Alzheimer’s disease: A review of its visual system neuropathology. Optical coherence tomography—a potential role as a study tool in vivo

Abstract

Alzheimer's disease (AD) is a prevalent, long-term progressive degenerative disorder with great social impact. It is currently thought that, in addition to neurodegeneration, vascular changes also play a role in the pathophysiology of the disease. Visual symptoms are frequent and are an early clinical manifestation; a number of psychophysiologic changes occur in visual function, including visual field defects, abnormal contrast sensitivity, abnormalities in color vision, depth perception deficits, and motion detection abnormalities. These visual changes were initially believed to be solely due to neurodegeneration in the posterior visual pathway. However, evidence from pathology studies in both animal models of AD and humans has demonstrated that neurodegeneration also takes place in the anterior visual pathway, with involvement of the retinal ganglion cells' (RGCs) dendrites, somata, and axons in the optic nerve. These studies additionally showed that patients with AD have changes in retinal and choroidal microvasculature. Pathology findings have been corroborated in in-vivo assessment of the retina and optic nerve head (ONH), as well as the retinal and choroidal vasculature. Optical coherence tomography (OCT) in particular has shown great utility in the assessment of these changes, and it may become a useful tool for early detection and monitoring disease progression in AD. The authors make a review of the current understanding of retinal and choroidal pathological changes in patients with AD, with particular focus on invivo evidence of retinal and choroidal neurodegenerative and microvascular changes using OCT technology.

OCT in Alzheimer’s disease: thinning of the RNFL and superior hemiretina

“…Only one TD-OCT study reported correlation between MMSE scores and macular volume [14]. Also, metaanalyses tried to determine the utility of OCT as a tool for evaluating disease progression, and prognostic significance of macular and RNFL thickness, but their conclusions failed to determine a correlation between RNFL and the clinical severity of dementia [30][31][32][33][34] .…”

Choroidal thinning: Alzheimer's disease and aging

“…Since the first study of Spaide et al, measuring choroid by enhanced depth imaging (EDI) optical coherence tomography (OCT) [18], it took about 5 years for the firsts studies to be published using this technique to assess choroidal thickness (CT) in patients with AD. Choroidal thickness has shown to be reduced in patients with AD comparing with controls [19][20][21] as review by Cunha et al [22].…”

“…Choroidal thickness has shown to be reduced in patients with AD comparing with controls [19], [20], [21] as review by Cunha et al. [22].…”

Visual Features in Alzheimer’s Disease: From Basic Mechanisms to Clinical Overview

“…As described earlier, aberrant APP cleavage leads to neurotoxic A β aggregation, enabling inflammatory processing, degeneration, and thinning in all quadrants of the retina in these layers, but mainly in the superior and inferior quadrants. These layers are present in a third of the macula; therefore, any alterations can contribute to reduced macula and fovea volume, which may partially explain the ocular manifestations that these patients exhibit [ 25 , 48 , 121 – 124 ]. Study in retinas from postmortem patients with AD found a reduction in the number of GCL neurons related to progressive aging [ 125 ].…”