Ophthalmological and cognitive data in t-AD and PCA

Alzheimer's disease (AD) manifests commonly as an amnestic syndrome (tAD), but also as a rarer focal type, such as Posterior Cortical Atrophy (PCA-AD), which primarily impairs visuospatial functions. In addition to the brain atrophy, retinal degeneration has been demonstrated, associated with the accumulation of Ab and Tau protein in this tissue, which shares a common origin with the brain. Additionally, retrograde trans-synaptic degeneration from the brain could affect the retina. We hypothesized that such dying-back phenomenon would be more important in PCA-AD than in tAD and that this would be reflected on specific optical coherence tomography (OCT) measures.Twenty-nine AD patients were categorized into 15 typical and 14 PCA forms. Complaints and symptoms were evaluated using a specific screening battery developed to detect PCA (Q-ACP questionnaire, neuropsychological parietal and non-parietal scales). Neuroimaging was performed to determine brain atrophy and its lateralization. OCT imaging allowed to measure the volumes of the macular ganglion cell layer (GCL) and of the retinal nerve fiber layer (RNFL) of the optic nerve.While the global RNFL thickness and GCL volume were not statistically different, PCA-AD patients showed more thinning than tAD in the inferior temporal (IT) sector on both eyes. Moreover, the amount of thinning in this sector was correlated with the score at the Q-ACP questionnaire and at the neuropsychological parietal scales.We propose that the thinning in the IT sector reflects the retrograde damage to the magnocellular pathway which constitutes a major feed of the dorsal visual stream primarily damaged in PCA.

阿尔茨海默病（Alzheimer's disease, AD）通常表现为典型遗忘型阿尔茨海默病（tAD），但也存在少见的局灶亚型，如主要损害视空间功能的后部皮层萎缩型阿尔茨海默病（Posterior Cortical Atrophy, PCA-AD）。除脑萎缩外，已有研究证实视网膜变性与该组织内β淀粉样蛋白（Ab）和Tau蛋白的沉积相关，而视网膜与脑具有共同的发育起源。此外，脑内的逆行跨突触变性亦可累及视网膜。我们提出假说：此类逆行溃变现象在PCA-AD患者中较tAD患者更为显著，且可通过特定的光学相干断层扫描（Optical Coherence Tomography, OCT）指标体现。

本研究共纳入29例AD患者，按亚型分为15例典型遗忘型（tAD）与14例后部皮层萎缩型（PCA-AD）。采用专为筛查后部皮层萎缩开发的特异性评估组合（Q-ACP问卷、神经心理学顶叶量表与非顶叶量表）对患者的主诉与临床症状进行评估。通过神经影像学检查明确脑萎缩情况及其偏侧化特征。利用光学相干断层扫描（OCT）成像技术，测量了黄斑神经节细胞层（macular ganglion cell layer, GCL）体积与视神经视网膜神经纤维层（retinal nerve fiber layer, RNFL）体积。

尽管整体RNFL厚度与GCL体积无统计学差异，但PCA-AD患者双眼颞下（inferior temporal, IT）象限的视网膜变薄程度均显著高于tAD患者。此外，该象限的视网膜变薄程度与Q-ACP问卷得分及神经心理学顶叶量表得分呈显著正相关。

我们认为，颞下（IT）象限的视网膜变薄，反映了大细胞通路的逆行性损伤——该通路是背侧视觉通路的主要输入来源，而背侧视觉通路正是PCA-AD患者的主要受损靶点。