The optic nerve head in acquired optic neuropathies

Normal-Tension Glaucoma Complicated by a Giant Internal Carotid-Ophthalmic Artery Aneurysm

Purpose. We describe a patient with normal tension glaucoma (NTG) of several years whose management was complicated by the presence of a giant internal carotid-ophthalmic artery aneurysm. Observations. A 72-year-old woman presented to our glaucoma clinic with accelerated deterioration of her vision in her left eye (OS) over a 1-month period. Her ophthalmic history was most notable for bilateral NTG diagnosed 3 years prior which had been treated with several laser trabeculoplasty OS and topical bimatoprost 0.01% eye drops in both eyes (OU). Upon evaluation, her visual acuity OS had worsened, and visual field (VF) testing showed extensive progressive losses temporally and pericentrally OS over a year with stable IOP measurements and no neurological complaints. Given her atypical NTG progression, she was referred for an urgent neurological evaluation which revealed an unruptured giant left internal carotid-ophthalmic aneurysm. Following the successful treatment of the aneurysm with platinum coils, she continued to demonstrate additional bilateral ophthalmic changes including further progression of VF loss and RNFL thinning OS > OD on follow-up. Conclusion and Importance. Overall, this report describes a unique complication in the management of a patient with chronic bilateral NTG in the form of a giant internal carotid-ophthalmic aneurysm. Moreover, it highlights the need for clinicians to maintain a degree of suspicion for compressive lesions of the optic nerve when presented with atypical progression of VFs and/or visual acuity loss in glaucomatous patients.

Axonal Transport Defects in Retinal Ganglion Cell Diseases

For the survival and maintenance of retinal ganglion cells (RGCs), axonal transportation is fundamental. Axonal transportation defects can cause severe neuropathies leading to neuronal loss. Axonal transport defects usually precede axonal degeneration and RGC loss in disease models. To date, the main causes of axonal transport defects have not been fully understood. Therefore, elucidation of the mechanisms that lead to transport defects will help us to develop novel therapeutic targets and early diagnostic tools. In this review, we provide an overview of optic neuropathies and axonal degeneration with a focus on axonal transport.

Diagnostic assessment of glaucoma and non-glaucomatous optic neuropathies via optical texture analysis of the retinal nerve fibre layer

The clinical diagnostic evaluation of optic neuropathies relies on the analysis of the thickness of the retinal nerve fibre layer (RNFL) by optical coherence tomography (OCT). However, false positives and false negatives in the detection of RNFL abnormalities are common. Here we show that an algorithm integrating measurements of RNFL thickness and reflectance from standard wide-field OCT scans can be used to uncover the trajectories and optical texture of individual axonal fibre bundles in the retina and to discern distinctive patterns of loss of axonal fibre bundles in glaucoma, compressive optic neuropathy, optic neuritis and non-arteritic anterior ischaemic optic neuropathy. Such optical texture analysis can detect focal RNFL defects in early optic neuropathy, as well as residual axonal fibre bundles in end-stage optic neuropathy that were indiscernible by conventional OCT analysis and by red-free RNFL photography. In a diagnostic-performance study, optical texture analysis of the RNFL outperformed conventional OCT in the detection of glaucoma, as defined by visual-field testing or red-free photography. Our findings show that optical texture analysis of the RNFL for the detection of optic neuropathies is highly sensitive and specific.

Diversified Treatment Options of Adult Stem Cells for Optic Neuropathies

Optic neuropathies refer to a group of ocular disorders with abnormalities or dysfunction of the optic nerve, sharing a common pathophysiology of retinal ganglion cell (RGC) death and axonal loss. RGCs, as the retinal neurons in the central nervous system, show limited capacity in regeneration or recovery upon diseases or after injuries. Critically, there is still no effective clinical treatment to cure most types of optic neuropathies. Recently, stem cell therapy was proposed as a potential treatment strategy for optic neuropathies. Adult stem cells, including mesenchymal stem cells and hematopoietic stem cells, have been applied in clinical trials based on their neuroprotective properties. In this article, the applications of adult stem cells on different types of optic neuropathies and the related mechanisms will be reviewed. Research updates on the strategies to enhance the neuroprotective effects of human adult stem cells will be summarized. This review article aims to enlighten the research scientists on the diversified functions of adult stem cells and consideration of adult stem cells as a potential treatment for optic neuropathies in future clinical practices.

Brain Organoids: Tiny Mirrors of Human Neurodevelopment and Neurological Disorders

Unravelling the complexity of the human brain is a challenging task. Nowadays, modern neurobiologists have developed 3D model systems called "brain organoids" to overcome the technical challenges in understanding human brain development and the limitations of animal models to study neurological diseases. Certainly like most model systems in neuroscience, brain organoids too have limitations, as these minuscule brains lack the complex neuronal circuitry required to begin the operational tasks of human brain. However, researchers are hopeful that future endeavors with these 3D brain tissues could provide mechanistic insights into the generation of circuit complexity as well as reproducible creation of different regions of the human brain. Herein, we have presented the contemporary state of brain organoids with special emphasis on their mode of generation and their utility in modelling neurological disorders, drug discovery, and clinical trials.

Optic neuropathies: characteristic features and mechanisms of retinal ganglion cell loss

Optic neuropathy refers to dysfunction and/or degeneration of axons of the optic nerve with subsequent optic nerve atrophy. A common feature of different optic neuropathies is retinal ganglion cell (RGC) apoptosis and axonal damage. Glaucoma and optic neuritis are the two major degenerative causes of optic nerve damage. Here, we review the anatomy and pathology of the optic nerve, and etiological categories of optic neuropathies, and discuss rodent models that can mimic these conditions. Electrophysiology can reveal signature features of RGC damage using the pattern electroretinogram (PERG), scotopic threshold response (STR) and photopic negative response (PhNR). The amplitude of the visual evoked potential (VEP) also reflects RGC axonal damage. The neurotrophin-mediated survival pathways, as well as the extrinsic and intrinsic cell apoptotic pathways, play a critical role in the pathogenesis of RGC loss. Finally, promising neuroprotective approaches based on the molecular signaling are analyzed for the treatment of optic neuropathies.

Protective effects of 7,8-dihydroxyflavone on retinal ganglion and RGC-5 cells against excitotoxic and oxidative stress

A preferential loss of retinal ganglion cells (RGCs) is observed in glaucoma and optic neuritis. Loss of tropomyosin-related kinase receptor B (TrkB)-mediated signaling has been implicated in this degeneration. Our study indicates that 7,8-dihydroxyflavone (7,8 DHF) robustly upregulates the TrkB signaling in the primary rat RGCs and the retinal neuronal precursor RGC-5 cell line by promoting phosphorylation of TrkB receptor, leading to enhanced TrkB receptor tyrosine kinase activity. The flavonoid derivative 7,8 DHF acts a potent TrkB agonist and upregulates the downstream AKT and MAPK/ERK survival signaling pathways in a TrkB-dependent manner in both primary rat RGCs as well as the RGC-5 cell line. Excitotoxicity and oxidative injury have been alleged in the specific RGC degeneration in various forms of glaucoma. A novel finding of this study is that treatment with 7,8 DHF protects these cells significantly from excitotoxic and oxidative stress-induced apoptosis and cell death. 7,8 DHF also promotes neuritogenesis by stimulating neurite outgrowth, suggesting a possible therapeutic strategy for protection of RGCs in various optic neuropathies.

Approach to the patient with acute monocular visual loss

Acute visual loss in one eye is a common symptom brought to the attention of the practicing neurologist. In this circumstance, it is critical to identify whether visual loss is due to an optic neuropathy or an ocular disorder (especially retinal disease). This review addresses the elements of the history and examination that are useful in evaluating a patient with visual loss, with the goals of correctly localizing the lesion and constructing a likely differential diagnosis.

Mitochondrial oxidative phosphorylation compensation may preserve vision in patients with OPA1-linked autosomal dominant optic atrophy

Autosomal Dominant Optic Atrophy (ADOA) is the most common inherited optic atrophy where vision impairment results from specific loss of retinal ganglion cells of the optic nerve. Around 60% of ADOA cases are linked to mutations in the OPA1 gene. OPA1 is a fission-fusion protein involved in mitochondrial inner membrane remodelling. ADOA presents with marked variation in clinical phenotype and varying degrees of vision loss, even among siblings carrying identical mutations in OPA1. To determine whether the degree of vision loss is associated with the level of mitochondrial impairment, we examined mitochondrial function in lymphoblast cell lines obtained from six large Australian OPA1-linked ADOA pedigrees. Comparing patients with severe vision loss (visual acuity [VA]<6/36) and patients with relatively preserved vision (VA>6/9) a clear defect in mitochondrial ATP synthesis and reduced respiration rates were observed in patients with poor vision. In addition, oxidative phosphorylation (OXPHOS) enzymology in ADOA patients with normal vision revealed increased complex II+III activity and levels of complex IV protein. These data suggest that OPA1 deficiency impairs OXPHOS efficiency, but compensation through increases in the distal complexes of the respiratory chain may preserve mitochondrial ATP production in patients who maintain normal vision. Identification of genetic variants that enable this response may provide novel therapeutic insights into OXPHOS compensation for preventing vision loss in optic neuropathies.