Increasing evidence indicates that changes in the redox system may contribute to the pathogenesis of multiple optic neuropathies. Optic neuropathies are characterized by the neurodegeneration of the inner-most retinal neurons, the retinal ganglion cells (RGCs), and their axons, which form the optic nerve. Often, optic neuropathies are asymptomatic until advanced stages, when visual impairment or blindness is unavoidable despite existing treatments. In this review, we describe systemic and, whenever possible, ocular redox dysregulations observed in patients with glaucoma, ischemic optic neuropathy, optic neuritis, hereditary optic neuropathies (i.e., Leber’s hereditary optic neuropathy and autosomal dominant optic atrophy), nutritional and toxic optic neuropathies, and optic disc drusen. We discuss aspects related to anti/oxidative stress biomarkers that need further investigation and features related to study design that should be optimized to generate more valuable and comparable results. Understanding the role of oxidative stress in optic neuropathies can serve to develop therapeutic strategies directed at the redox system to arrest the neurodegenerative processes in the retina and RGCs and ultimately prevent vision loss.

The main risk factor for primary open-angle glaucoma (POAG) is increased intraocular pressure (IOP). It is of interest that about half of the patients have an IOP within the normal range (normal-tension glaucoma, NTG). Additionally, there is a group of patients with a high IOP but no glaucomatous neurodegeneration (ocular hypertension, OHT). Therefore, risk factors other than IOP are involved in the pathogenesis of glaucoma. Since the retina has a very high oxygen-demand, decreased autoregulation and a fluctuating oxygen supply to the retina have been linked to glaucomatous neurodegeneration. To assess the significance of these mechanisms, we have utilized a human experimental model, in which we stress participants with a fluctuating oxygen supply. Levels of oxidative stress molecules, antioxidants, and lipid mediators were measured in the plasma. Patients with NTG, OHT, and control subjects were found to have similar levels of oxidative stress markers. In contrast, patients with OHT had a higher level of total antioxidant capacity (TAC) and pro-homeostatic lipid mediators. Thus, we suggest that OHT patients manage fluctuating oxygen levels more efficiently and, thus, are less susceptible to glaucomatous neurodegenerations, due to enhanced systemic antioxidant protection.

BACKGROUND Retinal organoids serve as excellent human-specific disease models for conditions affecting otherwise inaccessible retinal tissue from patients. They permit the isolation of key cell types affected in various eye diseases including retinal ganglion cells (RGCs) and Müller glia. AIM To refine human-induced pluripotent stem cells (hiPSCs) differentiated into three-dimensional (3D) retinal organoids to generate sufficient numbers of RGCs and Müller glia progenitors for downstream analyses. METHODS In this study we described, evaluated, and refined methods with which to generate Müller glia and RGC progenitors, isolated them via magnetic-activated cell sorting, and assessed their lineage stability after prolonged 2D culture. Putative progenitor populations were characterized via quantitative PCR and immunocytochemistry, and the ultrastructural composition of retinal organoid cells was investigated. RESULTS Our study confirms the feasibility of generating marker-characterized Müller glia and RGC progenitors within retinal organoids. Such retinal organoids can be dissociated and the Müller glia and RGC progenitor-like cells isolated via magnetic-activated cell sorting and propagated as monolayers. CONCLUSION Enrichment of Müller glia and RGC progenitors from retinal organoids is a feasible method with which to study cell type-specific disease phenotypes and to potentially generate specific retinal populations for cell replacement therapies.

Purpose Autoregulation is essential for a constant circulation of O2. The apparent dissimilarity of vulnerability towards increased intraocular pressure in patients with normal‐tension glaucoma (NTGs) and individuals with ocular hypertension (OHTs) has been linked to disturbed autoregulation. The retina is particularly O2‐dependent and susceptible towards oxidative stress. The purpose was to evaluate the impact of a fluctuating O2 level on retinal vessel diameters and plasma levels of vasoregulators, nitric oxide (NO) and endothelin‐1 (ET‐1), and total antioxidant capacity (TAC) in strictly characterized NTGs, OHTs and age‐matched controls. Methods NTGs (n = 10–16), OHTs (n = 9–10) and controls (n = 9–14) were exposed to 2 h of hypoxia followed by 30 min of normoxia. Fundus pictures and blood samples were taken before hypoxia (“baseline”), during hypoxia (“hypoxia”) and after hypoxia (“recovery”). NO, ET‐1 and TAC was measured in plasma. Retinal arterial and vein diameters were measured with MATLAB. Results Retinal arteries dilated in NTGs and OHTs during hypoxia, while controls constricted. No significant changes were seen in retinal veins. During hypoxia controls and NTGs increased plasma levels of ET‐1 and NTGs sustained a high level in recovery. OHTs did not regulate ET‐1 but maintained a lower level compared to NTGs during hypoxia and recovery. No significant differences were seen in NO. OHTs had a higher TAC compared to NTGs and controls throughout the experiment. Conclusions The present study suggests a link between NTG and dysfunctional autoregulation. ET‐1 increase in controls and NTGs during hypoxia. As a vasoconstrictor, a vascular constriction is expected as evident in controls. The observed dilation in NTGs therefore might indicate that molecular mechanisms for vasoregulation are abolished. Surprisingly, OHTs present a similar pattern of autoregulation to NTGs but there is a prominent difference in the TAC. The higher level of TAC in OHTs compared to NTGs and controls indicates that the antioxidant defence might be important in providing resistance towards glaucomatous neurodegeneration.

PurposeNeurodegenerative retinal diseases are a significant course for blindness. Diseases such as glaucoma, which is the leading course of irreversible blindness in the world, and other inner retinal conditions such as inherited mitochondrial neuropathies are poorly understood. The treatment options for these diseases are often limited and insufficient to prevent blindness. Common for most of these diseases is the loss of the retinal ganglion cells (RGC).MethodsTo elucidate the underlying pathological and protective pathways in these inner retinal diseases, respectively, we aim to assess retinal organoids generated from patient‐specific induced pluripotent stem cells (iPSC) and their controls. We have previously established the method of extracting RGCs from our retinal organoids via magnetic‐activated cell sorting (MACS).ResultsThe subsequent characterization of these RGCs was performed using cell‐specific markers such as CD90, BRN3a and RBPMS via qPCR and immunocytochemistry. Electron microscopy was used to investigate the intracellular organelle conditions of the RGCs. Future experiments are aimed at respiratory capacity analysis, metabolomics, transcriptomics and proteomics of RGCs extracted via MACS from retinal organoids derived from patient iPSCs in hopes of identifying the differences and possibly cellular mechanisms contributing to neurodegenerative retinal diseases in patients compared to healthy controls.ConclusionsThis could potentially lead to further understanding of disease mechanisms in patients with inner retinal diseases. In addition, this could establish a diseases model to test new treatment options such as neuroprotective drugs.