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The Mechanism of Macular Sparing
Annual Review of Vision Science ( IF 5.0 ) Pub Date : 2021-09-15 , DOI: 10.1146/annurev-vision-100119-125406
Jonathan C Horton 1 , John R Economides 1 , Daniel L Adams 1
Affiliation  

Patients with homonymous hemianopia sometimes show preservation of the central visual fields, ranging up to 10°. This phenomenon, known as macular sparing, has sparked perpetual controversy. Two main theories have been offered to explain it. The first theory proposes a dual representation of the macula in each hemisphere. After loss of one occipital lobe, the back-up representation in the remaining occipital lobe is postulated to sustain ipsilateral central vision in the blind hemifield. This theory is supported by studies showing that some midline retinal ganglion cells project to the wrong hemisphere, presumably driving neurons in striate cortex that have ipsilateral receptive fields. However, more recent electrophysiological recordings and neuroimaging studies have cast doubt on this theory by showing only a minuscule ipsilateral field representation in early visual cortical areas. The second theory holds that macular sparing arises because the occipital pole, where the macula is represented, remains perfused after occlusion of the posterior cerebral artery because it receives collateral flow from the middle cerebral artery. An objection to this theory is that it cannot account for reports of macular sparing in patients after loss of an entire occipital lobe. On close scrutiny, such reports turn out to be erroneous, arising from inadequate control of fixation during visual field testing. Patients seem able to detect test stimuli on their blind side within the macula or along the vertical meridian because they make surveillance saccades. A purported treatment for hemianopia, called vision restoration therapy, is based on this error. The dual perfusion theory is supported by anatomical studies showing that the middle cerebral artery perfuses the occipital pole in many individuals.In patients with hemianopia from stroke, neuroimaging shows preservation of the occipital pole when macular sparing is present. The frontier dividing the infarcted territory of the posterior cerebral artery and the preserved territory of the middle cerebral artery is variable, but always falls within the representation of the macula, because the macula is so highly magnified. For physicians, macular sparing was an important neurological sign in acute hemianopia because it signified a posterior cerebral artery occlusion. Modern neuroimaging has supplanted the importance of that clinical sign but at the same time confirmed its validity. For patients, macular sparing remains important because it mitigates the impact of hemianopia and preserves the ability to read fluently.

中文翻译:


黄斑保留的机制

同名偏盲患者有时会显示中央视野保留,范围可达 10°。这种被称为黄斑保留的现象引发了永久的争议。有两种主要的理论来解释它。第一个理论提出了黄斑在每个半球的双重表示。在失去一个枕叶后,假设剩余枕叶中的备用表示可以维持盲半区的同侧中央视力。这一理论得到了研究的支持,这些研究表明,一些中线视网膜神经节细胞投射到错误的半球,可能会驱动具有同侧感受野的纹状皮层中的神经元。然而,最近的电生理记录和神经影像学研究通过在早期视觉皮层区域仅显示微小的同侧场表示,对这一理论产生了怀疑。第二种理论认为,黄斑保留的出现是因为代表黄斑的枕极在大脑后动脉闭塞后仍然保持灌注,因为它接收来自大脑中动脉的侧支血流。对该理论的反对意见是,它不能解释患者在丧失整个枕叶后保留黄斑的报告。经过仔细审查,这些报告被证明是错误的,这是由于视野测试期间对注视的控制不足造成的。患者似乎能够在黄斑内的盲侧或沿垂直经线检测到测试刺激,因为他们会进行监视扫视。一种所谓的偏盲治疗,称为视力恢复疗法,就是基于这个错误。解剖学研究支持双重灌注理论,表明大脑中动脉灌注许多个体的枕极。在中风偏盲患者中,神经影像学显示当存在黄斑保留时枕极保留。大脑后动脉梗塞区和大脑中动脉保留区的分界线是可变的,但总是在黄斑的表现范围内,因为黄斑被高度放大。对于医生来说,黄斑保留是急性偏盲的一个重要神经系统体征,因为它表示大脑后动脉闭塞。现代神经影像学已经取代了这种临床症状的重要性,但同时也证实了它的有效性。对于患者来说,保留黄斑仍然很重要,因为它可以减轻偏盲的影响并保持流畅阅读的能力。

更新日期:2021-09-17
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