Retrochiasmal Visual Pathways Research Articles

Macular OCT's Proficiency in Identifying Retrochiasmal Visual Pathway Lesions in Multiple Sclerosis-A Pilot Study.

Optical coherence tomography (OCT) is a non-invasive imaging technique based on the principle of low-coherence interferometry that captures detailed images of ocular structures. Multiple sclerosis (MS) is a neurodegenerative disease that can lead to damage of the optic nerve and retina, which can be depicted by OCT. The purpose of this pilot study is to determine whether macular OCT can be used as a biomarker in the detection of retrochiasmal lesions of the visual pathway in MS patients. We conducted a prospective study in which we included 52 MS patients and 27 healthy controls. All participants underwent brain MRI, visual field testing, and OCT evaluation of the thicknesses of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell layer (GCL), and macular inner plexiform layer (IPL). OCT measurements were adjusted for optic neuritis (ON). VF demonstrated poor capability to depict a retrochiasmal lesion identified by brain MRI (PPV 0.50). In conclusion, the OCT analysis of the macula appears to excel in identifying retrochiasmal MS lesions compared to VF changes. The alterations in the GCL and IPL demonstrate the most accurate detection of retrochiasmal visual pathway changes in MS patients.

A RARE CASE : HOMONYMOUS HEMIANOPIA IN CHILDREN

Abstract
 Introduction : Homonymous hemianopia (HH) is a visual field loss in the same halves of the visual field of each eye that is caused by numerous lesion affecting the retrochiasmal visual pathway. Homonymous hemianopia in children is a rare disabling condition and might be found as an initial presentation of brain tumors.
 Case Illustration : A 12 years old boy came with chief complaint of partially vision loss on the left side of vision accompanied by intermittent headache. Ophthalmological examination showed visual acuity of 1.0 on both eyes. Visual field examination revealed left homonymous hemianopia (figure 1). These findings were relevant to the result of his brain Computed Tomography (CT) scan, which showed vascular mass in the right occipital lobe caused by suspected arteriovenous malformation mixed diffuse type (figure 2). The patient was referred to neurosurgeon for further management.
 Discussion : Visual field defect depends on location of the lesion and can be used to recognize optic pathway diseases. Homonymous hemianopia occurs in retrochiasmal lesions that could happened either in adult or children. Unusual presentation of HH in children caused by brain tumor such as arteriovenous malformation. It might occur in up to 27% and can be detected radiologically with either brain CT scan or Magnetic Resonance Imaging (MRI).
 Conclusion : Visual field loss in pediatric patient might be challenging. Proper and prompt diagnosis is important to detect underlying condition and determine further management of the patient.

Known genes, new genes and new phenotypes in mitochondrial eye diseases

Primary mitochondrial diseases together represent a major cause of inherited neurological disorders that, due to dysfunction of the mitochondrial respiratory chain, can affect many parts of body, especially high energy demand organs, such as liver, heart, kidney, muscle and the eye. As the eye is particularly vulnerable to mitochondrial dysfunction, approximately half of all the patients with confirmed mitochondrial disease will develop significant ocular involvement and the complication that patients are most afraid of is visual loss. This can arise either from a primary optic neuropathy (the most common ocular involvement), from outer retinal degeneration, or in some cases from retrochiasmal visual pathway involvement resulting in varying patterns of visual field defects. To date, inherited optic neuropathies have been linked with pathogenic variants in over 40 genes across both the mitochondrial (mtDNA) and nuclear (nDNA) genomes with maternal (mtDNA) inheritance, autosomal dominant, recessive and x‐linked inheritance observed. Inherited optic neuropathies are a significant cause of blindness in both the paediatric and adult population with an estimated prevalence of 1 in 10 000 in the UK. The prevalence is estimated low because of the difficulty in making a confirmed molecular diagnosis due to multiple factors: mutations have been identified in both genomes, a limited number of genes are included in next generation sequencing (NGS) panels, phenocopies etc. Current genetic testing strategies for inherited eye diseases fail to identify pathogenic variants in a significant proportion of cases suggesting that previously unidentified genes harbouring pathogenic variants remain to be identified. However, whole exome sequencing (WES) and particularly whole genome sequencing (WGS), and unbiased interrogation of genomic variants offers an unparalleled opportunity to detect variants in both uncharacterised genes and non‐coding regions of the genome leading to previously unknown gene‐disease associations. This presentation highlights the power of unbiased WGS to elucidate the missing heritability in mitochondrial eye diseases and reports novel gene‐disease associations and novel phenotypes associated with known genes defects.

New genes and new phenotypes

AbstractPrimary mitochondrial diseases together represent a major cause of inherited neurological disorders that, due to dysfunction of the mitochondrial respiratory chain, can affect many parts of body, especially high energy demand organs, such as liver, heart, kidney, muscle and the eye. As the eye is particularly vulnerable to mitochondrial dysfunction, approximately half of all the patients with confirmed mitochondrial disease will develop significant ocular involvement and the complication that patients are most afraid of is visual loss. This can arise either from a primary optic neuropathy (the most common ocular involvement), from outer retinal degeneration, or in some cases from retrochiasmal visual pathway involvement resulting in varying patterns of visual field defects. To date, inherited optic neuropathies have been linked with pathogenic variants in over 40 genes across both the mitochondrial (mtDNA) and nuclear (nDNA) genomes with maternal (mtDNA) inheritance, autosomal dominant, recessive and x‐linked inheritance observed. Inherited optic neuropathies are a significant cause of blindness in both the paediatric and adult population with an estimated prevalence of 1 in 10 000 in the UK. The prevalence is estimated low because of the difficulty in making a confirmed molecular diagnosis due to multiple factors: mutations have been identified in both genomes, a limited number of genes are included in next generation sequencing (NGS) panels, phenocopies etc. Current genetic testing strategies for inherited eye diseases fail to identify pathogenic variants in a significant proportion of cases suggesting that previously unidentified genes harbouring pathogenic variants remain to be identified. However, whole exome sequencing (WES) and particularly whole genome sequencing (WGS), and unbiased interrogation of genomic variants offers an unparalleled opportunity to detect variants in both uncharacterised genes and non‐coding regions of the genome leading to previously unknown gene‐disease associations. This presentation highlights the power of unbiased WGS to elucidate the missing heritability in mitochondrial eye diseases and reports novel gene‐disease or gene‐phenotype associations.

Visual Field Defect Patterns Associated With Lesions of the Retrochiasmal Visual Pathway.

Perimetry is widely used in the localization of retrochiasmal visual pathway lesions. Although macular sparing, homonymous paracentral scotomas, and quadrantanopias are regarded as features of posterior retrochiasmal visual pathway lesions, incongruous hemianopia is regarded as a hallmark of anterior lesions. Recent studies have questioned the specificity of these defect patterns. Retrospective record review conducted in a single, academic, medical center using an electronic search engine with the terms ""homonymous hemianopia," "optic tract," "temporal lobectomy," "visual field defect," and "MRI." Patients were included if they had reliable, automated, static visual fields, high-quality reviewable MRI scans, and pertinent lesions. MRI lesions were assigned to 1 of 6 retrochiasmal visual pathway segments by the study neuroradiologist. Two study authors independently reviewed the visual fields and designated 10 different defect patterns. From an original cohort of 256 cases, only 83 had MRI-defined lesions that were limited to particular retrochiasmal segments and had visual field defect patterns that allegedly permitted localization to those particular segments. The 5 contralateral nerve fiber bundle defects were exclusive to optic tract tumors with rostral extension. Pie-in-the-sky defects were exclusive to Meyer loop lesions. Among 22 fields with macular sparing, 86% arose from the visual cortex or posterior optic radiations. Among 31 fields with homonymous quadrantanopias, 77% arose from Meyer loop, visual cortex, or posterior optic radiations. Among 13 fields with homonymous paracentral scotomas, 69% arose from visual cortex or posterior optic radiations. Optic tract lesions accounted for 70% of incongruous hemianopias but that pattern occurred uncommonly. In correlating discrete MRI-defined retrochiasmal lesions with visual field defect patterns identified on static perimetry, this study showed that macular sparing, homonymous paracentral scotomas, and quadrantanopias localized to the visual cortex and posterior optic radiations segments but not exclusively. It has differed from an earlier study in showing that incongruous hemianopias occur predominantly from optic tract lesions.

Homonymous OCT-GCIPL Quadrantanopia without a Visual Field Defect

A 37-year-old woman with a large left parieto-occiptal porencephalic cyst was referred by neurosurgery to rule out papilledema. Her visual acuity was 20/20, there was no relative afferent pupillary defect, and Humphrey 24-2 SITA-Fast visual field testing was unremarkable (Fig A). There was no papilledema, but OCT of the ganglion cell-inner plexiform layer (GCIPL) showed right homonymous quadrantanopic thinning (Fig B). Review of the magnetic resonance imaging (top, sagittal T1; bottom left, fluid-attenuated inversion recovery [FLAIR]; bottom right, axial T2) showed a large cerebrospinal fluid–containing cyst compressing the parieto-occipital lobes in the location of the left retrochiasmal visual pathways (Fig C) (Magnified version of Fig A-C is available online at www.aaojournal.org).

Recent advances and future directions on the use of optical coherence tomography in neuro-ophthalmology.

Optical coherence tomography (OCT) is a noninvasive imaging technique used to qualitatively and quantitatively analyze various layers of the retina. OCT of the retinal nerve fiber layer (RNFL) and ganglion cell–inner plexiform layer (GCIPL) is particularly useful in neuro-ophthalmology for the evaluation of patients with optic neuropathies and retrochiasmal visual pathway disorders. OCT allows for an objective quantification of edema and atrophy of the RNFL and GCIPL, which may be evident before obvious clinical signs and visual dysfunction develop. Enhanced depth imaging OCT allows for visualization of deep structures of the optic nerve and has emerged as the gold standard for the detection of optic disc drusen. In the evaluation of compressive optic neuropathies, OCT RNFL and GCIPL thicknesses have been established as the most important visual prognostic factor. There is increasing evidence that inclusion of OCT as part of the diagnostic criteria for multiple sclerosis (MS) increases its sensitivity. Moreover, OCT of the RNFL and GCIPL may be helpful in the early detection and monitoring the treatment of conditions such as MS and Alzheimer's disease. OCT is an important aspect of the neuro-ophthalmologic assessment and its use is likely to increase moving forward.

Factors Associated With Lack of Vision Improvement in Children With Cortical Visual Impairment.

Improvement in vision has been noted in children with cortical visual impairment (CVI), resulting from disparate types of brain injury. The purpose of our study was to determine the risk factors associated with poor recovery of vision in this group of patients. Case records of children who were born before 2010 with at least 4 follow-up visits for CVI were reviewed for underlying etiologies of CVI, visual acuity (VA), and associated neurological and ophthalmological disorders. VA was assessed in 6 qualitative grades. Changes in VA were recorded as the difference between the grades of VA at presentation and the last follow-up visit. The outcome was calculated as a ratio of actual improvement to potential improvement in grades of qualitative VA. Multiple linear regression determined factors associated with lack of vision improvement in all children and based on etiology. Fifty-three children with CVI were identified. The median age at presentation was 13.6 months (range: 2.9-76.4 months) and the median follow-up was 5.8 years (1.1-16.3 years). CVI resulted from central nervous system (CNS) malformation (9.4%), hypoxic/inflammatory injury (15.1%), seizures (24.5%), and combined causes (51.0%). Vision improvement was noted in 83% of children. Lack of VA improvement was associated with older age at presentation in all children with CVI and within each etiological group except CNS malformation. None of the other investigated variables were associated with poor recovery of VA. Most of the children with CVI showed improvement in vision. Older age at presentation, but not etiology of CVI, was associated with poor improvement in VA.

Hémianopsie latérale homonyme post-traumatique et atteinte des cellules ganglionnaires : à propos de 3 cas

Homonymous lateral hemianopia follows an attack on the contralateral retrochiasmal visual pathways. In three patients with post-traumatic homonymous hemianopia, optical coherence tomographic (OCT) study of the ganglion cell layer thickness showed hemiretinal thinning contralateral to the visual field defect. This involvement could be explained by trans-synaptic degeneration of the pre-geniculate visual pathways, whose cell nuclei correspond to ganglion cells, which synapse with the damaged retrogeniculate visual pathways.

Agreement of driving simulator and on-road driving performance in patients with binocular visual field loss.

On-road testing is considered the standard for assessment of driving performance; however, it lacks standardization. In contrast, driving simulators provide controlled experimental settings in a virtual reality environment. This study compares both testing conditions in patients with binocular visual field defects due to bilateral glaucomatous optic neuropathy or due to retro-chiasmal visual pathway lesions. Ten glaucoma patients (PG), ten patients with homonymous visual field defects (PH), and 20 age- and gender-matched ophthalmologically normal control subjects (CG and CH, respectively) participated in a 40-min on-road driving task using a dual brake vehicle. A subset of this sample (8 PG, 8 PH, 8 CG, and 7 CH) underwent a subsequent driving simulator test of similar duration. For both settings, pass/fail rates were assessed by a masked driving instructor. For on-road driving, hemianopia patients (PH) and glaucoma patients (PG) showed worse performance than their controls (CH and CG groups): PH 40%, CH 30%, PG 60%, CG 0%, failure rate. Similar results were obtained for the driving simulator test: PH 50%, CH 29%, PG 38%, CG 0%, failure rate. Twenty-four out of 31 participants (77%) showed concordant results with regard to pass/fail under both test conditions (p > 0.05; McNemar test). Driving simulator testing leads to results comparable to on-road driving, in terms of pass/fail rates in subjects with binocular (glaucomatous or retro-chiasmal lesion-induced) visual field defects. Driving simulator testing seems to be a well-standardized method, appropriate for assessment of driving performance in individuals with binocular visual field loss.

Inherited eye-related disorders due to mitochondrial dysfunction.

Genetic disorders due to mitochondrial dysfunction are not uncommon and the majority of these patients will have eye-related manifestations, including visual loss from the optic nerve and retinal disease, visual field loss from retrochiasmal visual pathway damage, and ptosis and ocular dysmotility from extraocular muscle involvement. Defects in both the nuclear and mitochondrial genomes cause mitochondrial dysfunction via several mechanisms, including impaired mitochondrial energy production, oxidative stress, mitochondrial DNA instability, abnormalities in the regulation of mitochondrial dynamics and mitochondrial quality control, and disturbed cellular interorganellar communication. Advances in our understanding of the molecular genetic basis of mitochondrial disease have not only improved genetic diagnosis, but they have provided important insights into the pathophysiologic basis of these disorders and potential therapeutic targets. In parallel, more sophisticated techniques for genetic manipulation are facilitating the development of animal and in vitro models that should prove powerful and versatile tools for disease modelling and therapeutic experimentation. Effective therapies for mitochondrial disorders are beginning to translate from bench to bedside along the paths of neuroprotection, gene replacement and stem cell-based regenerative paradigms. Additionally, preventing the transmission of pathogenic mtDNA mutations from mother to child is now a reality with in vitro fertilization mitochondrial replacement techniques.

Homonymous hemimacular thinning in retrochiasmal lesions

PurposeTo evaluate the thickness of macular retina and determine which retinal layers are most affected by retrochiasmal visual pathways lesions.MethodsMean retinal thickness utilizing automated intraretinal layer segmentation of spectral domain optical coherence tomography scans was performed in 40 eyes of 40 patients with retrochiasmal visual pathways lesions and compared with 60 eyes of control subjects.Multiple linear regression analysis was used to determine the relationship between retinal thickness and follow‐up, age and gender.ResultsGanglion cell and inner plexiform layer was thinner in the temporal hemiretina ipsilateral and in the nasal hemiretina contralateral than in healthy controls.The mean thickness was significantly reduced in lesions over 6 months of duration, with no differences in correlations with age or gender.ConclusionsThis study demonstrate ganglion cell and inner plexiform thinning in the hemimacular area. These results support the concept that transneuronal retrograde degeneration of the retinal ganglion cells can be detected by OCT in humans with retrochiasmal visual pathways lesions.This homonymous hemimacular thinning in OCT represents an imaging biomarker that can be of valu in diagnosis, prognosis and clinical trials of neuroprotectives therapies.

Homonymous hemimacular thinning in retrochiasmal lesions

PurposeTo evaluate the thickness of macular retina and determine which retinal layers are most affected by retrochiasmal visual pathways lesions.MethodsMean retinal thickness utilizing automated intraretinal layer segmentation of spectral domain optical coherence tomography scans was performed in 40 eyes of 40 patients with retrochiasmal visual pathways lesions and compared with 60 eyes of control subjects. Multiple linear regression analysis was used to determine the relationship between retinal thickness and follow‐up, age and gender.ResultsGanglion cell and inner plexiform layer was thinner in the temporal hemiretina ipsilateral and in the nasal hemiretina contralateral than in healthy controls.The mean thickness was significantly reduced in lesions over 6 months of duration, with no differences in correlations with age or gender.ConclusionsThis study demonstrate ganglion cell and inner plexiform thinning in the hemimacular area. These results support the concept that transneuronal retrograde degeneration of the retinal ganglion cells can be detected by OCT in humans with retrochiasmal visual pathways lesions.This homonymous hemimacular thinning in OCT represents an imaging biomarker that can be of valu in diagnosis, prognosis and clinical trials of neuroprotectives therapies.

Imaging of Retrochiasmal and Higher Cortical Visual Disorders.

Retrochiasmal visual pathways include optic tracts, lateral geniculate nuclei, optic radiations, and striate cortex (V1). Homonymous hemianopsia and field defect variants with relatively normal visual acuity suggest that the lesions involve retrochiasmal pathways. From V1, visual input is projected to higher visual association areas that are responsible for perception of objects, faces, colors, and orientation. Visual association areas are classified into ventral and dorsal pathways. Damage to the ventral stream results in visual object agnosia, prosopagnosia, and achromatopsia. Balint syndrome, visual inattention, and pure alexia are examples of dorsal stream disorders. Posterior cortical atrophy can involve ventral and dorsal streams, often preceding dementia.

Genetic causes of acute visual loss

AbstractGenetic causes of acute visual loss are relatively rare, but these still need to be considered in the differential diagnosis, especially in the relevant clinical context. In this presentation, classical genetic disorders affecting the optic nerve will be discussed with a particular focus on Leber hereditary optic neuropathy (LHON). LHON is a primary mitochondrial DNA (mtDNA) disorder and three point mutations within the mitochondrial genome account for the vast majority of cases, namely: m.3460G>A, m.11778G>A and m.14484T>C. It typically affects young adult males who present with bilateral severe visual loss in the second or third decade of life. In addition to the canonical LHON mutations, other pathogenic mtDNA mutations have been reported that can result in both syndromic and non‐syndromic optic neuropathies. Acute visual loss in genetic disorders can also be secondary to pathology involving the retrochiasmal visual pathways, for example, in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke‐like episodes). The cardinal clinical manifestations in this group of patients are homonymous hemianopic visual field defects or cortical blindness.

Reversible homonymous hemianopia secondary to occipital lobe seizures

Occipital lobe infarcts, hemorrhages, or metastatic tumors can present with complex visual hallucinations, sensory or proprioceptive abnormalities, speech dysfunction, visual loss, and homonymous hemianopia (HH). Treatment of occipital lobe seizures is by single or multiple antiepileptic drugs. We present a case of idiopathic occipital lobe epilepsy where the seizures were controlled by antiepileptic drugs, but the HH did not subside until treated with high dose intravenous (IV) steroids.

Imaging of the optic chiasm and retrochiasmal visual pathways

The exploration of the chiasmal and retrochiasmal visual pathways is based on magnetic resonance imaging. A bitemporal hemianopsis suggests a lesion of the optic chiasm while homonymous lateral hemianopsis should lead to a search for a lesion of the retrochiasmal visual pathways. The causes of chiasmal impairment are mainly tumoral. The exploration protocol is based on MRI with T1-weighted sagittal sections, then T2- and T1-weighted coronal sections with and without injection. In case of a retrochiasmal syndrome, the MRI exploration protocol is a function of the type of occurrence of the deficiency and the context.

Photophobia Associated With a Demyelinating Lesion of the Retrochiasmal Visual Pathway

To present two patients in whom photophobia was a predominant presenting symptom of retrochiasmal demyelination. Observational case report. Two women who experienced an acute onset of photophobia underwent neuroophthalmic examination and investigations at a single institution. Examination revealed a homonymous visual field defect in both patients. Magnetic resonance imaging (MRI) demonstrated a hyperintense lesion in the area of the right posterior thalamus in one patient and enhancing lesions in the deep white matter of the temporal lobes bilaterally with contrast enhancement of the right optic tract in the second patient. Additional investigations, including lesion biopsy in the first patient, revealed demyelination as the most likely etiology. Improvement of photophobia, visual field defect, and radiographic abnormalities was documented over the next three to four months without accompanying treatment in both patients. Central pathology, including demyelination of the retrochiasmal visual pathway, should be considered in patients who experience acute photophobia.

Homonymous Hemianopia in Stroke

Previous reports have suggested that most cases of homonymous hemianopia (HH) are caused by occipital stroke. However, these reports have not always been supported by brain imaging. We reviewed the medical records of all patients seen in our unit between 1989 and 2004 who had HH documented by formal perimetry or confrontation visual fields and had undergone brain imaging. HHs were divided into those caused by stroke and by non-stroke conditions. The clinical and visual field characteristics were compared in the two groups. Among 850 patients with 902 HHs, 629 (69.7%) resulted from stroke, of which 531 (84.4%) were from infarction and 98 (15.6%) from primary intraparenchymal hemorrhage. Non-stroke causes included head trauma (123), brain tumor (102), neurosurgical procedures (22), multiple sclerosis (13), and miscellaneous conditions (13). Occipital lesions most commonly resulted from stroke. The configuration of the HH did not predict where in the retrochiasmal visual pathway the responsible lesion lay. Ischemic stroke causes most HHs from lesions in the occipital lobe that generally do not produce other neurologic manifestations. The configuration of the HH does not predict the location of the lesion within the retrochiasmal visual pathway.

Homonymous hemianopias: clinical-anatomic correlations in 904 cases

Homonymous hemianopia (HH) impairs visual function and frequently precludes driving. Most knowledge of HH is based on relatively few cases with clinical-anatomic correlations. The objective of this study was to describe the clinical characteristics and clinical-anatomic correlations of HH. The authors reviewed medical records of all patients with HH seen in their service between 1989 and 2004. Demographic characteristics, characteristics of visual field defects, causes of visual field defects, neuroradiologic definition of lesion location, and associated neurologic deficits were recorded. A total of 904 HH were found in 852 patients. A total of 340 HH (37.6%) were complete and 564 HH (62.4%) were incomplete. Homonymous quadrantanopia (264 HH, 29%) was the most common type of incomplete HH, followed by homonymous scotomatous defects (116 HH, 13.5%), partial HH (114 HH, 13%), and HH with macular sparing (66 HH, 7%). A total of 407 HH (45.0%) were isolated. Causes of HH included stroke (629 HH, 69.6%), trauma (123, 13.6%), tumor (102, 11.3%), brain surgery (22, 2.4%), demyelination (13, 1.4%), other rare causes (13, 1.4%), and unknown etiology (2, 0.2%). The lesions were most commonly located in the occipital lobes (45%) and the optic radiations (32.2%). Every type of HH, except for unilateral loss of temporal crescent and homonymous sectoranopia, was found in all lesion locations along the retrochiasmal visual pathways. This study shows that HH is usually secondary to stroke, head trauma, and tumors. The authors conclude that although the characteristics of visual field defects can be helpful in lesion location, specific visual field defects do not always indicate specific brain locations.—Author’s abstract