Intracranial Visual Pathway Research Articles

Possible association of dose rate and the development of late visual toxicity for patients with intracranial tumours treated with pencil beam scanned proton therapy

Background and purposeRare but severe toxicities of the optic apparatus have been observed after treatment of intracranial tumours with proton therapy. Some adverse events have occurred at unusually low dose levels and are thus difficult to understand considering dose metrics only. When transitioning from double scattering to pencil beam scanning, little consideration was given to increased dose rates observed with the latter delivery paradigm. We explored if dose rate related metrics could provide additional predicting factors for the development of late visual toxicities.Materials and methodsRadiation-induced intracranial visual pathway lesions were delineated on MRI for all index cases. Voxel-wise maximum dose rate (MDR) was calculated for 2 patients with observed optic nerve toxicities (CTCAE grade 3 and 4), and 6 similar control cases. Additionally, linear energy transfer (LET) related dose enhancing metrics were investigated.ResultsFor the index cases, which developed toxicities at low dose levels (mean, 50 GyRBE), some dose was delivered at higher instantaneous dose rates. While optic structures of non-toxicity cases were exposed to dose rates of up to 1 to 3.2 GyRBE/s, the pre-chiasmatic optic nerves of the 2 toxicity cases were exposed to dose rates above 3.7 GyRBE/s. LET-related metrics were not substantially different between the index and non-toxicity cases.ConclusionsOur observations reveal large variations in instantaneous dose rates experienced by different volumes within our patient cohort, even when considering the same indications and beam arrangement. High dose rate regions are spatially overlapping with the radiation induced toxicity areas in the follow up images. At this point, it is not feasible to establish causality between exposure to high dose rates and the development of late optic apparatus toxicities due to the low incidence of injury.

White Matter Alterations of Visual Pathway in Thyroid Eye Disease: A Fixel-Based Analysis.

Thyroid eye disease (TED), particularly its sight-threatening complication, dysthyroid optic neuropathy (DON), profoundly impacts patients' visual health. The pathological changes in the white matter (WM) fibers within the intracranial visual pathway in TED have been infrequently studied. Understanding these changes holds crucial importance for exploring the pathogenesis and prognosis of TED. To utilize fixel-based analysis (FBA) to clarify the type of microstructural damage occurring in the visual pathway in TED. Prospective. 28 TED with DON patients (11 males and 17 females), 28 TED without DON (non-DON) patients (12 males and 16 females), and 28 healthy controls (HCs) (12 males and 16 females). 3 T; multishell diffusion MRI using echo planar imaging. Fiber density (FD) and fiber-bundle cross-section (FC) were calculated to characterize WM microstructural alteration in TED visual pathway. The correlations between FBA metrics and visual field index and mean deviation were examined. One-way analysis of variance, Kruskal-Wallis, t-tests, Mann-Whitney U, Chi-square, and Pearson correlation, were conducted with false discovery rate and family wise error corrections. Significance was set at P < 0.05. Both DON and non-DON groups showed significant FD loss in the right optic tract compared with HCs, with DON patients experiencing more severe FD loss. Only DON patients had FD loss in the right optic radiation (OR) compared with the non-DON patients and HCs, with no FC difference across groups. FD in DON patients' ORs significantly correlated with visual field index (r = 0.857) and mean deviation (r = 0.751). Both DON and non-DON affect the WM microstructure of the visual pathway to varying extents. Visual field metrics can reflect the severity of FD damage to the OR in the visual pathway of DON patients. 2. Stage 3.

Diagnosis of dysthyroid optic neuropathy: combined value of orbital MRI and intracranial visual pathway diffusion kurtosis imaging.

To evaluate the combined performance of orbital MRI and intracranial visual pathway diffusion kurtosis imaging (DKI) in diagnosing dysthyroid optic neuropathy (DON). We retrospectively enrolled 61 thyroid-associated ophthalmopathy (TAO) patients, including 25 with DON (40 eyes) and 36 without DON (72 eyes). Orbital MRI-based apical muscle index (MI), diameter index (DI) of the optic nerve (ON), area index (AI) of the ON, apparent diffusion coefficient (ADC) and signal intensity ratio (SIR) of the ON, DKI-based kurtosis fractional anisotropy (KFA) and mean kurtosis (MK) of the optic tract (OT), optic radiation (OR), and Brodmann areas (BAs) 17, 18, and 19 were measured and compared between groups. The diagnostic performances of models were evaluated using receiver operating characteristic curve analyses and compared using the DeLong test. TAO patients with DON had significantly higher apical MI, apical AI, and SIR of the ON, but significantly lower ADC of the ON than those without DON (p < 0.05). Meanwhile, the DON group exhibited significantly lower KFA across the OT, OR, BA17, BA18, and BA19 and lower MK at the OT and OR than the non-DON group (p < 0.05). The model integrating orbital MRI and intracranial visual pathway DKI parameters performed the best in diagnosing DON (AUC = 0.926), with optimal diagnostic sensitivity (80%) and specificity (94.4%), followed by orbital MRI combination (AUC = 0.890), and then intracranial visual pathway DKI combination (AUC = 0.832). Orbital MRI and intracranial visual pathway DKI can both assist in diagnosing DON. Combining orbital and intracranial imaging parameters could further optimize diagnostic efficiency. The novel finding could bring novel insights into the precise diagnosis and treatment of dysthyroid optic neuropathy, accordingly, contributing to the improvement of the patients' prognosis and quality of life in the future. • Orbital MRI and intracranial visual pathway diffusion kurtosis imaging can both assist in diagnosing dysthyroid optic neuropathy. • Combining orbital MRI and intracranial visual pathway diffusion kurtosis imaging optimized the diagnostic efficiency of dysthyroid optic neuropathy.

Evaluation and comparison of global-feature-based and local-feature-based segmentation algorithms in intracranial visual pathway delineation.

Intracranial visual pathway is related to the effective transmission of visual signals to brain. It was not only the target organ of diseases but also the organs at risk in radiotherapy thus its delineation plays an important role in both diagnosis and treatment planning. Traditional manual segmentation method suffered from time- and labor- consuming as well as intra- and inter- variability. In order to overcome these problems, state-of-the-art segmentation models were designed and various features were extracted and utilized, but it's hard to tell their effectiveness on intracranial visual pathway delineation. It's because that these methods worked on different dataset and accompanied with different training tricks. This study aimed to research the contribution of global features and local features in delineating the intracranial visual pathway from MRI scans. The two typical segmentation models, 3D UNet and DeepMedic, were chosen since they focused on global features and local features respectively. We constructed the hybrid model through serially connecting the two mentioned models to validate the performance of combined global and local features. Validation results showed that the hybrid model outperformed the individual ones. It proved that multi scale feature fusion was important in improving the segmentation performance.

Diffusion tensor imaging of the visual pathway in glaucomatous optic nerve atrophy

In Germany more than one million inhabitants suffer from glaucoma, more than 100,000 are threatened with blindness because glaucoma is often diagnosed too late or not at all. Diagnosis and monitoring is usually carried out "only" by examination of the retina and not the whole visual pathway. However, the eye is just "the tip of the iceberg" of the actual visual pathway, which extends through the brain to the visual cortex. The interdisciplinary holistic assessment of the whole visual pathway in glaucoma is of crucial importance because glaucoma is a complex neurodegenerative disease. Subtypes, such as normal tension glaucoma (NTG), seem to originate from primary damage to the intracranial visual pathway with secondary retrograde retinal degeneration. Recent studies including glaucoma patients and healthy controls could show that diffusion tensor imaging with calculation of diffusion coefficients, i.e. fractional anisotropy (FA), mean and radial diffusivity (MD and RD) as markers of axonal integrity, provide the potential to assess the intracranial visual pathway with a high correlation to established ophthalmological examinations. In particular, calculation of FA maps of the visual pathway and accompanying voxel-based approaches, can be integrated into clinical routine. Thus, detection of glaucoma-related intracranial alterations, even in early stages of the disease, as well as differentiation of different glaucoma subtypes, is made possible. Furthermore, the diagnosis of normal tension glaucoma seems to be possible much earlier with these new imaging techniques compared to established ophthalmological work-up. Moreover, holistic imaging provides new insights into the pathophysiology of this form of glaucoma. This review article gives an overview of these novel magnetic resonance imaging techniques for assessment of the visual pathway in glaucomatous optic nerve atrophy and reveals the potential of an interdisciplinary approach.

Electrophysiology in the diagnosis of albinism

AbstractAlbinism is a genetically determined disorder of melanin synthesis associated with intracranial visual pathway misrouting, with the majority of fibres from each eye usually decussating to the contralateral cerebral hemisphere. The presentation will detail the use of flash and pattern appearance VEPs in the demonstration of this albino misrouting. It will be demonstrated that the misrouting has a highly variable expression, including uni‐ocular misrouting, and is a spectrum of disease rather than an all‐or‐none phenomenon.

Early stage development of the glycine‐1 re‐uptake inhibitor SCH 900435: central nervous system effects compared with placebo in healthy men

To report the first three studies with SCH 900435, a selective glycine-1 re-uptake inhibitor in development for treating schizophrenia, using systematic evaluations of pharmacodynamics to understand the observed effects. Three double-blind, placebo-controlled studies (single, visual effect and multiple dose) were performed. In the single and multiple dose study SCH 900435 (0.5-30 mg) was given to healthy males and frequent pharmacokinetic and pharmacodynamic measurements were performed. The visual effects study incorporated visual electrophysiological measures of macular, retinal and intracranial visual pathway function. In the single dose study (highest difference, 95% CI, P) increases in smooth pursuit eye movements (8, 12 mg (-6.09, 10.14, -2.04, 0.013), 30 mg), pupil : iris ratio (20 and 30 mg (-0.065, 0.09, -0.04, <0.0001)), VAS colour perception (30 mg (-9.48, 13.05, -5.91, <0.0001)) and changes in spontaneous reports of visual disturbance were found, while FSH (8 mg (0.42, 0.18, 0.66, 0.0015), 12, 20 mg), LH (8-30 mg (1.35, 0.65, 2.05, 0.0003)) and EEG alpha2 activity decreased (12, 20, 30 mg (0.27, 0.14, 0.41, 0.0002)). A subsequent dedicated visual effects study demonstrated that visual effects were transient without underlying electrophysiological changes. This provided enough safety information for starting a multiple ascending dose study, showing less visual symptoms after twice daily dosing and titration, possibly due to tolerance. Several central nervous system (CNS) effects and gonadotropic changes resulted from administration of 8 mg and higher, providing evidence for CNS penetration and pharmacological activity of SCH 900435. Antipsychotic activity in patients, specificity of the reported effects for this drug class and possible tolerance to visual symptoms remain to be established.

‘Radiology of the Orbit and Visual Pathways’

Jonathan J. Dutton ‘Radiology of the Orbit and Visual Pathways’ Saunders Elsevier 408 pages Price £129 ISBN: 978-1-4377-1151-6 Jonathan J. Dutton is a well-known Oculoplastic and Orbital surgeon. He has now written a book about the radiology of the orbit and the visual pathways. I have always admired clinicians who approach their subspeciality from a different angle, even a site that is usually dominated by another speciality. The following are the strengths of this book: Mr. Dutton is a clinican, he describes the typical clinical picture in most of the orbital diseases and then demonstrates the typical CT scan and MRI for those disease categories. The text is concise, but easy to understand. The pictures are as expected. In addition to that, the first 50 pages of the book describe the basic principles of the computed tomography and magnetic resonance imaging, the anatomy of the orbit and the intracranial visual pathways, nice chapters that are very well illustrated. At the same time, this book is available on the internet at expertconsult.com. It contains an activation code, and you can study it in your computer. The problem with books is that they are in one shelf, usually in one room, but many doctors have quite a few working stations, and it therefore handy to have such a book on the internet. While this book has been lying on my table waiting to be reviewed, I have found it useful and been using it in my clinical practice and teaching. That is the best recommendation I can give a book, it is practical, nice book indeed. I would like to extend my gratitude to the author.

Neuro-Ophthalmology of Systemic Disease

Many neuro-ophthalmologic conditions may result from systemic disease or its treatments. This article provides an update on optic neuropathies, eye movement disorders, and intracranial visual pathway lesions that occur most commonly with systemic disease, are clinical emergencies, or have been identified or clarified in recent publications.

Neuroradiologie der intrakraniellen Sehbahn

The clinical symptoms of lesions affecting the intracranial visual pathway vary as widely as their aetiology. The anatomy, the basics of neuro-ophthalmology and MRI protocols are touched on in the first part of this serial paper; in addition the most important pathological entities affecting the sellar region are presented. The focus is on the differentiation between extrinsic and intrinsic lesions, but in addition to this vascular lesions are presented with reference to illustrative cases.

Anatomy of the visual system

This brief systemic overview presents the anatomic details of the orbit with respect to imaging modalities CT and MR. The structures of the four orbital compartments, intrakonal and extrakonal space, globe and optic nerve are demonstrated in detail on different CT and MR views (axial, coronal, in soft tissue and bone window, T1-weighted, T2-weighted) with corresponding diagrams. The intracranial visual pathway is explained in detail with emphasis to the striate cortex and extrastriate visual association cortex, presented with diagrams and high-resolution MR.

Diagnostic value of magnetic resonance imaging and planimetric measurement of optic disc size in confirming optic nerve hypoplasia

Purpose: This study set out to evaluate magnetic resonance imaging (MRI) and measurement of optic disc size as diagnostic tools for confirming the diagnosis of optic nerve hypoplasia (ONH) in children with impaired growth. Methods: MRI was performed to study the size of the intracranial visual pathways, and image analysis measurements of fundus photographs were performed to determine the size of the optic disc. Results from these investigations were compared with those using the gold standard for diagnosis of ONH, which was the clinical eye examination (visual function, ophthalmoscopic signs, or both). Forty children (median age, 9 years; range, 3 to 19 years) with impaired growth were included in the study. Results: The prevalence of ONH among the children was 15%. MRI classification of the visual pathways had a higher positive predictive value than image analysis measurement of the optic disc size (1.0 vs 0.6). Conclusions: MRI is a good tool for confirming the diagnosis of ONH and may thus facilitate early detection. On the other hand, a small optic disc per se is not a definite indicator of ONH but should encourage further investigation with MRI, especially if there is a clinical suspicion of ONH. (J AAPOS 1999;3:104-8)

NEURORADIOLOGY IN OPHTHALMOLOGY

Technical advances made in diagnostic neuroimaging during the past 20 years have played an important role in the practice of ophthalmology. Various diagnostic tests are now routinely used to image the globe, orbit, and intracranial visual pathways. With so many different imaging modalities available, choosing the appropriate study to evaluate a clinical problem has become more difficult. This discussion highlights the current techniques available to image the eye, ocular adnexa, and brain. It also provides guidance on the selection of the appropriate imaging modality and several examples of imaging characteristics of pathologic lesions.

MR of uncommon congenital and vascular lesions of the intracranial visual pathways

The MR findings of two patients with rare congenital abnormalities of the optic pathways are reported and illustrated, including one case of unilateral aplasia of the optic chiasm, tract, and visual radiations and another patient with anophthalmos. In three other patients with unusual vascular causes of visual disturbance, MR was important in early establishment of an accurate diagnosis and had consequent implications for decisions regarding further patient management.

Visual evoked potentials in the assessment of patients with non-functioning chromophobe adenomas.

The results of visual evoked potential (VEP) examination in 34 patients with histologically confirmed chromophobe adenoma are described and discussed in relation to the clinical, radiological and surgical findings. The VEP is shown to be a reliable method of assessing the function of the intracranial visual pathways which is often more sensitive than conventional methods of examination.

Homonymous hemianopia: A retrospective study of 140 cases

A retrospective study of 140 cases of homonymous hemianopia was performed. There was a relatively high percentage of occipital lesions, most of which were of vascular origin. For examination of the visual field when a lesion is present in the intracranial visual pathway, campimetry is frequently superior to perimetry, and their combination is sometimes necessary. It was strongly felt that CT scan should be applied to all patients with homonymous hemianopia. Visual agnosia is apt to be overlooked in cases of occipital lesion.

Intracranial Visual Pathway Disturbances and their Visual Field

Intracranial Visual Pathway Disturbances and their Visual Field