Potential Applications of Spectral-Domain Optical Coherence Tomography (SD-OCT) in the Study of Alzheimer's Disease

Abstract

Alzheimer's Disease (AD) is the most common subtype of dementia. As the prevalence of dementia is projected to increase, the burden of the disease on society is expected to become increasingly significant. The link between eye pathology and neurodegenerative diseases has been established in multiple studies. In particular, optic nerve parameters associated with neuronal loss in AD include retinal ganglion cells (RGC). Retinal ganglion cells are similar to neurons in the cerebral cortex, and have been correlated to neurodegeneration in AD. Ocular imaging techniques such as optical coherence tomography (OCT) have provided a rapid and non-invasive method for quantifying optic nerve parameters in vivo. Spectral domain (SD)-OCT has shown good potential in the study of the optic nerve in AD as it enables more comprehensive assessment of RGCs. Earlier generation OCT techniques only assess the retinal nerve fibre layer, which consists of RGC axons. Spectral domain-OCT offers ultra-high scan speed and image resolution, enabling improved sampling of retinal layers. Retinal layers such as the ganglion cell-inner plexiform layer (GC-IPL), which contain the dendrites and nuclei of RGCs, can be assessed with SD-OCT. This article presents a review of literature associating eye pathology with AD, and explores the potential of SD-OCT in future AD studies. Spectral domain-OCT has the potential to draw more links between optic nerve pathology and neurodegeneration.

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

“…In addition, one study using SD-OCT showed a diffuse reduction of the RNFL and GCL combined in AD [49], although the authors were not able to determinate which layer was most affected by AD. Later studies have demonstrated IPL thinning in AD patients [41,50,52,56,57]. This reduction of ganglion cell complex thickness (GC-IPL and RNFL layers) in AD occurs to a larger extent than that accounted for age-related GC-IPL loss alone (about 0.3 μm/ year) [54].…”

“…Increased cup-to-disc ratio has been reported to correlate with RNFL thinning in AD [40][41][42], and cup-to-disc ratio may be correlated with duration of disease [37]. This method, however, has certain disadvantages, as it is manual and highly subjective to each individual observer [41].…”

“…OCT is a reliable non-invasive, trans-pupillary technique that provides high-resolution cross-sectional images of RNFL and macular volume, allowing visualization of axons of the central nervous system (CNS) and evaluation of RNFL thickness [39,41]. Peripapillary RNFL thickness (RNFLT) is …”

“…Spectral-domain OCT (SD-OCT), a Fourier domain OCT technique, provided dramatically increased scanning speed and higher axial resolution when compared to TD-OCT technology, allowing the study of RGC and analysis of the GC-IPL layers [41,49]. SD-OCT has been validated as a reliable technique for detecting subclinical RNFL and retinal atrophy in AD [64][65][66].…”

“…It has also an improved signalto-noise ratio as compared to TD-OCT, providing higher image resolution. SS-OCT additionally offers some advantages over SD-OCT, including higher detection efficiency, increased sensitivity with image depth, reduced fringe washout and longer imaging range, higher penetration into the ONH and choroid, and lowered sensitivity to ocular opacities [41].…”