Structural brain alterations in primary open angle glaucoma: a 3T MRI study

Elevated Intraocular Pressure Moderated Brain Morphometry in High-tension Glaucoma: a Structural MRI Study

High-tension glaucoma (HTG) is one of the most common forms of primary open angle glaucoma. The purpose of this study was to assess in HTG brain, whether the elevated intraocular pressure (IOP) had an effect on the brain morphological alterations via structural MRI. We acquired T1WI structural MRI images from 56 subjects including 36 HTG patients and 20 healthy controls. We tested whether the brain morphometry was associated with the mean IOP in HTG patients. Moreover, we conducted moderation analysis to assess the interactions between subject type (HTG - healthy controls) and IOP. In HTG group, cortical thickness was negatively correlated with the mean IOP in the left rostral middle frontal gyrus, left pars triangularis, right precentral gyrus, left postcentral gyrus, left superior temporal gyrus (p < 0.05, FDR corrected). Four of the five regions negatively correlated with mean IOP showed reduced cortical thickness in HTG group compared with healthy controls, which were the left rostral middle frontal gyrus, left pars triangularis, left postcentral gyrus and left superior temporal gyrus (p < 0.05, FDR corrected). IOP moderated the interaction between subject type and cortical thickness of the left rostral middle frontal gyrus (p = 0.0017), left pars triangularis (p = 0.0011), left postcentral gyrus (p = 0.0040) and left superior temporal gyrus (p = 0.0066). Elevated IOP may result brain morphometry alterations such as cortical thinning. The relationship between IOP and brain morphometry underlines the importance of the IOP regulation for HTG patients.

Ability to Process Multisensory Information Is Impaired in Open Angle Glaucoma

PRCIS

Patients with glaucoma demonstrated deficiencies in their ability to process multisensory information when compared with controls, with those deficiencies being related to glaucoma severity. Impaired multisensory integration (MSI) may affect the quality of life in individuals with glaucoma and may contribute to the increased prevalence of falls and driving safety concerns. Therapeutic possibilities to influence cognition in glaucoma should be explored.

PURPOSE

Glaucoma is a neurodegenerative disease of the optic nerve that has also been linked to cognitive health decline. This study explored MSI as a function of glaucoma status and severity.

METHODS

MSI was assessed in 37 participants with open angle glaucoma relative to 18 age-matched healthy controls. The sound-induced flash illusion was used to assess MSI efficiency. Participants were presented with various combinations of simultaneous visual and/or auditory stimuli and were required to indicate the number of visual stimuli observed for each of the 96 total presentations. Central retinal sensitivity was assessed as an indicator of glaucoma severity (MAIA; CenterVue).

RESULTS

Participants with glaucoma performed with equivalent capacity to healthy controls on unisensory trials ( F1,53 =2.222, P =0.142). Both groups performed equivalently on congruent multisensory trials involving equal numbers of auditory and visual stimuli F1,53 =1.032, P =0.314). For incongruent presentations, that is, 2 beeps and 1 flash stimulus, individuals with glaucoma demonstrated a greater influence of the incongruent beeps when judging the number of flashes, indicating less efficient MSI relative to age-matched controls ( F1,53 =11.45, P <0.002). In addition, MSI performance was positively correlated with retinal sensitivity ( F3,49 =4.042, P <0.025), adjusted R ²=0.15).

CONCLUSIONS

Individuals with open angle glaucoma exhibited MSI deficiencies that relate to disease severity. The type of deficiencies observed were similar to those observed among older individuals with cognitive impairment and balance issues. Impaired MSI may, therefore, be relevant to the increased prevalence of falls observed among individuals with glaucoma, a concept that merits further investigation.

Abnormal Topological Organization of White Matter Structural Networks in Normal Tension Glaucoma Revealed via Diffusion Tensor Tractography

BACKGROUND

Normal tension glaucoma (NTG) is considered a neurodegenerative disease with glaucomatous damage extending to diffuse brain areas. Therefore, this study aims to explore the abnormalities in the NTG structural network to help in the early diagnosis and course evaluation of NTG.

METHODS

The structural networks of 46 NTG patients and 19 age- and sex-matched healthy controls were constructed using diffusion tensor imaging, followed by graph theory analysis and correlation analysis of small-world properties with glaucoma clinical indicators. In addition, the network-based statistical analysis (NBS) method was used to compare structural network connectivity differences between NTG patients and healthy controls.

RESULTS

Structural brain networks in both NTG and NC groups exhibited small-world properties. However, the small-world index in the severe NTG group was reduced and correlated with a mean deviation of the visual field (MDVF) and retinal nerve fiber layer (RNFL) thickness. When compared to healthy controls, degree centrality and nodal efficiency in visual brain areas were significantly decreased, and betweenness centrality and nodal local efficiency in both visual and nonvisual brain areas were also significantly altered in NTG patients (all p < 0.05, FDR corrected). Furthermore, NTG patients exhibited increased structural connectivity in the occipitotemporal area, with the left fusiform gyrus (FFG.L) as the hub (p < 0.05).

CONCLUSIONS

NTG exhibited altered global properties and local properties of visual and cognitive-emotional brain areas, with enhanced structural connections within the occipitotemporal area. Moreover, the disrupted small-world properties of white matter might be imaging biomarkers for assessing NTG progression.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Disentangling the genetic overlap and causal relationships between primary open-angle glaucoma, brain morphology and four major neurodegenerative disorders

BACKGROUND

Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by progressive degeneration of the optic nerve that leads to irreversible visual impairment. Multiple epidemiological studies suggest an association between POAG and major neurodegenerative disorders (Alzheimer's disease, amyotrophic lateral sclerosis, frontotemporal dementia, and Parkinson's disease). However, the nature of the overlap between neurodegenerative disorders, brain morphology and glaucoma remains inconclusive.

METHOD

In this study, we performed a comprehensive assessment of the genetic and causal relationship between POAG and neurodegenerative disorders, leveraging genome-wide association data from studies of magnetic resonance imaging of the brain, POAG, and four major neurodegenerative disorders.

FINDINGS

This study found a genetic overlap and causal relationship between POAG and its related phenotypes (i.e., intraocular pressure and optic nerve morphology traits) and brain morphology in 19 regions. We also identified 11 loci with a significant local genetic correlation and a high probability of sharing the same causal variant between neurodegenerative disorders and POAG or its related phenotypes. Of interest, a region on chromosome 17 corresponding to MAPT, a well-known risk locus for Alzheimer's and Parkinson's disease, was shared between POAG, optic nerve degeneration traits, and Alzheimer's and Parkinson's diseases. Despite these local genetic overlaps, we did not identify strong evidence of a causal association between these neurodegenerative disorders and glaucoma.

INTERPRETATION

Our findings indicate a distinctive and likely independent neurodegenerative process for POAG involving several brain regions although several POAG or optic nerve degeneration risk loci are shared with neurodegenerative disorders, consistent with a pleiotropic effect rather than a causal relationship between these traits.

FUNDING

PG was supported by an NHMRC Investigator Grant (#1173390), SM by an NHMRC Senior Research Fellowship and an NHMRC Program Grant (APP1150144), DM by an NHMRC Fellowship, LP is funded by the NEIEY015473 and EY032559 grants, SS is supported by an NIH-Oxford Cambridge Fellowship and NIH T32 grant (GM136577), APK is supported by a UK Research and Innovation Future Leaders Fellowship, an Alcon Research Institute Young Investigator Award and a Lister Institute for Preventive Medicine Award.

An Association Between Large Optic Cupping and Total and Regional Brain Volume: The Women's Health Initiative

PURPOSE

To investigate the relationships between optic nerve cupping and total and regional brain volumes.

DESIGN

Secondary analysis of randomized clinical trial data.

METHODS

Women 65 to 79 years of age without glaucoma with cup-to-disc ratio (CDR) measurements from the Women's Health Initiative (WHI) Sight Examination study and magnetic resonance imaging (MRI)-based total and regional brain volumes from the WHI Memory Study MRI-1 were included. Large CDR was defined as 0.6 or greater in either eye. Generalized estimating equation models were used to account for intra-brain correlations between the right and left sides. The final analysis was adjusted for demographic and clinical characteristics and for total brain volume (for regional analyses).

RESULTS

Final analyses included 471 women, with the mean age ± SD was 69.2 ± 3.6 years; 92.8% of the subjects were white. Of 471 women, 34 (7.2%) had large CDR. Controlling for total brain volume and for demographic and clinical characteristics, lateral ventricle volume was 3.01 cc larger for subjects with large CDR compared to those without large CDR (95% CI = 0.02 to 5.99; P = .048). Furthermore, frontal lobe volume was 4.78 cc lower for subjects with large CDR compared to those without (95% CI = -8.71, -0.84; P = 0.02), and occipital lobe volume was 1.86 cc lower for those with large CDR compared to those without (95% CI = -3.39, -0.3; P =.02).

CONCLUSIONS

Our analysis suggests that in women aged 65 years or more, large CDR is associated with lower relative total brain volume and absolute regional volume in the frontal and occipital lobes. Enlarged CDR in individuals without glaucoma may represent a sign of optic nerve and brain aging, although more longitudinal data are needed.

Impact of glaucoma on the spatial frequency processing of scenes in central vision

Glaucoma is an eye disease characterized by a progressive vision loss usually starting in peripheral vision. However, a deficit for scene categorization is observed even in the preserved central vision of patients with glaucoma. We assessed the processing and integration of spatial frequencies in the central vision of patients with glaucoma during scene categorization, considering the severity of the disease, in comparison to age-matched controls. In the first session, participants had to categorize scenes filtered in low-spatial frequencies (LSFs) and high-spatial frequencies (HSFs) as a natural or an artificial scene. Results showed that the processing of spatial frequencies was impaired only for patients with severe glaucoma, in particular for HFS scenes. In the light of proactive models of visual perception, we investigated how LSF could guide the processing of HSF in a second session. We presented hybrid scenes (combining LSF and HSF from two scenes belonging to the same or different semantic category). Participants had to categorize the scene filtered in HSF while ignoring the scene filtered in LSF. Surprisingly, results showed that the semantic influence of LSF on HSF was greater for patients with early glaucoma than controls, and then disappeared for the severe cases. This study shows that a progressive destruction of retinal ganglion cells affects the spatial frequency processing in central vision. This deficit may, however, be compensated by increased reliance on predictive mechanisms at early stages of the disease which would however decline in more severe cases.

Altered dynamic functional connectivity in the primary visual cortex in patients with primary angle-closure glaucoma

Purpose

Glaucoma is the main blindness-causing disease in the world. Previous neuroimaging studies demonstrated that glaucoma not only causes the loss of optic ganglion cells but also leads to the abnormal function of the optic nerve pathway and the visual cortex. However, previous studies also reported that patients with glaucoma have dysfunction in the visual cortex in a static state. Whether or not patients with primary angle-closure glaucoma (PACG) were accompanied by dynamic functional connectivity (FC) changes in the primary visual cortex (V1) remains unknown.

Methods

A total of 34 patients with PACG (23 men and 11 women) and 34 well-matched healthy controls (HCs) were enrolled in the study. The dynamic functional connectivity (dFC) with the sliding window method was applied to investigate the dynamic functional connectivity changes in the V1.

Results

Compared with HCs, patients with PACG showed increased dFC values between left V1 and bilateral calcarine (CAL). Meanwhile, patients with PACG showed increased dFC values between right V1 and bilateral CAL.

Conclusion

Our study demonstrated that patients with PACG showed increased dFC within the visual network, which might indicate the increased variability FC in the V1 in patients with PACG.

Genetic Factors Implicated in the Investigation of Possible Connections between Alzheimer's Disease and Primary Open Angle Glaucoma

Both Alzheimer's disease (AD) and primary open angle glaucoma (POAG) are diseases of primary global neurodegeneration with complex pathophysiologies. Throughout the published literature, researchers have highlighted similarities associated with various aspects of both diseases. In light of the increasing number of findings reporting resemblance between the two neurodegenerative processes, scientists have grown interested in possible underlying connections between AD and POAG. In the search for explanations to fundamental mechanisms, a multitude of genes have been studied in each condition, with overlap in the genes of interest between AD and POAG. Greater understanding of genetic factors can drive the research process of identifying relationships and elucidating common pathways of disease. These connections can then be utilized to advance research as well as to generate new clinical applications. Notably, AD and glaucoma are currently diseases with irreversible consequences that often lack effective therapies. An established genetic connection between AD and POAG would serve as the basis for development of gene or pathway targeted strategies relevant to both diseases. Such a clinical application could be of immense benefit to researchers, clinicians, and patients alike. This paper aims to summarize the genetic associations between AD and POAG, describe common underlying mechanisms, discuss potential areas of application, and organize the findings in a review.

Microglia activation in the hippocampus mediates retinal degeneration-induced depressive-like behaviors via the NLRP3/IL-1β pathway

Epidemiological studies have shown that patients with glaucoma are more prone to depression, but the mechanism of comorbid depression in patients with glaucoma remains unknown. Excessive neuroinflammation has been shown to participate in glaucoma-induced retinal degeneration and hippocampal neural apoptosis in depression. However, little research has been conducted to determine whether neuroinflammation contributes to glaucoma-induced depression. Since the degeneration of retinal ganglion cells is a hallmark of glaucoma, we investigated the role of microglia-induced neuroinflammation in retinal degeneration-induced depression and its potential mechanism. An N-methyl-D-aspartate (NMDA)-induced retinal degeneration model was established, and behavioral tests were conducted at 3, 7, 14, and 21 days after retinal degeneration. After tissue collection, we used immunohistochemistry to assess the activation of microglia and real-time polymerase chain reaction to measure the levels of pro-inflammatory cytokines and the NOD-, LRR-, and pyrin-domain containing protein 3 (NLRP3) inflammasome. The mice exhibited depressive-like behaviors 14 and 21 days after retinal degeneration, based on the open field test, tail suspension test, and forced swimming test. Mice also displayed a lower body weight gain than the control group. In addition, microglial activation was observed in the hippocampus. Microglial proliferation was first observed in the dentate gyrus on day 3, while the number of microglia in cornu ammonis 1 grew the most. Moreover, not only was the expression of pro-inflammatory cytokines, including interleukin-1β, interleukin-18, and interleukin-6 promoted, but the messenger ribonucleic acid levels of the NLRP3 inflammasome were also increased. In conclusion, our research shows that NMDA-induced retinal degeneration can induce depressive-like behaviors, which may be attributed to hippocampal neuroinflammation.

Activation of lesion projection zone in primary visual cortex is dependent on bilateral central vision loss in patients with end-stage glaucoma

PURPOSE

To investigate activation of the lesion projection zone (LPZ) in the primary visual cortex during end-stage glaucoma using functional magnetic resonance imaging (fMRI), as well as the relationship between fMRI responses and clinical data.

METHODS

Twelve subjects with bilateral end-stage glaucoma (group A), 12 with unilateral end-stage glaucoma (group B) and 12 healthy controls (group C) were enrolled. fMRI was performed under two testing stimuli conditions: passive viewing of a full-field flickering checkerboard and active viewing of a one-back task with scene images. In fMRI analysis, the primary visual cortex was divided into six regions of interest (ROIs). The beta values of the six ROIs were compared across the three groups using one-way analysis of variance under two viewing conditions. Associations between the fMRI beta value and clinical data including multifocal electroretinogram (mfERG), microperimeter-1 and optical coherence tomography were analysed by Spearman correlation.

RESULTS

The beta values for ROIs 1-3 representing the LPZ were significantly different between the three groups under active viewing conditions, whereas no significant changes were detected under passive viewing. In group A, there were significant differences between all six ROIs for the two viewing conditions, while no significant differences were found in groups B and C. In group A, the P-wave amplitudes of the mfERG was significantly correlated with the beta values of ROIs 1 and 2 under active viewing. In addition, the P-wave latencies of the mfERG were significantly correlated with the beta values for ROIs 2-5. No associations were found between fMRI beta values and clinical data in groups B and C.

CONCLUSIONS

Activation of the LPZ in the primary visual cortex was observed in patients with bilateral end-stage glaucoma under active viewing conditions. These changes were correlated with residual retinal function.

Reduced brain subcortical volumes in patients with glaucoma: a pilot neuroimaging study using the region-of-interest-based approach

Background

While numerous neuroimaging studies have demonstrated that glaucoma is associated with smaller volumes of the visual cortices in the brain, only a few studies have linked glaucoma with brain structures beyond the visual cortices. Therefore, the objective of this study was to compare brain imaging markers and neuropsychological performance between individuals with and without glaucoma.

Methods

We identified 64 individuals with glaucoma and randomly selected 128 age-, sex-, and education level-matched individuals without glaucoma from a community-based cohort. The study participants underwent 3 T brain magnetic resonance imaging and neuropsychological assessment battery. Regional cortical thickness and subcortical volume were estimated from the brain images of the participants. We used a linear mixed model after adjusting for potential confounding variables.

Results

Cortical thickness in the occipital lobe was significantly smaller in individuals with glaucoma than in the matched individuals (β = − 0.04 mm, P = 0.014). This did not remain significant after adjusting for cardiovascular risk factors (β = − 0.02 mm, P = 0.67). Individuals with glaucoma had smaller volumes of the thalamus (β = − 212.8 mm³, P = 0.028), caudate (β = − 170.0 mm³, P = 0.029), putamen (β = − 151.4 mm³, P = 0.051), pallidum (β = − 103.6 mm³, P = 0.007), hippocampus (β = − 141.4 mm³, P = 0.026), and amygdala (β = − 87.9 mm³, P = 0.018) compared with those without glaucoma. Among neuropsychological battery tests, only the Stroop color reading test  score was significantly lower in individuals with glaucoma compared with those without glaucoma (β = − 0.44, P = 0.038).

Conclusions

We found that glaucoma was associated with smaller volumes of the thalamus, caudate, putamen, pallidum, amygdala, and hippocampus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02807-x.

Study of normal-tension glaucoma based on OCTA and VBM-DARTEL analysis

The aim of the present study was to investigate the detection value of optical coherence tomography angiography (OCTA) and voxel-based morphometry with diffeomorphic anatomical registration through exponentiated lie algebra (VBM-DARTEL) in normal-tension glaucoma (NTG), as well as the correlation between the two functional indicators. A total of 30 patients (15 males, 15 females) with NTG and 30 (15 males, 15 females) age-, sex- and education-matched healthy controls underwent OCTA and 3.0 T MRI scanning. The OCTA technique was used to scan the optic disc area of all subjects and measure the density of blood vessels around the optic disc; 3.0 T MRI scanning was used to obtain MRI images of the brain structure and the VBM-DARTEL method was applied for image processing using Matlab7.11R2010b (MathWorks). Imaging data were compared between the groups using two-samples t-tests to identify differences in the density of blood vessels around the optic disc and the change in brain parenchyma. Correlation analysis was used to explore associations between the density of blood vessels around the optic disc and the change in brain parenchyma in NTG. The results indicated that the vascular density around the optic disc in the NTG group was significantly decreased compared with that in the control group; the vascular density was decreased with disease progression. The difference between the two groups was statistically significant (P<0.05). The VBM-DARTEL analysis indicated that the volume of the left middle frontal gyrus, right superior frontal gyrus, right precuneus, right angular gyrus and right middle occipital gyrus was decreased, whereas the volume of the right anterior central gyrus was increased. The area under the receiver operating characteristic curve for the local volume difference in brain parenchyma to predict the diagnosis of NTG was >0.7. The area of brain parenchyma reduction was positively correlated with the density of blood vessels around the optic disc (P<0.05), whereas the right anterior central gyrus was negatively correlated with vascular density. In conclusion, OCTA and VBM-DARTEL technology may facilitate non-invasive monitoring of changes in NTG structure and function, and provide non-invasive diagnostic imaging support in the early stage of the disease. These advantages are of great importance in the diagnosis and follow-up of NTG.

MRI findings suggestive of Alzheimer's disease in patients with primary open angle glaucoma - a single sequence analysis using rapid 3D T1 spoiled gradient echo

OBJECTIVE

Primary open-angle glaucoma (POAG) is a degenerative optic neuropathy disease which has somewhat similar pathophysiology to Alzheimer's disease (AD). This study aims to determine the presence of medial temporal atrophy and parietal lobe atrophy in patients with POAG compared to normal controls using medial temporal atrophy (MTA) scoring and posterior cortical atrophy (PCA) scoring system on T1 magnetization-prepared rapid gradient-echo.

METHODS

50 POAG patients and 50 normal subjects were recruited and an MRI brain with T1-magnetization-prepared rapid gradient-echo was performed. Medial temporal lobe and parietal lobe atrophy were by MTA and PCA/Koedam scoring. The score of the PCA and MTA were compared between the POAG group and the controls.

RESULTS

There was a significant statistical difference between PCA score in POAG and the healthy control group (p-value = 0.026). There is no statistical difference between MTA score in POAG compared to the healthy control group (p-value = 0.58).

CONCLUSION

This study suggests a correlation between POAG and PCA score. Potential application of this scoring method in clinical diagnosis and monitoring of POAG patients.

ADVANCES IN KNOWLEDGE

The scoring method used in AD may also be applied in the diagnosis and monitoring of POAGMRI brain, specifically rapid volumetric T1 spoiled gradient echo sequence, may be applied in POAG assessment.

Characteristics of the Fractional Amplitude of Low-Frequency Fluctuation in Ocular Hypertension Patients: A Resting-State fMRI Study

Background

The fractional amplitude of low-frequency fluctuation (fALFF) method has been underutilized in research on the pathogenesis and clinical manifestations of ocular hypertension (OH).

Purpose

This study uses resting state functional magnetic resonance imaging (rs-fMRI) and fALFF to investigate the nature of spontaneous brain activity in OH patients and the relationship, if any, between changes in activity and clinical features.

Materials and Methods

A total of 18 subjects (9 females and 9 males) with ocular hypertension (OH) and 18 healthy controls (HCs) matched for gender, age, and educational level were recruited to this study. All participants underwent an rs-fMRI scan, and spontaneous brain activity was assessed using the fALFF method. Receiver operating characteristic curves were plotted to investigate differences between OH and HC groups.

Results

The fALFF values of OH patients were significantly higher in the left precuneus lobe (LP), compared with the same region in controls (P < 0.05). Conversely, values in the left anterior cingulate lobe (LAC), were significantly lower (P < 0.05) in OH than in controls. However, no significant association was found between the mean fALFF values and clinical characteristics in either brain area.

Conclusion

High spontaneous activity in two brain areas may reflect neuropathological mechanisms underpinning visual impairment in OH patients.

Anatomical Evidence for the Neural Connection from the Emotional Brain to Autonomic Innervation in the Anterior Chamber Structures of the Eye

OBJECTIVE

Previous studies have shown that the autonomic nervous system (ANS), which can be affected by emotions, is important in the occurrence or progression of glaucoma. The autonomic innervation distributed in the anterior chamber (AC) structures might play an efferent role in the neural regulation of intraocular pressure (IOP). This study aimed to investigate the anatomic neural connection from the emotional brain to autonomic innervation in the AC.

METHODS

A retrograde trans-multisynaptic pseudorabies virus encoded with an enhanced green fluorescent protein (PRV531) and non-trans-synaptic tracer FAST Dil were injected into the right eye of mice, respectively. Fluorescent localization in the emotional brain and preganglionic nuclei was studied. Five and a half days after PRV531 injection into the right AC, fluorescent signals were observed in several emotional brain regions, including the amygdala, agranular insular cortex, lateral septal nuclei, periaqueductal gray, and hypothalamus. Autonomic preganglionic nuclei, including Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus, were labeled using PRV531.

RESULTS

The sensory trigeminal nuclei were not labeled using PRV531. The fluorescence signals in the nuclei mentioned above showed bilateral distribution, primarily on the ipsilateral side. Seven days after injecting FAST Dil into the AC, we observed no FAST Dil-labeled neurons in the central nervous system.

CONCLUSION

Our results indicate a neural connection from the emotional brain to autonomic innervation in the AC, which provides anatomical support for the emotional influence of IOP via the ANS.

Visual Tract Degradation in Bilateral Normal-Tension Glaucoma-Cortical Thickness Maps and Volumetric Study of Visual Pathway Areas

The aim of the study was to evaluate changes in the central visual pathways during the early and advanced stages of bilateral normal-tension glaucoma (NTG).

METHODS

The studied groups constituted patients with bilateral normal-tension glaucoma of the same stage (n = 45) and age-matched healthy volunteers (n = 17). All patients underwent ophthalmic examination and examination on a 1.5 Tesla Magnetic Resonance Scanner (Optima 360, GE Healthcare). Volume and cortical thickness analyses were performed using the open-source automated software package FreeSurfer.

RESULTS

There was a significant difference in lateral geniculate nuclei volume between the control and advanced glaucoma groups in the right hemisphere (p = 0.03) and in the left hemisphere between the early and advanced glaucoma patients (p = 0.026). The optic chiasm volume differed significantly between the control and advanced NTG groups (p = 0.0003) and between early and advanced glaucoma patients (p = 0.004). Mean cortical thickness analysis revealed a significant increase in values in the advanced glaucoma group in the right Brodmann area 17 (BA17) (p = 0.007) and right BA18 (p = 0.049) as compared to early NTG. In the left BA18 area, the mean thickness of the cortex in the early glaucoma group was significantly lower than in the control group (p = 0.03).

CONCLUSIONS

The increase in the grey matter thickness in the V1 region with more-advanced glaucoma stages may reflect compensatory hypertrophy. Additionally, the regions of the brain early affected during glaucoma with reduced thickness were the right lateral occipital gyrus and left lingual gyrus. The most prominent change during the course of glaucoma was the increase in grey matter thickness in the right cuneus.

Advanced Diffusion MRI of the Visual System in Glaucoma: From Experimental Animal Models to Humans

Glaucoma is a group of ophthalmologic conditions characterized by progressive retinal ganglion cell death, optic nerve degeneration, and irreversible vision loss. While intraocular pressure is the only clinically modifiable risk factor, glaucoma may continue to progress at controlled intraocular pressure, indicating other major factors in contributing to the disease mechanisms. Recent studies demonstrated the feasibility of advanced diffusion magnetic resonance imaging (dMRI) in visualizing the microstructural integrity of the visual system, opening new possibilities for non-invasive characterization of glaucomatous brain changes for guiding earlier and targeted intervention besides intraocular pressure lowering. In this review, we discuss dMRI methods currently used in visual system investigations, focusing on the eye, optic nerve, optic tract, subcortical visual brain nuclei, optic radiations, and visual cortex. We evaluate how conventional diffusion tensor imaging, higher-order diffusion kurtosis imaging, and other extended dMRI techniques can assess the neuronal and glial integrity of the visual system in both humans and experimental animal models of glaucoma, among other optic neuropathies or neurodegenerative diseases. We also compare the pros and cons of these methods against other imaging modalities. A growing body of dMRI research indicates that this modality holds promise in characterizing early glaucomatous changes in the visual system, determining the disease severity, and identifying potential neurotherapeutic targets, offering more options to slow glaucoma progression and to reduce the prevalence of this world's leading cause of irreversible but preventable blindness.

Application of advanced magnetic resonance imaging in glaucoma: a narrative review

Glaucoma is a group of eye diseases characterized by progressive degeneration of the optic nerve head and retinal ganglion cells and corresponding visual field defects. In recent years, mounting evidence has shown that glaucoma-related damage may not be limited to the degeneration of retinal ganglion cells or the optic nerve head. The entire structure of the visual pathway may be degraded, and the degradation may even extend to some non-visual brain regions. We know that advanced morphological, functional, and metabolic magnetic resonance technologies provide a means to observe quantitatively and in real time the state of brain function. Advanced magnetic resonance imaging (MRI) techniques provide additional diagnostic markers for glaucoma, which are related to known potential histopathological changes. Many researchers in China and globally have conducted clinical and imaging studies on glaucoma. However, they are scattered, and we still need to systematically sort out the advanced MRI related to glaucoma. We reviewed literature published in any language and included all studies that were able to be translated into English from 1 January 1980 to 31 July 2021. Our literature search focused on emerging magnetic resonance neuroimaging techniques for the study of glaucoma. We then identified each functional area of the brain of glaucoma patients through the integration of anatomy, image, and function. The aim was to provide more information about the occurrence and development of glaucoma diseases. From the perspective of neuroimaging, our study provides a research basis to explain the possible mechanism of the occurrence and development of glaucoma. This knowledge gained from these techniques enables us to more clearly observe the damage glaucoma causes to the whole visual pathway. Our study provides new insights into glaucoma-induced changes to the brain. Our findings may enable the progress of these changes to be analyzed and inspire new neuroprotective therapeutic strategies for patients with glaucoma in the future.

Adaptive and maladaptive brain functional network reorganization after stroke in hemianopia patients: an EEG-tracking study

OBJECTIVE

Hemianopia following occipital stroke is believed to be mainly due to local damage at or near the lesion site. Yet, MRI studies suggest functional connectivity network (FCN) reorganization also in distant brain regions. Because it is unclear if reorganization is adaptive or maladaptive, compensating for, or aggravating vision loss, we characterized FCNs electrophysiologically to explore local and global brain plasticity and correlated FCN reorganization with visual performance.

METHODS

Resting-state EEG was recorded in chronic, unilateral stroke patients and healthy age-matched controls (n=24 each). The correlation of oscillating EEG activity was calculated with the imaginary part of coherence between pairs of interested regions, and FCN graph theory metrics (degree, strength, clustering coefficient) were correlated with stimulus detection and reaction time.

RESULTS

Stroke brains showed altered FCNs in the alpha- and beta-band in numerous occipital, temporal and frontal brain structures. On a global level, FCN had a less efficient network organization while on the local level node networks reorganized especially in the intact hemisphere. Here, the occipital network was 58% more rigid (with a more "regular" network structure) while the temporal network was 32% more efficient (showing greater "small-worldness"), both of which correlated with worse or better visual processing, respectively.

CONCLUSIONS

Occipital stroke is associated with both local and global FCN reorganization, but this can be both, adaptive and maladaptive. We propose that the more "regular" FCN structure in the intact visual cortex indicates maladaptive plasticity where less processing efficacy with reduced signal/noise ratio may cause perceptual deficits in the intact visual field. In contrast, reorganization in intact temporal brain regions is presumably adaptive, possibly supporting enhanced peripheral movement perception.

Visual cortex damage in a ferret model of ocular hypertension

PURPOSE

We aimed to analyze the changes in the visual cortex of a ferret model of ocular hypertension (OH) using cytochrome oxidase (CO) staining.

STUDY DESIGN

Experimental.

METHODS

OH was induced in 9 ferrets by means of injection of cultured conjunctival cells into the anterior chamber of the right eye. Three ferrets were used as the controls. CO staining was performed to assess the metabolic intensity at the II-III and IVC layers of the visual cortex.

RESULTS

The intensities of CO staining in the right and left II-III layers of the primary visual cortex (V1) in the OH ferrets were 39.8 ± 10.3 and 41.9 ± 9.2 arbitrary units, respectively. In the control ferrets, the intensity was 88.1 ± 8.1 arbitrary units. The intensity of CO staining of the II-III layers obtained from the OH eyes was significantly lower than that from the control eyes (unpaired t test, P < .01). The intensities of CO staining in the right and left IVC layers of V1 in the OH ferrets were 60.3 ± 12.8 and 60.0 ± 13.5 arbitrary units, respectively. In the control ferrets, the intensity was 111.4 ± 9.6 arbitrary units. The CO staining intensity of the IVC layer obtained from the OH eyes was significantly lower than that from the control eyes (unpaired t test, P < .01).

CONCLUSION

The CO staining intensity was reduced in the visual cortex from OH eyes. This study revealed that OH causes metabolic change in the visual cortex.

Binocular Integrated Visual Field Deficits Are Associated With Changes in Local Network Function in Primary Open-Angle Glaucoma: A Resting-State fMRI Study

In glaucoma participants, both structural and functional brain changes have been observed, but we still have insufficient understanding of how these changes also affect the integrity of cortical functional networks, and how these changes relate to visual function. This is relevant, as functional network integrity may affect the applicability of future treatments, as well as the options for rehabilitation or training. Here, we compare global and local functional connectivity in local and global brain networks between glaucoma and control participants. Moreover, we study the relationship between functional connectivity and visual field (VF) loss. For our study, 20 subjects with primary open-angle glaucoma (POAG) and 24 age-similar healthy participants were recruited to undergo an ophthalmic assessment followed by two resting-state (RS) (f)MRI scans. For each scan and for each group, the ROIs with eigenvector centrality (EC) values higher than the 95th percentile were considered the most central brain regions (“hubs”). Hubs for which we found a significant difference in EC in both scans between glaucoma and healthy participants were considered to provide evidence for network changes. In addition, we tested the notion that a brain region's hub function in POAG might relate to the severity of a participant's VF defect, irrespective of which eye contributed mostly to this. To determine this, for each participant, eye-independent scores were derived for: (1) sensitivity of the worse eye – indicating disease severity, (2) sensitivity of both eyes combined – with one eye potentially compensating for loss in the other, or (3) difference in eye sensitivity – potentially requiring additional network interactions. By correlating each of these VF scores and the EC values, we assessed whether VF defects could be associated with centrality alterations in POAG. Our results show that no functional connectivity disruptions were found at the global brain level in POAG participants. This indicates that in glaucoma global brain network communication is preserved. Furthermore, for the Lingual Gyrus, identified as a brain hub, we found a positive correlation between the EC value and the VF sensitivity of both eyes combined. The fact that reduced local network functioning is associated with reduced binocular VF sensitivity suggests the presence of local brain reorganization that has a bearing on functional visual abilities.

Improving the Quantification of the Lateral Geniculate Nucleus in Magnetic Resonance Imaging Using a Novel 3D-Edge Enhancement Technique

The lateral geniculate nucleus (LGN) is a small, inhomogeneous structure that relays major sensory inputs from the retina to the visual cortex. LGN morphology has been intensively studied due to various retinal diseases, as well as in the context of normal brain development. However, many of the methods used for LGN structural evaluations have not adequately addressed the challenges presented by the suboptimal routine MRI imaging of this structure. Here, we propose a novel method of edge enhancement that allows for high reliability and accuracy with regard to LGN morphometry, using routine 3D-MRI imaging protocols. This new algorithm is based on modeling a small brain structure as a polyhedron with its faces, edges, and vertices fitted with one plane, the intersection of two planes, and the intersection of three planes, respectively. This algorithm dramatically increases the contrast-to-noise ratio between the LGN and its surrounding structures as well as doubling the original spatial resolution. To show the algorithm efficacy, two raters (MA and ML) measured LGN volumes bilaterally in 19 subjects using the edge-enhanced LGN extracted areas from the 3D-T1 weighted images. The averages of the left and right LGN volumes from the two raters were 175 ± 8 and 174 ± 9 mm³, respectively. The intra-class correlations between raters were 0.74 for the left and 0.81 for the right LGN volumes. The high contrast edge-enhanced LGN images presented here, from a 7-min routine 3T-MRI acquisition, is qualitatively comparable to previously reported LGN images that were acquired using a proton density sequence with 30–40 averages and 1.5-h of acquisition time. The proposed edge-enhancement algorithm is not limited only to the LGN, but can significantly improve the contrast-to-noise ratio of any small deep-seated gray matter brain structure that is prone to high-levels of noise and partial volume effects, and can also increase their morphometric accuracy and reliability. An immensely useful feature of the proposed algorithm is that it can be used retrospectively on noisy and low contrast 3D brain images previously acquired as part of any routine clinical MRI visit.

Slowed Saccadic Reaction Times in Seemingly Normal Parts of Glaucomatous Visual Fields

Purpose: In eye movement perimetry, peripheral stimuli are confirmed by goal-directed eye movements toward the stimulus. The saccadic reaction time (SRT) is regarded as an index of visual field responsiveness, whereas in standard automated perimetry (SAP), the visual field sensitivity is tested. We investigated the relation between visual field sensitivity and responsiveness in corresponding locations of the visual field in healthy controls and in patients with mild, moderate and advanced glaucoma.

Materials and Methods: Thirty-four healthy control subjects and 42 glaucoma patients underwent a 54-point protocol in eye movement perimetry (EMP) and a 24-2 SITA standard protocol in a Humphrey Field Analyzer. The visual field points were stratified by total deviation sensitivity loss in SAP into 6 strata. A generalized linear mixed model was applied to determine the influence of the various factors.

Results: The generalized linear mixed model showed that the mean SRT increased with increasing glaucoma severity, from 479 ms in the control eyes to 678 ms in the eyes of patients with advanced glaucoma (p < 0.001). Mean SRTs significantly increased with increasing SAP sensitivity loss. Even at the locations where no sensitivity loss was detected by SAP (total deviation values greater or equal than 0 dB), we found lengthened SRTs in mild, moderate and advanced glaucoma compared to healthy controls (p < 0.05) and in moderate and advanced glaucoma compared to mild glaucoma (p < 0.05). At locations with total deviation values between 0 and −3 dB, −3 and −6 dB and −6 and −12 dB, we found similar differences.

Conclusions: The lengthened SRT in areas with normal retinal sensitivities in glaucomatous eyes, i.e., planning and execution of saccades to specific locations, precede altered sensory perception as assessed with SAP. Better understanding of altered sensory processing in glaucoma might allow earlier diagnosis of emerging glaucoma.

Functional Dynamics of Deafferented Early Visual Cortex in Glaucoma

In advanced retinitis pigmentosa with retinal lesions, the lesion projection zone (LPZ) in the early visual cortex can be driven during visual tasks, while it remains unresponsive during passive viewing. We tested whether this finding translates to advanced glaucoma, a major cause of acquired blindness. During visual stimulation, 3T fMRI scans were acquired for participants with advanced glaucoma (n = 4; age range: 51–72) and compared to two reference groups, i.e., advanced retinitis pigmentosa (n = 3; age range: 46–78) and age-matched healthy controls with simulated defects (n = 7). The participants viewed grating patterns drifting in 8 directions (12 s) alternating with uniform gray (12 s), either during passive viewing (PV), i.e., central fixation, or during a one-back task (OBT), i.e., reports of succeeding identical motion directions. As another reference, a fixation-dot task condition was included. Only in glaucoma and retinitis pigmentosa but not in controls, fMRI-responses in the lesion projection zone (LPZ) of V1 shifted from negative for PV to positive for OBT (p = 0.024 and p = 0.012, respectively). In glaucoma, these effects also reached significance in V3 (p = 0.006), while in V2 there was a non-significant trend (p = 0.069). The general absence of positive responses in the LPZ during PV underscores the lack of early visual cortex bottom-up plasticity for acquired visual field defects in humans. Trends in our exploratory analysis suggesting the task-dependent LPZ responses to be inversely related to visual field loss, indicate the benefit of patient stratification strategies in future studies with greater sample sizes. We conclude that top-down mechanisms associated with task-elicited demands rather than visual cortex remapping appear to shape LPZ responses not only in retinitis pigmentosa, but also in glaucoma. These insights are of critical importance for the development of schemes for treatment and rehabilitation in glaucoma and beyond.

Monitoring the haemodynamic response to visual stimulation in glaucoma patients

In this paper, we used time-domain functional near infrared spectroscopy (TD-fNIRS) to evaluate the haemodynamic response function (HRF) in the occipital cortex following visual stimulation in glaucomatous eyes as compared to healthy eyes. A total of 98 subjects were enrolled in the study and clinically classified as healthy subjects, glaucoma patients (primary open-angle glaucoma) and mixed subjects (i.e. with a different classification for the two eyes). After quality check data were used from HRF of 73 healthy and 62 glaucomatous eyes. The amplitudes of the oxygenated and deoxygenated haemoglobin concentrations, together with their latencies with respect to the stimulus onset, were estimated by fitting their time course with a canonical HRF. Statistical analysis showed that the amplitudes of both haemodynamic parameters show a significant association with the pathology and a significant discriminating ability, while no significant result was found for latencies. Overall, our findings together with the ease of use and noninvasiveness of TD-NIRS, make this technique a promising candidate as a supporting tool for a better evaluation of the glaucoma pathology.

Cerebral Modifications in Glaucoma and Macular Degeneration: Analysis of Current Evidence in Literature and Their Implications on Therapeutic Perspectives

Glaucoma and macular degeneration are leading causes of irreversible blindness, significantly compromising the quality of life and having a high economic and social impact. Promising therapeutic approaches aimed at regenerating or bypassing the damaged anatomical-functional components are currently under development: these approaches have generated great expectations, but to be effective require a visual network that, despite the pathology, maintains its integrity up to the higher brain areas. In the light of this, the existing findings concerning how the central nervous system modifies its connections following the pathological damage caused by glaucoma and macular degeneration acquire great interest. This review aims to examine the scientific literature concerning the morphological and functional changes affecting the central nervous system in these pathological conditions, summarizing the evidence in an analytical way, discussing their possible causes and highlighting the potential repercussions on the current therapeutic perspectives.

Altered spontaneous cortical activity in mild glaucoma: A quantitative EEG study

Functional neuroimaging studies have reported alterations in cortical activity indicating glaucoma as a progressive neurodegenerative disease. Hence the current study aimed to assess the cortical activity using high-density EEG in patients with mild glaucoma during resting state. Treatment-naive 37 patients with primary open angle glaucoma (POAG), 34 patients with primary angle closure glaucoma (PACG), and 32 healthy controls were included in the study. Resting state EEG i.e., eyes closed (EC) and eyes open conditions (EO) were acquired using 128-channel for 3 min. After preprocessing, the current density of 6239 voxels of the data was estimated using sLORETA. In comparison to healthy controls, PACG had higher activity at cingulate gyri, medial and superior frontal gyri during EO only. POAG had significantly higher activity at precentral gyrus and middle frontal gyrus during EC, whereas at cingulate gyri, frontal gyri, precentral gyri, paracentral lobule, sub-gyral region, postcentral gyrus, and precuneus during EO. POAG had significantly higher activity at precuneus and cuneus compared to PACG during EO. Intraocular pressure and mean-deviation of visual fields had a positive correlation with cortical activity. Results of the study indicate physiological alterations not only at the level of retina but also at brain even in the early stages of the disease. These alterations in the cortical activity were more in POAG than PACG. Controlling the IOP alone might be insufficient in glaucoma because of widespread alterations in cortical activity. These findings might enhance the current understanding of cortical involvement in glaucoma.

Carotenoids in the Management of Glaucoma: A Systematic Review of the Evidence

Primary open-angle glaucoma (POAG) remains a leading cause of irreversible blindness globally. Recent evidence further substantiates sustained oxidative stress, and compromised antioxidant defenses are key drivers in the onset of glaucomatous neurodegeneration. Overwhelming oxidative injury is likely attributed to compounding mitochondrial dysfunction that worsens with age-related processes, causing aberrant formation of free radical species. Thus, a compromised systemic antioxidant capacity exacerbates further oxidative insult in glaucoma, leading to apoptosis, neuroinflammation, and subsequent tissue injury. The purpose of this systematic review is to investigate the neuroprotective benefits of the macular carotenoids lutein, zeaxanthin, and meso-zeaxanthin on glaucomatous neurodegeneration for the purpose of adjunctive nutraceutical treatment in glaucoma. A comprehensive literature search was conducted in three databases (PubMed, Cochrane Library, and Web of Science) and 20 records were identified for screening. Lutein demonstrated enhanced neuroprotection on retinal ganglion cell survival and preserved synaptic activity. In clinical studies, a protective trend was seen with greater dietary consumption of carotenoids and risk of glaucoma, while greater carotenoid levels in macular pigment were largely associated with improved visual performance in glaucomatous eyes. The data suggest that carotenoid vitamin therapy exerts synergic neuroprotective benefits and has the capacity to serve adjunctive therapy in the management of glaucoma.

Transneuronal Degeneration in the Brain During Glaucoma

The death of retinal ganglion cells (RGCs) is a key factor in the pathophysiology of all types of glaucoma, but the mechanism of pathogenesis of glaucoma remains unclear. RGCs are a group of central nervous system (CNS) neurons whose soma are in the inner retina. The axons of RGCs form the optic nerve and converge at the optic chiasma; from there, they project to the visual cortex via the lateral geniculate nucleus (LGN). In recent years, there has been increasing interest in the dysfunction and death of CNS and retinal neurons caused by transneuronal degeneration of RGCs, and the view that glaucoma is a widespread neurodegenerative disease involving CNS damage appears more and more frequently in the literature. In this review, we summarize the current knowledge of LGN and visual cortex neuron damage in glaucoma and possible mechanisms behind the damage. This review presents an updated and expanded view of neuronal damage in glaucoma, and reveals new and potential targets for neuroprotection and treatment.

White matter alterations in glaucoma and monocular blindness differ outside the visual system

The degree to which glaucoma has effects in the brain beyond the eye and the visual pathways is unclear. To clarify this, we investigated white matter microstructure (WMM) in 37 tracts of patients with glaucoma, monocular blindness, and controls. We used brainlife.io for reproducibility. White matter tracts were subdivided into seven categories ranging from those primarily involved in vision (the visual white matter) to those primarily involved in cognition and motor control. In the vision tracts, WMM was decreased as measured by fractional anisotropy in both glaucoma and monocular blind subjects compared to controls, suggesting neurodegeneration due to reduced sensory inputs. A test-retest approach was used to validate these results. The pattern of results was different in monocular blind subjects, where WMM properties increased outside the visual white matter as compared to controls. This pattern of results suggests that whereas in the monocular blind loss of visual input might promote white matter reorganization outside of the early visual system, such reorganization might be reduced or absent in glaucoma. The results provide indirect evidence that in glaucoma unknown factors might limit the reorganization as seen in other patient groups following visual loss.

Higher Dementia Incidence in Older Adults with Poor Visual Acuity

Background

Longitudinal evidence of poor visual acuity associating with higher risk of incident dementia is mixed. This study aimed to examine if poor visual acuity was associated with higher dementia incidence in a large community cohort of older adults, independent of the possible biases relating to misclassification error, reverse causality, and confounding effects due to health problems and behaviors.

Methods

A total of 15,576 community-living older adults without dementia at baseline were followed for 6 years to the outcome of incident dementia, which was diagnosed according to the ICD-10 or a Clinical Dementia Rating of 1 to 3. Visual acuity was assessed using the Snellen’s chart at baseline and follow-up. Important variables including demographics (age, sex, education, and socioeconomic status), physical and psychiatric comorbidities (cardiovascular risks, ophthalmological conditions, hearing impairment, poor mobility, and depression), and lifestyle behaviors (smoking, diet, physical, intellectual, and social activities) were also assessed.

Results

Over 68,904 person-years of follow-up, 1,349 participants developed dementia. Poorer visual acuity at baseline was associated with higher dementia incidence in 6 years, even after adjusting for demographics, health problems, and lifestyle behaviors, and excluding those who developed dementia within 3 years after baseline. Compared with normal vision, the hazard ratio of dementia was 1.19 (p = .31), 2.09 (p < .001), and 8.66 (p < .001) for mild, moderate, and severe visual impairment, respectively.

Conclusions

Moderate-to-severe visual impairment could be a potential predictor and possibly a risk factor for dementia. From a clinical perspective, older adults with poor visual acuity might warrant further risk assessment for dementia.

Is Mental Stress the Primary Cause of Glaucoma?

The prognosis of going blind is very stressful for patients diagnosed with "glaucoma". Worries and fear of losing independence is a constant mental burden, with secondary risks of depression and social isolation. But stress is not only a result of glaucoma but also a possible cause (risk factor). This should not be surprising, given that chronic stress can trigger "psychosomatic" organ dysfunctions anywhere in the body. Why should the organ "eye" be an exception? Indeed, glaucoma patients often suspect that severe emotional stress caused their visual field loss or "foggy vision". The hypothesis that stress is a possible cause of glaucoma is supported by different observations: (i) acute and chronic stress increases intraocular pressure and (ii) long-term stress can lead to vascular dysregulation of the microcirculation in the eye and brain ("Flammer's syndrome"), leading to partial hypoxia and hypoglycaemia (hypo-metabolism). Even if nerve cells do not die, they may then become inactive ("silent" neurons). (iii) Degenerative changes have been reported in the brain of glaucoma patients, affecting not only anterograde or transsynaptic areas of the central visual pathway, but degeneration is also found (iv) in brain areas involved in emotional appraisal and the physiological regulation of stress hormones. There are also psychological hints indicating that stress is a cause of glaucoma: (v) Glaucoma patients with Flammer's syndrome show typical personality traits that are associated with low stress resilience: they often have cold hands or feet, are ambitious (professionally successful), perfectionistic, obsessive, brooding and worrying a lot. (vi) If stress hormone levels and inflammation parameters are reduced in glaucoma patients by relaxation with meditation, this correlates with normalisation of intraocular pressure, and yet another clue is that (vii) visual field improvements after non-invasive current stimulation therapy, that are known to improve circulation and neuronal synchronisation, are much most effective in patients with stress resilient personalities. An appreciation of stress as a "cause" of glaucoma suggests that in addition to standard therapy (i) stress reduction through relaxation techniques should be recommended (e.g. meditation), and (ii) self-medication compliance should not be induced by kindling anxiety and worries with negative communication ("You will go blind!"), but communication should be positive ("The prognosis is optimistic").

Data-Driven Parcellation Approaches Based on Functional Connectivity of Visual Cortices in Primary Open-Angle Glaucoma

Purpose

Functional changes have been observed between diseased and healthy subjects, and functional brain atlases derived from healthy populations may fail to reflect functional characteristic of the diseased brain. Therefore the aim of this study was to generate a visual atlas based on functional connectivity from primary open-angle glaucoma (POAG) patients and to prove the applicability of the visual atlas in functional connectivity and network analysis.

Methods

Functional magnetic resonance images were acquired from 36 POAG patients and 20 healthy controls. Two data-driven approaches, K-means and Ward clustering algorithms, were adopted for visual cortices parcellation. Dice coefficient and adjusted Rand index were used to assess reproducibility of the two approaches. Homogeneity index, silhouette coefficient, and network properties were adopted to assess functional validity for the data-driven approaches and frequently used brain atlas. Graph theoretical analysis was adopted to investigate altered network patterns in POAG patients based on data-driven visual atlas.

Results

Parcellation results demonstrated asymmetric patterns between left and right hemispheres in POAG patients compared with healthy controls. In terms of evaluating metrics, K-means performed better than Ward clustering in reproducibility. Data-driven parcellations outperformed frequently used brain atlases in terms of functional homogeneity and network properties. Graph theoretical analysis revealed that atlases generated by data-driven approaches were more conducive in detecting network alterations between POAG patients and healthy controls.

Conclusions

Our findings suggested that POAG patients experienced functional alterations in the visual cortices. Results also highlighted the necessity of data-driven atlases for functional connectivity and functional network analysis of POAG brain.

Retinal biomarkers for Alzheimer's disease and vascular cognitive impairment and dementia (VCID): implication for early diagnosis and prognosis

Cognitive impairment and dementia are major medical, social, and economic public health issues worldwide with significant implications for life quality in older adults. The leading causes are Alzheimer's disease (AD) and vascular cognitive impairment/dementia (VCID). In both conditions, pathological alterations of the cerebral microcirculation play a critical pathogenic role. Currently, the main pathological biomarkers of AD-β-amyloid peptide and hyperphosphorylated tau proteins-are detected either through cerebrospinal fluid (CSF) or PET examination. Nevertheless, given that they are invasive and expensive procedures, their availability is limited. Being part of the central nervous system, the retina offers a unique and easy method to study both neurodegenerative disorders and cerebral small vessel diseases in vivo. Over the past few decades, a number of novel approaches in retinal imaging have been developed that may allow physicians and researchers to gain insights into the genesis and progression of cerebromicrovascular pathologies. Optical coherence tomography (OCT), OCT angiography, fundus photography, and dynamic vessel analyzer (DVA) are new imaging methods providing quantitative assessment of retinal structural and vascular indicators-such as thickness of the inner retinal layers, retinal vessel density, foveal avascular zone area, tortuosity and fractal dimension of retinal vessels, and microvascular dysfunction-for cognitive impairment and dementia. Should further studies need to be conducted, these retinal alterations may prove to be useful biomarkers for screening and monitoring dementia progression in clinical routine. In this review, we seek to highlight recent findings and current knowledge regarding the application of retinal biomarkers in dementia assessment.

[Modern view on normal-tension glaucoma]

Glaucoma is a chronic progressive optic neuropathy that causes irreversible loss of visual functions. From the clinical point of view, normal-tension glaucoma (NTG) is regarded in Russian taxonomy as a clinical form of standard primary open-angle glaucoma in which the IOP values stay within the normal range, but the typical progressive visual functions loss is still present. The results of the latest studies put in question the traditional views of NTG pathophysiology that are based solely on intraocular pressure values. New capabilities of diagnostic visualization of central nervous system have considerably broadened our knowledge of the NTG development mechanisms. This article reviews current understanding of the pathogenesis of NTG and its connection to vascular and immune factors, translaminar pressure difference etc. The review also considers the relationship between glaucoma and cognitive defects associated with Alzheimer's and Parkinson's diseases.

Glaucoma, but not cataracts, predicts lower verbal fluency performance: 3.8-year follow-up from the ELSA-Brasil study

Glaucoma, cataracts, and cognitive decline are most common in older ages. Although cross-sectional studies showed that these disorders are associated, follow-up studies are lacking. To investigate this issue, baseline and follow-up data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) were employed. We evaluated participants ≥ 55 years-old at follow-up without diagnosis of dementia, stroke, and other eye conditions except for glaucoma and cataracts. Cognition was evaluated using delayed word recall, verbal fluency, and trail making (version B) tests. Regression models were employed to investigate associations between glaucoma and cognition, adjusted by several confounders. Out of 3,867 participants, 379 and 118 presented cataracts and glaucoma, respectively. Only glaucoma was apredictor of lower verbal fluency (B = -0.23, 95% CI -035 to -012, p< 0.001). Other associations were not significant (ps>0.57). Our results suggest that glaucoma may be related to declining cognition.

Altered information flow and microstructure abnormalities of visual cortex in normal-tension glaucoma: Evidence from resting-state fMRI and DKI

Normal tension glaucoma (NTG) is a neurodegenerative disease involves multiple brain areas, but the mechanism remains unclear. The aim of this study is to investigate the correlation between structural injury and functional reorganization in the brain of NTG, using resting-state functional MRI and diffusion kurtosis imaging (DKI) data acquired for 26 NTG patients and 24 control subjects. Granger causality analysis (GCA) was used to calculate the effective connectivity (EC) between visual cortices and the whole brain to reflect the information flow. The fractional anisotropy (FA), mean kurtosis (MK), axial kurtosis (AK), and radial kurtosis (RK) derived from DKI of visual cortices were extracted to evaluate structural injury. Microstructural abnormalities were detected in bilateral BA17, BA18, and BA19. NTG patients showed significantly decreased EC from BA17 to higher visual cortices and increase EC from higher visual cortices to BA17. The EC from BA17 to posterior cingulate cortex (PCC) and from PCC to BA17 both significantly increased, while the EC from right BA18 and BA19 to PCC significantly decreased. Decreased EC between somatosensory cortex and BA17, as well as the decreased ECs between supramarginal gyrus (SMA) and BA17/BA19 were detected. Several abnormal ECs were significantly correlated with microstructural injuries of BA17 and BA18. In conclusion, NTG causes reorganization of information flows among visual cortices and other brain areas, which is consistent with brain microstructural injury.

Enhanced Gray Matter Volume Compensates for Decreased Brain Activity in the Ocular Motor Area in Children with Anisometropic Amblyopia

Purpose

Anisometropic amblyopia usually occurs during early childhood and results in monocular visual deficit. Recent neuroimaging studies have demonstrated structural and functional alterations in pediatric anisometropic amblyopia (PAA) patients. However, the relationship between structural and functional alterations remains largely unknown. The aim of this study was to investigate the relationship between structural and functional alterations in PAA patients.

Materials and Methods

Eighteen PAA patients and 14 healthy children underwent a multimodal MRI scanning including T1WI and functional MRI (fMRI). Voxel-based morphometry was used to assess structural alterations between PAA patients and healthy children. Regional homogeneity (ReHo) was used to investigate changes in local spontaneous brain activity in the enrolled subjects. Correlations between structural, functional alterations, and clinical information were analyzed in the PAA group.

Results

Compared with healthy children, PAA patients exhibited significantly reduced ReHo of spontaneous brain activity in the right superior temporal gyrus (STG) and right middle frontal gyrus (MFG) and increased gray matter volume in the right lobules 4 and 5 of the cerebellum. The gray matter volume of the right lobules 4 and 5 of the cerebellum was negatively correlated with the ReHo values of the right MFG.

Conclusions

Our findings may suggest that PAA patients experience structural and functional abnormalities in brain regions related to oculomotor and visual-spatial information. In addition, the increased gray matter volume may compensate the decreased brain activity in the oculomotor regions, which reflects compensatory or neural plasticity in PAA patients.

Frequency-specific oscillations synchronization in primary angle-closure glaucoma

Background

Previous neuroimaging studies demonstrated that patients with primary angle-closure glaucoma were accompanied by abnormal neuronal activity.

Purpose

To investigate frequency-dependent local oscillations synchronization in primary angle-closure glaucoma using the regional homogeneity method.

Material and Methods

In total, 37 individuals with primary angle-closure glaucoma (20 men, 17 women) and 37 normal-sighted controls (20 men, 17 women) closely matched in age, sex, and education underwent resting-state MRI scans. We compared the different regional homogeneity values in full band (0.01–0.08 Hz) and two different frequency bands (slow-4: 0.027–0.073 Hz and slow-5: 0.010–0.027 Hz) between two groups.

Results

Compared to the normal-sighted group, the primary angle-closure glaucoma group showed decreased regional homogeneity values in the left calcarine and left postcentral in full band. The primary angle-closure glaucoma group showed increased regional homogeneity values in the bilateral superior medial frontal lobe in the slow-4 band. The primary angle-closure glaucoma group exhibited decreased regional homogeneity values in the right calcarine in the slow-5 band. Specifically, we found that the regional homogeneity values in the right superior frontal lobe were greater in the slow-4 than in the slow-5 band, whereas regional homogeneity in the left calcarine, right pallidum, left inferior occipital gyrus, left superior occipital gyrus, left postcentral/angular gyrus, left paracentral lobule, left superior parietal gyrus, and right precuneus gyrus were greater in the slow-5 than in the slow-4 band.

Conclusion

Primary angle-closure glaucoma groups showed abnormal regional homogeneity in visual network (calcarine) and default mode network (superior medial frontal lobe) at two frequency bands. Moreover, the regional homogeneity signals in slow-5 band showed closely related to the severity of individuals with primary angle-closure glaucoma.

Brain morphological alterations of cerebral cortex and subcortical nuclei in high-tension glaucoma brain and its associations with intraocular pressure

PURPOSE

To investigate brain morphological alterations of high-tension glaucoma patients and explore the association between brain morphological changes and elevated intraocular pressure.

METHODS

Thirty-six patients with high-tension glaucoma and 20 healthy controls were collected and underwent structural MRI scan. Surface-based morphometry and voxel-based morphometry were applied to assess cortical thickness and subcortical gray matter volume of the enrolled subjects. The association between brain morphometry and intraocular pressure was assessed by partial correlation.

RESULTS

Compared with healthy controls, high-tension glaucoma patients showed decreased cortical thickness in the bilateral superior temporal gyrus, bilateral superior parietal gyrus, bilateral lateral occipital gyrus, left fusiform gyrus, left medial orbitofrontal gyrus, right precentral gyrus, and right superior frontal gyrus (p < 0.05). High-tension glaucoma patients also showed reduced gray matter volume in the right hippocampus, bilateral putamen, and bilateral thalamus (p < 0.05). In addition, brain morphological correlates of mean intraocular pressure were found in the left rostral middle frontal gyrus, right precentral gyrus, and left postcentral gyrus in high-tension glaucoma group (p < 0.05).

CONCLUSION

High-tension glaucoma patients experienced morphological reduction in the visual and nonvisual areas throughout the entire brain. Elevated intraocular pressure may contribute to the reduction of cortical thickness in certain areas in the progression of the disease.

Cholinergic nervous system and glaucoma: From basic science to clinical applications

The cholinergic system has a crucial role to play in visual function. Although cholinergic drugs have been a focus of attention as glaucoma medications for reducing eye pressure, little is known about the potential modality for neuronal survival and/or enhancement in visual impairments. Citicoline, a naturally occurring compound and FDA approved dietary supplement, is a nootropic agent that is recently demonstrated to be effective in ameliorating ischemic stroke, traumatic brain injury, Parkinson's disease, Alzheimer's disease, cerebrovascular diseases, memory disorders and attention-deficit/hyperactivity disorder in both humans and animal models. The mechanisms of its action appear to be multifarious including (i) preservation of cardiolipin, sphingomyelin, and arachidonic acid contents of phosphatidylcholine and phosphatidylethanolamine, (ii) restoration of phosphatidylcholine, (iii) stimulation of glutathione synthesis, (iv) lowering glutamate concentrations and preventing glutamate excitotoxicity, (v) rescuing mitochondrial function thereby preventing oxidative damage and onset of neuronal apoptosis, (vi) synthesis of myelin leading to improvement in neuronal membrane integrity, (vii) improving acetylcholine synthesis and thereby reducing the effects of mental stress and (viii) preventing endothelial dysfunction. Such effects have vouched for citicoline as a neuroprotective, neurorestorative and neuroregenerative agent. Retinal ganglion cells are neurons with long myelinated axons which provide a strong rationale for citicoline use in visual pathway disorders. Since glaucoma is a form of neurodegeneration involving retinal ganglion cells, citicoline may help ameliorate glaucomatous damages in multiple facets. Additionally, trans-synaptic degeneration has been identified in humans and experimental models of glaucoma suggesting the cholinergic system as a new brain target for glaucoma management and therapy.

In vivo Probabilistic Structural Atlas of the Inferior and Superior Colliculi, Medial and Lateral Geniculate Nuclei and Superior Olivary Complex in Humans Based on 7 Tesla MRI

Despite extensive neuroimaging research of primary sensory cortices involved in auditory and visual functions, subcortical structures within these domains, such as the inferior and superior colliculi, the medial and lateral geniculate nuclei and the superior olivary complex, are currently understudied with magnetic resonance imaging (MRI) in living humans. This is because a precise localization of these nuclei is hampered by the limited contrast and sensitivity of conventional neuroimaging methods for deep brain nuclei. In this work, we used 7 Tesla multi-modal (T₂-weighted and diffusion fractional anisotropy) 1.1 mm isotropic resolution MRI to achieve high sensitivity and contrast for single-subject brainstem and thalamic nuclei delineation. After precise coregistration to stereotactic space, we generated an in vivo human probabilistic atlas of auditory (medial geniculate nucleus, inferior colliculus, and superior olivary complex) and visual (lateral geniculate nucleus and superior colliculus) subcortical nuclei. We foresee the use of this atlas as a tool to precisely identify the location and shape of auditory/visual deep nuclei in research as well as clinical human studies.

Diffusivity and quantitative T1 profile of human visual white matter tracts after retinal ganglion cell damage

In patients with retinal ganglion cell diseases, recent diffusion tensor imaging (DTI) studies have revealed structural abnormalities in visual white matter tracts such as the optic tract, and optic radiation. However, the microstructural origin of these diffusivity changes is unknown as DTI metrics involve multiple biological factors and do not correlate directly with specific microstructural properties. In contrast, recent quantitative T1 (qT1) mapping methods provide tissue property measurements relatively specific to myelin volume fractions in white matter. This study aims to improve our understanding of microstructural changes in visual white matter tracts following retinal ganglion cell damage in Leber's hereditary optic neuropathy (LHON) patients by combining DTI and qT1 measurements. We collected these measurements from seven LHON patients and twenty age-matched control subjects. For all individuals, we identified the optic tract and the optic radiation using probabilistic tractography, and evaluated diffusivity and qT1 profiles along them. Both diffusivity and qT1 measurements in the optic tract differed significantly between LHON patients and controls. In the optic radiation, these changes were observed in diffusivity but were not evident in qT1 measurements. This suggests that myelin loss may not explain trans-synaptic diffusivity changes in the optic radiation as a consequence of retinal ganglion cell disease.

•

Retinal ganglion cell damage affects diffusivity and T1 along visual pathways.

•

DTI metric identified white matter change in both optic tract and optic radiation.

•

T1 measurement in optic radiation did not exhibit abnormality, unlike DTI metric.

•

Myelin loss may not be a major cause of diffusivity change along optic radiation.

Residual vision activation and the brain-eye-vascular triad: Dysregulation, plasticity and restoration in low vision and blindness - a review

Vision loss due to ocular diseases such as glaucoma, optic neuropathy, macular degeneration, or diabetic retinopathy, are generally considered an exclusive affair of the retina and/or optic nerve. However, the brain, through multiple indirect influences, has also a major impact on functional visual impairment. Such indirect influences include intracerebral pressure, eye movements, top-down modulation (attention, cognition), and emotionally triggered stress hormone release affecting blood vessel dysregulation. Therefore, vision loss should be viewed as the result of multiple interactions within a “brain-eye-vascular triad”, and several eye diseases may also be considered as brain diseases in disguise. While the brain is part of the problem, it can also be part of the solution. Neuronal networks of the brain can “amplify” residual vision through neuroplasticity changes of local and global functional connectivity by activating, modulating and strengthening residual visual signals. The activation of residual vision can be achieved by different means such as vision restoration training, non-invasive brain stimulation, or blood flow enhancing medications. Modulating brain functional networks and improving vascular regulation may offer new opportunities to recover or restore low vision by increasing visual field size, visual acuity and overall functional vision. Hence, neuroscience offers new insights to better understand vision loss, and modulating brain and vascular function is a promising source for new opportunities to activate residual vision to achieve restoration and recovery to improve quality of live in patients suffering from low vision.

Frequency-dependent neural activity in primary angle-closure glaucoma

OBJECTIVE

In this study, we aimed to investigate the frequency-dependent spontaneous neural activity in primary angle-closure glaucoma (PACG) using the amplitude of low-frequency fluctuations (ALFF) method.

PATIENTS AND METHODS

In total, 52 PACG individuals (24 males and 28 females) and 52 normal-sighted controls (NS; 24 males and 28 females) who were closely matched in age, sex, and education underwent resting-state magnetic resonance imaging scans. A repeated-measures ANOVA and post hoc two-sample t-tests were conducted to analyze the different ALFF values in two different frequency bands (slow-4, 0.027-0.073 Hz and slow-5, 0.010-0.027 Hz) between the two groups. Pearson's correlation analysis was conducted to reveal the relationship between the mean ALFF values and clinical variables in the PACG group.

RESULTS

Compared to the NS group, the PACG group had high ALFF values in the right inferior occipital gyrus and low ALFF values in the left middle occipital gyrus, left precentral gyrus, and left postcentral gyrus in the slow-4 band. The PACG group had high ALFF values in the right inferior occipital gyrus and low ALFF values in the left inferior parietal lobule, left postcentral gyrus, and right precentral/postcentral gyrus in the slow-5 band. Specifically, we found that the abnormal ALFF values in the bilateral posterior cingulate gyrus and bilateral precuneus were higher in the slow-4 than in the slow-5 band, whereas ALFF in the bilateral frontal lobe, right fusiform, and right cerebellum posterior lobe were higher in the slow-5 than in the slow-4 band. The greater mean ALFF values of the right inferior occipital gyrus were associated with smaller retinal nerve fiber layer thickness and greater visual fields in PACG group in the slow-4 band.

CONCLUSION

Our results highlighted that individuals in the PACG group showed abnormal spontaneous neural activities in the visual cortices, sensorimotor cortices, frontal lobe, frontoparietal network, and default mode network at two frequency bands, which might indicate impaired vision and cognition and emotion function in PACG individuals. These findings offer important insight into the understanding of the neural mechanism of PACG.

Normal tension glaucoma: from the brain to the eye or the inverse?

Glaucoma is a chronic, progressive optic neuropathy characterized by the loss of peripheral vision first and then central vision. Clinically, normal tension glaucoma is considered a special subtype of glaucoma, in which the patient's intraocular pressure is within the normal range, but the patient experiences typical glaucomatous changes. However, increasing evidence has challenged the traditional pathophysiological view of normal tension glaucoma, which is based only on intraocular pressure, and breakthroughs in central nervous system imaging may now greatly increase our knowledge about the mechanisms underlying normal tension glaucoma. In this article, we review the latest progress in understanding the pathogenesis of normal tension glaucoma and in developing imaging techniques to detect it, to strengthen the appreciation for the connection between normal tension glaucoma and the brain.