Recovery of visual functions after early acquired occipital damage

Recovery of Visual Field After Awake Stimulation Mapping of the Optic Pathway in Glioma Patients

Brain mapping during awake craniotomy for gliomas can help preserve neurological functions, including maintenance of central and peripheral vision. However, the consecutive changes in the visual field remain unknown. We retrospectively assessed 14 patients who underwent awake craniotomy for gliomas infiltrating into the optic radiation. Cortico-subcortical direct electrical stimulation (DES) was intraoperatively applied until transient visual symptoms were elicited and recorded. The visual fields were examined consecutively in the preoperative period and postoperative subacute and chronic periods. To evaluate the anatomo-functional validity of the recordings, all DES-elicited points were overlaid onto a three-dimensional template that included the optic radiation, using voxel-based morphometry (VBM) mapping. All patients experienced visual symptoms that were classified as phosphenes, blurred vision, or hallucinations during DES, and surgical resection was limited to within the functional boundaries. In VBM, almost all the subcortical positive mapping points overlapped with the surface of the optic radiation, and the distribution of sites that induced visual phenomena in the upper or lower visual fields could be differentiated in the anatomical space. We observed no postoperative visual deficit in four patients (29%), time-dependent improvements in five out of eight patients that presented transient quadrantanopia or partial visual defect (36% out of 57%), and permanent hemianopsia (14%) in two patients with occipital lesions. Intraoperative DES that identifies and preserves optic radiation in awake craniotomy for gliomas is a reliable and effective technique to reduce risk of permanent deficits, but has a low success rate in patients with occipital involvement.

Lessons Learned from 23 Years of Experience in Testing Visual Fields of Neurologically Impaired Children

We sought to investigate the reliability of standard conventional perimetry (SCP) in neurologically impaired (NI) children using the examiner-based assessment of reliability scoring system and to determine the difference in time to diagnosis of a visual field defect between SCP and a behavioural visual field (BVF) test. Patient records of 115 NI children were retrospectively analysed. The full field peritest (FFP) had best reliability with 44% 'good' scores versus 22% for Goldmann perimetry (p < .001). The mean age of NI children able to perform SCP was 8.3 years versus 4.6 years for the BVF test (p < .001). Use of the BVF test may significantly reduce time to diagnosis.

Cerebral Visual Impairment and Clinical Assessment: The European Perspective

This paper summarizes the multidisciplinary pediatric assessment methods of 3 European centers for identifying and assessing cerebral visual impairment in childhood. It describes a comprehensive neurodevelopmental assessment evaluation in which visual aspects play an important part. Developmental trajectories and the heterogeneity of the clinical picture are emphasized. Multidisciplinary ophthalmology and neurodisability/neurology teamwork together with the parent and teachers, to reach an integrated and individualized perspective for the individual child, are described. This comprehensive assessment is the starting point for habilitation programs and interventions, that can support and meet the child's needs and help them reach their optimal potential. Future developments in classification of the cerebral visual impairment conditions, building on the child's individual assessment profile, will further enhance the direction of clinical, educational, and research progress.

Childhood Stroke and Vision: A Review of the Literature

OBJECTIVE

Here we review the current literature regarding visual outcome after perinatal and childhood stroke.

BACKGROUND

Visual deficits following stroke in adults are common and have been previously reviewed. Less is known about visual deficits following stroke in neonates and older children. Most of the literature regarding this subject has focused on preterm infants, or on other types of brain injury. This review summarizes the types of visual deficits seen in term infants following perinatal stroke and children following childhood stroke and predictors of outcome. This review suggests areas for future research.

METHODS

We performed Ovid MEDLINE searches regarding visual testing in children, vision after childhood stroke, neuroplasticity of vision, treatment of visual impairment after stroke, and driving safety concerns after stroke.

RESULTS

Visual field defects were the most commonly reported visual deficits after perinatal and childhood stroke. There is a significant lack of literature on this subject, and most is in the form of case reports and case series. Children can experience significant visual morbidity after stroke, and have the potential to show some recovery, but guidelines on assessment and treatment of this population are lacking.

CONCLUSIONS

There were limitations to this study, given the small amount of literature available. Although stroke in children can result in severe visual deficits, most children regain at least a portion of their vision. However, more research is needed regarding visual assessment of this population, long-term visual outcomes, specific predictors of recovery, and treatment options.

Functional outcomes following lesions in visual cortex: Implications for plasticity of high-level vision

Understanding the nature and extent of neural plasticity in humans remains a key challenge for neuroscience. Importantly, however, a precise characterization of plasticity and its underlying mechanism has the potential to enable new approaches for enhancing reorganization of cortical function. Investigations of the impairment and subsequent recovery of cognitive and perceptual functions following early-onset cortical lesions in humans provide a unique opportunity to elucidate how the brain changes, adapts, and reorganizes. Specifically, here, we focus on restitution of visual function, and we review the findings on plasticity and re-organization of the ventral occipital temporal cortex (VOTC) in published reports of 46 patients with a lesion to or resection of the visual cortex early in life. Findings reveal that a lesion to the VOTC results in a deficit that affects the visual recognition of more than one category of stimuli (faces, objects and words). In addition, the majority of pediatric patients show limited recovery over time, especially those in whom deficits in low-level vision also persist. Last, given that neither the equipotentiality nor the modularity view on plasticity was clearly supported, we suggest some intermediate possibilities in which some plasticity may be evident but that this might depend on the area that was affected, its maturational trajectory as well as its structural and functional connectivity constraints. Finally, we offer suggestions for future research that can elucidate plasticity further.

Irreversible Loss of Vision in a Child due to Occipital Infarction after Gastroenteritis

A 2½-year-old girl developed a bilateral occipital infarct following severe gastroenteritis with bilateral vision of light perception. Evaluations for sickle cell anemia, hemolytic anemia and coagulopathies were negative. Cortical blindness is an uncommon but dramatic complication of gastroenteritis, hence the need of prompt hydration and other supportive measures to avoid irreversible visual loss or mental sequela.

Failure in developing high-level visual functions after occipitoparietal lesions at an early age: a case study

Previous functional magnetic resonance imaging (fMRI) studies have identified several regions in the ventral visual pathway that are specialized for processing faces, words and general objects. However, little is known about the origin of the functional selectivity of these regions. Here, we reported a pediatric patient who suffered a left occipitoparietal lesion in the first year after birth from a subdural hematoma. After the hematoma was removed at the age of six, the hemianopia in the right visual field was alleviated, and no obvious deficits in low-level vision were observed in the patient at the age of twelve. In line with the behavioral observations, meridian mappings with fMRI showed that the early visual cortex of the left hemisphere was significantly activated, which was similar to that of the intact right hemisphere. However, the left ventral temporal cortex failed to show selective responses for faces, words and objects, which were in contrast to the normal selective responses for these objects in the right counterpart. Therefore, it is likely that the development of object selectivity in the ventral temporal cortex depends on visual inputs from the early visual cortex at an early age.

Visual perception in preterm children: what are we currently measuring?

Over the past two decades, cerebral visual impairment has been recognized as a principal deficit in preterm children, and in particular those with cerebral palsy. We review the current knowledge of visual processing deficits in these children, and provide an overview of the tools for assessing cerebral visual impairment. Commercially available instruments are usually directed at evaluating visuospatial skills rather than detecting object recognition difficulties. Particularly in children aged 3 years or younger and in children with multiple handicaps, cerebral visual impairment is difficult to diagnose. This difficulty may be attributable to limitations specific to the instrument, such as a test that is inappropriate for age, or to child-specific limitations such as motor impairment or speech delay. We therefore include an overview of relevant neuroimaging findings reported in these children, focusing on the most recent imaging modalities. Novel techniques such as diffusion tensor imaging may provide sensitive markers of cerebral visual impairment in situations where clinical diagnosis is difficult, and such approaches may allow for early intervention.

What does Neural Plasticity Tell us about Role of Primary Visual Cortex (V1) in Visual Awareness?

The complete loss of visual awareness resulting from a lesion to the primary visual cortex (V1) suggests that this region is indispensable for conscious visual perception. There are however a number cases of conscious perception in the absence of V1 which appear to challenge this conclusion. These include reports of patients with bilateral V1 lesions sustained at an early age whose conscious vision has spontaneously recovered, as well as stroke patients who have recovered some conscious vision with the help of rehabilitation programs. In addition, the phenomenon of hemianopic completion and percepts induced by brain stimulation suggest that V1 may not be necessary for conscious perception in all circumstances. Furthermore, that the visual abilities in the cat are associated with the recovery of normal extrastriate tuning properties rather than emulation of V1 functions suggests that there is nothing unique about the functional properties of this region in visual awareness. Rather, the dramatic effect of a V1 lesion on visual awareness may be due to its role in providing the majority of extrastriate visual input, the loss of which abolishes normal neural responsiveness throughout the visual cortex.

Visual activation of extra-striate cortex in the absence of V1 activation

When the primary visual cortex (V1) is damaged, there are a number of alternative pathways that can carry visual information from the eyes to extrastriate visual areas. Damage to the visual cortex from trauma or infarct is often unilateral, extensive and includes gray matter and white matter tracts, which can disrupt other routes to residual visual function. We report an unusual young patient, SBR, who has bilateral damage to the gray matter of V1, sparing the adjacent white matter and surrounding visual areas. Using functional magnetic resonance imaging (fMRI), we show that area MT+/V5 is activated bilaterally to visual stimulation, while no significant activity could be measured in V1. Additionally, the white matter tracts between the lateral geniculate nucleus (LGN) and V1 appear to show some degeneration, while the tracts between LGN and MT+/V5 do not differ from controls. Furthermore, the bilateral nature of the damage suggests that residual visual capacity does not result from strengthened interhemispheric connections. The very specific lesion in SBR suggests that the ipsilateral connection between LGN and MT+/V5 may be important for residual visual function in the presence of damage to V1.