视网膜假体的研究进展

目前视网膜假体是所有视觉假体中研究最成熟、最广泛的一种,其研究目标是帮助失明患者恢复有用视力,尤其针对因视网膜色素变性和年龄相关性黄斑变性等致视力丧失者.依电刺激部位不同,视网膜假体分为视网膜上假体和视网膜下假体.前者通过玻璃体手术将微电极植入并固定于视网膜上;后者通过巩膜途径或玻璃体途径将微电极置于视网膜神经上皮层和视网膜色素上皮层之间.近年来对视网膜上假体的阵列电极、刺激电流等进行了改进;对视网膜下假体的芯片、供能方式等做了改进.有望为不可逆盲者提供帮助.     

用于外层视网膜病变的表层型人工视网膜技术

老年黄斑变性和色素性视网膜炎是两种主要外层视网膜变性疾病，也是致盲的主要眼病。对于这种光感受器受损的视网膜疾病，人工视网膜技术是一种非常有希望的治疗途径。现在的人工视网膜技术都是基于神经电刺激发展起来的。在过去的二十多年时间里，人工视网膜技术主要分为两大方向：外层型和表层型。两种人工视网膜技术各有优缺点。对于表层型人工视网膜，植入更为方便，并且可以利用玻璃腔的空间对植入物进行散热。本文首先从视网膜多层结构的信号转换和传递功能出发，简单的介绍了人工视网膜技术的概念；概括了表层型视网膜电刺激需要考虑的一些重要方面；最后总结了美国、德国和日本的研究者研究的几种表层型人工视网膜方案。可以肯定，随着各相关学科的发展，人工视网膜将在不久的将来得到广泛的应用。     

视网膜干细胞移植任重而道远

进行性视网膜感光细胞的死亡是许多视网膜变性疾病的共同特征。现有的治疗方法不能恢复已经丧失的视功能。视网膜干细胞移植研究的不断深入在为视网膜变性患者带来希望的同时也面临一些严峻挑战：如何获得理想的视网膜干细胞？如何诱导视网膜干细胞分化成视杆及视锥细胞？如何诱导移植的细胞与受体细胞形成功能性突触连接？感光细胞丧失的早期,内部的视网膜神经通路是完整的,新的感光细胞只需与双极细胞形成突触连接就能恢复完整的视网膜神经通路。而感光细胞替换通常比其它神经元更直接更容易。因为感光细胞是感觉神经元,只在一个方向上与双极细胞一水平细胞形成连接。另外,视网膜特殊的层状结构决定了视网膜外层的感光细胞层是视网膜干细胞移植最理想的位置。视网膜干细胞研究的进展、视网膜变性疾病的特征及视网膜的特殊结构让我们有理由相信,干细胞移植的成功将首先来自视网膜感光细胞移植。     

视网膜假体的研究进展

视觉通路上的任何疾病都会影响视觉信号的传导,严重者甚至导致不可逆性盲.视网膜假体的研究是指在视网膜的不同部位植入相应的视网膜微电极,由植入物产生电信号或者释放神经递质,刺激并激活视网膜细胞产生神经冲动,从而使盲人或濒于盲的眼重新获得有用或部分有用视力.笔者分别介绍3类视网膜假体的结构组成、作用机制、植入方式、影响因素、优缺点及植入后效果和生物相容性等,以供同道参考.     

视网膜修复与再生的研究进展

视网膜退行性疾病,如年龄相关性黄斑变性、视网膜色素变性等,均是由视网膜细胞变性凋亡而引起.视网膜细胞损伤后难以自我修复.近年来研究者们通过视网膜移植、组织工程学、基因修复、药物保护及视觉假体等方法对视网膜进行修复或促进其再生.     

视网膜假体的研究进展

人工视觉的研究是指在视路的不同部位植入不同的视觉假体，由植人物假体产生电信号，刺激并激活视觉系统，从而使失明或频于失明的眼重新获得部分有用视力。本就近年来研究最为活跃的视网膜假体的实验基础、种类、植入方法、生物相容性及长期稳定性、优缺点等作一介绍。     

人工视网膜的研究现状

对于年龄相关性黄斑变性和视网膜色素变性等疾病导致的神经性盲,目前尚无有效治疗手段.人工视网膜是所有视觉假体中研究最广泛、最成熟的一种,通过医学、工程等多领域专家的共同推进,人工视网膜可能会发展成为神经性盲的临床修复技术     

视网膜视细胞的成片移植

目的 探索用准分子激光切削技术制备视网膜单层细胞植片,经内入路视网膜下腔的单层视细胞成片移植。方法 用准分子激光对大鼠视网膜进行切削,制取单层视细胞植片,此后,按内入路手术方法进行了兔视网膜下腔的异种移植。结果 切削后所得视细胞植片由单层视细胞组成,结构完整,包括外丛状层、外核层和外节层;视细胞植片经明胶包埋后被准确植入宿主视网膜下腔中,移植术后第1,2天宿主观视网膜未能复位,呈脱离状态,移植物没能与视网膜色素上皮层相贴;移植后10天,宿主视网膜复位,视细胞移植片平铺于宿主视网膜下腔中,植片视细胞外节也宿主视网膜色素上皮层相贴;移植后10天,宿主视网膜复位,视细胞移植片平铺于宿主视网膜下腔中,植片视细胞外节与宿主视网膜色素上皮层相贴,未见明显免疫排异现象。结论 准分子激光制备单层视细胞植片方法简单、可行;初步观察到内入路单层视细胞成片移植后,视细胞植片能够在宿主视网膜下腔中以正常生理位置存活;视网膜下腔为理想的视网膜移植的受位。     

益视汤对脾气虚证兔视网膜脱离复位后视网膜组织形态的影响

目的:观察中药益视汤对脾气虚证兔视网膜脱离(retinaldetachment,RD)自动复位后视网膜组织结构恢复的影响。方法:将健康成年新西兰灰兔26只随机分为脾气虚型RD自动复位组(A组)、益视汤治疗组(B组)及空白对照组(C组),采用耗气破气加饥饱失常法建立脾气虚证动物模型,在显微镜下行视网膜下注射透明质酸钠术建立视网膜脱离自动复位动物模型,用光学显微镜分别观察比较术后10,20,30d视网膜组织结构的变化。结果:B组较A组兔视网膜组织结构紊乱明显改善,细胞水肿变性明显减轻。结论:益视汤能减轻脾气虚证对视网膜脱离自动复位后各层组织细胞的不良影响。     

兔眼视网膜下注射N-甲基右旋天冬氨酸诱导视网膜变性的组织病理学研究

目的研究视网膜下注射兴奋性氨基酸N-甲基右旋天冬氨酸（NMDA）对神经细胞变性的作用。方法取12只1个月龄有色家兔,视网膜下注射10μl（30mmol／L）NMDA（溶剂为DMEM-F12）,形成视网膜隆起,在注射12、24、48h及1周后分别处死家兔,取其视网膜组织进行免疫组织化学检测和电镜观察。应用抗Calretinin、Calbindin、PKCα抗体,分别标记视网膜无长突细胞、水平细胞及视杆双极细胞;采用原位缺口末端标记技术（TUNEL）技术标记凋亡细胞。结果损伤早期（12～24h）,实验组视网膜可见散在细胞核固缩浓染的光感受器细胞,并有无长突细胞和神经节细胞的早期严重变性;中期（48h）视网膜各层神经元均出现病理性改变;损伤晚期（1周）视网膜各层细胞数目明显减少。损伤早期,TUNEL技术标记的阳性细胞位于视网膜各层。免疫组织化学和形态学计量资料显示视网膜下注射NMDA后,水平细胞、无长突细胞及神经节细胞数目明显减少,视杆双极细胞数目基本无变化。超微结构观察显示有凋亡、坏死、水肿变性及混合型细胞死亡等多种变性形式。结论视网膜下聚集NMDA时,光感受器细胞、水平细胞、视杆双极细胞、无长突细胞及神经节细胞均表现为视网膜兴奋性毒性反应,与以往体内及体外研究结果显示的仅有内核层神经元死亡情况不同。     

Stand des subretinalen Implantatprojekts

The development of a subretinal prosthesis has come to a stage where human trials are forthcoming. Subretinal prostheses are designed to replace degenerated photoreceptors in diseases such as retinitis pigmentosa or age-related macular degeneration. Microphotodiode arrays are implanted between retinal pigment epithelium and retina. Our group has collected convincing evidence for the principle feasibility of a subretinal prosthesis. Animal experiments have shown that subretinal electrical stimulation can successfully elicit spatially ordered responses in the visual cortex; visual acuity is estimated to reach 0.25 degrees of visual angle. Histological long-term examinations have demonstrated that the retina tolerates a subretinal implant well and also that the implant itself sustains the ocular environments. Surgical procedures have been successfully developed to implant complex subretinal devices.     

Subretinal displacement of photoreceptor nuclei in human retina

A quantitative study of the number and distribution of photoreceptors with displaced nuclei (PDN) in paraffin sections of 100 human eyes was conducted. The presence of PDN in the human was similar to the reported phenomenon of subretinal photoreceptor cells in the rat retina.PDN were distributed over the entire retina but occurred more frequently in the periphery and posterior pole. Cells with PDN subsequently degenerated and were removed by either subretinal macrophages or the retinal pigment epithelium (RPE). The number of PDN tended to increase with age. More PDN were found in eyes with age-related degenerative disorders, such as senile macular degeneration and senile cataract, than in normal eyes. The number of PDN was also increased in eyes with diabetes mellitus and systemic infections (septicemia and systemic fungi infections). PDN were also observed in the macular, where displacement of photoreceptor nuclei and their subsequent degeneration would have a greater impact on visual acuity than in other areas of the retina.Displacement of the photoreceptor nuclei into the subretinal space and their subsequent necrosis is a general phenomenon, undoubtedly contributing to photoreceptor cell loss in the human retina, and may be one of the important factors accounting for the decline in vision which accompanies old age.     

Neuroprotective effect of subretinal implants in the RCS rat

PURPOSE: Retinal prosthetics have been designed to interface with the neural retina by electrically stimulating the remaining retinal circuits after photoreceptor degeneration. However, the electrical stimulation provided by the subretinal implant may also stimulate neurotrophic factors that provide neuroprotection to the retina. This study was undertaken to determine whether electrical stimulation from a subretinal photodiode-based implant has a neuroprotective effect on photoreceptors in the RCS rat, a model of photoreceptor degeneration. METHODS: Eyes of RCS rats were implanted with an active or inactive device or underwent sham surgery before photoreceptor degeneration. Outer retinal function was assessed with electroretinogram (ERG) recordings weekly until 8 weeks after surgery, at which time retinal tissue was collected and processed for morphologic assessment, including photoreceptor cell counts and retinal layer thickness. RESULTS: At 4 to 6 weeks after surgery, the ERG responses in the active-implant eyes were 30% to 70% greater in b-wave amplitude than the responses from eyes implanted with inactive devices, those undergoing sham surgery, or the nonsurgical control eyes. At 8 weeks after surgery the ERG responses from active-implant eyes were not significantly different from the control groups. However, the number of photoreceptors in eyes implanted with the active or inactive device was significantly greater in the regions over and around the implant versus sham-surgical and nonsurgical control eyes. CONCLUSIONS: These results suggest that subretinal electrical stimulation provides temporary preservation of retinal function in the RCS rat. In addition, implantation of an active or inactive device into the subretinal space causes morphologic preservation of photoreceptors in the RCS rat until 8 weeks after surgery. Further studies are needed to determine whether the correlation of neuropreservation with subretinal implantation is due to electrical stimulation and/or a mechanical presence of the implant in the subretinal space.     

Retinal S-antigen in human subretinal fluid

Studies in experimental models of retinal detachment have proposed that the degree of visual recovery following retinal reattachment depends upon the extent of photoreceptor degeneration. A means of assessing this degeneration would help in establishing postoperative prognosis. S-antigen (S-Ag) is a unique retinal protein found in outer segment disc membranes and photoreceptor cells. In 36 cases of human rhegmatogenous retinal detachment, subretinal fluid (SRF) concentrations of S-Ag, measured by radioimmunoassay, ranged from 43 to 170 ng/ml (serum: 1-28 ng/ml). Analysis of variance showed a positive correlation with the duration of detachment (P less than 0.001). There was a two-fold increase in S-Ag concentrations during the first 2 weeks of detachment (P less than 0.005), with constant levels thereafter. These findings reflect progressive photoreceptor degeneration and/or ongoing synthesis of outer segment proteins in the detached retina that stop after the second week of detachment. SRF S-Ag levels may provide a prognostic indicator of visual recovery after reattachment as well as a sensitive measure of retinal metabolic activity during detachment.     

Müller cell and neuronal remodeling in retinal detachment and reattachment and their potential consequences for visual recovery: a review and reconsideration of recent data

Recent evidence suggests that the adult mammalian retina is far more plastic than was previously thought. Retinal detachment induces changes beyond the degeneration of outer segments (OS). Changes in photoreceptor synapses, second- and even third-order neurons may all contribute to imperfect visual recovery that can occur after successful reattachment. Changes that occur in Müller cells have obvious effects through subretinal fibrosis and proliferative vitreoretinopathy, but other unidentified effects seem likely as well. Reattachment of the retina induces its own set of responses aside from OS re-growth. Reattachment halts the growth of Müller cell processes into the subretinal space, but induces their growth on the vitreal surface. It also induces the outgrowth of rod axons into the inner retina.     

Photoreceptor allografts in a feline model of retinal degeneration

· Background: Photoreceptor transplants provide a potential means to restore function in a degenerate retina and/or rescue degenerating host photoreceptors by trophic influences. We have examined photoreceptor allografts in the Abyssinian cat model of hereditary photoreceptor degeneration to determine the viability and influence of such transplants on the host retina. · Methods: Small pieces of 3- to 5-day-old normal kitten retina containing undifferentiated photoreceptors were injected into the subretinal space of adult Abyssinian cats at an early stage of retinal degeneration using standard vitreo-retinal surgical techniques. The retinas were examined by ophthalmoscopy and fundus photography, then by light and electron microscopy at different times after surgery. · Results: Such allografts survive for at least 6 months after surgery. The photoreceptors develop outer segments, invariably in rosettes. The transplants gradually integrate with the host retina but detach the host photoreceptor layer from the retinal pigment epithelium (RPE), which tends to reduce the number of host photoreceptors over the transplant. There is no slowing of the photoreceptor degeneration in neighboring non-detached retina. Inflammation or rejection was not detected. · Conclusion: Undifferentiated, neonatal photoreceptor allografts survive and develop outer segments in the subretinal space of the Abyssinian mutant feline retina. The allografts gradually integrate with the host neural retina without inducing rejection. In the vicinity of the transplant there is increased loss of host photoreceptors, considered to be due to their detachment from the RPE layer. There is no evidence of any rescue of host photoreceptors elsewhere in this mutant retina. Received: 10 November 1997 Revised version received: 19 March 1998 Accepted: 23 March 1998     

Dark adaptation in locally detached retina

Nonrhegmatogenous retinal detachments were formed in the eyes of Dutch rabbits by subretinal injection of Hanks' balanced salt solution. The electroretinogram (ERG) was recorded locally from the acutely detached retina, and simultaneously from the surrounding attached retina (vitreal ERG [VERG]), before and after exposure to diffuse intense irradiation. Light adaptation elevated b-wave threshold for both the local ERG (LERG) and VERG by about 3 log units; thresholds for both responses recovered fully within 60-90 min after the irradiation. The normal time course of dark adaptation of the LERG suggests the occurrence of substantial rhodopsin regeneration in the rod photoreceptors of nonrhegmatogenously detached retina. These results differ from reports that visual pigment regeneration is slow in central serous chorioretinopathy, possibly because our detachments were studied within hours of formation, whereas some photoreceptor degeneration may be present in older clinical detachments.     

Transplantation of neuroblastic progenitor cells as a sheet preserves and restores retinal function

Diseases affecting the outer retina are incurable once photoreceptors are lost, and these diseases usually cause retinal pigment epithelium (RPE) dysfunction. However, the inner retina can remain functional for some time, even though retinal remodeling occurs as compensation for photoreceptor loss. If the damaged part can be replaced with neuroblastic progenitor and RPE cells as sheets with a beneficial effect on function, vision loss may be prevented and vision may be restored. This review presents an overview of the research of transplanting sheets of neural retina, with or without its RPE, to the subretinal space. In different animal models of retinal degeneration, retinal transplants can morphologically reconstruct a damaged retina, and restore visual sensitivity. Good morphological integration of transplants with the host retina can occur, whereas other transplants exhibit a glial barrier. Synaptic connections between transplant and host have been indicated by transsynaptic tracing. Retinal transplants can restore and preserve visual responses in a small area of the superior colliculus corresponding to the placement of the transplant in the retina. The beneficial effect of retinal transplantation likely involves two mechanisms: trophic effects, e.g., rescue of host cones; and synaptic connectivity between transplant and host retina.     

Progress in vitreoretinal surgery for proliferative diabetic retinopathy

Diseases affecting the outer retina are incurable once photoreceptors are lost, and these diseases usually cause retinal pigment epithelium (RPE) dysfunction. However, the inner retina can remain functional for some time, even though retinal remodeling occurs as compensation for photoreceptor loss. If the damaged part can be replaced with neuroblastic progenitor and RPE cells as sheets with a beneficial effect on function, vision loss may be prevented and vision may be restored. This review presents an overview of the research of transplanting sheets of neural retina, with or without its RPE, to the subretinal space. In different animal models of retinal degeneration, retinal transplants can morphologically reconstruct a damaged retina, and restore visual sensitivity. Good morphological integration of transplants with the host retina can occur, whereas other transplants exhibit a glial barrier. Synaptic connections between transplant and host have been indicated by transsynaptic tracing. Retinal transplants can restore and preserve visual responses in a small area of the superior colliculus corresponding to the placement of the transplant in the retina. The beneficial effect of retinal transplantation likely involves two mechanisms: trophic effects, e.g., rescue of host cones; and synaptic connectivity between transplant and host retina.     

Retinal transplants restore visually evoked responses in rats with photoreceptor degeneration

PURPOSE: To assess whether transplantation of intact sheets of fetal retina with retinal pigment epithelium (RPE) into a retina with photoreceptor degeneration restores visually evoked responses. METHODS: Sheets of fetal retina with RPE were transplanted into the subretinal space of Royal College of Surgeons (RCS) rats at 37 to 69 days of age. Sixty-three days to 10 months after transplantation, multiunit visual responses were recorded in the superior colliculus (SC) of transplanted rats, age-matched untransplanted rats, and rats with sham surgery. RESULTS: In 19 of 29 RCS rats with transplants, visually evoked responses were recorded from and restricted to a small area of the SC that corresponds topographically to the portion of the retina in which the transplant was placed. Outside of this area, no visual responses were evoked. Visually evoked responses were never recorded in age-matched, nontransplanted RCS rats. Visually evoked responses were recorded in 6 of 13 RCS rats with sham surgery, but these responses were significantly different from responses in rats with transplants. CONCLUSIONS: These results demonstrate that this transplantation technique restores visually evoked responses in the brain. Although the underlying mechanism is unknown, we propose that the central visual response results from increased synaptic efficacy within the host retina. If it can be established that functional connections between the transplant and the host retina produce the effect, then it would indicate that the technique could be explored as a therapeutic strategy in some diseases of retinal degeneration.