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APVRS丨眼底影像技术进展一日千里,不看又out了

玻璃体视网膜  作者:国际眼科时讯  2017/12/12 21:16:00
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内容概要:科学技术的进步为眼科的发展奠定了基石,大量新兴技术的涌现给眼科领域的诊断和治疗带来了空前的飞跃。

Dr. Sadda’s comments with International Ophthalmology Times

APVRS 2017

Srinivas Sadda is the President and Chief Scientific Officer of the Doheny Eye Institute, the Stephan J. Ryan-Arnold and Mabel Beckman Endowed Chair, and Professor of Ophthalmology at UCLA, David Geffen School of Medicine. Professor Sadda led the OCT interpretation master class at the 2017 APVRS Meeting and is one of the key opinion leaders in retinal ocular imaging. International Ophthalmology Times had the opportunity to sit down with Professor Sadda to ask some questions related to the latest advances in the field of retinal imaging.

Optical coherence tomography angiography (OCTA) has recently been developed to study retinal and choroidal microvasculature without the need for dye. IOT asked Professor Sadda about the clinical applications of this new technology. “There are many potential applications for OCT angiography, but keep in mind that it is a relatively new technology. It still has limitations. It is still a technology that is a work in progress”, he pointed out. But there are some applications, especially for evaluating the retinal circulation, that are probably already ready and useful in clinical practice. “For example, for identifying a condition such as macular telangiectasis, I don’t think we need dye-based angiography anymore. In my opinion, there is enough evidence already that OCT angiography is sufficient for that purpose. Also, looking for macular non-perfusion is another area where OCT angiography clearly shines compared to dye-based angiography. Additionally, I find it useful even in patients with choroidal neovascularization or where we suspect choroidal neovascularization on clinical examination or structural OCT, but the dye-based angiography is difficult to interpret. In those situations, I find that if you can actually see the choroidal neovascularization on the OCT angiogram, it can be quite useful.” (Figure 1) There are some limitations with this technology. It doesn’t necessarily show all the vascular lesions if their flow is too fast or too slow. It doesn’t show leakage. And there a number of artifacts that have to be managed. “If you are skilled at interpreting these images though, I think it can be very useful for the applications that have been identified” Professor Sadda said.

IOT asked about the characteristics of OCTA imaging of the macular capillary network in glaucoma. “Looking at the capillary network around the optic nerve looks to be more valuable than the macular capillary network for glaucoma. Not surprisingly, when you lose nerve fibers in glaucoma, you lose the capillaries as well. That is why we can see capillary loss around the nerve in the setting of glaucoma, and we have published on that. We think this will be a useful tool. Sometimes, there are patients where the nerve fiber layer thickness may be artifactitiously affected (in a patient with papilledema, for example) and in those cases, we believe that OCT angiography could be particularly useful because the capillary loss may give you early evidence that the nerve fibers are being lost.”

The Classification of Atrophy Consensus Meetings (CAM) were recently conducted to evaluate the advantages and disadvantages of various imaging modalities to detect and quantify atrophy on the basis of the collective analysis of a large series of clinical cases of late-stage non-neovascular and neovascular age-related macular degeneration. The aim was to provide recommendations on the use of these modalities in natural history studies and clinical trials. Professor Sadda was involved in these discussions. “This large group of experts from around the world recognized that we now know there are many different ways of developing atrophy. In the setting of AMD, you can develop atrophy after choroidal neovascularization, for example. We also recognized that we were using OCT as the main tool in the clinic, so we felt that it was important to develop systems where we would be able to identify and follow atrophy on OCT. But to do that, we need to know how to recognize it.” The criteria that emerged from these consensus meetings were recently published in Ophthalmology. They included identifying a zone of signal hypertransmission into the deeper layers of at least 250microns in diameter, associated with an overlying defect in the RPE, as well as thinning of the overlying retina. “If we see those three criteria, and can exclude the possibility of an RPE tear, then those are the OCT criteria we use for identifying atrophy in the setting of AMD”, Professor Sadda explained.

Another area of research Professor Sadda has recently published in Ophthalmology related to the kinetics of geographic atrophy progression in AMD and the factors that are relevant to geographic atrophy lesion enlargement. “There are a whole host of factors’, he outlined. “For example, we know that lesions that are larger grow faster, simply because they have a larger perimeter.

Multifocal lesions grow faster, again because they have a larger perimeter. Lesions tend to grow faster away from the foveal center rather than towards the foveal center, which is why we have foveal sparing with this disease. So location is an important factor. There are certain autofluorescence patterns such as banded or trickling or other diffuse patterns that can be associated with faster growth, so those are also relevant.” Understanding the kinetics of geographic atrophy is important when thinking about selecting patients for potential enrolment in future trials.

Fundus autofluorescence (FAF) is a non-invasive retinal imaging modality used in clinical practice. IOT asked Professor Sadda to summarize the pitfalls when analyzing FAF images. “I would say the biggest thing is to know the instrument you are using to capture the autofluorescence images. Are you using a confocal device that suppresses lens autofluorescence? Or a flash fundus system where you have to manage lens autofluorescence and might have to use a longer wavelength? That would mean you need to think about what wavelength you are using. Is it blue or green or infrared? (Figure 2). That affects what you are going to see on the autofluorescence images. You also need to know the state of bleaching of the fundus. If you have a patient who has been exposed to a flash of light first, that will bleach the photopigment in the photoreceptors and unmask additional RPE fluorescence that can confound your assessment as well. You also need to remember that the center of the macula, especially with blue autofluorescence because of luteal pigment, can also interfere with the autofluorescence signal. As with any form of imaging, you always have to looking out for other artifacts. Those would be the main pitfalls I would keep in mind when interpreting these images. I think it is a powerful tool, but we do need to be keep these issues in mind in order to make an accurate assessment.”

编者按:科学技术的进步为眼科的发展奠定了基石,大量新兴技术的涌现给眼科领域的诊断和治疗带来了空前的飞跃。在刚刚召开的第11届亚太玻璃体视网膜学会大会(APVRS2017)上,Srinivas Sadda教授主持了“OCT大师班”,并且担任视网膜成像的主要决策者之一。会议期间,《国际眼科时讯》有幸采访了Sadda教授,就视网膜成像领域最新进展相关问题进行了讨论。

专家简介

undefinedSrinivas Sadda

任多希尼眼科研究所的总裁兼首席科学官,Stephan J. Ryan-Arnold和Mabel Beckman讲席教授,以及加州大学洛杉矶分校David Geffen医学院的眼科教授。

不可不知的OCTA

光学相干断层扫描血管成像(Optical coherence tomography angiography, OCTA)近来已被开发运用于研究视网膜和脉络膜微血管,且不需要依赖造影剂。Sadda教授介绍了关于OCTA这项新技术的临床应用。Sadda教授首先指出,OCTA虽然有许多潜在的应用,但是作为医生,我们要记住,目前这还是一项相对较新的技术,还在不断发展中,仍然具有局限性。尽管如此,还是有一些临床实践中的应用,特别是在评估视网膜循环方面,非常有效。例如,Sadda教授认为,当要识别黄斑毛细血管扩张症时,医师不需要再次使用造影剂来进行血管造影,因为已经有足够的证据表明OCTA的效果。并且与基于造影剂的血管造影相比,寻找黄斑非灌注区是OCTA的另一个亮点。此外,Sadda教授发现,对于脉络膜新生血管患者,或者怀疑是脉络膜新血管的患者(临床检查、结构OCT检查后),运用OCTA可以很好地观察,但是基于染料的血管造影却难以显示。如果能够通过OCTA直接观察到脉络膜新生血管,势必非常有用。Sadda教授也简单谈了谈该技术的局限性。他指出,如果血流速度太快或太慢,OCTA不一定会显示出所有的血管病变。而且OCTA难以显示渗漏,并且还需要一些额外的人工操作。当然,如果医师擅长解读这些图像,Sadda教授认为这对已被公认的应用会非常有帮助。

“无所遁形”的毛细血管

Sadda教授随后向我们介绍了OCTA在青光眼黄斑毛细血管网的成像特点。他指出,观察青光眼毛细血管网的价值高于黄斑。毛细血管网围绕视神经,并沿着视神经纤维向外辐射。Sadda教授的研究表明,当青光眼患者的神经纤维丢失,毛细血管也会随之减少,这一发现目前已经发表。Sadda教授认为这将成为非常实用的工具。有时患者的神经纤维层厚度可能受到影响(例如视乳头水肿的患者),在这种情况下,OCTA可以识别毛细血管的减少,并进一步反应神经纤维丢失的情况。

OCT查萎缩,专家共识

萎缩分类共识会议(CAM)最近召开,会议以大量晚期非新生血管性AMD和新生血管性AMD的临床病例进行聚类分析为基础,评估了各种成像方式在萎缩的检测和定量方面的优缺点,旨在为这些成像方式在自然病史研究和临床试验中的应用提供建议。Sadda教授参与了这一会议。他指出,来自世界各地的专家都认识到,有多种不同原因可以导致萎缩。例如在AMD中,萎缩可以发生在脉络膜新生血管生成以后。同样,专家们也认识到,临床上OCT已经作为主要的工具,因此升级OCT系统,运用OCT能够识别和追踪萎缩显得尤为重要。共识会议中制定的标准发表在Ophthalmology上,包括确定一个信号高度传导区域(在眼球直径方向上,至少深入250微米)、与RPE的缺陷相关、视网膜变薄。Sadda教授指出,只要排除RPE撕裂,以上这三个标准就是AMD患者发生萎缩的OCT标准。

萎缩程度不一,源于诸多因素

Sadda教授最近在Ophthalmology上发表了另一领域的研究,即AMD患者黄斑地图样萎缩进展的动力学,以及地图样萎缩病变扩大相关因素。Sadda教授指出,有大量因素与其相关,比如病变越大,增长越快,因其周长更大。病变位置也是一个重要的因素,离中心凹远的病变比靠近中心凹的病变发展更快,这就是为什么该疾病很少累及中心凹。病变形态的不同也与病变扩大相关。Sadda教授强调,在未来试验筛选患者时,了解地图样萎缩的动力学是非常重要的。

想要用好FAF,这些你得知道

眼底自发荧光(FAF)是临床上使用的非侵入性视网膜成像技术,可以显示光感受器-RPE的退行性改变程度。Sadda教授最后和我们分享了在分析FAF图像时应注意的陷阱。他认为最重要的是,我们要了解用来捕获自发荧光图像的仪器。我们是否使用了抑制镜头自发荧光的共聚焦设备?是否使用了需要控制镜头自发荧光或者需要使用更长波长的眼底成像系统?这意味着我们需要考虑正在使用的什么样的波长,是蓝色、绿色还是红外线?这都会影响我们分析自发荧光图像。我们还需了解,当使用蓝色自发荧光时要注意黄斑的中心,因为中心凹点叶黄素会吸收蓝光,干扰自发荧光信号。和其他任何形式的成像一样,医师要多多留意人为因素的影响。Sadda教授表示,以上这些就是他分析图像时铭记于心的陷阱。Sadda教授最后强调,FAF是个强大的工具,但我们还是需要处处留心,以便做出准确的评估。


 
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