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In inherited retinal diseases such retinitis pigmentosa, characterized by progressive loss of light sensitive neurons (photoreceptors), cell therapy is now considered as an attractive strategy. Photoreceptor cell replacement would be valuable for restoring function to retinas in a way that is independent from the cause of the disease. With advances in stem cell biology, considerable strides have been made towards the generation of retinal cells, in particular with the development of 3D culture systems allowing the generation of retinal organoids from pluripotent stem cells. In this review, we present a state-of-the art of preclinical strategies conducted in animal models for photoreceptor replacement from stem cell-derived photoreceptors and we discuss the important obstacles to overcome in the future., (© 2020 médecine/sciences – Inserm.)

The neuroretina is a functional unit of the central nervous system that converts a light signal into a nerve impulse. Of neuroectodermal origin, derived from the diencephalon, the neuroretina is a layered tissue composed of six types of neuronal cells (two types of photoreceptors: cones and rods, horizontal, bipolar, amacrine and ganglion cells) and three types of glial cells (Müller glial cells, astrocytes and microglial cells). The neuroretina lays on the retinal pigmentary epithelium, that together form the retina. The existence of the internal and external blood-retinal barriers and intra-retinal junctions reflects the fineness of regulation of the retinal exchanges with the circulation and within the retina itself. The central zone of the human retina, which is highly specialized for visual acuity, has anatomical specificities. Recent imaging methods make it possible now to enrich our knowledge of the anatomical and functional characteristics of the retina, which are still imperfectly described., (© 2020 médecine/sciences – Inserm.)

Generation of retinal organoids from pluripotent stem cells represents an important advance in the study of retinal development and offer new perspectives for the study of retinal diseases missing suitable animal models. Understanding the key stages of retinal development in vertebrates enabled to design protocols to generate self-organized three-dimensional structures derived from pluripotent stem cells and containing all retinal cell types. In addition to their application in basic research, such as the characterization of molecular and cellular mechanisms in retinal pathophysiology, these miniature organs also open up encouraging prospects in the field of cell therapy or the screening of therapeutic molecules, although some obstacles remain to be overcome., (© 2020 médecine/sciences – Inserm.)

Introduction: Circumpapillary retinal nerve fiber layer (cpRNFL) analysis by spectral domain optical coherence tomography (SD-OCT) has become essential for the assessment of glaucoma patients. The foveal projection is conventionally below the disc plane, creating an angle with the horizontal meridian, the disc-fovea angle. The purpose of this study is to evaluate the role of adjustment of cpRNFL analysis based on this angle., Materials and Methods: This study concerns 40 control eyes and 55 eyes affected with and followed for primary open angle glaucoma (POAG). After precise localization of the optic disc center and the axis connecting it to the center of the fovea, a circular peripapillary scan is performed with Spectralis OCT (Heidelberg Engineering, Germany). The mean thickness in each of six papillary sectors and the global mean thickness of the cpRNFL were evaluated. The ROC (receiver operating characteristic) analysis evaluated the diagnostic capabilities of the various sectors before and after adjustment of the analysis for the disc-fovea angle., Results: The disc-fovea angle was not different between the two groups (-7.0 ± 1.2° for controls vs. -6.6 ± 1.2° for POAG, P=0.70). There is a significant variance of this angle in both groups (the angle varies in the control group between -22.5° to +1.8° and in the POAG group between -18° to +2.4°). The global mean and inferior temporal (IT) thickness of the cpRNFL show the best diagnostic performance. Adjustment for disc-fovea angle does not increase the diagnostic accuracy of the various sectors analyzed. Although there is an increase in the area under the curve for the IT sector after adjustment, it is not statistically significant (0.910 ± 0.056 vs. 0.936 ± 0.045, P=0.06)., Conclusions: There is a significant variation in disc-fovea angle. In this study, accounting for it does not significantly improve the diagnostic capabilities of cpRNFL in patients with POAG., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Retinitis pigmentosa (RP) is a hereditary retinal disease leading to blindness, which affects two million people worldwide. Restoring vision in these blind patients was proposed by gene delivery of microbial light-activated ionic channels or pumps "optogenetic proteins" to transform surviving cells into artificial photoreceptors. This therapeutic strategy was validated in blind animal models of RP by recording at the level of the retina and cortex and by behavioural tests. The translational potentials of these optogenetic approaches have been evaluated using in vitro studies on post-mortem human retinal tissues. Here, we review these recent results and discuss the potential clinical applications of the optogenetic therapy for RP patients., (© Société de Biologie, 2013.)

Introduction: The retina is located in a highly oxygenated environment and is therefore particularly susceptible to oxidative damage. Blueberries have a high antioxidant potential since they are rich in anthocyans. The aim of this study was to investigate the cytoprotective role of blueberries on human retinal cells., Materials and Methods: Blueberry extract was incubated at 0.05% and 0.1% for 15 minutes or 24 hours on a human retinal cell line. Then oxidative stress was induced by 150 microM tert-butylhydroperoxide (tBHP) for 1 hour. Intracellular metabolism, reactive oxygen species, superoxide anion, and mitochondrial apoptosis were evaluated using Alamar blue, DCFDA, dihydroethidium, and nonylacridine orange dyes, respectively. Tests were performed using cytofluorometry adapted to microplates., Results: Blueberry protected cells against tBHP-induced cytotoxicity. It increased cell viability, decreased oxidative stress and mitochondrial apoptosis. After a 24-hour preincubation time, blueberry totally inhibited tBHP-induced cytotoxicity., Conclusion: Blueberry seems to be a potent antioxidant and could be easily added to food complements to prevent or limit ocular pathologies induced by oxidative stress.

Retinal dystrophies are rarely curable diseases and several avenues of research are being pursued, such replacement therapies and pharmacological treatment. Among them, the transplantation of functional retinal cells has been envisaged in order to restore vision in patients who have these diseases by repopulating the damaged retina and/or by rescuing retinal neurons from further degeneration. Over the past few years, identification and characterization of stem cells has opened new avenues in cell-replacement therapy. Since retinal stem cells are already present during embryonic development, they persist in the adult mammalian eye only in the ciliary marginal zone, even a stem cell potential has been described for the Müller glia in the retina. This result opened possibilities of regeneration by mobilizing endogenous stem cells to respond to injury. Regarding the transplantation studies, in all experiments using different types of stem cells (retinal progenitors, neural stem cells, bone marrow-derived stem cells and ES cells), despite their incorporation within the host's retina, the transplanted cells failed to express retina-specific markers and to establish synaptic connections. Therefore, the true potential of the different stem cells in retina repair can only be realized with more information about mechanisms that regulate their proliferation and differentiation; and by development of techniques that allow their prospective identification and enrichment.

Purpose: To determine the role of different ocular tissues in the development of the human fetal neuroretina heterotopically implanted in nude mice., Material and Methods: Fifty eight eyeballs obtained from legally aborted 6- to 7-week-old embryos or 8- to 10-week-old fetuses were heterotopically implanted in nude mice. Over a period of 1-245 days, all the grafts were removed for light and electron microscopy observations., Results: All grafts were successful. Twenty six exhibited a normal histological organization of the choriocapillaris, the retinal pigment epithelium, and the neuroretina in the posterior part of the eye. Photoreceptor differentiation was observable approximately 80 days after transplantation and was complete at 166 days. The anterior part of the retina was always dysplasic. Twenty three eyes had a dysplasic neuroretina with folds, rosettes, and necrotized areas. In absence of retinal pigment epithelium, the neuroretina was always dysplasic or absent. Nine eyes were atrophic without any differentiation of the neuroretina., Conclusion: These results demonstrate that the development of a stratified neuroretina requires both rapid revascularization and normal development of retinal pigment epithelium. When these conditions are not met, the neuroretina becomes dysplasic or atrophic or disappears.

Purpose: To analyse the correlation between changes in the nerve fiber layer and the appearance of defects in the visual field in primary open angle glaucoma (POAG)., Material: and methods: Digital image processing of the nerve fiber layer and examination of the visual field (30-2 Humphrey) was performed in 450 patients. The conditions for obtaining the digital images are presented., Results: Defects of the nerve fiber layer were evaluated qualitatively and quantitatively using automatic perimetry and the correlation was estimated. The results are discussed., Conclusion: Examination of patients suspected of having POAG is much more precise when using both techniques performed the same day. Thus it will be possible to save time for: early diagnosis, monitoring the treatment, limiting the progression of glaucoma.

The retina, 350 microns thick membrane, has to transform the light stimulus into visual data. Cones and rods are essential to this phototransduction. Retina structure is now well explored using investigations such as echography, and angiography. Fluorescein angiography and indocyanin green angiography have improved our knowledge of many ocular diseases, especially in age related macular degeneration and in diabetic retinopathy.

This study is the first demonstration of glial fibrillary acidic protein (GFAP)-immunoreactivity in the retina of the lamprey Lampetra fluviatilis. This immunoreactivity is expressed on one hand, in radial processes and somata which belong to Müller cells and, on the other hand, in horizontal fibers in the intermediate plexus between horizontal cells. The tracing of these fibers to Müller cells or horizontal cells is discussed.

Transduction of a visual signal is a complex process. It involves photochemical, enzymatic and ionic reactions. An electrophysiological response is generated on absorption of a photon by a photoreceptor cell's pigment molecule, then propagates to the synapses. The first photochemical reaction, isomerization of retinal, in vertebrates occurs in the photoreceptor cells--rods and cones--of the retina, so changes conformation and activity of a pigment-bound protein, rhodopsin, in membranes of intracellular discs. Rhodopsin becomes enzymatically active and catalyses the activation by GTP of a great number of transducins, which in turn activate cGMP phosphodiesterase. This enzymatic chain propagates and greatly enhances hydrolysis of cytoplasmic cGMP. One photon incites hydrolysis of 10(5) cGMP molecules in 100 ms. Local cGMP decrease frees it from specific binding sites in cytoplasm occupied by proteinaceous canals in cell membrane around the activated disc. In darkness high cGMP concentration, hence binding, kept canals open, maintaining high cellular cation permeability, especially to Na+, and a strong cellular depolarization. Ca2+ influx, also allowed, balanced Na+ movement. Canal closure induces local hyperpolarization, the first electrophysiological response, which propagates through the cell to synaptic contacts. It also lowers intracellular Ca2+ concentration which initiates cGMP synthesis--from GTP by a guanylate cyclase controlled negatively by recoverin, a calcium-dependent protein--to restore cGMP towards at rest level. Although all macromolecules involved in this now fairly complete scheme have been isolated and characterized, cloned and sequenced, no three-dimensional structure has yet been established. The proteins are membrane-bound rather than in independent crystal form, which renders such structural studies difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Birds are an excellent material for the study of retinal adaptation. In this work, the purpose of the authors is to analyse differences between electroretinograms of species of diurnal habits (Falconiformes) and electroretinograms of species of nocturnal habits (Strigiformes). The same is done on histology material about the two types of retina. The electroretinography answers and the retina histology can be correlated with the different species habits.

In situ hybridization of nucleic acid probes, encoding the key enzymes of the synthesis of neurotransmitters, with sections of retina is a new method giving complementary informations to the data obtained by immunocytochemistry and autoradiography. It will allow a better characterization of amacrin cells, whatever might be their type, and a refined understanding of their function. It is an accurate tool to investigate the mechanisms of retinal degenerations and spontaneous or experimental microphtalmia.

Kainic acid administered intravitreally induced mitogenic effects in the adult rat retina at doses ranging from 60 nm to 200 nm. Similar effects resulted from the injection of domoic acid at doses ranging from 20 nm to 400 nm, and ouabain. L-glutamate, N-methyl D-aspartate and quisqualate provoked similar cytotoxic effects, i.e., swelling and vasuolization of the outer plexiform, inner nuclear and inner plexiform layer, and cell pycnosis. The latter induced no mitoses. The use of Rompun ketamine as anesthetic blocked the mitogenic effects. The immunohistochemical labelling of both glial fibrillary acidic protein and S100 protein in the dividing cells and the location of dividing nuclei in the inner nuclear layer are arguments for their Müllerian nature. We suggest that the mitogenic effects could account for reactive gliosis observed in some clinical conditions.

Immunoreactive neuropeptides have been found in cultures of neuroretina cells obtained from 7 day Chick embryos. Methionine-enkephalin and thyroliberin (TRH) were present in a large number of neurons, while somatostatin, beta-melanotropin (MSH) and alpha-endorphin were occasionally seen in a few neurons. In cultures devoid of neurons and probably made of Müller (astroglial) cells, methionine-enkephalin, alpha-MSH and TRH were each detected in 60 to 80% of the cells. Immunoreactive methionine enkephalin was also localized in Müller cells in retina sections of 10 and 20 day old embryos.

The unilateral resection have been done entirely or in part of the primary visual cortex in 10 cats with various postoperational delays. In all cases, some large and medium axons in the primary optic tract show signs of degeneration, leading to their disappearance along with an important glial reaction. As there in similar signs of degeneration, but apparently less important in all normal cats used for control, it is worth-while to reconsider the notion of retrograde transneuronal degeneration after cortical lesion.

The central efferent connections to the retina in Microcebus were identified using the retrograde axonal transport of fluorescent dyes. After unilateral intraocular injection of the tracer, two populations of labeled neurons were observed. Fluorescent neurons were located immediately posterior to the optic chiasma, in the anterior part of the arcuate nuclei. In addition, fluorescent neurons were observed in the suprachiasmatic nuclei; the latter pathway appears to close up an anatomical retino-hypothalamo-retinal loop between the suprachiasmatic nucleus and the retina.

Color discrimination in the red portion of the visual spectrum was studied for different retinal locations under "behavioural" fixation. In spite of the different distribution of coloured oil-droplets, the discrimination function remains the same.

Two different immunohistochemical double labelling techniques have allowed the demonstration of a GABA-immunoreactivity in the dopamine amacrine cells of the rat retina. The functional implications of such a colocalization are of importance because antagonist effects of these two neurotransmitters on retinal horizontal cells have been demonstrated.

1. Intracellular recordings were made from the retinula units of the cricket Nemobius sylvestris. The half width of the angular sensitivity function was estimated at 4,4 degrees. This mean acceptance angle is slightly smaller than the interommatidial angle. In these conditions of light adapted state and for ommatidia of the central eye region, an overlapping between adjacent ommatidia occurs, but only below the 50% sensitivity level. 2. Extracellular positive responses with the waveform of a smoothed retinula receptor potential were recorded and their origin from lamina is postulated. They were strongly influenced by lateral interactions with the neighbouring ommatidia, and it was concluded that a lateral inhibition in the first optic ganglion of the cricket does exist.

The examination of 16 human retina stained in toto according to the Gallego method (1953) demonstrated the presence of centrifugal optic fibers. These fibers appear as large argyrophilic axons and can be traced as of the papille, amongst the centripetal optic fibers. The centrifugal fibers show a high degree of ramification which may extend over a quarter of the total retinal surface and terminate in the internal plexiform layer. Elsewhere the existence of perivascular and intravascular axon terminals as well as short axon ganglion nerve cells were demonstrated.

An intravitreal injection of the D isomer of the alpha-amino adipic acid (alpha-aa) entails the progressive disappearance of the ERG b wave as well as that of tectal evoked potentials (TEP). These physiological effects are concomitant with a specific glial cell damage in frog and chicken retinas. At low concentrations, the L isomer is more gliotoxic than the D isomer; the ERG b wave is suppressed while TEP are always recorded. At higher concentrations, the L isomer suppresses TEP and damages both glial and neuronal cells.

Using an anti-human S-100 protein antibody, the Müller cells of the retina of the monkey Macacus irus were immunostained in the neural retina and in the ora serrata. In the anterior part of the retina (blind retina), all the cells were immunostained with the anti-S-100 protein antibody.

Immunoreactive neuropeptides have been found in cells of permanent lines originating from nervous (cerebellum, retina) and non nervous (mesenchyme, kidney, bladder, colon, lung, melanocyte) tissues. The pattern of neuropeptides varied from one cell type to another, but all the cell lines studied contained immunoreactive alpha-endorphin and methionin-enkephalin.

The retinal projections in Caiman sclerops have been re-examined using the radio-autographic method for tracing axonal pathways. Following the intraocular injection of a mixture of [3H]proline and [3H]fucose, label transported in the rapid phase of axonal flow was found only on controlateral side to the injection in the nuceli, supra-opticus, ovalis, geniculatus lateralis pars dorsalis and pars ventralis, geniculatus pretectalis, lentiformis mesencephali, griseus tectalis, opticus tegmenti and in the superficial layers of the tectum opticum (layers 1 to 6). Label transported in the slow phase confirms the absence of an ipsilateral optic component. No controlateral retinofugal fasicule crossing over in the posterior commissure as previously described in this species using the Nauta method (3) was observed. In comparison with degeneration study in Caiman sclerops (3) the radio-autographic results demonstrated more accurately the sites of termination of retinofugal fibers.

The phenylethanolamine-N-methyltransferase immunoreactive cells were demonstrated by the first postnatal day in whole-mounted retinas. They were distributed all over the retina in young rats (more numerous in the superior temporal quadrant) and were restricted to the superior retina in adult rats.