The optic nerve head in hereditary optic neuropathies

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.

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.

Comparison of Lamina Cribrosa Morphology in Normal Tension Glaucoma and Autosomal-Dominant Optic Atrophy

Purpose

To compare lamina cribrosa (LC) morphology in patients with normal tension glaucoma (NTG) and autosomal-dominant optic atrophy (ADOA).

Methods

This cross-sectional study matched 24 patients diagnosed with ADOA (24 eyes) by age and retinal nerve fiber layer thickness with 48 patients diagnosed with NTG (48 eyes) by age with 48 healthy controls (48 eyes). Optic nerve heads were scanned by enhanced-depth imaging (EDI) optical coherence tomography (OCT). The LC curvature index (LCCI) and LC depth (LCD) on B-scan images obtained using EDI-OCT were measured at seven locations spaced equidistantly across the vertical optic disc diameter and compared among the NTG, ADOA, and control groups.

Results

Mean LCCI and LCD were significantly greater in NTG than in ADOA and healthy eyes (P < 0.001 each) but did not differ significantly in ADOA and healthy eyes.

Conclusions

NTG eyes have a more posteriorly curved and deeper LC than ADOA and healthy eyes. This finding provides insight into the role of LC morphology in NTG and provides a clinical clue to distinguish between NTG and ADOA.

Current perspective of neuroprotection and glaucoma

Glaucoma is the second leading cause of blindness worldwide and is most notably characterized by progressive optic nerve atrophy and advancing loss of retinal ganglion cells (RGCs). The main concomitant factor is the elevated intraocular pressure (IOP). Existing treatments are focused generally on lowering IOP. However, both RGC loss and optic nerve atrophy can independently occur with IOP at normal levels. In recent years, there has been substantial progress in the development of neuroprotective therapies for glaucoma in order to restore vital visual function. The present review intends to offer a brief insight into conventional glaucoma treatments and discuss exciting current developments of mostly preclinical data in novel neuroprotective strategies for glaucoma that include recent advances in noninvasive diagnostics going beyond IOP maintenance for an enhanced global view. Such strategies now target RGC loss and optic nerve damage, opening a critical therapeutic window for preventative monitoring and treatment.

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.

Optic atrophy differentially diagnosed as spinocerebellar ataxia from Leber hereditary optic neuropathy by gene mutation analysis

Optic atrophy describes a group of diseases of retinal ganglion cells and axons that eventually lead to loss of vision. Optic atrophy has both congenital and acquired causes, and its diagnosis (or differential diagnosis) is complicated. This case report describes a 20-year-old man who presented with a 1-year history of progressive vision loss in both eyes and no obvious systemic symptoms. Fundus examination revealed bilateral optic atrophy. Based on clinical characteristics, visual field analysis and pattern visual evoked potential examination, the presumptive diagnosis was Leber hereditary optic neuropathy (LHON). Analysis of mitochondrial DNA indicated the absence of all of three common mutations associated with LHON (m.3460G>A, m.11778G>A, m.14484T>C). Detailed questioning of the patient revealed a history of prolonged language development and poor balance. Neurological examination indicated abnormal co-ordination, suggesting the presence of inherited spinocerebellar ataxia (SCA). Analysis of the SCA7 gene revealed a high number of trinucleotide repeats [(CAG)(n), n > 64], confirming the diagnosis of SCA. The aetiology of optic atrophies is complicated and the molecular genetic detection approach provides the best information for diagnosing these diseases.

Mitochondrial disorders and the eye

The clinical significance of disturbed mitochondrial function in the eye has emerged since mitochondrial DNA (mtDNA) mutation was described in Leber's hereditary optic neuropathy. The spectrum of mitochondrial dysfunction has become apparent through increased understanding of the contribution of nuclear and somatic mtDNA mutations to mitochondrial dynamics and function. Common ophthalmic manifestations of mitochondrial dysfunction include optic atrophy, pigmentary retinopathy, and ophthalmoplegia. The majority of patients with ocular manifestations of mitochondrial disease also have variable central and peripheral nervous system involvement. Mitochondrial dysfunction has recently been associated with age-related retinal disease including macular degeneration and glaucoma. Therefore, therapeutic targets directed at promoting mitochondrial biogenesis and function offer a potential to both preserve retinal function and attenuate neurodegenerative processes.

Optic disc evaluation in optic neuropathies: the optic disc assessment project

OBJECTIVE

Optic nerve morphology is affected by genetic and acquired disease. Glaucoma is the most common optic neuropathy; autosomal-dominant optic atrophy (ADOA) and Leber's hereditary optic neuropathy (LHON) are the most prevalent hereditary optic neuropathies. These 3 entities can exhibit similar topographical changes at the optic nerve head. Both ADOA and LHON have been reported to be misdiagnosed as glaucoma. Our aim was to determine whether glaucoma subspecialists and neuro-ophthalmologists can distinguish these diagnoses on optic disc assessment alone.

DESIGN

Observational study.

PARTICIPANTS

Twenty-three optic nerve experts.

METHODS

We randomized and masked 60 high-resolution stereoscopic optic disc photographs (15 ADOA images, 15 LHON, 15 glaucoma, and 15 normal controls). Experts were asked to assess the discs on 12 conventional topographic features and assign a presumptive diagnosis. Intra- and interanalysis was performed using the index of qualitative variation and absolute deviation.

MAIN OUTCOME MEASURES

Can glaucoma specialists and neuro-ophthalmologists distinguish among the disease entities by optic nerve head phenotype.

RESULTS

The correct diagnosis was identified in 85%, 75%, 27%, and 16% of the normal, glaucoma, ADOA, and LHON disc groups, respectively. The proportion of correct diagnoses within the ADOA and LHON groups was significantly lower than both normal and glaucomatous (P<0.001). Where glaucoma was chosen as the most likely diagnosis, 61% were glaucomatous, 34% were pathologic but nonglaucomatous discs, and 5% were normal. There was greater agreement for individual parameters assessed within the normal disc set when compared with pathologic discs (P<0.05). The only parameter to have a significantly greater agreement within the glaucomatous disc set when compared with ADOA or LHON disc sets was pallor, whereby experts agreed on is absence in the glaucomatous discs but were not in agreement on its presence or its absence in the ADOA and LHON discs (P<0.01).

CONCLUSIONS

Optic neuropathies can result in similar topographic changes at the optic disc, particularly in late-stage disease, making it difficult to differentiate ADOA and LHON from glaucoma based on disc assessment alone. Other clinical parameters such as acuity, color vision, history of visual loss, and family history are required to make an accurate diagnosis.

Genome-wide association identifies ATOH7 as a major gene determining human optic disc size

Optic nerve assessment is important for many blinding diseases, with cup-to-disc ratio (CDR) assessments commonly used in both diagnosis and progression monitoring of glaucoma patients. Optic disc, cup, rim area and CDR measurements all show substantial variation between human populations and high heritability estimates within populations. To identify loci underlying these quantitative traits, we performed a genome-wide association study in two Australian twin cohorts and identified rs3858145, P = 6.2 × 10⁻¹⁰, near the ATOH7 gene as associated with the mean disc area. ATOH7 is known from studies in model organisms to play a key role in retinal ganglion cell formation. The association with rs3858145 was replicated in a cohort of UK twins, with a meta-analysis of the combined data yielding P = 3.4 × 10⁻¹⁰. Imputation further increased the evidence for association for several SNPs in and around ATOH7 (P = 1.3 × 10⁻¹⁰ to 4.3 × 10⁻¹¹, top SNP rs1900004). The meta-analysis also provided suggestive evidence for association for the cup area at rs690037, P = 1.5 × 10⁻⁷, in the gene RFTN1. Direct sequencing of ATOH7 in 12 patients with optic nerve hypoplasia, one of the leading causes of blindness in children, revealed two novel non-synonymous mutations (Arg65Gly, Ala47Thr) which were not found in 90 unrelated controls (combined Fisher's exact P = 0.0136). Furthermore, the Arg65Gly variant was found to have very low frequency (0.00066) in an additional set of 672 controls.

Blood pressure treatment in acute ischemic stroke: a review of studies and recommendations

PURPOSE OF REVIEW

Elevated blood pressure (BP) is frequent in patients with acute ischemic stroke. Pathophysiological data support its usefulness to maintain adequate perfusion of the ischemic penumba. This review article aims to summarize the available evidence from clinical studies that examined the prognostic role of BP during the acute phase of ischemic stroke and intervention studies that assessed the efficacy of active BP alteration.

RECENT FINDINGS

We found 34 observational studies (33,470 patients), with results being inconsistent among the studies; most studies reported a negative association between increased levels of BP and clinical outcome, whereas a few studies showed clinical improvement with higher BP levels, clinical deterioration with decreased BP, or no association at all. Similarly, the conclusions drawn by the 18 intervention studies included in this review (1637 patients) were also heterogeneous. Very recent clinical data suggest a possible beneficial effect of early treatment with some antihypertensives on late clinical outcome.

SUMMARY

Observational and interventional studies of management of acute poststroke hypertension yield conflicting results. We discuss different explanations that may account for this and discuss the current guidelines and pathophysiological considerations for the management of acute poststroke hypertension.

Genetically determined optic neuropathies

PURPOSE OF REVIEW

The present review focuses on recent advances in the knowledge of hereditary optic neuropathies resulting from retinal ganglion cell degeneration, mostly due to mitochondrial dysfunctions.

RECENT FINDINGS

Autosomal dominant optic atrophy, the most common hereditary optic neuropathy, appears to have a more variable clinical presentation than previously thought. Acute visual loss, reversible visual loss, or visual loss associated with extraocular symptoms (deafness, extraocular ophthalmoplegia, multiple sclerosis-like disease) are infrequent, though possible presentations. In Leber's hereditary optic neuropathy, recent findings suggest that the large variability of the clinical expression could be modulated by several factors: genetic (downregulation of the OPA1 gene), environmental (smoking), and anatomic (predisposition of the optic nerve head to axonal loss). Globally, hereditary optic neuropathies may represent an underestimated cause of unexplained and sporadic optic atrophy.Recent advances, such as the discovery of a new gene involved in autosomal recessive optic neuropathy, reinforce the central role played by mitochondrial dysfunctions in the pathogenesis of optic neuropathies.

SUMMARY

Hereditary optic neuropathies may have a heterogenous presentation and serve as a paradigm for neurodegenerative diseases affecting mitochondrial structure, plasticity, and function.

The optic nerve head in acquired optic neuropathies

Acquired optic neuropathies are a common cause of blindness in adults, and are associated with characteristic morphological changes at the optic nerve head. Accurate and prompt clinical diagnosis, supplemented with imaging where appropriate, is essential to optimize management of the optic neuropathy and to counsel the patient appropriately on its natural history. History taking, optic disc findings, visual field assessment and imaging of the nerve head and surrounding retinal nerve fiber layer are all paramount to achieving the correct diagnosis. This Review highlights the optic nerve head features that are common to the acquired optic neuropathies, and describes the features that can be used to differentiate these various conditions.