Discordance between subjective perimetric visual fields and objective multifocal visual evoked potential-determined visual fields in patients with hemianopsia

Optical coherence tomography and visual evoked potentials in evaluation of optic chiasm decompression

Chiasmal compression is a known cause of visual impairment, often leading to surgical decompression of the optic chiasm (OC). A prospective study was held at University Hospital in Hradec Králové to explore sensitivity of optical coherence tomography (OCT) and visual evoked potentials (VEPs) to OC compression and eventual changes after a decompression. 16 patients with OC compression, caused by different sellar pathologies, were included. The main inclusion criterion was the indication for decompressive surgery. Visual acuity (VA), visual field (VF), retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL) thickness, and peak time and amplitude of pattern-reversal (P-VEPs) and motion-onset VEPs (M-VEPs) were measured pre- and postoperatively. The degree of OC compression was determined on preoperative magnetic resonance imaging. For M-VEPs, there was a significant postoperative shortening of the peak time (N160) (p < 0.05). P100 peak time and its amplitude did not change significantly. The M-VEPs N160 amplitude showed a close relationship to the VF improvement. Thinner preoperative RNFL does not present a statistically important limiting factor for better functional outcomes. The morphological status of the sellar region should be taken into consideration when one evaluates the chiasmal syndrome. M-VEPs enable detection of functional changes in the visual pathway better than P-VEPs.

Preoperative visual evoked potential in the prediction of visual outcome after pituitary macroadenomas surgery

OBJECTIVE

The purpose of the present study is to investigate longitudinal changes in Visual evoked potential (VEP) parameters as an objective test after transsphenoidal surgery, its correlation with subjective tests and clinical value of VEP in the prediction of visual outcome.

METHODS

Fifty patients with pituitary macroadenoma who underwent surgical removal of the tumor recruited in this study. All the patients underwent ophthalmic examination, static automated perimetry (SAP), VEP and magnetic resonance imaging (MRI) preoperatively and 3 months after surgery.

RESULTS

Fifty patients with pituitary macroadenoma (size: 25.1 ± 9.9 mm) were recruited in the study. Before surgery, the pattern of VEP showed a prolonged latency with reduced amplitude in eyes with abnormal visual acuity or abnormal visual field. The P100 wave latencies and amplitudes showed significant correlation with visual acuity and SAP scores. After surgery, visual acuity and visual field improvements were seen in 51% and 65.6% of eyes, respectively. Mean SAP and visual acuity scores increased significantly (p < 0.01), P100 wave latency declined and amplitude improved after surgery but not significantly. The mean age of patients, size of tumors and preoperative P100 wave latency were significantly lower in eyes with visual field and acuity improvement.

CONCLUSION

VEP is a helpful quantitative and objective complementary test to visual acuity and SAP exams for assessing pre-operative visual abnormalities and post-operative visual outcome in patients with pituitary macroadenoma.

Using sellar region tumor's size as a predictor of psychophysical and electrophysiological perimetric visual losses: a logistic regression approach

BACKGROUND

Sellar region tumor growth represents an important cause of visual loss due to mechanical compression of the optic nerve apparatus. Many investigations have used non-invasive tools to evaluate the visual field consequences of this damage, and good associations have been reported between psychophysical and electrophysiological perimetries. Few reports have considered the tumor size as a predictor of visual field loss.

AIMS

In the present study, we evaluated the association between the visual perimetry measured by Humphrey visual field analyzer and multifocal visual evoked cortical potential (mfVECP) and the tumor size.

METHODS

Our sample was composed of 14 patients diagnosed with sellar tumors by magnetic resonance imaging. We accounted the number of sectors with negative visual responses for both methods. A simple logistic regression analysis was used to evaluate the association between the tumor dimensions and the visual field features RESULTS: Three patients had preserved visual fields, three patients showed hemianopic defects, and eight patients had generalized visual field losses at both evaluations. We observed that the three maximum diameters of the tumor and total tumor volume had different predictive abilities regarding the extent of visual field loss when using psychophysical and mfVECP data. The maximum craniocaudal diameter of the tumor was the better predictor of the psychophysical measurements, whereas for the mfVECP results, all tumor dimensions and volumes had similar values that predict visual field losses.

CONCLUSION

Tumor size as a predictor of visual loss has potential to assist in the clinical intervention and to prevent the irreversible visual impairment caused by tumors of the sellar region.

Reorganization of Visual Callosal Connections Following Alterations of Retinal Input and Brain Damage

Vision is a very important sensory modality in humans. Visual disorders are numerous and arising from diverse and complex causes. Deficits in visual function are highly disabling from a social point of view and in addition cause a considerable economic burden. For all these reasons there is an intense effort by the scientific community to gather knowledge on visual deficit mechanisms and to find possible new strategies for recovery and treatment. In this review, we focus on an important and sometimes neglected player of the visual function, the corpus callosum (CC). The CC is the major white matter structure in the brain and is involved in information processing between the two hemispheres. In particular, visual callosal connections interconnect homologous areas of visual cortices, binding together the two halves of the visual field. This interhemispheric communication plays a significant role in visual cortical output. Here, we will first review the essential literature on the physiology of the callosal connections in normal vision. The available data support the view that the callosum contributes to both excitation and inhibition to the target hemisphere, with a dynamic adaptation to the strength of the incoming visual input. Next, we will focus on data showing how callosal connections may sense visual alterations and respond to the classical paradigm for the study of visual plasticity, i.e., monocular deprivation (MD). This is a prototypical example of a model for the study of callosal plasticity in pathological conditions (e.g., strabismus and amblyopia) characterized by unbalanced input from the two eyes. We will also discuss the findings of callosal alterations in blind subjects. Noteworthy, we will discuss data showing that inter-hemispheric transfer mediates recovery of visual responsiveness following cortical damage. Finally, we will provide an overview of how callosal projections dysfunction could contribute to pathologies such as neglect and occipital epilepsy. A particular focus will be on reviewing noninvasive brain stimulation techniques and optogenetic approaches that allow to selectively manipulate callosal function and to probe its involvement in cortical processing and plasticity. Overall, the data indicate that experience can potently impact on transcallosal connectivity, and that the callosum itself is crucial for plasticity and recovery in various disorders of the visual pathway.

Multifocal Visual Evoked Potential (mfVEP) and Pattern-Reversal Visual Evoked Potential Changes in Patients with Visual Pathway Disorders: A Case Series

The purpose of this study was to evaluate multifocal visual evoked potential (mfVEP) and pattern-reversal visual evoked potential (PVEP) changes in patients with pathology at various levels of the visual pathway determined by other methods. Six patients with different visual pathway disorders, including vascular ischaemic events and compressive optic neuropathy, were reviewed. All patients were tested with both mfVEP and full-field and half-field PVEPs. Results were assessed in relation to other diagnostic tests such as magnetic resonance imaging, Humphrey visual field test, and optical coherence topography. The cases in this study demonstrate a potential higher sensitivity of mfVEP compared with conventional PVEPs in detecting lesions affecting the peripheral field, horizontal hemifields, and lesions of the post-chiasmal pathway. The limitation of the PVEP in this setting is probably due to phase cancellation and overrepresentation of the macular region. mfVEP provides a more accurate assessment of visual defects when compared with conventional PVEP. The independent assessment of different areas of the visual field improves the detection and localization of lesions and provides an objective topographical map that can be used in clinical practice as an adjunct to other diagnostic tests and to assess disease progression.

Role of inter-hemispheric transfer in generating visual evoked potentials in V1-damaged brain hemispheres

Partial cortical blindness is a visual deficit caused by unilateral damage to the primary visual cortex, a condition previously considered beyond hopes of rehabilitation. However, recent data demonstrate that patients may recover both simple and global motion discrimination following intensive training in their blind field. The present experiments characterized motion-induced neural activity of cortically blind (CB) subjects prior to the onset of visual rehabilitation. This was done to provide information about visual processing capabilities available to mediate training-induced visual improvements. Visual Evoked Potentials (VEPs) were recorded from two experimental groups consisting of 9 CB subjects and 9 age-matched, visually-intact controls. VEPs were collected following lateralized stimulus presentation to each of the 4 visual field quadrants. VEP waveforms were examined for both stimulus-onset (SO) and motion-onset (MO) related components in postero-lateral electrodes. While stimulus presentation to intact regions of the visual field elicited normal SO-P1, SO-N1, SO-P2 and MO-N2 amplitudes and latencies in contralateral brain regions of CB subjects, these components were not observed contralateral to stimulus presentation in blind quadrants of the visual field. In damaged brain hemispheres, SO-VEPs were only recorded following stimulus presentation to intact visual field quadrants, via inter-hemispheric transfer. MO-VEPs were only recorded from damaged left brain hemispheres, possibly reflecting a native left/right asymmetry in inter-hemispheric connections. The present findings suggest that damaged brain hemispheres contain areas capable of responding to visual stimulation. However, in the absence of training or rehabilitation, these areas only generate detectable VEPs in response to stimulation of the intact hemifield of vision.

Spontaneous recovery and treatment effects in patients with homonymous visual field defects: a meta-analysis of existing literature in terms of the ICF framework

Homonymous visual field defects (HVFDs) are a common consequence of posterior brain injury. Most patients do not recover spontaneously and require rehabiliation. To determine whether a certain intervention may help an individual patient, it is necessary to predict the patient's level of functioning and the effect of specific training. We provide an overview of both the existing literature on HVFDs in terms of the International Classification of Functioning, Disability, and Health (ICF) components and the variables predicting the functioning of HVFD patients or the effect of treatment. We systematically analyzed 221 publications on HVFD. All variables included in these articles were classified according to the ICF, as developed by the World Health Organization, and checked for their predictive value. We found that ICF helps to clarify the scope of the existing literature and provides a framework for designing future studies, which should consider including more outcome measures related to Activities and Participation. Although several factors have been described that predict HVFD patients' level of functioning or the effects of training, additional research is necessary to identify more.

Multifocal visual evoked potentials in unilateral compressive optic neuropathy secondary to orbital tumors

OBJECTIVE

To evaluate the effects of unilateral compressive optic neuropathy secondary to orbital tumors and the removal of the tumors on amplitude and latency of multifocal visual evoked potentials (mfVEPs) and to compare these responses with visual field defects seen on static automated perimetry.

METHODS

Static automated and mfVEP recordings were obtained from 14 patients with orbital tumors affecting one optic nerve. Monocular and interocular amplitude and latency analyses were performed.

RESULTS

The change in the mfVEP amplitude agreed with visual field findings with regard to topography and severity of deviation from normal in 10 patients. For 4 patients with normal visual field, the changes in the mfVEP were of significance. The delay in recordable responses from affected eyes ranged from 2.56 to 18.28 ms (interocular analysis) and 0.1 to 21.86 ms (monocular analysis). Ten patients whose tumor was totally removed showed a recovery of the visual field and mfVEP to various degrees. Visual field of 6 patients showed within normal limits after total removal of the tumor, and the defects of mfVEP in 3 patients remained apparent, while the mfVEP of the other 3 patients showed a complete recovery.

CONCLUSIONS

Various orbital tumors can cause compressive optic neuropathy. Compressive optic neuropathy secondary to orbital tumors results in mfVEP amplitude reduction and latency prolongation. The changes in measures of mfVEP due to orbital tumors are consistent with the visual field changes in most patients. In some patients, the subjective visual field results and objective mfVEP are discordant. The objective changes of mfVEP may appear earlier than the defect of visual field, and thus it may be able to identify subtle defects that are undetectable with Humphrey perimetry. Postoperatively, recovery of the mfVEP may be later than that of visual field in some patients. The mfVEP changes may assist in both early diagnosis and follow-up of the compressive optic neuropathy secondary to orbital tumors.

Objective visual field determination in forensic ophthalmology with an optimized 4-channel multifocal VEP perimetry system: a case report of a patient with retinitis pigmentosa

We present the case of a 59-year-old male patient with progressive vision impairment and consecutive visual field narrowing ("tunnel view") for 7 years and a known retinitis pigmentosa for 5 years. The remaining Goldmann perimetric visual field at time reported was less than 5°. A request for blindness-related social benefits was rejected because an ophthalmologic expert assessment suggested malingering. This prompted us to assess an objective determination of the visual field using multifocal VEPs. Objective visual field recordings were performed with a four-channel multifocal VEP-perimeter using 58 stimulus fields (pattern reversal dartboard stimulus configuration). The correlated signal data were processed using an off-line method. At each field, the recording from the channel with the maximal signal-to-noise ratio (SNR) was retained, thus resulting in an SNR optimized virtual recording. Analysis of VEP signals was performed for each single field and concentric rings and compared to an average response measured in five healthy subjects. Substantial VEP responses could be identified in three fields within the innermost ring (eccentricity, 1.7°) for both eyes, although SNR was generally low. More eccentric stimuli did not elicit reliable VEP responses. The mfVEP recording was correlated with perimetric visual field data. The current SNR optimization by using the channel with the largest SNR provides a good method to extract useful data from recordings and may be appropriate for the use in forensic ophthalmology.

Rehabilitation of hemianopia

PURPOSE OF REVIEW

Homonymous hemianopia is the commonest form of acquired homonymous visual field defect; the usual causes are stroke, head injury and intracranial tumours. This impairment can affect a variety of cognitive visual functions, including visual search, safe navigation through changing environments and reading. A number of rehabilitative techniques have been tried with varying degrees of success. They broadly fall into three main groups: optical therapies, in which the damaged visual field is brought into view by the use of optical devices; eye movement-based therapies, in which the damaged visual field is more effectively sampled with compensatory or adaptive eye movements; and visual field restitution therapies, in which vision in the damaged field is itself improved. These techniques all rely on mass practice. This review provides an up-to-date summary of these approaches.

RECENT FINDINGS

All of the three main approaches to rehabilitation of homonymous visual field defect have been pursued in recent years and all appear capable of providing a moderate amount of 'real-world' improvement to patients. Controversy still reigns over the mechanism of action of all but the optical methods. Patients have to practice for many hours to feel the benefit of all of these techniques, with the eye movement-based therapies requiring the least amount of exposure.

SUMMARY

The evidence base for these types of behavioural therapy is getting stronger all the time. Future studies that take on the difficult task of controlling for placebo effects will allow patients' subjective ratings of success to be used as a convincing outcome measure. Without doubt, the literature would also benefit from bigger studies that include more patients; however, one could argue that given the clear negative effect that homonymous visual field defect has on patients' lives, these therapies should be more widely available already.