The Mechanism of Macular Sparing.
The Mechanism of Macular Sparing.
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DOI：
10.1146/annurev-vision-100119-125406
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发表时间：
2021-09-15
影响因子：
6
通讯作者：
Adams DL
中科院分区：
文献类型：
--
作者：
Horton JC;Economides JR;Adams DL
同型偏视患者有时表现出中央视野的保留，范围可达10°。这种现象被称为黄斑保留，一直引起争议。人们提出了两种主要理论来解释这一现象。第一种理论提出了黄斑在每个半球的双重表征。在失去一个枕叶后，假设在剩余的枕叶中的备用表征维持盲半视野的同侧中央视觉。这一理论得到了一些研究的支持，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，可能驱动纹状皮层中具有同侧接受野的神经元。然而，最近的电生理记录和神经成像研究对这一理论提出了质疑，因为在早期视觉皮层区域只显示了极小的同侧野表征。第二种理论认为黄斑保留的产生是因为黄斑所在的枕极在大脑后动脉闭塞后仍保持灌注，因为枕极接受来自大脑中动脉的侧支血流。对这一理论的反对意见是，它不能解释失去整个枕叶后黄斑保留的报告。仔细观察，这些报告被证明是错误的，因为在视野测试中对注视的控制不足。患者似乎能够检测到盲区黄斑内或沿垂直经络的测试刺激，因为他们会进行监视扫视。一种号称治疗偏视的疗法，称为视力恢复疗法，就是基于这个错误。双重灌注理论得到解剖学研究的支持，表明大脑中动脉在许多个体中灌注枕极。脑卒中偏盲患者，神经影像学显示黄斑保留时枕极保留。大脑后动脉梗死区域和大脑中动脉保留区域的边界是可变的，但总是落在黄斑的表现范围内，因为黄斑被高度放大了。对于医生来说，黄斑保留是急性偏盲的一个重要的神经学标志，因为它表明大脑后动脉闭塞。现代神经影像学已经取代了该临床征象的重要性，但同时也证实了其有效性。对于患者来说，保留黄斑仍然很重要，因为它可以减轻偏视的影响，并保持流利阅读的能力。
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.
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