrepresentation in hemianopia without neglect

We used a visual distance reproduction task (endpoint task) to evaluate horizontal space representation in two left brain damaged (LBD) and three right brain damaged (RBD) patients with contralateral homonymous hemianopia and no neglect. All patients were examined in the chronic phase of the stroke and were aware of their visual field defect. Along with contralesional deviation in the line bisection task, all patients estimated size (Landmark task) and distances in the contralesional space as being longer than equivalent size and distances located in the ipsilesional space. Misreproduction of distances was abolished or reduced when the task was performed in the ipsilesional head-centred space with the head turned contralesionally. This finding points out that misrepresentation of horizontal space linked to hemianopia can be modulated by combined proprioceptive input from eye and neck muscles. The pattern of misrepresentation found in chronic hemianopic patients is opposite to the one described in chronic neglect patients with concomitant hemianopia. These different patterns of space misrepresentation are the likely consequence of the presence, in hemianopics, and the absence, in neglect patients with hemianopia, of compensatory strategies based on the non-retinotopic and multimodal coding of spatial positions falling in the retinotopically organised blind field.     

A perceptual discrimination task abnormally facilitates reflexive saccades in Parkinson's disease

Numerous studies have shown that Parkinson's disease (PD) affects the ability to generate voluntary saccades and the ability to suppress reflexive saccades. The effects of PD on the generation of reflexive saccades, however, are not clear. Some studies report impairments, but there are also reports of abnormal facilitation or hyper-reflexivity of the saccade system in PD. Meanwhile, it has been reported that the concurrent performance of a perceptual discrimination task facilitates saccade initiation and reduces saccade latencies in healthy subjects [A. Montagnini & L. Chelazzi (2005)Vis. Res., 45, 3391-3401; L. Trottier & J. Pratt (2005)Vis. Res., 45, 1349-1354]. To investigate the circumstances under which the saccade system may appear hyper-reflexive in PD, we compared reflexive saccades with and without a concurrent perceptual discrimination task in 20 PD patients and 20 controls. Without the discrimination task, the PD group produced reflexive saccades at normal latencies. The discrimination task reduced saccade latencies more in the PD group than in the control group, resulting in abnormally short mean reflexive saccade latencies in the PD group. The discrimination task increased saccade gain in both groups, but saccades in the PD group remained hypometric as compared with saccades in the control group. We conclude that the attentional demands of this paradigm revealed a hypersensitivity to visual inputs in the PD group.     

Saccadic adaptation in children

Saccades are fast-orienting eye movements. Saccadic adaptation, a form of motor learning, is a corrective change in the amplitude of saccades in response to error. The aim of the study was to ascertain whether saccadic adaptation occurs in typically developing children. We recorded saccades with an infrared eye tracker in 39 children, aged 8 to 19 years, at baseline to 12-degree horizontal target steps and after an adaptive task. During the adaptive task, a saccadic hypometric error was induced. This task consisted of 200 12-degree target steps that stepped backward 3 degrees during the initial saccade and without the participants' awareness. The initial saccade triggered the back-step. This paradigm required a corrective reduction of the amplitude of the initial saccades in response to the induced error. Saccadic adaptation was achieved in 26 participants, whose mean saccadic amplitudes decreased by 13% (P < .05). Saccadic adaptation was not influenced by age. We conclude that children as young as 8 years old have established functions of the neural circuits responsible for the motor learning required for saccadic adaptation.     

Traumatic homonymous hemianopia

Objective

To describe the characteristics of patients with homonymous hemianopia from traumatic brain injury (TBI) seen in our unit between 1989 and 2004.

Methods

Only patients with a history of TBI, who had detailed clinical information and results of neuroimaging, were included in our study. Demographic characteristics, clinical features, types of visual field defects, location of lesion and evolution of visual field defects were recorded.

Results

Of the 880 patients with homonymous hemianopia seen in our unit, 103 patients (112 with homonymous hemianopia) had TBI (74 men and 29 women, mean age 30.7 (SD 15.3) years). Median time from injury to initial visual field testing was 5 (range 0.5–360) months. In all, 64 (57.1%) patients sustained injuries that were motor vehicle‐related; 19 (17%) violence‐related; 17 (15.2%) due to falls; and 12 (10.7%) because of other blunt head trauma. Visual field defects included complete homonymous hemianopia in 44 (39.3%) patients and incomplete homonymous hemianopia in 68 (60.7%) patients. The lesion was occipital in 14 (12.5%) patients, associated with optic radiation in 26 (23.2%) and the optic tract in 12 (10.7%), and multiple in 60 (53.6%).

Conclusion

Most cases of homonymous hemianopia from TBI were motor vehicle‐related. Patients were younger, more often male, and had multiple brain lesions more often than patients with homonymous hemianopia from causes other than TBI. A median delay of 5 months was observed before the documentation of the homonymous hemianopia, which may have a major effect on the success of rehabilitation and driving training in these young patients.Retrochiasmal visual field deficits account for a quarter of the visual sequelae caused by traumatic brain injuries (TBI) and constitute one of the most common neuro‐ophthalmological consequences of head trauma.¹ Homonymous visual field deficits may affect patients'' ability to drive, to read and to continue in their current employment.^2,3,4,5 Despite the disabling nature of these visual field deficits, there is little known about the nature and course of these injuries, and this lack of knowledge has hampered the development of rehabilitative treatments aimed at reducing their effect. Our study describes the characteristics of homonymous hemianopia secondary to TBI in a large series.     

A case of multiple sclerosis with incongruous homonymous hemianopia due to lateral geniculate body lesion]

We report a rare case of a 31-year-old woman who was diagnosed as multiple sclerosis with homonymous hemianopia due to a demyelinative lesion in the lateral geniculate body. Paresthesia appeared in the distal parts of both legs from September, 2002. She complained of loss of visual field in both eyes 2 months later. Since a left asymmetric wedge-shaped homonymous hemianopia was detected by Octopus automatic perimetry, she was referred to our hospital on December 2, 2002. Neurological examination showed subjective paresthesia in the distal parts of both legs in addition to Lhermitte's sign. Brain MRI showed demyelinated lesions in the lateral geniculate body on the right and periventricular areas of the lateral ventricles. Spinal MRI revealed a demyelinated lesion in the upper cervical cord. She was diagnosed as multiple sclerosis and underwent a steroid pulse therapy. Homonymous hemianopia resolved a few days later.     

Usefulness of multifocal VEP in a child requiring perimetry

We examined the reliability of multifocal visual evoked potentials for evaluating visual-field defects in a child with epilepsy and an arachnoid cyst. Multifocal visual evoked potentials were measured both when perimetry was difficult and several years later, when kinetic perimetry became possible in a child with epilepsy and homonymous hemianopia, as suggested by computed tomography of the brain. The peak latency and amplitude of response waves were used for assessment. The recordings of multifocal visual evoked potentials at both times revealed marked decreases in amplitude in the left visual hemifield. This area of decreased amplitude corresponded to the location of the lesion observed with imaging techniques, and was consistent with the left homonymous hemianopia observed via kinetic perimetry. The objective evaluation of visual-field defects through multifocal visual evoked potentials may be useful in children in whom conventional perimetry is difficult.     

Line bisection in unilateral homonymous visual field defects

The contralesional line bisection error in unilateral homonymous hemianopia is a frequent but neglected clinical phenomenon. Our knowledge about this bisection error is based on small samples of hemianopic patients. Moreover, horizontal line bisection has never been investigated in other unilateral visual field defects. The present study is the first to examine line bisection in a large, representative sample of patients with unilateral homonymous visual field defects. We investigated horizontal line bisection in 129 patients with left- or right-sided homonymous hemianopia (60.5%), upper and lower quadranopia (24.8%), and paracentral scotoma (14.7%), and determined the magnitude and direction of line bisection error. The contralesional horizontal line bisection error was present not only in patients with hemianopia but also in those with upper or lower quadranopia or paracentral scotoma. Neither the type nor the severity of the visual field defect was found to determine the bisection error. Only the side of the field defect seemed to determine the horizontal direction of the bisection error (left-/rightward). The contralesional bisection error is not a specifically “hemianopic” phenomenon. It is frequently associated with any unilateral homonymous visual field defect, i.e., hemianopia, upper/lower quadranopia, paracentral scotoma. Moreover, our results further support the recent finding that the contralesional bisection error is not a direct consequence of the visual field defect. Yet, they also suggest that, although the visual field defect does not seem to be the primary cause of the contralesional bisection error, it may nevertheless contribute to it.     

Slow saccades and hypometria in anticonvulsant toxicity

We report a patient with abnormal saccades in association with anticonvulsant toxicity (phenytoin 27.5 micrograms/ml, phenobarbital 18.8 micrograms/ml). The patient looked toward visual targets either with multiple, small, hypometric saccades or with single slow saccades. These abnormalities resolved when anticonvulsant levels returned to therapeutic range. Thus, slow saccades may be clinical evidence of anticonvulsant toxicity.     

A case of alien hand syndrome after right posterior cerebral artery territory infarction]

We report a 63-year-old right-handed man who presented an alien hand syndrome (AHS). He complained of clumsiness of his left hand and admitted to our hospital. On the first examination, he presented left homonymous hemianopia, left spatial neglect and left limb ataxia, but neither paralysis nor sensory impairment. A few days after, he complained that his left hand was controlled by someone else, and we considered this phenomenon as AHS. At that time, he lost sensation of almost all modalities including deep sensation on his left upper and lower limb. Magnetic resonance image examination was performed, and it showed acute cerebral infarction at right posterior cerebral artery territory including right thalamus (ventral posterior lateral nucleus). Generally, AHS is caused by left mediofrontal and callosal lesion (frontal type AHS), or by callosal with bilateral frontal or without frontal lesion (callosal type AHS). However, some cases were reported that they presented AHS after damage of the basal ganglia, right thalamus, right occipital or inferior parietal lobe. Some authors described this phenomenon as "sensory" or "posterior" type AHS. In such cases, included our case, we speculate that sensory impairment causes AHS. Especially in our case, AHS might be caused by not only the sensory impairment but also by left homonymous hemianopia and left spatial neglect. So, because of these symptoms, our patient could not recognize the motion of the left hand, and presented AHS. We think that this "sensory" or "posterior" type AHS should be distinguished from frontal and callosal type AHS.