Acute Retinal Injury Research Articles

New pathways to neurogenesis: Insights from injury-induced retinal regeneration.

The vertebrate retina is a tractable system for studying control of cell neurogenesis and cell fate specification. During embryonic development, retinal neurogenesis is under strict temporal regulation, with cell types generated in fixed but overlapping temporal intervals. The temporal sequence and relative numbers of retinal cell types generated during development are robust and show minimal experience-dependent variation. In many cold-blooded vertebrates, acute retinal injury induces a different form of neurogenesis, where Müller glia reprogram into retinal progenitor-like cells that selectively regenerate retinal neurons lost to injury. The extent to which the molecular mechanisms controlling developmental and injury-induced neurogenesis resemble one another has long been unclear. However, a recent study in zebrafish has shed new light on this question, using single-cell multiomic analysis to show that selective loss of different retinal cell types induces the formation of fate-restricted Müller glia-derived progenitors that differ both from one another and from progenitors in developing retina. Here, we discuss the broader implications of these findings, and their possible therapeutic relevance.

Photoreceptor regeneration occurs normally in microglia-deficient irf8 mutant zebrafish following acute retinal damage

Microglia are resident immune cells in the central nervous system, including the retina that surveil the environment for damage and infection. Following retinal damage, microglia undergo morphological changes, migrate to the site of damage, and express and secrete pro-inflammatory signals. In the zebrafish retina, inflammation induces the reprogramming and proliferation of Müller glia and the regeneration of neurons following damage or injury. Immunosuppression or pharmacological ablation of microglia reduce or abolish Müller glia proliferation. We evaluated the retinal architecture and retinal regeneration in adult zebrafish irf8 mutants, which have significantly depleted numbers of microglia. We show that irf8 mutants have normal retinal structure at 3 months post fertilization (mpf) and 6 mpf but fewer cone photoreceptors by 10 mpf. Surprisingly, light-induced photoreceptor ablation induced Müller glia proliferation in irf8 mutants and cone and rod photoreceptor regeneration. Light-damaged retinas from both wild-type and irf8 mutants show upregulated expression of mmp-9, il8, and tnfβ pro-inflammatory cytokines. Our data demonstrate that adult zebrafish irf8 mutants can regenerate normally following acute retinal injury. These findings suggest that microglia may not be essential for retinal regeneration in zebrafish and that other mechanisms can compensate for the reduction in microglia numbers.

Identifying Hmga2 preserving visual function by promoting a shift of Müller glia cell fate in mice with acute retinal injury

BackgroundUnlike in lower vertebrates, Müller glia (MG) in adult mammalian retinas lack the ability to reprogram into neurons after retinal injury or degeneration and exhibit reactive gliosis instead. Whether a transition in MG cell fate from gliosis to reprogramming would help preserve photoreceptors is still under exploration.MethodsA mouse model of retinitis pigmentosa (RP) was established using MG cell lineage tracing mice by intraperitoneal injection of sodium iodate (SI). The critical time point for the fate determination of MG gliosis was determined through immunohistochemical staining methods. Then, bulk-RNA and single-cell RNA seq techniques were used to elucidate the changes in RNA transcription of the retina and MG at that time point, and new genes that may determine the fate transition of MG were screened. Finally, the selected gene was specifically overexpressed in MG cells through adeno-associated viruses (AAV) in the mouse RP model. Bulk-RNA seq technique, immunohistochemical staining methods, and visual function testing were used to elucidate and validate the mechanism of new genes function on MG cell fate transition and retinal function.ResultsHere, we found the critical time point for MG gliosis fate determination was 3 days post SI injection. Hmga2 was screened out as a candidate regulator for the cell fate transition of MG. After retinal injury caused by SI, the Hmga2 protein is temporarily and lowly expressed in MG cells. Overexpression of Hmga2 in MG down-regulated glial cell related genes and up-regulated photoreceptor related genes. Besides, overexpressing Hmga2 exclusively to MG reduced MG gliosis, made MG obtain cone’s marker, and retained visual function in mice with acute retinal injury.ConclusionOur results suggested the unique reprogramming properties of Hmga2 in regulating the fate transition of MG and neuroprotective effects on the retina with acute injury. This work uncovers the reprogramming ability of epigenetic factors in MG.

Differential Responses of Neural Retina Progenitor Populations to Chronic Hyperglycemia.

Diabetic retinopathy is a frequent complication of longstanding diabetes, which comprises a complex interplay of microvascular abnormalities and neurodegeneration. Zebrafish harboring a homozygous mutation in the pancreatic transcription factor pdx1 display a diabetic phenotype with survival into adulthood, and are therefore uniquely suitable among zebrafish models for studying pathologies associated with persistent diabetic conditions. We have previously shown that, starting at three months of age, pdx1 mutants exhibit not only vascular but also neuro-retinal pathologies manifesting as photoreceptor dysfunction and loss, similar to human diabetic retinopathy. Here, we further characterize injury and regenerative responses and examine the effects on progenitor cell populations. Consistent with a negative impact of hyperglycemia on neurogenesis, stem cells of the ciliary marginal zone show an exacerbation of aging-related proliferative decline. In contrast to the robust Müller glial cell proliferation seen following acute retinal injury, the pdx1 mutant shows replenishment of both rod and cone photoreceptors from slow-cycling, neurod-expressing progenitors which first accumulate in the inner nuclear layer. Overall, we demonstrate a diabetic retinopathy model which shows pathological features of the human disease evolving alongside an ongoing restorative process that replaces lost photoreceptors, at the same time suggesting an unappreciated phenotypic continuum between multipotent and photoreceptor-committed progenitors.

In vivo monitoring the dynamic process of acute retinal hemorrhage and repair in zebrafish with spectral-domain optical coherence tomography.

Retina, the only light sensor in the human eye, is hidden and extremely fragile. Optimized animal models and efficient imaging techniques are very important for the study of retinopathy. In this work, the rapid retinal injury process and the long-term retinal repair process were in vivo continuously evaluated with a novel imaging technology spectral-domain optical coherence tomography (SD-OCT) in a unique animal model zebrafish. Acute retinal injury was constructed on adult zebrafish by needle injection surgery. SD-OCT imaging was carried out immediately after the mechanical injury. The retinal hemorrhage, which lasted only 5 seconds, could be visualized dynamically by SD-OCT. The process of blood clearance and retinal repair was also evaluated because SD-OCT imaging is nondestructive. Both SD-OCT imaging results and behavioral analyzing results demonstrated that zebrafish retina could be repaired by itself within 15 days, which was confirmed by the results of pathological experiment.

MTOR regulates neuroprotective effect of immunized CD4+Foxp3+ T cells in optic nerve ischemia.

The therapeutic potential of targeting CD4+Foxp3+ regulatory T cells (Tregs) remains controversial under the condition of neuroinflammation. This study aims to explore the neuroprotective role of Tregs in optic nerve ischemia (ONI) and evaluate the therapeutic strategy of Tregs transfer with a focus on targeting the mammalian target of rapamycin (mTOR) pathway. Intraocular pressure was transiently increased in adult C57BL/6 mice to induce ONI. Mucosal tolerance of myelin basic protein (MBP) markedly increased retinal ganglion cell (RGC) survival after ONI through enhanced Tregs suppression. mTOR inhibition significantly promoted the frequency of MBP-immunized Tregs in vitro with increased production of anti-inflammatory cytokines. Transient rapamycin treatment highly promoted the immunosuppressive capacity of Tregs and inhibited retinal inflammation in ONI animals. Intravenous infusion of MBP-immunized Tregs, instead of regular Tregs, beneficially modulated immune activities of host retinal CD11b+ cells and CD4+ effector T cells, leading to significant improvement of RGC survival. Importantly, rapamycin treatment further enhanced the neuroprotective effect of Tregs transfer. Taken together, these findings reveal a fine regulation of mTOR signaling on immunized Tregs after acute retinal injury. Adoptive transfer with targeting-mTOR strategy markedly improves neuronal recovery after ONI, supporting the therapeutic potentials of Tregs in acute and chronic neurological disorder.

Acute retinal injury and the relationship between nerve growth factor, Notch1 transcription and short-lived dedifferentiation transient changes of mammalian Müller cells

Our aim is to define related molecular events on how dormant Müller glia cells re-enter the cell cycle, proliferate and produce new retinal neurons from initial injury to glial scar formation. Sodium iodate (NaIO3) was used to induce acute retinal injury. Long-Evans rats were administered with NaIO3 or phosphate-buffered saline by intraperitoneal injection. The proliferation, dedifferentiation and neurogenesis of Müller cells were analyzed by double-labeled fluorescence immunohistochemistry with primary antibodies – against Müller cells and specific cell markers. Possible molecules that limit the regenerative potential of Müller cells were also determined by immunofluorescence staining, quantitative RT-PCR, protein array, ELISA and Western blot. In the first 3–7days after NaIO3 administration, Müller cells were activated and underwent a fate switch, including transient proliferation, dedifferentiation and neurogenesis. Nerve growth factor (NGF) signaling concomitantly increased with the downregulation of p27Kip1 in Müller cells, which may promote Müller cells to re-enter the cell cycle. The transient increase of NGF signaling and the transient decrease of Notch signaling inhibited Hes1, which might enhance the neuronal differentiation of dedifferentiated Müller cells and suppress gliosis. Upregulated Notch and decreased NGF expressions limit dedifferentiation and neurogenesis, but induces retinal Müller cell gliosis at a later stage. We conclude that transient NGF upregulation and Notch1 downregulation may activate the transient proliferation, dedifferentiation and neurogenesis of Müller cells during NaIO3-induced acute retinal injury; which could be a therapeutic target for overcoming Müller cell gliosis. Such therapy could be potentially used for treating retinal-related diseases.

Neuroprotective and antiapoptotic activity of lineage-negative bone marrow cells after intravitreal injection in a mouse model of acute retinal injury.

We investigated effects of bone marrow-derived, lineage-negative cell (Lin−BMC) transplantation in acute retinal injury. Lin−BMCs were intravitreally injected into murine eyes at 24 h after NaIO3-induced injury. Morphology, function, and expression of apoptosis-related genes, including brain-derived neurotrophic factor (BDNF) and its receptor, were assessed in retinas at 7 days, 28 days, and 3 months after transplantation. Moreover, global gene expression at day 7 was analyzed by RNA arrays. We observed that Lin−BMCs integrated into outer retinal layers improving morphological retinal structure and induced molecular changes such as downregulation of proapoptotic caspase-3 gene, a decrease in BAX/BCL-2 gene ratio, and significant elevation of BDNF expression. Furthermore, transplanted Lin−BMCs differentiated locally into cells with a macrophage-like phenotype. Finally, Lin−BMCs treatment was associated with generation of two distinct transcriptomic patterns. The first relates to downregulated genes associated with regulation of neuron cell death and apoptosis, response to oxidative stress/hypoxia and external stimuli, and negative regulation of cell proliferation. The second relates to upregulated genes associated with neurological system processes and sensory perception. Collectively, our data demonstrate that transplanted Lin−BMCs exert neuroprotective function against acute retinal injury and this effect may be associated with their antiapoptotic properties and ability to express neurotrophic factors.

Dose-Dependent Retinal Changes Following Sodium Iodate Administration: Application of Spectral-Domain Optical Coherence Tomography for Monitoring of Retinal Injury and Endogenous Regeneration

Background: The purpose of this study was to demonstrate the progression of acute retinal injury by correlating histological sections with in vivo spectral-domain optical coherence tomography (SD-OCT) images.Methods: Male C57BL/6 mice were treated intravenously with two different sodium iodate (NaIO3) doses (35 mg/kg or 15 mg/kg). In vivo SD-OCT was performed up to 3 months post-injury. Ex vivo retinal histology, TUNEL and IsolectinB4 immunostaining were also conducted. Quantitative comparison of histopathological images and SD-OCT images was performed.Results: SD-OCT examination revealed that administration of 35 mg/kg NaIO3 was associated with progressive and irreversible retinal degeneration. On day 3 post-injury, we found numerous apoptotic cells in the outer nuclear layer (ONL) that strongly corresponded to hyper-reflective areas in the SD-OCT images. At 7 d post-injury, SD-OCT images showed irregular-shaped patterns of hyper-reflectivity in the retinal pigment epithelium (RPE) that corresponded with the accumulation of macrophages phagocytosing melanin granules and cell debris. Additionally, we documented hyper-reflective opacities in the vitreous that were most numerous at 7 d. At 3 months post-injury, the neurosensory retina was significantly thinner, predominantly due to progressive photoreceptor (PR) loss. In contrast, administration of 15 mg/kg NaIO3 did not induce hyper-reflectivity of ONL in SD-OCT images, which indicates a lack of massive PR cell death. At 3 months post-injury, SD-OCT images showed the complete restoration of outer retina lamination and restoration of hyper-reflective structural bands. Histological assessment of retinas acquired after the last SD-OCT imaging session revealed complete regeneration of the RPE and considerable improvement of PR architecture.Conclusions: Our findings showed the high level of effectiveness of SD-OCT imaging for monitoring dynamic changes in retinal morphology following acute retinal injury. Moreover, we demonstrated for the first time that SD-OCT can be used to non-invasively detect regeneration in the damaged retina.

Sodium Iodate Influences the Apoptosis, Proliferation and Differentiation Potential of Radial Glial Cells In Vitro

Background/Aims: Sodium iodate (NaIO₃)-induced acute retinal injury is typically used as an animal model for degenerative retinal disease; however, how NaIO₃ influences the apoptosis, proliferation and differentiation of endogenous retinal stem cells is unknown. Methods: We exposed a radial glial cells (RGCs) line (L2.3) to different NaIO₃ concentrations and determined the influence of NaIO₃ on apoptosis, proliferation, and differentiation using flow cytometry and immunofluorescence assays. We used a real-time polymerase chain reaction assay to analyze the levels of mRNAs encoding GSK-3β, AXIN2, β-catenin, TGF-β1, SMAD2, SMAD3, NOG (Noggin), and BMP4. Results: Cell density decreased dramatically as a function of the NaIO₃ dose. NaIO₃ increased apoptosis, inhibited mitosis, proliferation, and the Wnt/β-catenin pathway. CHIR99021 (Wnt agonist) treatment efficiently reversed the effects of NaIO₃ on the apoptosis and proliferation of RGCs. The number of neuronal class III β-tubulin-positive cells decreased markedly, whereas that of glial fibrillary acidic protein-positive cells increased significantly when RGCs were exposed to NaIO₃. During differentiation, the Nog mRNA level decreased and transforming growth factor-β1 (Tgf-β1) and Smad2/3 mRNA levels increased significantly when RGCs were exposed to NaIO₃. Conclusion: NaIO₃ increased apoptosis, influenced the proliferation of RGCs and drove them toward astrocytic differentiation, likely through inhibition of the Wnt/β-catenin and noggin pathways and activation of the TGF-β1/SMAD2/3 pathway.

Long-Term Neuroprotective Effects of NT-4–Engineered Mesenchymal Stem Cells Injected Intravitreally in a Mouse Model of Acute Retinal Injury

Retinal degenerative diseases targeting the RPE and adjacent photoreceptors affect millions of people worldwide. The field of stem cell- and gene-based therapy holds great potential for the treatment of such diseases. The present study sought to graft genetically engineered mesenchymal stem cells (MSCs) that continuously produce neurotrophin-4 (NT-4) into the murine eye after the onset of acute retinal injury. C57BL/6 mice were subjected to acute retinal damage using a low dose of sodium iodate (20 mg/kg of body weight), followed by intravitreal injection of lentivirally modified MSC-NT-4 into the right eye. At 3 months after the MSC transplantation grafted cell survival, retinal function and gene expression were analyzed. Immunofluorescence analysis confirmed that transplanted MSCs survived for at least 3 months after intravitreal injection and preferentially migrated toward sites of injury within the retina. MSC-NT-4 actively produced NT-4 in the injured retina and significantly protected damaged retinal cells, as evaluated by ERG and optical coherence tomography (OCT). Of importance, the long-term therapy with MSC-NT-4 was also associated with induction of prosurvival signaling, considerable overexpression of some subsets of transcripts, including several members of the crystallin β-γ superfamily (Cryba4, Crybb3, Cryba2, Crybb1, Crybb2, Cryba1, and Crygc) and significant upregulation of biological processes associated with visual perception, sensory perception of light stimulus, eye development, sensory organ development, and system development. Transplantation of genetically modified MSCs that produce neurotrophic growth factors may represent a useful strategy for treatment of different forms of retinopathies in the future.

Effect of Anterior Chamber Cannulation and Acute IOP Elevation on Retinal Macrophages in the Adult Mouse

To assess the retinal macrophage response to cannulation of the anterior chamber (AC) and acute elevation of intraocular pressure (IOP) in adult mice. Eyes from 12-month-old C57BL/6J WT mice were subject to IOP increase (50 mm Hg for 30 minutes) by direct cannulation of the AC. Fellow eyes were either cannulated without pressure increase or left untreated. Electroretinography was carried out prior to IOP elevation and 1 week later. Immunofluorescence staining was performed on frozen sections and retinal wholemounts 1 week after sham and IOP elevation. Eyes were assessed by epifluorescence and confocal microscopy and the density of vitreal hyalocytes and subretinal macrophages was calculated. The density of hyalocytes and subretinal macrophages was significantly increased 1 week after IOP elevation and AC cannulation compared with naïve eyes. CD68 and MHC Class II expression was upregulated in both cannulated eyes and eyes with elevated IOP. Electroretinographic signals derived from retinal ganglion cells were significantly reduced in response to acute IOP elevation, but not in response to cannulation alone. Cannulation of the AC causes an increase in hyalocyte density, microglial activation, and accumulation of macrophages in the subretinal space. These macrophage changes are similar to those observed in eyes subject to IOP elevation. Additional IOP elevation led to significant Müller cell activation, which was not evident after cannulation alone. These data highlight the importance of using appropriate controls in models of acute retinal injury.

Adjuvant stem cell‐based therapy in acute retinal injury after sodium iodate administration in mice

AbstractPurpose The aim of this study was to determine and optimize a new strategy of SC‐based therapy of selectively damaged retina after sodium iodate (NaIO3) administration in C57BL/6J mice.Methods To address this issue, we investigated the effects of NaIO3 administrated in two different concentrations, i.e. 40 and 20 mg per kg of the body mass. Electrophysiological function of the retina using dark‐and light‐adapted full field flash ERG as well as morphological characteristics, were determined at several time points after each dose administration. Next, we performed intravitreal transplantation of murine GFP+Lin‐ cells on the 1st day since NaIO3 administration. We analyzed the retinal functional changes as well as the number, localization and phenotype of intravitreally injected GFP+Lin‐ cells within recipients’ retinas.Results Our findings revealed that massive destruction of the tissue was associated with irreversible retinal dysfunction, whereas moderate retinal injury triggered regenerative mechanisms that restore bioelectrical function of the damaged retina.By employing SC‐based therapy we achieved noticeable improvement of the retinal function, particularly in the short‐term observation. We observed the presence and proliferation of the injected cells at the site of RPE injury.Conclusion Our study provides evidence that NaIO3‐induced retinal damage triggers a sequence of pathophysiological events dedicated to supporting the self‐regeneration of injured tissue. Our results indicate that if the scope of retinal destruction is profound, endogenous regeneration is ineffective and may ultimately require therapeutic transplantation of specific stem cell subpopulations and other adjuvant therapies.

Anti-Retinal Antibodies in Serum of Laser-Treated Rabbits

Retinal injuries that affect the photoreceptors and/or the retinal pigment epithelium (RPE) may result in the leakage of retinal proteins into the systemic circulation. This study was designed to determine whether an immune response is elicited after an acute retinal injury resulting in circulating anti-retinal antibodies in the serum. Fifty laser burns of different grades (minimally visible lesion [MVL], grade II [GII], or grade III [GIII] lesions) were created in the retinas of Dutch Belted rabbits. The degree of laser burns was confirmed by fundus imaging and histology. Serum samples were collected from the animals 3 months after the retinal injury. Candidate autoantigens were identified by two-dimensional (2-D) Western blots of rabbit retinal lysate probed with sera from either control or laser-treated animals. Candidate autoantigens were further characterized by immunostaining to confirm their retinal localization. Seven and 11 protein spots were selected from the MVL and GII laser-treated samples, respectively, for autoantigen identification. No protein spots were detected in the GIII laser-treated samples. Four candidate autoantigens were common to both MVL and GII lesions: dihydropyrimidinase-related protein 2, fructose-bisphosphate aldolase C, chaperonin-containing T-complex polypeptide 1 subunit zeta, and pyruvate kinase isozyme. Laser-induced retinal injuries resulted in circulating anti-retinal antibodies that were detectable 3 months after the injury. The response appeared to vary with the severity of the laser retinal damage. The identification of the candidate antigens in this study suggest that this approach may permit future development of new diagnostic methods for retinal injuries.

Increased Müller Cell De-Differentiation After Grafting of Retinal Stem Cell in the Sub-Retinal Space of Royal College of Surgeons Rats

In several vertebrate classes, the Müller glia are capable of de-differentiating, proliferating, and acquiring a progenitor-like state in response to acute retinal injury or in response to exogenous growth factors. Our previous study has shown that Müller cells can be activated and de-differentiated into retinal progenitors during Royal College of Surgeons (RCS) rats' degeneration, although the limited proliferation cannot maintain retinal function. We now report that rat retinal stem cells (rSCs) transplanted into RCS rats slowed the progression of retinal morphological degeneration and prevented the functional disruption. Further, we found that retinal progenitor cells labeled with Chx10 were increased significantly after rSCs transplantation, and most of them are mainly from activated Müller cells. rSCs transplantation also enhances neurogenic potential by producing more recoverin-positive photoreceptors, which was proved coming from Müller glia-derived cells. These results provide evidence that stem cell-based therapy may offer a novel therapeutic approach for the treatment of retinal degeneration, and that Müller glia in mammalian retina can be activated and de-differentiated by rSC transplantation and may have therapeutic effects.

Expression of neuroglobin gene in acute hypoxic-ischemic retinal injury of rat

目的 探讨大鼠急性缺血性视网膜损伤中脑红蛋白(NGB)基因的表达及变化.方法 随机将50~60日龄Wistar大鼠70只分为7组,左眼造模,制成高眼压诱导的视网膜急性缺血损伤模型,分别在眼压升高1、5、10、15、20、30、60min迅速取视网膜,对侧眼作为自身正常对照直接取视网膜.提取视网膜组织总RNA,用半定量RT-PCR进行检测.结果 检测中可见缺血1min组,NGB mRNA表达较对照组迅速增加(P=0.017),缺血5min达高峰,与对照组比较差异有统计学意义(P=0.000);10~15min开始降低,但仍然保持在高水平(10min,P=0.001;15min,P=0.038);20~30min已迅速降低,但仍高于对照组(20min,P=0.269;30min,P=0.402);60min相对于对照组水平略有降低,与对照组比较差异无统计学意义(P=0.384).结论 大鼠视网膜急性缺血损伤后NGB mRNA表达增强,提示NGB可能在视网膜缺氧的适应性调节过程中起了重要作用。

Morphologic study on protection of Acrysof IOL to acute retinal photic injury

目的 观察AcrySof Natural人工晶状体(IOL)对视网膜的保护作用.方法 以蓝光照射猪眼杯后极部视网膜,光照强度为20 J/cm2及40 J/cm2,设空白对照.照射方式:单独光照、透过AcrySof一片式IOL、透过AcrySof Natural IOL,照射后培养眼杯48 h,光镜和透射电镜观察.结果 相同光照强度下,单独光照组及AcrySof一片式IOL组视网膜各层损伤比无光照组及AcrySof Natural IOL组明显,而透过AcrySof Natural IOL照射组与无光照组相比,视网膜仍有部分损伤,但损伤明显较单独光照组及AcrySof一片式IOL组轻.照射方式相同时,40 J/cm2组比20 J/cm2组损伤明显.结论 20 J/cm2与40 J/cm2光照强度的蓝光均可造成新鲜离体猪视网膜的急性光损伤,且随能量增加,损伤加重.AcrySof一片式IOL与单独光照相比,视网光损伤程度相似.AcrySof Natural IOL与AcrySof一片式IOL相比,可减弱蓝光造成的视网膜急性光损伤。

In vivo dynamics of retinal injury and repair in the rhodopsin mutant dog model of human retinitis pigmentosa

Genetic and environmental factors modify the severity of human neurodegenerations. Retinal degenerations caused by rhodopsin gene mutations show severity differences within and between families and even within regions of the same eye. Environmental light is thought to contribute to this variation. In the naturally occurring dog model of the human disorder, we found that modest light levels, as used in routine clinical practice, dramatically accelerated the neurodegeneration. Dynamics of acute retinal injury (consisting of abnormal intraretinal light scattering) were visualized in vivo in real time with high-resolution optical imaging. Long term consequences included fast or slow retinal degeneration or repair of injury depending on the dose of light exposure. These experiments provide a platform to study mechanisms of neuronal injury, repair, compensation, and degeneration. The data also argue for a gene-specific clinical trial of light reduction in human rhodopsin disease.