Safety assessment of docosahexaenoic acid in X-linked retinitis pigmentosa: the 4-year DHAX trial

Impact of dietary protein and energy levels on fatty acid profile, gut microbiome and cecal metabolome in native growing chickens

The present study investigated the optimal concentration of dietary ME and CP for the fatty acid profile of meat, gut microbiome, and cecal metabolome in Danzhou chickens from 120 to 150 d of age. A total of seven hundred and twenty 120-d-old Danzhou female chickens, with a similar BW, were randomly allocated into 6 treatments with 6 replicates and each of 20 birds. The chickens were fed 2 levels of dietary ME (11.70 MJ/kg, 12.50 MJ/kg), and 3 levels of dietary CP (13%, 14%, and 15%). The results showed that dietary ME and CP levels didn't affect final BW, ADG, ADFI, and feed gain ratio (g: g) (P > 0.05). The serum concentrations of triglyceride, insulin, and glucose in the 12.50 MJ/kg group were the highest (P < 0.05). Dietary ME, CP levels, and their interactions affected (P < 0.05) the fatty acid content in the breast muscle, thigh muscle, and liver. The levels of C18:0, C20:0, C22:0, C22:1, C18:2, C18:3, C22:6, and SFA of the liver in the high ME group were higher than those in the low ME group (P < 0.05). The levels of C16:0, C14:1, C18:1, C22:5, SFA, MUFA and USFA in the low CP group were higher than the corresponding values in the other groups (P < 0.05). Dietary ME and CP levels altered the composition and relative abundance of microbiota in the cecum of chickens at various taxonomic levels to different extents. Significant effects of interactions were found between dietary ME and CP on the relative abundance of 10 species (P < 0.05), and among these species, 6 species belonged to the genus Bacteroides. Notably, the relative abundance of 2 probiotic species including Lactobacillus crispatus and Lactobacillus salivarius was significantly increased (P < 0.05) with increasing dietary ME level. There were 6 differential metabolites in the cecum, comprising thromboxane A2, 5,6-DHET, prostaglandin D2, 20-hydroxyeicosatetraenoic acid, 12(S)-HPETE and prostaglandin I2 significantly reduced (P < 0.05) with increasing the dietary ME level; all of them are involved in arachidonic acid metabolism. In conclusion, the present study suggested that the dietary levels of 12.50 MJ/kg ME and 14% CP enhanced meat quality in terms of fatty acid composition, and showed benefits for maintaining intestinal health via positive regulation of cecal microbiota in native growing Danzhou chickens.

Oxidative Stress and Antioxidant-Based Interventional Medicine in Ophthalmology

The different anatomical compartments of the eye are highly subjected to reactive oxygen species (ROS) generation due to internal factors, such as metabolic high oxygen consumption, as well as environmental factors, including UV light. An antioxidant defense system is endowed in the eye tissues to regulate ROS quantity and activity. When this homeostatic system is overwhelmed, oxidative stress occurs, causing cellular damage, chronic inflammation, and tissue degeneration. It also plays a significant role in the development and progression of various ocular diseases. Understanding the mechanisms underlying oxidative stress in ocular conditions is thus crucial for the development of effective prevention and treatment strategies. To track marketed products based on antioxidant substances as active ingredients, the databases of the European Medicines Agency and the U.S. Food and Drug Administration were consulted. Only a limited number of items were identified, which were either used as therapeutic treatment or during ocular surgery, including antioxidants, synthetical derivatives, or pro-drugs designed to enhance tissue permeation and activity. This review aims to provide an overview of the primary ocular pathologies associated with oxidative stress and of the available pharmacological interventions centered around antioxidant molecules. Such insights are essential for advancing the development of effective prevention and novel treatment approaches.

Emerging gene therapy products for RPGR-associated X-linked retinitis pigmentosa

INTRODUCTION

Mutations in the RPGR gene are responsible for one of the most prevalent and severe types of retinitis pigmentosa. Gene therapy has shown great promise to treat inherited retinal diseases, and currently, four RPGR gene therapy vectors are being evaluated in clinical trials.

AREAS COVERED

This manuscript reviews the gene therapy products that are in development for X-linked retinitis pigmentosa caused by mutations in RPGR, and the challenges that scientists and clinicians have faced.

EXPERT OPINION

The development of a gene therapy product for RPGR-associated retinal degeneration has been a great challenge due to the incomplete understanding of the underlying genetics and mechanism of action of RPGR, and on the other hand, due to the instability of the RPGR gene. Three of the four gene therapy vectors currently in clinical trials include a codon-optimized version of the human RPGR sequence, and the other vector contains a shortened version of the human RPGR. To date, the only Phase I/II results published in a peer-reviewed journal demonstrate a good safety profile and an improvement in the visual field using a codon optimized version of RPGRORF15.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Association between the number of visual fields and the accuracy of future prediction in eyes with retinitis pigmentosa

Purpose

To evaluate the minimum number of visual fields (VFs) required to precisely predict future VFs in eyes with retinitis pigmentosa (RP).

Methods

A series of 12 VFs (Humphrey Field Analyzer 10–2 test (8.9 years in average) were analysed from 102 eyes of 52 patients with RP. The absolute error to predict the 12th VF using the prior 11 VFs was calculated in a pointwise manner, using the linear regression, and the 95% CI range was determined. Then, using 3–10 initial VFs, next VFs (4th to 11th VFs, respectively) were also predicted. The minimum number of VFs required for the mean absolute prediction error to reach the 95% CI was identified. Similar analyses were iterated for the second and third next VF predictions. Similar analyses were conducted using mean deviation (MD).

Results

In the pointwise analysis, the minimum number of VFs required to reach the 95% CI for the 12th VF was five (first and second next VF predictions) and six (third next VF prediction). For the MD analysis, three (first and second next VF predictions) and four (third next VF prediction) VFs were required to reach 95% CI for the 12th VF.

Conclusions

The minimum number of VFs required to obtain accurate predictions of the future VF was five or six in the pointwise analysis and three or four in the analysis with MD.

The potential of marine resources for retinal diseases: a systematic review of the molecular mechanisms

We rely on vision more than on any other sense to obtain information about our environment. Hence, the loss or even impairment of vision profoundly affects our quality of life. Diet or food components have already demonstrated beneficial effects on the development of retinal diseases. Recently, there has been a growing interest in resources from marine animals and plants for the prevention of retinal diseases through nutrition. Especially fish intake and omega-3 fatty acids have already led to promising results, including associations with a reduced incidence of retinal diseases. However, the underlying molecular mechanisms are insufficiently explained. The aim of this review was to summarize the known mechanistic effects of marine resources on the pathophysiological processes in retinal diseases. We performed a systematic literature review following the PRISMA guidelines and identified 107 studies investigating marine resources in the context of retinal diseases. Of these, 46 studies described the underlying mechanisms including anti-inflammatory, antioxidant, antiangiogenic/vasoprotective, cytoprotective, metabolic, and retinal function effects, which we critically summarize. We further discuss perspectives on the use of marine resources for human nutrition to prevent retinal diseases with a particular focus on regulatory aspects, health claims, safety, and bioavailability.

Development and validation of a visual field cluster in retinitis pigmentosa

The aim was to establish and evaluate a new clustering method for visual field (VF) test points to predict future VF in retinitis pigmentosa. A Humphrey Field Analyzer 10-2 test was clustered using total deviation values from 858 VFs. We stratified 68 test points into 24 sectors. Then, mean absolute error (MAE) of the sector-wise regression with them (S1) was evaluated using 196 eyes with 10 VF sequences and compared to pointwise linear regression (PLR), mean sensitivity of total area (MS) and also another sector-wise regression basing on VF mapping for glaucoma (29 sectors; S2). MAE with S1 were smaller than with PLR when between the first-third and first-seventh VFs were used. MAE with the method were significantly smaller than those of S2 when between the first-sixth and first-ninth VFs were used. The MAE of MS was smaller than those with S1 only when first to 3rd and first to 4th VFs were used; however, the prediction accuracy became far larger than any other methods when larger number of VFs were used. More accurate prediction was achieved using this new sector-wise regression than with PLR. In addition, the obtained cluster was more useful than that for glaucoma to predict progression.

Safety of oil from Schizochytrium limacinum (strain FCC-3204) for use in food supplements as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the safety of Schizochytrium sp. oil as a novel food (NF) pursuant to Regulation (EU) 2015/2283. Schizochytrium sp. is a single-cell microalga. The strain FCC-3204, used by the applicant (Fermentalg), belongs to the species Schizochytrium limacinum. The NF, an oil rich in docosahexaenoic acid (DHA), is obtained from microalgae after enzymatic lysis. The applicant proposed to increase the use level of the NF as a food supplement, from 250 mg DHA/day (currently authorised for the general population, excluding pregnant and lactating women) to 3 g DHA/day for adults, excluding pregnant and lactating women. S. limacinum was attributed the qualified presumption of safety (QPS) status with the qualification 'for production purposes only'. Data provided by the applicant demonstrated the absence of viable cells in the NF. No toxicological studies were performed with the NF. However, based on the available toxicological data on oils derived from Schizochytrium sp., the QPS status of the source of the NF, the production process, the composition of the NF and the absence of viable cells in the NF, the Panel considers there are no concerns with regard to toxicity of the NF. The Panel considers that the data provided by the applicant are not sufficient to conclude on the safety of the NF at the proposed uses (3 g DHA/day as a food supplement) in adults. However, in 2012, the Panel concluded that supplemental intakes of DHA alone up to about 1 g/day do not raise safety concerns for the general population. The Panel concludes that the NF is safe for the use in food supplements at the maximum intake level of 1 g DHA/day for the target population (adults, excluding pregnant and lactating women).

[Influence of docosahexaenoic acid treatment on visual acuity, visual field and bioelectric potential of the retina in patients with retinitis pigmentosa]

Retinitis pigmentosa (PR) is manifested by decreased vision, night blindness and narrowing of the visual field. In RP, the level of docosahexaenoic acid (DHA) in blood plasma and red blood cells is significantly reduced. The largest amount of DHA is contained in the retina (30-40% of phospholipids). DHA increases membrane permeability, accelerates the release of vital proteins and retinal enzymes, provides differentiation of photoreceptors, and slows down apoptosis. The introduction of DHA in isolation or in combination with other fatty acids into the body increases its concentration and can be used for metabolism. While there is a known correlation between the level of DHA in the blood and certain retinal functions (visual acuity, light sensitivity, the value of bioelectric potential), many years of multicenter studies have not produced reliable data on the direct effect of isolated or combined use of DHA in maintaining retinal functions in PR. Despite inconsistent outcomes, the clinical trials should continue.

Optimized nonionic emulsifier for the efficient delivery of astaxanthin nanodispersions to retina: in vivo and ex vivo evaluations

Astaxanthin (AST) is a naturally occurring carotenoid with potent anti-oxidative and anti-inflammatory potency against chronic diseases. In this study, we suspended AST in different nonionic emulsifiers to produce nanodispersions. The basic physicochemical properties of the produced AST nanodispersions were verified to select the optimized nonionic emulsifier. Among the tested emulsifiers, Polysorbate 20 produced the AST nanoemulsions with smaller particle diameters, narrower size distributions, and higher AST contents among these emulsifiers. The N-methyl-N-nitrosourea (MNU) administered mouse is a chemically induced retinal degeneration (RD) model with rapid progress rate. AST suspended in Polysorbate 20 was demonstrated to ameliorate the dramatic consequences of MNU on retina architectures and function in several different tests encompassing from electrophysiology to histology and molecular tests. Furthermore, the multi-electrodes array (MEA) was used to detect the firing activities of retinal ganglion cells within the inner retinal circuits. We found that AST nanodispersions could restrain the spontaneous firing response, enhance the light induced firing response, and preserve the basic configurations of visual signal pathway in degenerative retinas. The MEA assay provided an appropriate example to evaluate the potency of pharmacological compounds on retinal plasticity. In summary, emulsifier type affects the basic physicochemical characteristic of AST nanodispersions. Polysorbate 20 acts as an optimized nonionic emulsifier for the efficient delivery of AST nanodispersions to retina. AST nanodispersions can alleviate the photoreceptor loss and rectify the abnormities in visual signal transmission.

Effects of a plant-based fatty acid supplement and a powdered fruit, vegetable and berry juice concentrate on omega-3-indices and serum micronutrient concentrations in healthy subjects

The major aim of this controlled, randomised, open-labelled, parallel-grouped, clinical trial was to investigate whether supplementation with different dosages of omega-3 fatty acids (0.5 g/d and 1 g/d) from a plant-based fatty acid supplement affected omega-3-indices (O3I) in well-nourished, healthy people. In addition, the combined ingestion of the plant-based fatty acid supplement, together with an encapsulated fruit, vegetable and berry (FVB) juice powder concentrate, was applied in order to observe the absorption of certain micronutrients and to examine some aspects related to the safe consumption of the products. The data demonstrate that the intake of only 0.5 g/day of omega-3 fatty acids from of a vegan supplement was able to increase the O3I significantly after 8 and 16 weeks. The combined ingestion with the FVB supplement concurrently increased serum concentrations of specific vitamins and carotenoids without effects on hepatic, kidney and thyroid function or changes in blood lipids.

Progesterone, Lipoic Acid, and Sulforaphane as Promising Antioxidants for Retinal Diseases: A Review

Oxidative stress has been documented to be a key factor in the cause and progression of different retinal diseases. Oxidative cellular unbalance triggers a sequence of reactions which prompt cell degeneration and retinal dysfunction, both hallmarks of several retinal pathologies. There is no effective treatment, yet, for many retinal diseases. Antioxidant treatment have been pointed out to be an encouraging palliative treatment; the beneficial effects documented involve slowing the progression of the disease, a reduction of cell degeneration, and improvement of retinal functions. There is a vast information corpus on antioxidant candidates. In this review, we expose three of the main antioxidant treatments, selected for their promising results that has been reported to date. Recently, the sulforaphane, an isothiocyanate molecule, has been unveiled as a neuroprotective candidate, by its antioxidant properties. Progesterone, a neurosteroid has been proposed to be a solid and effective neuroprotective agent. Finally, the lipoic acid, an organosulfur compound, is a well-recognized antioxidant. All of them, have been tested and studied on different retinal disease models. In this review, we summarized the published results of these works, to offer a general view of the current antioxidant treatment advances, including the main effects and mechanisms described.

Vitamins and Mineral Supplements for Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of inherited progressive retinal dystrophies that is present with progressive vision loss, night blindness, visual field reduction, and retinal pigmentation of the fundus. RP is an uncommon but clinically important disease. It is progressive and potentially blinding, and to date, no cure for RP has been identified and clinical interventions to retard disease progression are limited. Because of the nature of this disease, there has been great interest in the development of therapeutic interventions that may prevent its progression or restore the loss of visual function. Studies have indicated a possible role of vitamins and minerals in preventing the progression of RP: vitamin A has been reported to have an important role in the function of retinal photoreceptors; lutein is assumed to play a preventive role in fundus diseases; and docosahexaenoic acid, which is found within photoreceptor cell membranes, may have a functional role in preventing the progression of RP. Therefore, this study aimed to systematically review data from randomized clinical trials (RCTs) evaluating the safety and efficacy of vitamins and mineral supplements for the treatment of RP. We searched through relevant trials in the Cochrane Library, PubMed, Embase, Ovid, AMED, OpenGrey, ISRCTN registry, http://ClinicalTrials.gov, and the WHO ICTRP ranging from the respective dates of foundation to June 18, 2018. We reviewed eight randomized control trials (RCTs) with data for 1231 patients. The results indicated that patients with RP may experience delayed disease progression with vitamin and mineral supplementation. In a broader sense, this review suggests that the future trials on RP patients should consider more vitamins or mineral supplements and other outcome measures from the trials included in this review.

Cell-based therapeutic strategies for replacement and preservation in retinal degenerative diseases

Cell-based therapeutics offer diverse options for treating retinal degenerative diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP). AMD is characterized by both genetic and environmental risks factors, whereas RP is mainly a monogenic disorder. Though treatments exist for some patients with neovascular AMD, a majority of retinal degenerative patients have no effective therapeutics, thus indicating a need for universal therapies to target diverse patient populations. Two main cell-based mechanistic approaches are being tested in clinical trials. Replacement therapies utilize cell-derived retinal pigment epithelial (RPE) cells to supplant lost or defective host RPE cells. These cells are similar in morphology and function to native RPE cells and can potentially supplant the responsibilities of RPE in vivo. Preservation therapies utilize supportive cells to aid in visual function and photoreceptor preservation partially by neurotrophic mechanisms. The goal of preservation strategies is to halt or slow the progression of disease and maintain remaining visual function. A number of clinical trials are testing the safety of replacement and preservation cell therapies in patients; however, measures of efficacy will need to be further evaluated. In addition, a number of prevailing concerns with regards to the immune-related response, longevity, and functionality of the grafted cells will need to be addressed in future trials. This review will summarize the current status of cell-based preclinical and clinical studies with a focus on replacement and preservation strategies and the obstacles that remain regarding these types of treatments.

Effectiveness and safety of nutritional supplements in the treatment of hereditary retinal dystrophies: a systematic review

The hereditary retinal dystrophies (HRDs) are a group of genetically determined disorders that result in loss of the visual function. There is a lack of standard pharmacological treatments or widely accepted nutritional recommendations. The objective of this review is to summarise the scientific evidence on the effectiveness and safety of nutritional supplements for the treatment of HRDs. We conducted a scientific literature search on Medline and PreMedline, EMBASE, SCI-EXPANDED, SSCI, and The Cochrane Library up to August 2014. Experimental, quasi-experimental and controlled observational studies were selected. Eight studies were ultimately included, seven on retinitis pigmentosa (RP) and one on Best disease. Vitamin A, vitamin E, docosahexaenoic acid (DHA), lutein and β-carotene were assessed. A 15 000 IU daily dose of vitamin A was reported to have shown a small protective effect on the progression of RP, as was the use of the carotenoids lutein and β-carotene. Different DHA doses has no effect on RP or Best disease. No supplement showed severe adverse effects in the selected studies although strong evidence of toxicity exists for high doses of vitamin A and β-carotene in certain populations. The selected studies concluded that there may be a small beneficial effect of vitamin A, lutein and β-carotene on the progression of RP. The limited evidence available indicates some well-designed additional studies on combined supplements strategies may achieve more robust conclusions. Moreover, the scarcity of evidence available on the treatment of HRD other than RP with nutritional supplements supports the need for further research efforts.

Docosahexaenoic Acid Slows Visual Field Progression in X-Linked Retinitis Pigmentosa: Ancillary Outcomes of the DHAX Trial

PURPOSE

Docosahexaenoic acid (DHA) was supplemented in a single-site, placebo-controlled, randomized clinical trial designed to slow vision loss associated with X-linked retinitis pigmentosa (XLRP); the DHAX Trial. We previously reported no significant differences between supplemented and placebo groups in intent-to-treat analysis of primary ERG outcomes. Assessed herein are hypothesis-generating measures of ancillary visual function outcomes in participants fully adhering to trial protocol.

METHODS

Male participants with XLRP (range, 7-31 years) received 30 mg DHA/kg/d (n = 29) or placebo (n = 22) for 4 years. Visual outcomes were measured annually and red blood cell (RBC) DHA determined every 6 months.

RESULTS

Oral DHA supplementation increased mean RBC-DHA levels by 4-fold (P < 0.0001) over placebo. No group differences in progression were found for visual acuity (P = 0.11), shape discrimination (P = 0.18), or fundus appearance (P = 0.70). Optical coherence tomography (OCT) became available during year 2 of the trial; no group differences were seen in ellipsoid zone constriction (P = 0.87) over 2 years. Yearly rates of progression were reduced for dark-adapted thresholds (P = 0.06) and visual field sensitivity for foveal, macular, peripheral, total, and ellipsoid zone regions by DHA supplementation (P = 0.039, P = 0.031, P < 0.0001, P < 0.0001, and P = 0.033). Rates of visual field sensitivity decline were dependent on RBC-DHA (P = 0.046 to <0.0001).

CONCLUSIONS

Supplementation of DHA significantly elevated blood DHA levels and reduced the rate of progression in final dark-adapted thresholds and visual field sensitivity. From the relationship between RBC-DHA and the rate of field sensitivity loss, we can extrapolate that an RBC-DHA level of 17% could minimize the decline in field sensitivity. (ClinicalTrials.gov number, NCT00100230.)

Systematic Review of Randomized Clinical Trials on Safety and Efficacy of Pharmacological and Nonpharmacological Treatments for Retinitis Pigmentosa

Aims. Several treatments have been proposed to slow down progression of Retinitis pigmentosa (RP), a hereditary retinal degenerative condition leading to severe visual impairment. The aim of this study is to systematically review data from randomized clinical trials (RCTs) evaluating safety and efficacy of medical interventions for the treatment of RP. Methods. Randomized clinical trials on medical treatments for syndromic and nonsyndromic RP published up to December 2014 were included in the review. Visual acuity, visual field, electroretinogram, and adverse events were used as outcome measures. Results. The 19 RCTs included in this systematic review included trials on hyperbaric oxygen delivery, topical brimonidine tartrate, vitamins, docosahexaenoic acid, gangliosides, lutein, oral nilvadipine, ciliary neurotrophic factor, and valproic acid. All treatments proved safe but did not show significant benefit on visual function. Long term supplementation with vitamin A showed a significantly slower decline rate in electroretinogram amplitude. Conclusions. Although all medical treatments for RP appear safe, evidence emerging from RCTs is limited since they do not present comparable results suitable for quantitative statistical analysis. The limited number of RCTs, the poor clinical results, and the heterogeneity among studies negatively influence the strength of recommendations for the long term management of RP patients.

Pharmacological approaches to retinitis pigmentosa: A laboratory perspective

Retinal photoreceptors are highly specialized and performing neurons. Their cellular architecture is exquisitely designed to host a high concentration of molecules involved in light capture, phototransduction, electric and chemical signaling, membrane and molecular turnover, light and dark adaption, network activities etc. Such high efficiency and molecular complexity require a great metabolic demand, altogether conferring to photoreceptors particular susceptibility to external and internal insults, whose occurrence usually precipitate into degeneration of these cells and blindness. In Retinitis Pigmentosa, an impressive number of mutations in genes expressed in the retina and coding for a large varieties of proteins leads to the progressive death of photoreceptors and blindness. Recent advances in molecular tools have greatly facilitated the identification of the underlying genetics and molecular bases of RP leading to the successful implementation of gene therapy for some types of mutations, with visual restoration in human patients. Yet, genetic heterogeneity of RP makes mutation-independent approaches highly desirable, although many obstacles pave the way to general strategies for treating this complex disease, which remains orphan. The review will focus on treatments for RP based on pharmacological tools, choosing, among the many ongoing studies, approaches which rely on strong experimental evidence or rationale. For perspective treatments, new concepts are foreseen to emerge from basic studies elucidating the pathways connecting the primary mutations to photoreceptor death, possibly revealing common molecular targets for drug intervention.

Retinal microglia: just bystander or target for therapy?

Resident microglial cells can be regarded as the immunological watchdogs of the brain and the retina. They are active sensors of their neuronal microenvironment and rapidly respond to various insults with a morphological and functional transformation into reactive phagocytes. There is strong evidence from animal models and in situ analyses of human tissue that microglial reactivity is a common hallmark of various retinal degenerative and inflammatory diseases. These include rare hereditary retinopathies such as retinitis pigmentosa and X-linked juvenile retinoschisis but also comprise more common multifactorial retinal diseases such as age-related macular degeneration, diabetic retinopathy, glaucoma, and uveitis as well as neurological disorders with ocular manifestation. In this review, we describe how microglial function is kept in balance under normal conditions by cross-talk with other retinal cells and summarize how microglia respond to different forms of retinal injury. In addition, we present the concept that microglia play a key role in local regulation of complement in the retina and specify aspects of microglial aging relevant for chronic inflammatory processes in the retina. We conclude that this resident immune cell of the retina cannot be simply regarded as bystander of disease but may instead be a potential therapeutic target to be modulated in the treatment of degenerative and inflammatory diseases of the retina.