Impaired visual competition in patients with homonymous visual field defects

When You Do Not Get the Whole Picture: Scene Perception After Occipital Cortex Lesions

Background: Occipital cortex lesions (OCLs) typically result in visual field defects (VFDs) contralateral to the damage. VFDs are usually mapped with perimetry involving the detection of point targets. This, however, ignores the important role of integration of visual information across locations in many tasks of everyday life. Here, we ask whether standard perimetry can fully characterize the consequences of OCLs. We compare performance on a rapid scene discrimination task of OCL participants and healthy observers with simulated VFDs. While the healthy observers will only suffer the loss of part of the visual scene, the damage in the OCL participants may further compromise global visual processing. Methods: VFDs were mapped with Humphrey perimetry, and participants performed two rapid scene discrimination tasks. In healthy participants, the VFDs were simulated with hemi- and quadrant occlusions. Additionally, the GIST model, a computational model of scene recognition, was used to make individual predictions based on the VFDs. Results: The GIST model was able to predict the performance of controls regarding the effects of the local occlusion. Using the individual predictions of the GIST model, we can determine that the variability between the OCL participants is much larger than the extent of the VFD could account for. The OCL participants can further be categorized as performing worse, the same, or better as their VFD would predict. Conclusions: While in healthy observers the extent of the simulated occlusion accounts for their performance loss, the OCL participants' performance is not fully determined by the extent or shape of their VFD as measured with Humphrey perimetry. While some OCL participants are indeed only limited by the local occlusion of the scene, for others, the lesions compromised the visual network in a more global and disruptive way. Yet one outperformed a healthy observer, suggesting a possible adaptation to the VFD. Preliminary analysis of neuroimaging data suggests that damage to the lateral geniculate nucleus and corpus callosum might be associated with the larger disruption of rapid scene discrimination. We believe our approach offers a useful behavioral tool for investigating why similar VFDs can produce widely differing limitations in everyday life.

Useful Field of View Performance in the Intact Visual Field of Hemianopia Patients

Purpose

Postchiasmatic brain damage commonly results in an area of reduced visual sensitivity or blindness in the contralesional hemifield. Previous studies have shown that the ipsilesional visual field can be impaired too. Here, we examine whether assessing visual functioning of the “intact” ipsilesional visual field can be useful to understand difficulties experienced by patients with visual field defects.

Methods

We compared the performance of 14 patients on a customized version of the useful field of view test that presents stimuli in both hemifields but only assesses functioning of their intact visual half-field (iUFOV) with that of equivalent hemifield assessments in 17 age-matched healthy control participants. In addition, we mapped visual field sensitivity with the Humphrey Field Analyzer. Last, we used an adapted version of the National Eye Institute Visual Quality of Life-25 to measure their experienced visual quality of life.

Results

We found that patients performed worse on the second and third iUFOV subtests, but not on the first subtest. Furthermore, patients scored significantly worse on almost every subscale, except ocular pain. Summed iUFOV scores (assessing the intact hemifield only) and Humphrey field analyzer scores (assessing both hemifields combined) showed almost similar correlations with the subscale scores of the adapted National Eye Institute Visual Quality of Life-25.

Conclusions

The iUFOV test is sensitive to deficits in the visual field that are not picked up by traditional perimetry. We therefore believe this task is of interest for patients with postchiasmatic brain lesions and should be investigated further.

Functional connectivity of the Precuneus reflects effectiveness of visual restitution training in chronic hemianopia

Visual field defects in chronic hemianopia can improve through visual restitution training, yet not all patients benefit equally from this long and exhaustive procedure. Here, we asked if resting-state functional connectivity prior to visual restitution could predict training success. In two training sessions of eight weeks each, 20 patients with chronic hemianopia performed a visual discrimination task by directing spatial selective attention towards stimuli presented in either hemifield, while suppressing eye movements. We examined two effects: a sensitivity change in the attended (trained) minus the unattended (control) hemifield (i.e., a training-specific improvement), and an overall improvement (i.e., a total change in sensitivity after both sessions). We then identified five visual resting-state networks and evaluated their functional connectivity in relation to both training effects. We found that the functional connectivity strength between the anterior Precuneus and the Occipital Pole Network was positively related to the attention modulated (i.e., training-specific) improvement. No such relationship was found for the overall improvement or for the other visual networks of interest. Our finding suggests that the anterior Precuneus plays a role in attention-modulated visual field improvements. The resting-state functional connectivity between the anterior Precuneus and the Occipital Pole Network may thus serve as an imaging-based biomarker that quantifies a patient's potential capacity to direct spatial attention. This may help to identify hemianopia patients that are most likely to benefit from visual restitution training.

Homonymous hemianopsia versus unilateral spatial neglect rehabilitation strategies in stroke patients

Abstract Visual rehabilitation therapy is one of the most problematic issue in stroke rehabilitation. The difficulties consist in specific assessment of visual deficit and poor results reports by the authors of the clinical studies. Opposite, experimental studies reports encouraging results that give hopes in this specific rehabilitation therapy. There are still difficult to analyze different aquisitions concerning various visual residual deficits after stroke, the main rehabilitation targgets being motor rehabilitation in order to ensure at least a partial autonomy in day by day life. All the studies that proved there are chances for a better quality of life if there is an improvement of visual abilities together with motor and cognitive skills with a better rehabilitation prognosis. The aim of this paper is to make a brief report regarding two of the most important visual deficits after stroke as are homonymous hemianopsia and neglect. Starting with differential diagnosis, neuroplasticity and specific rehabilitation available method, the main issues are discussed. a better understanding of phenomena that are associated with spontaneous rehabilitation, or enhancing the progress of recuperation by various method, could be able to bring a new light and hopefully better results in rehabilitation for these patients Key words: stroke, visual impairment, visual rehabilitation, neuroplasticity, homonymous hemianopsia,